CPM300 Metallurgy

300 Metallurgy

Author: E.H. (Ned) Niccolls

AbstractThis section gives basic metallurgical information for Chevron engineers and inspectors supporting upstream operations, pipelines, refineries, and chemical plants.

Contents Page

310 Introduction 300-3

311 Metallurgy in Chevron’s Business

312 Glossary of Commonly Used Metallurgical Terms

313 Nature of Metals

314 Types of Steel Chevron Uses

315 Some Features of the Most Commonly Used Pressure Vessel Steels

316 Heat Treating Steels

317 Steel Making and Equipment Reliability

318 Metal Properties

319 Welding

320 Detailed Information on Higher Alloys 300-20

321 Stainless Steels

322 Nickel-Based Alloys

323 Titanium Alloys

324 Copper Alloys

330 High Temperature Degradation Mechanisms 300-27

331 Spheroidization

332 Graphitization

333 Temper Embrittlement

334 Creep Embrittlement

Chevron Corporation 300-1 February 2000

300 Metallurgy Corrosion Prevention and Metallurgy Manual

335 Sigma Phase Embrittlement of Stainless Steels (“Sigmatization”)

336 885°F Embrittlement of Ferritic Stainless Steels

337 Embrittlement Mechanisms in Nickel-Based Alloys

338 Creep

340 Avoiding Low Temperature Problems-Brittle Fracture 300-32

341 How To Use This Section

342 The Basics

343 Setting MDMT’s For New Equipment

344 Special Chevron Criteria

345 Setting MDMTs For Equipment Subject To In-Service Embrittlement

346 Setting MATs for Existing Equipment

347 Autorefrigeration

348 Notes on Hydrotest

349 Worked Examples

350 Fatigue and Thermal Fatigue 300-55

351 Endurance and Fatigue Limit

352 Factors Affecting Fatigue Life

360 Reference Tables 300-58

370 References 300-70

February 2000 300-2 Chevron Corporation

Corrosion Prevention and Metallurgy Manual 300 Metallurgy

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310 Introduction

311 Metallurgy in Chevron’s BusinessThe performance of materials plays a critical role in maintaining operations which in turn impacts the Company’s financial performance. Most pressure-containing materials used in producing, pipeline, refining and transportation operations are made of metal.

Metallurgy is fairly complex and usually best left to specialists. However, a working knowledge of metallurgy (as described in this section) will be helpful in the following situations:

• Troubleshooting routine problems, bad actors or unexpected equipment faiures.

• Specifying appropriate and necessary requirements for welding, heat treatiwelds, details in forming operations, etc., in work orders and project specifitions to assure reliable welds and other fabrication details.

• Assuring appropriate and cost effective choices of materials for new or repment equipment. These decisions should be based on an engineering analservice life, maintenance costs vs. initial capital cost, and made after consution with a specialist when appropriate.

• Understanding when the mechanical integrity of in-service equipment may have been affected by events causing the metal to exceed its design limitasuch as overheating from fires, exothermic reactions, mechanical friction, e

• Knowing when metallurgical issues need to be further analyzed; getting specialist counsel at appropriate times to assure safe, reliable facilities to support operations.

312 Glossary of Commonly Used Metallurgical TermsThis section explains words and phrases frequently used in metallurgy. ThrougSection 300, words in italics indicate that you can find their definitions here.

Alpha phase. The primary phase of metals. In steel, the primary phase is ferrite

Annealing. Heating a material to a high enough temperature so that on slow coothe material is soft, ductile and free from residual stress.

Austenite. The predominant high temperature (face centered cubic) phase in stthat is relatively stable at room temperature in 300 series stainless steels.

Bainite. An intermediate structure between pearlite and martensite. Bainite is thcommon structure found in Cr-Mo reactor steels.

Brittle Fracture. Fracture of metal at relatively low stress levels without signifi-cant deformation.



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Carbide precipitation. The combination of carbon with a metallic element to form a compound. In stainless steel, carbide precipitation can happen at elevated tempera-tures (including during welding), particularly at grain boundaries. Carbide precipita-tion can result in degradation of stress corrosion, cracking resistance or strength.

Cold working. Permanent time-dependent deformation at a temperature where it will strengthen a material and reduce its ductility. Sometimes referred to as work hardening or strain hardening.

Creep. Permanent deformation of a material under load at high temperature (> the melting temperature).

Crystallization. The separation of the solid phase from the liquid phase. Incor-rectly used to describe a fatigue failure. A fatigue failure is not crystallization because the failed metal is crystalline before it fails.

Delta phase. In steel, the high temperature body centered cubic phase. Sometimreferred to as delta ferrite.

Embrittlement. Severe loss of resistance to brittle fracture due to a chemical ormechanical property change.

Fatigue. Failure of a material due to exposure to cyclic stresses below the tensistrength.

Ferrite. The major (body centered cubic) phase in steel comprised of iron and carbon plus some trace elements.

Free machining. A property of a material due to the introduction of an ingredientthat makes machining easier and causes machining chips to break off easily. Insteels, the most common way to make them free machining is to add a significaamount of sulfur to the steel.

Gamma phase. In steel and stainless steel, the gamma phase is the austenitic p

Graphitization. Decay of carbides to carbon and iron in steel at elevated tempetures causing a loss in strength.

Hardenability. The ability of a material to strengthen upon rapid quenching fromelevated temperatures.

Heat affected zone (HAZ). The area next to a weld that is not melted but has a change in properties from the heat of welding.

Hot shortness. Brittleness of a metal at hot forming temperatures. In steel this isusually caused by high sulfur content.

Hydrogen embrittlement. Loss of ductility due to the absorption of hydrogen in the metal.

Impact test. A test to determine the resistance of a material to an impact load. Tmost commonly used test is the Charpy impact test where a notched specimenwith a hinged hammer and the impact strength is inversely proportional to the



amount the hinged hammer travels after impact. The results of these tests correlate reasonably well with the notch toughness.

Inclusions. Nonmetallic material contained in a solid metal.

Induction bending. The use of electric induction to heat a material to a high temperature so it can be bent without introducing a significant amount of residual stress in the material when it is cooled to room temperature.

Killed steel. Steel that has had silicon and sometimes aluminum added during the melt to reduce oxygen so that the bubbling from carbon dioxide evolution is stopped. This improves notch toughness. If only enough silicon is added to partially stop bubbling the steel, the steel is referred to as semi-killed. Semi-killing gives greater ingot yield but poorer impact properties than fully killed steel.

Martensite. The hard brittle structure formed by rapidly cooling steel from high temperatures.

Modulus of elasticity. The relation between stress and strain in the elastic range.

MDMT (Minimum design metal temperature). The lowest temperature a piece of equipment can safely be operated at without concern about brittle fracture.

Microstructure. The structure of a material revealed by viewing a polished and etched metal under the microscope.

Normalizing. Heating a steel to a temperature high enough so that fine grains are formed in the high temperature phase, and then cooling the steel rapidly enough so that the fine grains are maintained, but not so rapidly that structures such as marten-site are formed.

Notch toughness. The ability of a material to deform in the presence of a notch or defect under tensile stress without failure below the tensile strength.

Pearlite. A structure seen in steel at high magnification that consists of alternate layers of ferrite and iron carbide (cementite). Pearlite is formed by slow cooling from elevated temperatures.

Precipitation hardening. Hardening (strengthening) of a material by heating in a temperature range where a second phase precipitates.

Quench hardening. In steel, rapid cooling from elevated temperatures to form a hard, brittle structure.

Quenched and tempered. In steel, having heated in an intermediate temperature range to recover toughness while retaining the strength of the quenched material.

Recrystallization. Heating in a temperature range where fine grains form. The formation of strain free grains results from cold worked material or a change in crystal structure at high temperature.

Residual stress. The stress left in a material after all loads are removed. Commonly caused by welding or cold working.



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Sigma phase embrittlement. The formation phase called sigma at high tempera-ture in alloys containing iron and chromium. This phase tends to make a material brittle at room temperature and slightly above.

Spheroidizing. In steel, the causing of iron carbide to form spheres as a result of exposure to high temperatures.

Strain, elastic. The change in dimensions under load that is recovered after removal of the load.

Strain, plastic. The change in dimensions under load that is permanent after the load is removed.

Strain hardening. The increase in hardness (strength) as a result of permanent deformation.

Stress relief. Heating a material to a temperature, holding it at that temperature for a length of time, then followed by slow cooling so that most of the residual stresses are removed.

Temper. See quenched and tempered.

Temper embrittlement. Heating of steel, most commonly Cr - Mo steel, in a range where undesirable impurities diffuse to the grain boundaries causing a lost in tough-ness at room temperature and slightly above.

Transition Temperature. The temperature where the fracture surface of an impact test specimen is brittle and half ductile. Thus, the material is considered resistant (but not immune) to brittle fracture above this temperature and not resistant to brittle fracture below.

Ultimate tensile strength. The stress at which a material will fracture in a ductile manner under a short-term load.

Upper Shelf in impact strength tests. The temperature range where the fracture surface of an impact test specimen is fully ductile. Thus, the material is considered immune to brittle fracture in this range. Conversely, the Lower Shelf is the tempera-ture range where the fracture surface is completely brittle. Thus, the material is considered brittle in this range.

Yield strength. The maximum stress a material can withstand without significant permanent deformation.

313 Nature of MetalsThis section describes the nature of metals — their crystalline structure, chemiccomposition, and phase — all of which add to the complexity of working with metals. These variables must be managed to assure reliable operating equipmthey all affect critical properties such as strength, hardness, weldability and restance to fracture.



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Crystalline Structure All metals have crystalline structures. The photomicrograph in Figure 300-1 illus-trates the crystalline structure (microstructure) typical of carbon steels. The figure shows the irregular detail, texture, and variation in individual grains that are each separated by the irregular lines (grain boundaries). While crystals are regular in atomic structure, grains are crystals with irregular boundaries resulting when the growth of each is impacted by the growth of other grains, randomly precipitating as the liquid freezes to a crystalline solid. Grain boundaries frequently become impor-tant to metallurgists diagnosing problems because of both the physical and chem-ical discontinuities at the boundaries. In addition, atomic irregularities within the crystals can be significant, but usually they have their greatest effect on the macro-scopic properties of particular metals.

Chemical CompositionVirtually all metals used in our business are solutions or mixtures of several elements. “Solution” implies that the atoms are evenly distributed throughout thmetal while the phases in a metal are not usually evenly distributed. Many metaexist in different phases at different temperatures, some with mixed phases.

For example, the most common material we use is carbon steel, a solution of ircarbon, and frequently minor percentages of other elements such as manganemolybdenum. Most steels also have trace amounts of several of the following: pphorous, sulfur, silicon, copper, nickel, aluminum, chromium, vanadium, colum-

Fig. 300-1 Photograph of a Magnified Surface of Carbon Steel



bium, titanium. Carbon steel also contains a mixture of phases, with a separate phase of non-dissolved iron carbide. Figure 300-2 shows the chemistry for some typical steel grades used in industry pressure vessel shells.

This combination of chemistry and the presence of different phases (discussed below) become important as the metals are formed, welded, heat treated, exposed to corrosive environments, and exposed to different temperatures in service.

All these variables impact material properties such as strength, toughness, and ductility. Although steel is very common, it is a surprisingly complex material due to different phases and properties that can be obtained by variations in chemistry and heat treatment.

Fig. 300-2 Chemical Requirements (from ASTM A 516 (p.248, ASTM Vol. 01.04, 1998 Standard) (Copyright ASTM. Reprinted with permission.)

Elements

Composition, %

Grade 55[Grade 380]

Grade 50[Grade 415]

Grade 65[Grade 450]

Grade 70[Grade 485]

Carbon, max(1):

1/2 in. [12.5 mm] and under 0.18 0.21 0.24 0.27

Over 1/2 in. to 2 in. [12.5 to 50 mm], incl 0.20 0.23 0.26 0.28

Over 2 in. to 4 in. [50 to 100 mm], incl 0.22 0.25 0.28 0.30

Over 4 to 8 in. [100 to 200 mm], incl 0.24 0.27 0.29 0.31

Over 8 in. [200 mm] 0.26 0.27 0.29 0.31

Manganese:

1/2 in. [12.5] and under:

Heat analysis(2) 0.60-0.90 0.60-0.90 0.85-1.20 0.85-1.20

Product analysis(2) 0.55-0.98 0.55-0.98 0.79-1.30 0.79-1.30

Over 1/2 in [12.5]:

Heat analysis 0.60-1.20 0.85-1.20 0.85-1.20 0.85-1.20

Product analysis 0.55-1.30 0.79-1.30 0.79-1.30 0.79-1.30

Phosphorus, max(1) 0.035 0.035 0.035 0.035

Sulfur, max(1) 0.035 0.035 0.035 0.035

Silicon:

Heat analysis 0.15-0.40 0.15-0.40 0.15-0.40 0.15-0.40

Product analysis 0.13-0.45 0.13-0.45 0.13-0.45 0.13-0.45

(1) Applies to both heat and product analyses.(2) Grade 60 plates 1/2 in. [12.5 mm] and under in thickness may have 0.85-1.20% manganese on heat analysis, and 0.79-1.30% manganese

on product analysis.



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Other commonly used alloys have unique properties due to chemistry and the pres-ence of other phases. The particular chemistry or phase distribution in an alloy gives it the ability to resist particular corrosion mechanisms or high temperature effects in various applications. Common alloys include low alloy steels (low chrome-molyb-denum carbon steels), stainless steels, copper alloys, and high chrome and nickel alloys. Occasionally, titanium and other unique materials are used in alloys. By far, the most common metals used in the petrochemical industry are carbon and stain-less steels.

PhaseThe primary phases in carbon steel and stainless steel are ferrite or austenite. The atoms in a ferrite phase are arranged in a regular pattern called a “body centercubic” structure shown in Figure 300-3. The atoms in the austenite phase are arranged in another regular pattern called “face centered cubic” shown in Figure 300-4. These terms are of both practical and theoretical importance. Casteel is predominately ferrite (with some iron carbide) while many commonly usstainless steels (300 series) are austenitic (or at least mostly austenitic) at amband normal operating temperatures. Ferritic materials are magnetic, and austenare not (thus a magnet is often used to distinguish between ferritic and austenitmaterials).

Fig. 300-3 Ferrite Phase (Body Centered Cubic) (From “Structure and Properties of Engineering Materials”, Fourth Edition, 1977, McGraw-Hill Book Company. Used with permission.)

Fig. 300-4 Austenite Phase (Face-Centered Cubic) (From “Structure and Properties of Engi-neering Materials”, Fourth Edition, 1977, McGraw-Hill Book Company. Used with permission)



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314 Types of Steel Chevron Uses

Carbon SteelCarbon steel is by far the most commonly used material in Chevron. Carbon steel is essentially all iron, with a small amount (up to a few tenths of one percent) of carbon. Carbon steel is relatively inexpensive, easy to weld, and a “forgiving” mrial: its properties are predictable, it rarely fails without warning, and it is strongservice below 1000°F. However, mild carbon steel is normally limited to 800°F because of degradation (called graphitization) due to the breakdown of iron carbideafter long periods at elevated temperatures. (See Section 332 for further discusof graphitization.) Further, at 950°F, carbon steel is subject to excessive oxidatiwhen exposed to air.

Cast IronsCast irons-mostly iron with typically a few percent of carbon-are even less expesive than carbon steel. However, the high level of carbon is in the form of graphflakes or nodules. These nodules essentially cause the material to behave as ifwere full of small cracks, and so it is very brittle. Particularly for fire safety reasowe therefore rarely use cast irons except for water service.

Low to Medium AlloysTo increase strength and corrosion resistance at higher temperatures, one percnine percent chromium is added to carbon steel, often with a little molybdenumThis combination forms a class of materials that we loosely term “low to mediumalloys.” These alloys cost several times more than carbon steel, and more carebe taken in welding (they virtually always require heat treating after welding).

The low alloy materials (chrome-moly alloys) may form the “bainite” or “marten-site” microstructures as they cool during the initial manufacture of the steel (or, during welding). These microstructures have high strength (are very hard, oftenequivalent of more than 400 BHN) but their toughness is very poor. Fortunatelyheat treating the material in the range of 1300–1400°F (tempering), the toughness can be increased dramatically while still maintaining a high strength level-an exlent combination. For this reason, low alloy materials such as 2.25Cr-1Mo are uin our high pressure heavy wall equipment, such as hydroprocessing reactors. Usually these materials are used in the “Quenched and Tempered (Q&T) Condtion.” (See Section 316 for a discussion on heat treating.)

A potential problem with such alloys is that they are not as “forgiving” if exposedtemperature excursions. For example, in a fire the carbon steel components arrarely damaged by overheating, or by the rapid quenching from fire water. In contrast, the low alloy components might soften (held at high temperatures for long, they lose too much strength by becoming “overtempered”), or harden (dureformation of the very high hardness bainite or martensite microstructures fromquenching action of fire water).



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Stainless Steels and Nonferrous MaterialsAbove 11–12% chrome, the alloys form the general class of “stainless steels.” Avery rough general rule, the more money you are willing to spend in adding moalloy (more chrome, nickel, molybdenum) the more enhanced corrosion resistaand/or high temperature resistance you can achieve. A steel with more alloy thiron (for example, the nickel-based “Inconels” or “Hastelloys”) is a member of th“nonferrous” class of materials. Other nonferrous materials used occasionally bChevron include titanium, aluminum, and a few copper-based alloys. (Aluminumoften not very expensive, but it has poor fire resistance.)

315 Some Features of the Most Commonly Used Pressure Vessel SteelsSA-516 Grade 70 and SA-285 Grade C are the two most widely used plate steepressure vessels. SA-285 is not made to fine grain practice and can have comptively poor toughness, so its use is generally limited to lower pressure and thinnwall vessels up to ¾" thick. SA-516 Gr. 70 has better fracture toughness, particlarly in heavy sections, since it is made to fine grain practice and is required to a normalizing heat treatment if thicker than 1½". For this reason, today SA-516Gr.70 is the workhorse steel used for most moderate and high pressure servicewhere section thickness is greater than ¾".

SA-201 and SA-212 plate steels were commonly used prior to 1968, when theywere replaced by SA-515 and SA-516 specifications. The SA-201 Grades A & had minimum tensile strengths of 55 ksi and 60 ksi, and the SA-212 Grades A had minimum tensile strengths of 65 and 70 ksi. SA-212 had slightly higher limfor carbon content and a lower ductility requirement to accommodate its higherstrength. SA-201 and SA-212 could either be ordered for low temperature serv(meaning fine grain practice and probably a normalizing heat treatment) or for htemperature service (meaning coarse grain practice for better high temperaturestrength, but lower toughness). Since SA-201 and SA-212 steels may have eithhigh or low fracture toughness, Chevron assigns them to Curve A of ASME SecVIII Division I, Figure UCS-66 unless we know enough about the production anheat treatment history to be confident of their toughness. Pressure vessels madfrom these steels often have higher minimum pressurization temperatures thanmodern vessels.

The modern equivalent specifications are organized differently. SA-515 and SAboth have four grades: 55, 60, 65, and 70 ksi minimum tensile strengths. SA-51steel is made to coarse grain practice, whereas SA-516 is made to fine grain practice and is given a normalizing heat treatment if thicker than 1½". The finergrain size of SA-516 gives it much better toughness than SA-515 at any given strength level and plate thickness. The coarser grain size of SA-515 may theorcally give it better high temperature strength, but in practice the ASME allowabstresses for SA-515 and SA-516 are the same. Consequently, SA-515 is seldomtoday in petrochemical services.

Occasionally we find pressure vessel steels designated as “Code Case 1280”, is equivalent to SA-516 Grade 70, or “Code Case 1256”, which is equivalent to



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SA-442. These code cases predated the establishment of the now equivalent ASME specifications, and were in use for only a short period.

1960s and earlier vintage specifications often refer to the terms “firebox” quality(FBX) or “flange quality” steel. Firebox quality steels required more testing, tighcontrol of chemistry, and slightly higher ductility. Therefore, firebox quality steelwere generally used for pressure vessels.

Nozzles in carbon steel pressure vessels are typically made from SA-105 forginfrom SA-106 seamless pipe. There has been little change in these specificationover the years.

Iron-Carbon DiagramThe Iron-Carbon Phase diagram (Figure 300-5) is of particular use to experiencinspectors and experienced plant engineers concerned with damage mechanisoccurring in their plants. At the far left of the diagram we see the stable phase i“ferrite.” However, less than 0.02% of carbon is soluble in the ferrite phase. Thefore, carbon exists in two different forms in the steel: first, a small amount is dissolved in the atomic (crystalline) structure, being finely dispersed. The remaiof the carbon is combined with iron in the form of a separate phase called iron carbide. Iron carbide is a very hard, very strong material.

The combination of ferrite and cementite typically forms “pearlite.” Figure 300-6high magnification photo of a carbon steel, shows the white grains of ferrite. Thdarker material is the carbide, cementite. For these steels, the cementite often a long rod-like shape. These patches of alternating cementite and ferrite form wis called “pearlite.”

Let’s see what happens as we increase the temperature of a typical carbon steeabout 0.15% carbon. At most temperatures we deal with, the microstructure of steel is ferrite and pearlite. As you increase the temperature, the strength of thedecreases, but the microstructure of the steel does not change.

At 1100°F, the yield strength of the steel is about 1/3 of what it was at 80°F. That is why, when we stress relieve carbon steel welds at 1100–1200°F, we do not change the steel microstructurally, but the metal can “relax” and lower the residual stresto about 1/3 of the 80°F value.

As we go still higher in temperature, say a little above 1200°F, we start to see a microstructural change as the lamellar shape of the carbides in the pearlite becrounded, or “spheroidized.” This permanently reduces the high temperature stre(“creep strength”) of the material somewhat. Spheroidization is an indicator of tmetal becoming overheated and is actually a time-temperature phenomenon: thlower the temperature, the longer the process takes. Some very old vessels opating at about 900°F have developed spheroidized microstructures.

At still higher temperatures, we come to the “lower critical temperature” (“Ac1”)1330°F. Here, the austenite phase starts to appear. Austenite is a high temperaphase1, and it can dissolve much more carbon. The 1330°F temperature is truly “critical” to metallurgists–for example, if there is a fire, we are often interested toknow if the steel got hotter than 1330°F. Below 1330°F, the steel may soften a little,



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but will probably not suffer a severe consequence. If the steel gets hotter than 1330°F, it may end up with a very “mixed up” microstructure, with poor propertiedepending upon how it is subsequently cooled.

For this 0.15% carbon steel we see that above about 1590°F we are above the “upper critical temperature” (“Ac3”). Here the carbon is completely dissolved. (Iyou wish to gain the maximum hardness of a steel, you would raise its temperaabove this upper critical temperature to make sure all of the carbon was in solu

1. For many of the stainless steels Chevron uses, “austenite” is the stable phase for all practical temperatuincluding room temperature. The 300-series stainless steels, such as Type 304 SS, are called “austeniticless steels.”

Fig. 300-5 Heat Treating Temperatures in Relation to the Iron-Carbon Diagram



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then cool it as rapidly as possible-quench it-to form the highest hardness possible for that chemical composition).

Somewhat higher temperatures are used for annealing or normalizing. Normalizing is typically done at about 1650°F for carbon steel. Much higher temperatures are used for forging, and the steel actually melts at about 2800°F.

316 Heat Treating SteelsSteels have a wide range of properties, depending upon how they were formed in the mill, and then fabricated into the final product. Virtually all steels start “life” when the mill heats them above approximately 1650°F to develop the high tempera-ture austenite phase. Upon cooling, the austenite transforms to the stable lowetemperature ferrite phase structure.

Heat Treatment. As carbon steel cools from liquid, it transforms its crystalline structure. More importantly, as carbon steel cools below 1330°F (721°C), it canform a number of different arrangement and types of phases with various iron carbide content and distributions, depending on carbon content and cooling rateHeat treatment variations such as quenching, annealing, etc. are all chosen by lurgists to give specific and predictable properties.

Since desired properties are often mutually exclusive, treatment becomes a balancing act to achieve optimal properties for the specific application. The pratical aspect of this is to be aware that carbon steel, a common material, can bealtered during fabrication, subsequent heat-treating and welding operations. Thsame basic principles apply to alloys — in fact, many alloys are even more respsive to heat treatment practices.

Typical considerations when heat treating and welding include the following:

• Mechanical strength is very important in many machinery applications.

• Weldability is important in vessels, tanks, and piping where shop and field fabrication are common.

Fig. 300-6 Mixed Ferrite-Pearlite Microstructure

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• Resistance to brittle fracture (toughness) is critical in low temperature applitions, thick wall materials, and services that become saturated with hydrog

• Ductile (not hard) steels and welded areas are needed in services subject tsour service.

Note Refer to procedures in the Welding Manual and get expert counsel when appropriate to help assure mechanical integrity regarding heat treating and welding operations.

Metal Grain Size and Heat Treatment. In the next section, we note how the size of the grains of the metal affects metal properties. The heat treatment of the medetermines the grain size.

The following steps would be used to increase the grain size:

– use a higher austenitizing temperature (a typical austenitizing temperawould be approximately 1650°F)

– hold the austenitizing treatment longer, to allow more time for the graingrow

– slowly cool the steelLarge grain size improves some high temperature strength properties (creep), bnoted below, in most cases a fine grain size is what we really want. To achieve finer grain size, we would control the austenitizing temperature and time and racool the steel.

Cooling Rates: Annealing, Normalizing, and Quenching. A steel is annealed by slowly cooling it from the austenitizing temperature — typically by leaving the stin the turned-off heat treating furnace. A moderately fast cooling rate is achievenormalizing the steel, whereby the steel is cooled in air from the austenitizing temperature. A very fast cooling rate is obtained by dipping the steel or sprayinwith oil — this very rapid cooling is called “quenching.”

Quenching the steel produces high strength and hardness, but also high residustress and poor toughness. (See Section 318 for definitions.) Therefore, for maapplications, the steel is given a follow-up heat treatment at 1000 - 1400°F, depending upon the steel or alloy. This is called “tempering.” Tempering reducestrength somewhat, but it greatly improves the ductility and toughness of the stDone correctly, the quench and tempering process (“Q&T”) can produce steelsan excellent combination of strength and toughness.

317 Steel Making and Equipment Reliability For virtually all of our steel components—whether it is downhole tubing, line pippressure vessel plates, or plant piping—we seek the optimum combination of hstrength, high toughness, and low price. Both strength and toughness are founsteel with relatively small grain size, and with minimal defects.

For most process piping applications, and for many pressure vessel applicationannealed steel is good enough. If we do not specify a particular heat treatmentthe ASTM specification does not call it out for us), we may actually get a range



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heat treatments. For example, when vessel plates are stacked on top of each other to cool after the hot rolling process, the middle plates may have a slow cooled, annealed type structure, while the top plate may have cooled rapidly enough to have a much finer grain size. Also, if the steel is used in the “as-rolled” condition we typically will not be able to predict the microstructure, because the steel can covarious rates as it is being rolled (flattened) into shape.

If having a fine grain size is important to us, then for extra cost (perhaps 10–40extra for a typical carbon steel) we can require it be made to “fine grained pract(you may sometimes see the initials “FGP” on drawings). The steel maker will tcally adjust the chemistry slightly (for example, adding aluminum) to make surefine grain size can be achieved with practical cooling rates, and almost always normalizing heat treatment will be done. This normalizing both makes the grainsmaller, and it definitely makes the grain size more uniform. It is possible to normalize (heat treat) the steel and gain some benefit, without the raw steel itsebeing made to fine grain practice.

As the steel is first made, the nature of the cooling process tends to force imputo the center of the original cast ingot or slab. When the steel is flattened into thshape for plates by the rollers in the rolling mill, the defects in the steel are squetogether and flattened into “pancake shape” defects, called “inclusions.” This is such defects are typically found in the middle of the plate thickness (or the middof the pipe wall, if it is large diameter pipe made from plate). These types of defare seen less frequently in seamless pipe.

318 Metal PropertiesMetal properties affect the fitness of each piece of equipment to perform its opetion safely and dependably. Metals are the primary materials in equipment suchpressure vessels, piping, machinery, tanks, furnaces, platforms, structures, boletc.

These properties include:

Tensile strength. The limit of the materials ability to carry stress (loads) without failure.

Yield strength. The limit of the materials ability to carry stress (loads) without significant deformation.

Strain. The amount a material deforms compared to its original dimensions. Elastic strain is recovered when the stress is removed and the material returns to its orinal dimension; plastic strain results in a permanent deformation. See Figure 300-

Ductility. The ability to deform under stress.

Toughness. The ability of a material to resist brittle fracture in the presence of a notch. Usually measured by impact testing. (See Brittleness, below.)

Hardness. Resistance to surface penetration. In general, the harder the materiamore resistance to wear.



Thermal stability. The ability to operate without internal metallurgical changes. Examples are resistance to temper embrittlement in high temperature reactors and resistance to sigma phase formation in austenitic stainless steel furnace tubes.

Resistance to corrosion. The ability to operate in various chemical environments without decay of the metal.

Resistance to creep. the ability to operate under stress at high temperature without significant permanent deformation (important in furnace tubes and other high temperature applications.)

Brittleness. The tendency to shatter under load without much strain.

Weldability. The ability to be welded without resulting defects such as cracking or excessive hardness (frequently leading to subsequent cracking).

Fatigue resistance. The ability to resist cyclic loads without failure.

Fig. 300-7 Stress vs. Elongation Chart



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Controlling Metallurgical PropertiesRules of thumb.

1. Strength and toughness tend to be incompatible. Higher strength materials are usually less tough, and more brittle. The exception is that decreasing the grain size increases both strength and toughness.

2. Strength and hardness are closely related. High hardness materials are strong (and less tough, i.e., more brittle).

As the following examples illustrate, managing metallurgy is an exercise in balancing the various properties to assure performance. Many desirable properties are just not possible with any one material, so applications are compromises to cover all the design requirements. For example, strength is important in nearly all applications, but very strong steel may be too hard, and consequently too brittle to be used in low temperature services.

Common tools used to manage properties include:

• Chemistry. Usually controlled by choosing an appropriate ASTM standard fthe metal. Materials selection is usually done by specialists, and not discusfurther here. Chemistry is also controlled in the selection of various weldingconsumables (rod, wire). See the Welding Manual, and consult a specialist if in doubt.

• Heat treating. Commonly specified in ASTM metallurgy standards for stan-dard materials for plate, piping, etc., and also controlled in shop and field facation.

• Welding specifications. See Section 319. Also see the Welding Manual, and consult a specialist if in doubt.

• Operating limits. Metals must be operated within design conditions to avoidexcessive corrosive attack if process compositions exceed limits or if tempture limits are exceeded. Operating metals within design conditions avoids short term loss of strength or long term affects such as creep.

• Cold working. Occasionally there are limits on bending or other forming to prevent excessive hardening or susceptibility to stress corrosion cracking fcold working.

• Stress Relieving. Heating to remove residual stress due to welding or cold working.

• Postweld heat treatment (PWHT). PWHT after welding may be specified to restore mechanical properties, reduce hardness, increase resistance to brifracture, reduce the risk of stress corrosion cracking, or relieve residual stresses. PWHT is an important and common procedure specified after shoand field welding. It adds to the cost, and frequently significantly so, particularly for field welds in piping systems. PWHT and other heat treating operations are covered thoroughly in the Welding Manual, Section 150.



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Improving Metal Properties All steels start out as cast ingots, or as continuously cast slabs of material, as the material is cooled from its original molten state. In some cases, the steels are used as cast. Cast steels are much less brittle than cast irons, but for improved properties the steel is most often “worked” to at least some degree. Three methods of “workinthe steel are rolling, forging, and drawing.

• Rolling the steel into flat plates forces shut many of the defects or “gaps” inmaterial, thereby increasing the soundness of the material. Rolling also canbreak apart large grains, and make the material somewhat more homogeno

• Forging the steel-quite literally, hammering the steel into shape using very lhammers and dies-similarly closes up defects and improves the properties

• “Drawing” the material-in which the steel is pushed over a mandrel to form tubular shape for tubing or pipe-again helps improve the product, although cally such material has been fairly heavily worked before it gets to the drawmandrels.

Special Care for Thick MetalsAbove we noted the advantages of “working” the material by rolling, forging, etcOne of the problems with thick materials is that often they have not been rolledmuch, or forged as much, as the thinner material, so they tend to have more deand less homogeneous properties. (For our purposes, we consider “thick” mateto be more than about 1.5 inches thick.)

Another problem for thick materials is that it often is difficult for the material to have the optimum heat treating conditions throughout its thickness. Like a thicksteak cooking on the grill, the middle may tend to be a bit “raw.”

It is for these reasons that you will often see Chevron or industry specificationsfor metallurgical samples (especially toughness samples) taken at the “½T” postion (that is, at half-way through the thickness, in the middle). This is also one reason why some specific low alloy materials are used for thick equipment. As the case of the 2.25Cr-1Mo steel noted above, such materials are designed to bto “through-harden” effectively even if the vessel wall is many inches thick.

Two low alloy materials to watch out for in thick sections are the C-0.5Mo material, and the 1.25Cr material (especially the higher strength “Class 2” version). Iaddition to the general problems noted above for all thick materials, these mateare known to have particular problems maintaining good toughness. In any eveis always a good idea to obtain metallurgical consultation for any thick material.

Steel Purity Affects Mechanical PropertiesImpurities—primarily oxygen and sulfur—can greatly reduce the mechanical prerties of the steel. The toughness (that is, the resistance to fracture—see Section 340) is particularly sensitive to impurities.

Oxygen. Over the years, the steel makers have become increasingly skilled at didation practices. They add silicon to the violently boiling liquid steel primarily to



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remove oxygen. The silicon abruptly stops or “kills” the bubbling–hence the nam“killed steel.” Steel makers can partly or fully deoxidize the steel. Examples of “semi-killed” steel is A53 pipe and A285 plate2. Examples of “fully killed” steel are A106 pipe and A516 plate.

“Rimmed steels” have no special deoxidation–the interior portion of the steel inis full of gas pockets and impurities, and only the outer portion is used. Becausthis, rimmed steels are not used for modern vessels or piping.

Sulfur. Steel purity has greatly improved over the past few decades. The sulfur in 1990’s steels is typically less than that in a typical 1970s material (often less 0.010 wt.% today versus 0.025 wt.% in the 1970’s).

319 Welding Welding is a common and necessary process in both new construction and manance. However, welding must be conducted within tightly controlled variables assure reliable joints. By its nature, welding involves changing from a solid to liqphase and back to solid. During this operation, the equipment may undergo chain its local chemistry as well as changes in the crystalline structure and mechanproperties

Figure 300-8 is a sketch of typical microstructures at a butt weld of two plates, por vessel walls. This figure illustrates the various microstructures near the weldresulting from different thermal histories. Note the difference in the structure asweld progresses from the previously liquefied zone through the “heat affected z(HAZ) to the unaffected parent metal. The material affected by the welding prochas varying grain structures that affect strength, resistance to cracking, brittle failure, and may have slightly different chemistry that affects mechanical properand resistance to corrosion. Common concerns are hard welds that are prone tattack from dissolved sulfides in the process streams, or welds that contain so trapped hydrogen that they are prone to immediate or delayed cracking.

320 Detailed Information on Higher Alloys

321 Stainless SteelsThere are four major categories of stainless steels: austenitic, martensitic, ferritand duplex. We use the austenitic stainless steels the most, for their high-tempture sulfidation and oxidation resistance and their resistance to aqueous corrosThe major drawback of austenitic stainless steels is their tendency to undergo scorrosion cracking in aqueous chlorides above about 140°F. Austenitic stainlessteels are extremely versatile, and are used for piping, pressure vessels, weld overlay, and heat exchanger tubing. The austenitic steels contain chromium annickel as alloying elements.

2. Why are not all materials fully killed? Primarily, because fully killing the steel reduces the amount of steel a steel maker can get from a particular ingot.



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The ferritic and martensitic stainless steels contain chromium, but little or no nickel. They are not typically as corrosion resistant as the austenitic alloys, but have high ambient temperature strength in addition to relatively good corrosion resistance.

Duplex stainless steels have a mixed austenitic and ferritic microstructure. The duplex stainless steels are useful for their ability to withstand SCC in aqueous chlo-ride services. They are typically used for piping and heat exchanger tubing in aqueous chlorides where both corrosion and SCC resistance are needed.

A list of commonly-used stainless steels, their product form ASTM designations, and brief descriptions of corrosion resistance and mechanical properties appear in Figure 300-22 and Figure 300-23.

Austenitic Stainless SteelsAustenitic stainless steels contain significant amounts of chromium (16–26 wt.%and nickel (8–20 wt.%). The nickel causes these alloys to retain an austenitic mstructure as they cool. Most common in this group are the 300-series stainless such as Types 304, 304L, 316, 316L, 321, and 347. The primary advantages ofsteels are their high-temperature strength, oxidation and sulfidation resistance,

Fig. 300-8 Grain/Phase Diagram (Courtesy of Butterworth Heinemann Publishers)



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their resistance to corrosion in many aqueous environments. Above about 1000this class of steel surpasses all others for strength and creep resistance. In motemperature services we encounter, austenitic stainless steels are chosen for thability to resist corrosion by H2S and H2-H2S mixtures at elevated temperatures.

The austenitic stainless steels are susceptible to stress-corrosion cracking (SCaqueous chloride-containing environments. They should not be used in chloridecontaining water above 140°F. Section 420 of this manual gives more detail regarding SCC.

The least expensive, but also the least corrosion resistant of the 300-series stasteels is Type 304 which contains only 8 wt.% nickel. For most corrosive aqueoenvironments, Types 316, 316L, 321, or 347 will be used; these contain 10–12 nickel.

Types 304 and 316 are susceptible to intergranular corrosion and cracking if weand placed in corrosive aqueous environments, due to a phenomenon called sezation. For welded equipment and piping, Chevron uses only the low-carbon “L”-grades, like Types 304L and 316L, or the stabilized grades, like Types 321 a347. For use at temperatures above 700°F, Type 321 is used. For services abo800°F, Type 347 is used. Refer to Section 410 for more information regarding stization.

The carbon added to austenitic stainless steels imparts some strength but not amuch as in carbon and low-alloy steels due to the austenitic grain structure. Likwise, austenitic stainless steels are not hardenable through heat treatment. For“L” grades, such as 304L and 316L, carbon is intentionally left out (less than 0.03 wt.%) to reduce the susceptibility of the alloy to sensitization and intergrancorrosion.

In a few cases where corrosion resistance and elevated temperature strength isneeded simultaneously, high-carbon austenitic stainless steels may be used. Sless steel grades to which at least 0.04 wt.% carbon has been intentionally addalso known as “H” grades (such as Type 304H) to distinguish them for their strein high-temperature service.

The strength of Type 304H versus that for 304L is about the same at room temture, but at higher temperatures the Type 304L loses strength much more rapidthan does the 304H. The ASME Code allows 304H to be used to 1500°F but 30to be used only to 800–850°F.

Heat Treatment of Austenitic Stainless Steels. Austenitic stainless steels cannot be hardened by heat treatment but can be hardened by cold working. Dependinthe required service then, they are typically purchased one of two ways: either worked for maximum strength, or annealed for maximum resistance to corrosioand stress corrosion cracking (SCC).

Annealing is done by holding the stainless steel at about 1900°F for an hour peinch of thickness. For Types 316 and 317, which contain higher nickel content, annealing is typically done 100–200°F higher. Carbide precipitates and deleteribrittle phases (“sigma”) can form in austenitic stainless steels at temperatures



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between about 800°F and 1600°F, so it is important that the annealing temperabe sufficiently high, and that the subsequent cool down move rapidly through thembrittling and carbide precipitation range. Use of “L” grades reduces the risk ograin boundary carbide precipitation during heat treatment and therefore resists“sensitization.”

Since rapid cooling may leave high residual stresses in the finished product, strrelief at 1600°F may be done following cooling to eliminate residual stresses. Srelief is especially important if the steel is to be used in a SCC environment. Residual stress greatly increases the risk of stress-corrosion cracking of austenstainless steels.

A stabilizing anneal may be given to Types 321 and 347 stainless steel. These grades are known as stabilized grades because they contain elements (titaniumthe case of Type 321 and niobium in the case of Type 347) which form carbidesare more stable than iron carbides.

Stabilized carbides are important when the steel is to be used at elevated temptures. This is because at about 700°F and higher, the non-stabilized grades (suTypes 304 and 316) are susceptible to intergranular precipitation of chromium carbides (Cr23C6) which causes sensitization and can lead to intergranular crackand corrosion. By adding titanium (in the case of 321 stainless steel), titanium carbides (TiC) are formed in the steel, rather than iron carbides. Titanium carbiare more stable than iron carbides at elevated temperatures and do not transfograin boundary chromium carbides until at least 850°F. For use in the 850–900range, niobium (also called Cb) is added to form niobium carbides in 347 stainlsteel, which are stable at those temperatures.

The stabilizing anneal is performed at a temperature which is higher than the ircarbide dissolution temperature but lower than the TiC (or NbC) dissolution temature, usually at 1600–1650°F. By holding the steel at that temperature for fourhours, carbon in the steel reacts with either titanium or niobium, and little or no carbide remains. Later, when the steel is used in elevated temperature service,are fewer iron carbides to transform to grain boundary chromium carbides, andthe physical and mechanical properties are maintained even after years at elevservice temperatures.

Ferritic and Martensitic Stainless SteelsStainless steels that contain similar amounts of chromium to the austenitic stainsteels, but little or no nickel, transform to ferritic and/or martensitic structures upcooling. Ferritic and martensitic stainless steels contain less than 2.5 wt.% nickand may contain none. Chromium (12–25 wt.%) is added for corrosion resistanUpon cooling from the high-temperature austenitic structure, these steels transto either ferrite or martensite depending on carbon content.

The most common types used in the petrochemical industry are the “12-chromemartensitic Types 410 and ferritic Type 405 stainless steels. The two have verysimilar corrosion resistance and are commonly used for cladding and internals vessels in purely H2S service above 450°F. Owing to its martensitic structure, Ty410 is much harder and stronger than Type 405, and can be thought of as the c



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sion-resistant counterpart of martensitic low carbon steels. Due to its high strength, however, it can yield very hard welds. For this reason the Type 410S (low carbon) or Type 405 is typically chosen for welded construction if its strength is sufficient.

Heat Treatment of Ferritic and Martensitic Stainless Steels. The tensile strength of martensitic stainless steels like Type 410 can exceed 300 ksi. The very high strength and hardness makes these steels susceptible to stress-corrosion cracking in wet H2S environments, so they must be chosen carefully in petrochemical applica-tions. Only in cases where the process temperature is hot enough so that no liquid water exists or where there is no H2S present should martensitic stainless steels be considered.

If corrosion resistance is the primary need, and the strength of a martensitic struc-ture is not necessary for a particular application, Type 410 can be tempered or annealed. Tempering for several hours at 1200–1600°F yields tempered martewhich retains very high tensile strength, but is tougher and more ductile than quenched martensite.

Annealing at 1600°F followed by slow cooling coarsens and softens the martenenough that ductility can be raised from near zero to as high as 10% or so. Fersteels can also be purchased in the annealed condition if corrosion resistance, ductility, and toughness are required.

Duplex Stainless SteelsA common grade of duplex stainless steel for petrochemical services is Alloy 2It contains 22 wt.% chromium, 5.5 wt.% nickel, and 3 wt.% molybdenum. The intermediate nickel content causes the microstructure to be a mixture of ferritic phases and austenitic phases. Since the ferritic phases are not susceptible to cride stress-corrosion cracking, they act as barriers to crack propagation. Molybdenum increases the pitting resistance of the alloy; that, in addition to its good corrosion resistance and its ability to withstand cracking, makes the duplex stailess steels a good choice for heat exchanger bundles where SCC and corrosiotance are needed above 140°F in the presence of chlorides.

More information on duplex stainless steels will be added to the next revision ofsection.

322 Nickel-Based AlloysAside from the carbon steels, low-alloy steels, and stainless steels, the other mstructural alloys we use in the petrochemical industry are the nickel-based alloyThis group of alloys contains Monels, Hastelloys, and Inconels. For our purposwe also include Incoloys in this category.

Monel alloys are mixtures of mostly nickel (66 wt.%) and copper (31 wt.%). Mois used primarily for resistance to acids, and especially for resistance to corrosiohydrofluoric acid (HF).

Hastelloys typically contain at least 40 wt.% nickel and appreciable quantities (10–25 wt.%) of chromium and molybdenum. Hastelloy B and C are the most



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common Hastelloys we use; they have excellent resistance to corrosion in acids and are immune to chloride SCC. Typical uses are tubes for heat exchanger bundles in refinery and chemical plants where acids and chloride salts are likely.

Inconel 600, 601, and 625 contain 60–75 wt.% nickel and 15–20 wt.% chromiuand up to 10 wt.% molybdenum; they are primarily used for high-temperature strength and outstanding corrosion resistance. Incoloy alloys like 800 and 825 not technically considered nickel-based alloys because they are a mixture of abequal parts of iron, chromium, and nickel (20–40 wt.% each). These alloys canused in both corrosive aqueous environments and in high-temperature oxidatioapplications.

Incoloy 800H is commonly used in high-temperature services in chemical plantwhere operating temperatures may exceed 1200°F. Ethylene and styrene plantparticular, make use of Incoloy 800 and 800H pressure vessels, transfer pipingfurnace tubes. Incoloy 800H is distinguished from Incoloy 800 for its minimum carbon level of 0.04 wt.% and its high-temperature tensile strength. Whereas Incoloy 800 has excellent corrosion and SCC resistance in aqueous chlorides, extra carbon in Incoloy 800H allows it to be used for Code pressure vessels anpiping as high as 1650°F.

A major caution with Incoloy 800H is that it sensitizes to a very great degree; thfore, we must avoid using the H grade for aqueous services. Even the “standarIncoloy 800 has become more susceptible to sensitization in recent years due tmanufacturers’ trends to increasing the grain size. Contact a materials engineeyou are dealing with these alloys. Incoloy 825 finds use in effluent air coolers wammonium chloride salts form which would typically cause cracking of lesser austenitic stainless steels. The 825 grade is resistant to sensitization at elevatetemperatures due to titanium additions.

Heat Treatment of Nickel-Based AlloysLike carbon and low alloy steels and stainless steels, nickel-based alloys can bannealed in order to soften them and make then more formable and machineabAnnealing is typically done at very high temperatures but for short times. Temptures of 1600–2200°F are common depending on the alloy. In order to avoid oxidizing the annealed part, the anneal may be done in a reducing environmenwill typically last only 10–30 minutes. Annealing results in a completely recrystalized and homogenized grain structure.

If annealing is carried out for several hours, carbides and secondary phases widissolve back into solution. This treatment is described as solution annealing. Stion annealing homogenizes the part and results in an extremely soft material wcan be subsequently reheated (aged) at lower temperatures to yield specific mical properties. Age hardening typically consists of a series of hold times (usualseveral hours or longer) at progressively cooler temperatures from about 1400°down to 1100°F. The age hardening treatment precipitates strengthening carbidand intermetallic phases.



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323 Titanium AlloysOur use of titanium is mostly limited to heat exchanger bundles and tubesheets where numerous corrosion mechanisms are at work and no other material has suffi-cient corrosion resistance. Although expensive, titanium bundles have been found to be cost effective in FCC overhead streams, where chloride pitting and cracking, and ammonium bisulfide corrosion can occur simultaneously. Titanium is also used for bundles and tubesheets in seawater coolers in refineries and on offshore platforms where the exchanger sees seawater on one side and corrosion from hot aqueous chlorides and/or sour water on the other.

We commonly use three grades of titanium alloys. Ti Grade 2 is commercially pure, with at least 98.885 wt.% titanium. Ti Grade 7 contains 0.12–0.25 wt.% palladiuTi Grade 7 has the greatest pitting resistance of the three Ti alloys we use, but the most expensive. Both Grades 2 and 7 have 40 ksi minimum yield strength a50 ksi minimum tensile strength at ambient temperature.

Ti Grade 12 is the strongest. Grade 12 contains 0.8 wt.% nickel and 0.3 wt.% molybdenum, and has 55 ksi minimum yield strength and 70 ksi minimum tensistrength.

High-strength structural grades of titanium which contain aluminum, vanadium,chromium, and molybdenum are also available, but they are primarily used for aircraft, aerospace, and military applications. These structural alloys of titaniumclassified as alpha, beta, or alpha-beta alloys depending on their microstructurewe will not discuss them further here because of their limited use in our industry

324 Copper AlloysThe copper alloys Chevron uses the most are:

• Brass — primarily copper and zinc

• Bronze — primarily copper and tin

• Copper Nickel — primarily copper and nickel

As noted below, the copper alloys have good corrosion resistance to water, butare relatively weak and have very poor fire resistance. See Section 215 for a mcomplete description of the corrosion resistance and potential problems with thalloys.

BrassesOur largest use of copper alloys is for heat exchanger bundles. Admiralty brassthe most commonly used of the copper alloys for heat exchanger tubing becauits resistance to corrosion in water. A potential problem of brass is its susceptibto ammonia or sulfate stress corrosion cracking.

About 28 wt.% zinc and 1 wt.% tin are added to copper to make Admiralty brasfew variations of Admiralty brass are the arsenical, antimonial and phosphorizeinhibited Admiralty alloys. In these “inhibited” alloys, about 0.1 wt.% max. of



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arsenic, antimony, or phosphorus are added to the alloy to prevent dezincification in hot water. Dezincification is localized corrosion of zinc phases in the alloy, which can leave exchanger tubes porous and brittle. Arsenical Admiralty is the most effec-tive, and the most used by Chevron.

Tubesheets of similar copper alloys are highly recommended for use with copper alloy tubes, although carbon steel tubesheets can be used in less severe environ-ments (low chloride content and cool temperatures). Naval rolled brass (copper plus about 35 wt.% zinc and 1 wt.% tin) is the most common tubesheet material for use with Admiralty tubes.

BronzesBronzes are copper-based alloys which are alloyed with tin, aluminum, and/or silicon, but with less zinc than the brass alloys. Due to their lower zinc content, bronzes are not as susceptible to SCC as the brasses, but they are also not as corro-sion resistant. For this reason, we do not use much bronze in Company applica-tions. Where SCC and impingement resistance are needed in conjunction with excellent corrosion resistance, we typically upgrade Admiralty brass by jumping directly to copper-nickel alloys.

Copper-Nickel AlloysThe two common copper-nickel alloys which are used as upgrades for Admiralty brass are “70-30 Cu-Ni” and “90-10 Cu-Ni.” The 70-30 alloy contains approxi-mately 70 wt.% copper plus 30 wt.% nickel plus a small (<1 wt.%) iron additionThe 90-10 alloy is about 89% copper plus 10% nickel plus 1 wt.% iron. Coppernickel alloys are more resistant than Admiralty to wet acid corrosion. They alsoresist ammonia and sulfate SCC.

Impingement attack is a scouring away of protective scales on soft copper alloydue to contact with turbulent or high velocity fluid. Impingement attack can occuon Admiralty brass in water streams where flow exceeds about 5 fps. In such cupgrading to 90-10 or 70-30 may be necessary. The copper-nickel alloys generresist impingement attack to greater than 10-15 fps.

The nickel content of the copper-nickel alloys makes them more susceptible thaother copper alloys to corrosion in ammonium bisulfide and H2S environments.Stainless steels and titanium alloys should be considered for upgrades to Admibrass in sulfur-containing environments.

330 High Temperature Degradation MechanismsThis section describes the most common ways the metals we use can be damawhen exposed to high temperatures, with or without stress being applied. An adtional damage mechanism—high temperature hydrogen attack—involves tempture and hydrogen, and is covered in Section 440 of this manual.

All but one of the damage mechanisms listed in Figure 300-9 below are only acon one type of metal, or family of metals. However, all of these metals (in fact, amaterials) are subject to the creep damage mechanism.



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331 SpheroidizationAbove about 1000°F, carbides will agglomerate or “spheroidize,” and lose sometheir strengthening effect in carbon steels and low-alloy steels. Aside from somreductions in ambient temperature strength, spheroidization can cause decreascreep and stress-rupture life, especially in furnace tubes which commonly run ispheroidizing temperature range.

332 GraphitizationGraphitization of carbon steels and carbon-molybdenum (C-½Mo) steels can oafter thousands of hours above 800°F for carbon steel, and 850°F for C-½Mo. Graphitization occurs most prominently in welds and weld heat affected zones (HAZ), and results in the dissolution of iron carbides to iron and elemental carb(graphite). Linking together or alignment of graphite nodules and flakes causessharp decreases in ductility and toughness, which can make a material susceptfailure from mechanical and thermal shock. Graphitization is eliminated in low-alloy steels by the addition of 0.5 wt.% or more of chromium.

333 Temper EmbrittlementBoth 1¼Cr-½Mo and 2¼Cr-1Mo exhibit an increase in ductile-to-brittle transition temperature (DBTT) after long-time service in the range 650–1100°F. This is knas temper embrittlement (TE). Temper embrittlement can cause these alloys tosignificant toughness, so that they may fracture in a brittle manner even at elevtemperatures, in some cases up to 350°F. The 2¼Cr-1Mo alloy exhibits far greater increases in DBTT than 1¼Cr-½Mo, and for most of our applications temper embrtlement is only a concern with 2¼Cr-1Mo.

Embrittlement is due to segregation of impurity elements to grain boundaries, which causes the fracture path to change from transgranular to intergranular. The worst temperature for embrittlement is about 850°F. Welds and weld heat affected zoare most severely affected by TE, followed by plates and forgings. The tramp

Fig. 300-9 Susceptibility of Metal Types to Damage Mechanisms

Damage Mechanism Metal Type Susceptible to Damage

Spheriodization Carbon steel and low-alloy steels

Graphitization Carbon and C-0.5Mo steels

Temper embrittlement Low-alloy steels

Creep embrittlement Low alloy steels

Sigmitization Austenitic stainless steels (primarily)

885F embrittlement Ferritic stainless steels (primarily)

Intermetallic embrittlement of nickel alloys Nickel alloys

Creep All metals



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elements which play the greatest role in temper embrittlement are antimony, tin, phosphorus, and arsenic. In modern steel making practice, the levels of antimony and arsenic in the steel should be zero. Tin and phosphorus, while usually present, should be controlled to less than 0.01 wt.% to reduce the effects of TE.

Temper embrittlement is important in hydroprocessing reactors, since reactors are typically fabricated from thick-walled 2¼Cr-1Mo in order to resist high-tempera-ture hydrogen attack at temperatures in the 800°F range. Thick-walled vessels more susceptible to brittle fracture even in the absence of temper embrittlemenconcern is heightened when reactors operate in the embrittling range.

Concerns for in-service temper embrittlement cause us to warm these reactorsbefore pressurizing them. A minimum pressurizing temperature (MPT) is choseeach reactor depending on the performance of its fabrication heats to a “step cotest.” The “step cooling test,” developed by Chevron, is an accelerated temper embrittlement test which predicts the amount of embrittlement which will occur heat of steel after long service (100,000 hrs or more) in the embrittling temperarange.

334 Creep EmbrittlementThis damage occurs in the temperature range of about 900–1100°F and involvelow alloy chrome-molybdenum steels, particularly 1Cr and 1.25Cr alloys. As thename implies, it occurs in the creep range of these alloys (see the description ocreep in Section 338). Essentially the same or related mechanisms sometimes the names “stress rupture cracking”, “reheat cracking”, or “strain aging.”

As discussed in Section 338, when materials are exposed to temperatures in thcreep range under stress, they will slowly stretch or deform, until eventually thefail by creep cracking. A unique feature of creep embrittlement is that the matercracks or ruptures with very little deformation.

In terms of the microstructure of the material, the form of damage is “low ductiliintergranular fracture”—cracking along the grain boundaries of the material. Creembrittlement occurs when the grains of the material are substantially harder (stronger) than the grain boundaries. This is caused by precipitation of molyb-denum carbides in the grains (which strengthens the grains), or segregation of elements or impurities in the grain boundaries which weakens the grain boundaor both.

Creep embrittlement has the following characteristics:

1. Creep embrittlement is more severe for higher tensile strength materials, pularly above 110 ksi.

2. Susceptibility of a material to creep embrittlement depends upon grain sizetype of microstructure, in addition to the chemistry effects noted above. A coarse grained material is more susceptible than a fine grained one.



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3. Often, creep embrittlement is most severe when small amounts of creep strain occur over long periods of time. Therefore, it is more severe at the lower temperatures in the creep range.

4. Creep embrittlement is characterized by the low stress rupture ductility.

5. Ambient temperature properties of the material may be little affected by creep embrittlement.

6. Creep embrittlement, unlike some other forms of embrittlement, is not revers-ible by heat treating the material.

From the description above we can see that we are vulnerable to this mechanism when we deal with the low chrome alloys in the creep range. The problem tends to show up near welds, particularly at the coarse Heat Affected Zones. Creep embrit-tlement cracking has been a significant problem with Rheniformer reactors, particu-larly at nozzles. It has also been reported at long seams of some high temperature piping. In addition to the metallurgical factors noted above, ensuring smooth welds is a significant help in avoiding creep embrittlement.

335 Sigma Phase Embrittlement of Stainless Steels (“Sigmatization”)Holding austenitic and ferritic stainless steels within the temperature range 1100–1800°F allows formation of a brittle intermetallic “sigma” phase (γ). Sigma phase formation results in significant reductions in ductility at temperatures belo500°F. At elevated temperatures, adequate toughness and ductility usually remDuring plant start-up and shutdown, however, reduced ambient temperature ductility can cause mechanical and thermal shock failures.

Aside from the formation of sigma phase during high-temperature operation, wecan become sigmatized during post-weld heat treatment. In order to reduce theof sigmatization in austenitic stainless steel welds, the ferrite content of the wellimited by Chevron specifications to the range 3–10%.

Estimated ferrite content of solidified weld metal may be determined from chemical composition of weld consumables using diagrams known as Schaeffler or DeLong diagrams. A ferritescope can also measure ferrite by determining the magnetic response of the weld, since ferrite is magnetic while austenite is not. Consult the Welding Manual for more information concerning welding of austeniticand ferritic stainless steels and determination of ferrite content in welds.

336 885°F Embrittlement of Ferritic Stainless SteelsHeat treatment of ferritic or martensitic stainless steels must avoid slow cooling through the 700–1000°F temperature range due to the formation of brittle phasThe phenomenon is known as 885°F embrittlement and results from the formatof brittle intermetallic chromium-nickel phases known as “alpha-prime” (α'). The 885°F embrittlement problem is a major reason why Chevron does not use the ferritic or martensitic (400 series) stainless steels for high temperature piping orfurnace tube applications.



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337 Embrittlement Mechanisms in Nickel-Based AlloysThousands of hours of service at temperatures in the 1000–1400°F range can embrittlement of nickel-based alloys due to formation of brittle intermetallic phaHigh-carbon Incoloy 800HT is especially susceptible to embrittlement. Failuresembrittled Incoloy 800HT have occurred in chemical plant services where operating temperature routinely reaches 1000°–1200°F. The embrittlement is due toprecipitation and coarsening of brittle grain boundary phases containing nickel,aluminum, and titanium. Embrittlement is manifested by grain boundary crackinnear zero creep ductility, and inability to perform weld repair without cracking.

Use of these alloys in oxidizing environments complicates the problem becausesame process that causes the precipitation of grain boundary phases dilutes chmium there and reduces local oxidation resistance. Failures due to stress-assisgrain boundary oxidation (SAGBO) are notable for their oxidized and cracked gboundaries, while the remainders of the grains appear unaffected. Consult a mlurgist when nickel-based alloys are to be used in very high temperature service

338 CreepAnother high-temperature degradation mechanism is creep. All metallic materiaincluding stainless steels, nickel alloys, titanium alloys, etc., are susceptible to creep. As temperature rises, metals soften and lose some of their strength. Thiof strength causes the material to stretch very slowly over long periods of time elevated temperature.

A typical creep curve is shown in Figure 300-10. Creep occurs in three distinct stages. In the first stage, the amount of stretching is rather fast but does not laslong. In fact, many stainless steels undergo no Stage 1 creep at all. Most of thelife occurs in Stage 2 during which the material expands at a slow but steady raStage 3, which is shorter than Stage 2, growth accelerates rapidly. If a materialenters Stage 3 creep, it can fail without warning and cause a catastrophic failur

We use some materials at very high temperatures (especially furnace tube matrials) with the knowledge that creep may occur, and that we must inspect at regintervals to determine if and when creep is occurring. It is then up to our best eneering judgement to determine if the tubes can continue to operate in Stage 2until the next shutdown, or if there is a risk that they will enter Stage 3 creep anfail before the next shutdown.

The life of a tube can be reduced significantly by what might appear to be only small increase in temperature. Creep life is typically reduced by half for each 25increase in temperature, so that a furnace tube which might last 10 years undenormal operating pressure at 1000°F, will last only 2½ years at 1050°F.

The approximate temperature at which significant creep deformation begins to occur for some alloys is shown in Figure 300-11. Further discussion of creep iscontained in the Fired Heater and Waste Heat Recovery Manual. The Appendix of the Fired Heater and Waste Heat Recovery Manual contains API Recommended Practice RP 530, “Calculation of Heater Tube Thickness in Petroleum Refinerie



which can assist the engineer in choosing furnace tube metallurgy and predicting remaining furnace tube service life as a function of stress and temperature.

340 Avoiding Low Temperature Problems-Brittle FractureSections 341 and 342 are useful to all readers. The rest of Section 340 is for senior inspectors and senior plant engineers.

341 How To Use This SectionWhile brittle fracture of pressure equipment is rare, there have still been occasional cases in our industry in recent years (see Figure 300-12 below). Because brittle frac-ture of pressure equipment is usually catastrophic, the subject warrants our careful attention.

Fig. 300-10 Typical Creep Curve

Fig. 300-11 Typical Temperatures at Which Significant Creep Deformation Occurs*

Material Typical Temperature for Creep

Carbon Steel 800°F

2¼Cr-1 Mo 900°F

9Cr-1 Mo 950°F

T347SS 1100°F

* Be careful - if stresses are high, significant creep can occur at lower temperatures.



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At about ambient temperature and below, carbon steel, low alloy steels, and some stainless steels undergo a “ductile-to-brittle transformation.” If the material is higstressed while in the brittle condition, it may suffer a brittle fracture. With a ductfracture, the metal stretches substantially and often the equipment will leak, bufracture violently. However, a brittle fracture fails suddenly, without warning, andwith a large, immediate, release of energy.

This section outlines the basics of brittle fracture, then details the process Chevand the industry uses to avoid brittle fracture of pressure vessels, piping and ta

• The basics:

– lists the major factors causing brittle fracture– defines the terminology of “Minimum Design Metal Temperature” and

related concepts– outlines the concept of staying below certain pressures when at cold

temperatures– summarizes the development of the industry brittle fracture guidelines,

help give perspective as to where all the various Code, industry, and Chevron standards fit in

• Setting MDMT’s for New Equipment:

– Briefly explains the process for establishing safe limits for new equipme– Notes the temperature maps for helping establish “Critical Exposure

Temperatures”

Fig. 300-12 Piece of Fractured Clear Creek LPG Vessel



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• Special Chevron Criteria:

– Identifies the few specific materials and details where we believe curreindustry guidelines are inappropriate or insufficient

– Notes that these criteria apply to both new and existing equipment

• Setting MDMT’s for Equipment Subject to In-Service Embrittlement

– Identifies which materials are subject to this embrittlement– Provides guidelines for adjusting the MDMT to accommodate this emb

tlement

• Setting MDMT’s for Existing Equipment:

– Provides a step-by-step process for establishing a MDMT for existing equipment

• Autorefrigeration:

– Briefly reviews the concept of autorefrigeration– Explains how to select materials to take into account autorefrigeration– Outlines some options in dealing with possible autorefrigeration effects

existing pressure equipment

342 The Basics

Major Factors Causing Brittle FractureAvoiding brittle fracture involves dealing with some basic facts:

1. Carbon steels and low alloy steels become more brittle at lower temperatu

2. The thicker the steel, the more brittle it behaves.

3. The higher the stress, the more susceptible we are to brittle fracture.

4. The more brittle the material, the smaller the flaw size we can tolerate withcausing a brittle fracture.

5. Some alloy steels can become embrittled in service, and require special consideration.

In our discussion below, we shall see how each of these factors comes into pla

Helpful DefinitionsIt will be useful to first clarify some terminology:

Minimum Design Metal Temperature (MDMT): This is defined in the ASME Code (Section VIII Div. 1, UG-20) as “…the lowest (temperature) expected in service. Consideration shall include the lowest operating temperature, operatioupsets, autorefrigeration, atmospheric temperature, and any other sources of cooling.”



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Critical Exposure Temperature (CET): The CET is terminology used by API Recommended Practice 579 (see “Historical Perspective” below). It is determinfrom the anticipated process and atmospheric conditions, and is defined as “...tlowest metal temperature derived from either the operating or atmospheric contions.” As explained in more detail below, the CET is the lowest metal temperatthe equipment will see when under significant stress. “Significant stress” in moscases is taken as 8 ksi.

Minimum Allowable Temperature (MAT): RP 579 defines this as “…the permis-sible lower metal temperature limit for a given material at a specified thickness based upon its resistance to brittle fracture.” The MAT is derived from mechanicdesign information, materials specifications and/or materials data.

In simple language, the CET is the lowest temperature we expect the equipmensee, and the MAT is the lowest temperature which the equipment material can shandle. We want to make sure the CET is always above the MAT.

Minimum Pressurizing Temperature (MPT): Chevron has used this terminologyfor many years, but it is not found in the Code or RP 579. It means essentially tsame as MDMT or MAT.

Staying Below Certain Pressures When at Cold TemperaturesThe Minimum Design Metal Temperature or the Minimum Allowable Temperatufor any particular piece of equipment is the lowest temperature at which we knohas good resistance to fracture. The Critical Exposure Temperature is more clorelated to the operation of that piece of equipment.

Every new piece of equipment must have a Minimum Design Metal TemperaturAs explained below, it is determined by the manufacturer, based on the mechanand materials data for that piece of equipment. The manufacturer should documit on the “U-1 form”, and we should record it on our Safety Instruction Sheets.

As explained in more detail below, either the Critical Exposure Temperature or Minimum Allowable Temperature can be one temperature at a particular pressuor can be a set of temperatures over a range of pressures. In setting the CET fvessels and piping, we must consider both atmospheric and process conditionsincluding the lowest one-day mean atmospheric temperatures, the lowest tempture under normal operating conditions, startup, shutdown and upset conditionsfuture hydrotests, possible autorefrigeration, and shock chilling.

Typically a project or plant will establish a Critical Exposure Temperature that isrealistic for their climate and process, and then ensure that the Minimum DesigMetal Temperatures of the equipment are below the CET. In some cases this ispractical for all pieces of equipment.

For example - suppose the MDMT for a thick vessel is 70°F, but we know that in the winter months the actual metal temperature may go down to, say, 30°F during a shutdown. For such a case we take advantage of the fact that at low enough st(below 8 ksi) our risk of brittle fracture is negligible, even if the material is brittleIn this case, we must ensure that the vessel is not stressed above 8 ksi (generamembrane stress) any time the metal temperature is below 70°F. In past Chevron



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terminology, we would say that the “Minimum Pressurizing Temperature” for thipiece of equipment is 70°F.

Chevron and industry practice is to avoid pressurizing equipment whenever theequipment is below the MDMT (or the “MPT”). The specific “rules” are:

• For Division 1 vessels built before 1999: stay below 40% of the Maximum Allowable Working Pressure whenever you are below the MDMT.

• For Division 1 vessels built in 1999 and later: stay below 35% of the MaximAllowable Pressure whenever you are below the MDMT.

• For Division 2 vessels: stay below 25% of the Design Pressure whenever yare below the MDMT.

• For piping (ASME/ANSI B 31.3 Code) stay below 40% of the Design Presswhenever you are below the MDMT.

• For tanks, applied stress is a function of fill height rather than internal pres-sure. As explained below, the methodology for determining MDMT's is the same, using exemption curves found in API Standard 650.

Although the wording is different, each of the guidelines above ends up requirinyou stay below about the same 8 ksi level any time you are below the MinimumDesign Metal Temperature. Some of the RP-579 wording is also a little differenbut again RP-579 leads to the same results.

Historical Perspective The paragraphs below summarize the development of the industry brittle fractuguidelines, to help give perspective as to where all the various Code, industry, Chevron standards fit in.

Prior to the 1960s, the Code did not address testing requirements for operating to -20°F. In the 1960s, the Division 2 of Section VIII introduced the first “exemp-tion curves”, in which impact testing was required of materials, unless they werexempted by the material curves in that Code.

From 1969 to 1982, Chevron developed proprietary exemption curves for equipment constructed to Section VIII, Division 1, though this was not required by theCode. In 1983 the Chevron curves were revised.

From 1987 to today, the Section VIII Division 1 code has included exemption curves. These were compiled from the Division 2 curves, an API document (API 650), the British Standard 5500 curves, the Chevron proprietary curves, antwo other major users. It is unclear as to the original basis for the Division 2 curFor some years the Codes were inconsistent in the curves they used for settingMDMTs, but in recent years they have essentially standardized on the same cu

In 1990 the API issued Recommended Practice 920, “Prevention of Brittle Fracof Pressure Vessels.” This document pertained to both new and existing vesselit specifically dealt with the issue that many existing vessels successfully operaalthough they would not meet the current guidelines for avoiding brittle fracture



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In the mid-1990’s the ASME Code B31.3 issued the first exemption curves for piping. Prior to this time, all piping was considered suitable down to -20°F. (Even now, the ASME Section VIII pressure vessel code assumes all piping components of pressure vessels to have the same properties, so there is still some inconsistency).

In the late 1990s, a major industry-wide “Fitness For Service” effort was startedgive a more rigorous, formal, and industry-standardized basis for how to deal wequipment which is in service, with defects. The (very large) resource documenthis effort is API Recommended Practice 579, which is expected to be issued in2000. API RP 579 will supersede the previous API RP 920 document. RP 579 uand extends current Code methodology, and in turn the ASME will adopt the RP 579 methodology when it issues its “Post Construction Code” (coming someyears in the future).

The terminology “Critical Exposure Temperature” and “Minimum Allowable Temperature” comes from RP 579. RP 579 does not use the traditional Chevrowording of “Minimum Pressurizing Temperature.” We are adopting the RP 579 methodology, which is consistent with our past practice. We are also adopting tRP 579 terminology, but for those who are used to thinking in terms of “MinimuPressurizing Temperatures” we will also use that term.

As noted below, it is our position that when the Minimum Design Metal Temperature (or MP’s) have been calculated using the older Chevron guidelines, those lations are still valid today, even when in some cases the current curves may bsomewhat more conservative. Any new MDMT’s (or MPT’s) should be calculateusing the current Code curves, except for the few cases where our guidelines amore conservative.

A Caution Regarding the “Rules” for Pressurizing EquipmentAbove we noted that we must not pressure Division 1 vessels above 40% or 35% of their MAWP whenever they are below the MDMT, depending upon when the vessel was built. More precisely, this depends upon which edition of the Code was used.

These rules are based on staying below about 8 ksi membrane stress. In 1999 the ASME Code increased the allowable stresses for Division 1 vessels (effectively allowing thinner vessels).This means that to stay below the “safe” stress while we must reduce the pressure by the same amount.

343 Setting MDMT’s For New Equipment

Determining the MDMT for Pressure Vessels and PipingFor new equipment the manufacturer should determine the MDMT. For ASME Code vessels and piping, the MDMT is determined from “exemption curves” givin the Code. These are:

• For Div. 1 vessels, ASME Section VIII Div. 1 Figure UCS-66 and its notes • For Div. 2 vessels, ASME Section VIII Div. 2 Figure AM-218.1 and its notes• For process plant piping, ASME/ANSI 31.3 Figure 323.2.2 and its notes



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Actually, in the latest editions of the Codes, these curves are almost identical. Figure 300-14 on page 300-45 can also be used for existing equipment.

The basic methodology for determining the MDMT is rather simple:

1. From the appropriate exemption curve, note the Minimum Design Metal Temperature for that particular material and thickness.

2. Repeat step (1) separately for every component of the vessel (heads, shell, nozzles, etc.).

3. Take the highest (most conservative) MDMT of all the components as the MDMT for the entire vessel.

Some special notes:

• For any alloy (non-carbon steel) vessel, always consult a materials engi-neer in setting the MDMT. Alloy materials can embrittle in some services, and the MDMT set by the fabricator may not be adequate for the long term.also the discussion below in Section 345.

• For Division 1 vessels, the MDMT for all B16.5 flanges is set at -20°F, while the nuts are set at -50°F.

• The Division 1 exemption curves extend all the way to six inches; but evenwhen the base metal is exempt, the welds of that material must be impact tif the material is thicker than 4 inches.

• For Division 1 vessels, the Welding Procedure Qualification must generallyimpact tested if the base metals require impact testing. (See paragraph UCfor more details.)

• For Division 2 vessels, there are special rules for some alloy materials (pargraph AM-213), but just follow the advice above to always consult a mate-rials engineer when dealing with an alloy vessel.

• Chevron has more conservative requirements for MDMT’s of a few specificmaterials. See Section 344.

Tanks The methodology for tanks is much the same. Refer to the set of tank exemptiocurves in API Standard 650, “Welded Steel Tanks for Oil Storage” and also to Chevron’s Tank Manual.

Advising Suppliers on Desired MDMT’s for Chevron Projects Typically the Chevron representative will tell the supplier the desired MDMT's fothe equipment, based upon the geographic location of the equipment. Often thedesired temperature is equal to the “lowest one-day mean temperature” for thespecific location. For locations in the contiguous U.S. and Southern Canada, thlow one-day means are shown on the map given in Figure 300-13 (reprinted froAPI Standard 650, “Welded Steel Tanks for Oil Storage”).


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If the MDMT of the supplier’s standard material is greater than what we want foour particular location, our options are:

1. Upgrade the material to one which will meet our desired MDMT’s

2. Charpy impact test the material at the desired MDMT’s. The test requiremeare spelled out in the relevant Code. Note that while the testing itself (“Chaimpact testing”) is inexpensive, the supplier may increase the cost of the mrial for fear of not passing the test.

3. Accept the higher MDMT and put in engineering controls, such as establishMinimum Pressuring Temperature limits to ensure that the material is not significantly stressed whenever it is colder than the MDMT (see example opage 300-35.

The Chevron representative must advise the supplier where Chevron requires conservative treatment in selecting MDMTs for a few specific materials. This is explained in Section 344.

344 Special Chevron CriteriaWith very few exceptions, Chevron follows the Code requirements for determinthe MDMTs and whether or not materials must be impact tested. The few exceptions are due to our belief that the Code is not conservative enough for a few materials.

Chevron Exceptions

All grades of SA-285 and SA-515 steels thicker than ¾" should go on Curve A, not Curve B. The Codes assign the higher strength Grade C of SA-285, and Grades 65 and 70 of SA-515, to the most conservative Curve A. Chevron agrees, but lacking any additional data we assign all grades of these materials to Curve A, while the Code allows SA-285 Grades A and B, and SA-515 Grade 60 to be on curve B. Specifically, we say SA-285 and SA-515 steels thicker than ¾" should be assigto Curve A. Our logic is that since the SA-285 may be a semi-killed steel, and S515 is a coarse-grained material, the toughness characteristics do not warrant tmore conservative curve (at least for relatively thick sections) unless we can sesupporting data.

SA-106 and SA-53 pipe thicker than ¾" should go on Curve A, not Curve B, unless normalized. SA-106 and SA-53 pipe can have coarse grain and quite poor toughness properties, particularly if they are thick. Often this thick pipe is used in high pressure and critical services. Therefore, we assign the material to the more conservative curve (at least for relatively thick sections) unless we can see supporting data.

For “obsolete” materials, refer to Section 346. Because the Codes address only new equipment, they do not refer to some older materials that are no longer specified, but which we still have in our plants. Section 346 assigns these older materials to the appropriate curves.



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Selection of MDMT for Vessel and Piping SupportsThe vessel support or skirt where it immediately attaches to the vessel is subject to essentially the same temperature as the vessel shell. A failure in that attachment could propagate into the vessel shell and threaten the reliability of the vessel itself. Therefore, our Chevron pressure vessel specifications call for skirts and other vessel supports to be suitable for the same Minimum Design Metal Temperature as the vessel.

Saddle-type supports of horizontal vessels are less critical. For new equipment it is still generally good practice to have them meet the same Minimum Design Metal Temperature criteria as the vessel.

Piping supports do not have any special criteria. We are not aware that brittle frac-ture emanating from piping supports has been an issue in the industry.

345 Setting MDMTs For Equipment Subject To In-Service Embrittlement Please contact a materials engineer whenever the potential for in-service embrittle-ment is encountered—essentially, whenever dealing with alloy vessels.

High AlloysUnder special circumstances 300-series and 400-series stainless steel can suffsevere in-service embrittlement (so called “sigmatization” and “885 embrittlemerespectively). For Chevron, these materials rarely limit Minimum Design Metal Temperatures, because the sigmatization embrittlement does not occur until ab1100°F; and we avoid using the 400-series stainless steels in pressure-containiapplications precisely because of the embrittlement problems. Other high alloyssuch as the “Incoloys”, can also experience various embrittlement mechanisms

Low AlloysLow alloys (1Cr, 1.25Cr, 2.25Cr, and 5Cr) are subject to “temper embrittlement”they are exposed to temperatures above about (conservatively) 650°F. This subject is discussed in more detail in Section 333, but the net effect is that the “ductile-brittle transition temperature” increases. That is, the equipment will be brittle athigher temperatures than when it was new.

An outline of how we deal with the 1Cr, 1.25Cr, and 2.25Cr materials is given below. The 5Cr material is not used for vessels, and we have not encountered practical embrittlement problems of 5Cr piping (there are rare instances of 5Cr furnace tube embrittlement).

1Cr and 1.25 Cr-0.5Mo Pressure Vessels. In-service embrittlement of these vessels is covered in more detail in a 1990 memorandum3. Our guidelines for estab-lishing MDMTs for these vessels are:

• For normalized and tempered 1Cr or 1.25Cr steels operating above 750°F, use Curve A of the Code exemption curves (Division 1 or 2).

• For annealed 1Cr or 1.25Cr steels operating at any temperature, also use Curve A (Division 1 or 2).



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• For normalized, or normalized and tempered, 1Cr or 1.25Cr steels operatinbelow 750°F, use Curve B (Division 1 or 2).

2.25Cr-1Mo Pressure Vessels. Ever since the problem of temper embrittlement olow alloy steels was first recognized in the late 1960's and 1970's, particularly o2.25Cr hydroprocessing vessels, there have been numerous studies and memoissued on the subject4. Our guidelines for establishing MDMTs for these vessels a

• For 2.25Cr-1Mo Class 2 higher strength steels (typically Code Division 2) steels, typically used for large hydroprocessing reactors and vessels, each should already have an MDMT (MPT) already assigned which takes into account that particular vessels' vintage and metallurgy. Contact CRTC Materials and Equipment Engineering if you cannot find such documentation.

• For 2.25Cr-1Mo Class 1 lower strength steels (typically Code Division 1) steels, vessel MDMTs (MPTs) are set at either 160F (for steels purchased pto 1983, which were not screened for susceptibility to temper embrittlementat 120°F (for steels purchased for the 1983 RLOP project or later, which didundergo temper embrittlement screening).

1Cr, 1.25Cr, and 2.25Cr Piping. For temperatures above about 750°F for low alloy piping (1Cr, 1.25Cr, 2.25Cr), we must consider the potential effects of temembrittlement, as we do for the vessels. The ASME VIII Code allows essentiallpipe material to be on Curve B, while the ASME/ANSI B31.3 assigns a blanket 20F to such low alloy materials (such as SA-335 Gr P22, 2.25Cr-1Mo). Please contact CRTC Materials and Equipment Engineering for guidance in setting MDMTs of alloy piping operating above 750°F.

In truth, we have not made special precautions for such alloy piping in the pastreasons we have not had problems are most likely because:

1. The piping is unlikely to see low temperatures while under stress-for examthe process of heating the reactors to meet the MDMT requirements for a hydroprocessing vessel would be more than adequate to protect the pipingthe same circuit, and

2. The piping alloys should not temper embrittle to nearly the same degree ashigh strength (especially quench and tempered) vessel materials.

Nevertheless, for 1Cr, 1.25Cr and 2.25Cr piping operating above 750°F we should follow the same guidelines as outlined for pressure vessels above.

3. “Minimum Pressurizing Temperatures for Vessels Made of 1Cr-0.5Mo and 1.25Cr-0.5Mo Steels”, 1/16/19MEE file 47.50.01, 45.70.04

4. Two useful summaries are: “Minimum Pressurizing Temperature for 2.25Cr-1Mo Hydrotreater Reactors”,September 9, 1983, MEE file 45.70.04; and “Minimum Pressurizing Temperature Class I 2.25Cr-1Mo SteDecember 15, 1988, MEE file 45.70.04.



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346 Setting MATs for Existing Equipment

Pressure Vessels and PipingThis section guides field personnel in determining the Critical Exposure Tempera-tures and Minimum Allowable Temperatures (equivalent to “MPT”s) for an existpressure vessel or piping system. Tanks follow a very similar methodology whicdescribed below.

Information needed to assess your equipment includes:

• operating pressure and maximum allowable working pressure,

• normal operating and design temperatures,

• materials of construction, including the specific grades of steel (e.g., “A516Grade 70”),

• as-fabricated or current wall thickness of each component,

• thickness of welds (best found on fabrication drawings),

• history of weld repairs and alterations,

• heat treatment history (was the material specially heat treated, such as norized? Were the welds postweld heat treated)?

• Type of process fluid (e.g., can the fluid induce autorefrigeration of the vessSee Section 347.

• Lowest one-day mean temperature at the equipment location (e.g., Figure 300-13).

For vessels, much of this information can be found on the U-1 Form “Manufac-turer’s Data Report.”

Level 1, Level 2, and Level 3 Brittle Fracture AssessmentsThe (to be published) API RP 579 gives procedures for assessing pressure vespiping, and tanks which are labeled “Level 1”, “Level 2”, and “Level 3.” Field personnel should be familiar with the “Level 1” requirements described below. ALevel 1 assessment relies either on having Charpy impact test results for the pular steel used, or on the use of industry accepted impact test exemption curvethe general grade of steel used.

If a pressure vessel fails a Level 1 assessment (that is, the assessment finds thvessel could be subject to temperatures below the MDMT), then a Level 2 assement may be done. Some aspects of a Level 2 assessment are briefly outlined If a vessel fails a Level 2 assessment, a Level 3 assessment can be made whicwould use sophisticated fracture mechanics and risk analyses performed on a by case basis. We recommend consulting with MEE for help with Level 2 or Levassessments.



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Step 1. Check for an existing MDMT.

The first step is to find out if the equipment manufacturer has already specified the MDMT. This information should be on the Chevron Safety Instruction Sheet—if is not, be sure to add it when you complete work! The information may (should)also be found on the “U-1 Form” (Manufacturer’s data sheet), on the vessel namplate, or on the manufacturer's fabrication drawings. If you are uncertain how aMDMT was determined, you should recalculate it, or ask MEE for help.

Step 2. Use Charpy Impact Test Exemption Curves to Determine an MAT Based on Material and Thickness.

If no MDMT was found in Step 1, you can determine the MAT using the ASME Code exemption curves. The intent of the curves is to provide a temperature abwhich we can have confidence that all heats of a particular grade and thicknesssteel will have enough toughness that the steel can be used at full pressure (10MAWP) without risk of brittle fracture. Very roughly, we can expect the curves torepresent about 15 ft-lbs or better of charpy impact toughness, although this mabe strictly true in all cases.

The curves found in the various pressure vessel and piping codes are essentiasame. The draft API RP 579 uses one set of curves for all vessels and piping, awe will adopt the same approach here. Figure 300-14 gives the exemption curvNote that this set of curves may be used for both Division 1 and 2 pressure vesBy tweaking Curve B a bit, it is also used for piping (see note 5 in Figure 300-14As explained below, tanks use somewhat different curves.

Figure 300-15 tells which materials go on the different curves. In almost all casethe Chevron assignment of materials is the same as the Codes/RP 579. Howevexplained in Section 353, in a few cases we are more conservative than the Codes/RP 579. Also, the Codes/RP 579 do not reference some of the “obsoletematerials still found in our plants. In Figure 300-15 we have assigned these oldmaterials to the appropriate curves.

For welded assemblies comprised of more than two components (such as a noto-shell joint with a reinforcing pad), determine the governing thickness and persible MDMT for each of the individual joints of the welded assembly, and use thwarmest (most conservative) of the MDMT’s as the permissible MDMT of the entire assembly.

How to Determine the “Governing Thickness.”. In using the exemption curves, we need to know the thickness of the component. The “governing thickness” (tg) is defined in API RP 579 and the Code as follows:

• for butt joints, except those in flat heads and tubesheets, the nominal thicknof the welded joint. See Figure 300-16(A).

• for corner, fillet, or lap welded joints, including attachments, the thinner of ttwo parts joined. See Figure 300-16 (B) and Figure 300-17 (C).



o-

the d flat

• for flat heads or tubesheets, the thinner of the two parts joined or the compnent thickness divided by four, whichever is larger. See Figure 300-17 (D and E) and Figure 300-18 (F).

The governing thickness of a casting shall be its largest nominal thickness, andgoverning thickness of nonwelded parts, such as bolted flanges, tubesheets, anheads, is the component thickness divided by four. See Figure 300-17 (D).

Fig. 300-14 Minimum Allowable Metal Temperature for Pressurization of Equipment Without Impact Testing (Cour-tesy of ASME and Courtesy of American Petroleum Institute)

Notes:

1. Curves A through D define material specification classes in accordance with Table 3.313.4.

2. Equipment whose CET is above the appropriate material curve is exempt from further brittle fracture assessment.

3. This figure is from paragraph UCS-66 of the ASME Code Section VIII, Division 1, and API RP-579.

4. Curve A intersects the y-axis at -8°C (18°F), Curve B intersects the y-axis at -29° (-20°F), and Curves C and D intersect the y-axis at -48°C (-53°F).

5. These curves can also be used to evaluate piping components designed to ASME 1331.3. In this case, Curve B should be shifted to the right so that 1.27 mm (0.5 in.) corresponds to a temperature of -29°C (-20°F). To account for this shift in an assessment, an effective governing thickness equal to the actual governing thickness minus 2.69 mm (0.106 in.) can be used to determine the MAT.



Fig. 300-15 Assignment of Materials to the Curves in Figure 300-14 (1 of 2)

Curve Material (1, 2, 6)

A 1. All carbon and all low alloy steel plates, structural shapes and bars not listed in Curves B, C, and D below.

2. SA-216 Grades WCB and WCC if normalized and tempered or water-quenched and temperedSA-217 Grade WC6 if normalized and tempered or water-quenched and tempered.

3. The following specifications for obsolete materials are also included in Curve A: A7, A10, A30, A70, A113, A149, A150 (3).

4. The following specifications for obsolete materials are also included in Curve A: S1, S2, S25, S26, S27 (4)

5. A201 and A212 unless it can be established that the steel was produced by a fine-grain practice (5).

6. SA-285 through SA-515, all grades, in thicknesses greater than ¾"7. SA-53 through SA-106 pipe in thicknesses greater than ¾"

B 1. SA-216 Grades WCA if normalized and tempered or water-quenched and tempered SA-216 Grades WCB and WCC for thicknesses not exceeding 2 inches if produced to a fine grain practice and water quenched and tempered SA-217 Grade WC9 if normalized and temperedSA-285 Grades A and B (note: See Item 6 above, for Chevron restrictions greater than ¾")SA-414 Grade ASA-442 Grade 55 >1in. if not to fine grain practice and normalizedSA-442 Grade 60 if not to fine grain practice and normalizedSA-515 Grades 55 and 60 (note: See Item 4, above, for Chevron restrictions greater than ¾")SA-516 Grades 65 and 70 if not normalizedSA-612 if not normalized SA-662 Grade B if not normalized Code Case 1256 (equivalent to SA-442) if not normalized Code Case 1280 (equivalent to SA516) if not normalized

2. Except for cast steels, all materials of Curve A if produced to fine grain practice and normalized which are not listed for Curve C and D below

3. All pipe, fittings, forgings, and tubing not listed for Curves C and D below; (note: see Item 7 above for Chevron restrictions of A-53/A-106 pipe greater than ¾")

4. Parts permitted from ASME Code Section VIII, Division 1, paragraph UG-11 shall be included in Curve B even when fabri-cated from plate that otherwise would be assigned to a different curve.

5. A201 and A212 if it can be established that the steel was produced by a fine-grain practice.

C 1. SA-182 Grades 21 and 22 if normalized and tempered SA-302 Grades C and D SA-336 Grades F21 and 22 if normalized and tempered SA-387 Grades 21 and 22 if normalized and tempered SA-442 Grades 55 <1in. if not to fine grain practice and normalized SA-516 Grades 55 and 60 if not normalized SA-533 Grades B and C SA-662 Grade A

2. All material of Curve B if produced to fine grain practice and normalized and not listed for Curve D below



than .5",

,

ack

es

Division 1 Vessels may be allowed a reduction in the MDMT. For Division 1 vessels fabricated from P1 Group No. 1, or P1 Group No. 2 Code steels, you may reduce the MDMT by 30°F if the steel was postweld heat treated and the governing thickness is less than or equal to 1.5". This is allowed because vast experience with PWHT’d vessels has shown that they are far less susceptible to brittle fracture non-PWHT’d vessels. (The code requires PWHT for thicknesses greater than 1so this additional “credit” for non-required PWHT is not available for thicker vessels.)

Some Comments for Piping Systems. For establishing MDMTs of piping systemsthree aspects are worth considering:

1. For thicknesses less than ¾" we generally have not made an effort to go band establish MDMTs for existing systems. This decision is based upon theexcellent experience we have had with piping systems. However, operatingfacilities in cold climates (which can see temperatures significantly below freezing), or those that operate systems which can see process temperatur

D SA-203 SA-442 if to fine grain practice and normalized SA-508 Class 1 SA-516 if normalized SA-524 Classes 1 and 2 SA-537 Classes 1 and 2 SA-612 if normalized SA-662 if normalized SA-738 Grade A Code Case 1256 (equivalent to SA-442) if normalized Code Case 1280 (equivalent to SA-442) if normalized

Notes:1. When a material class or grade is not shown, all classes or grades are included.

2. The following apply to all material assignment notes

– Cooling rates faster than those obtained in air, followed by tempering, as permitted by the material specification, are considered to be equivalent to normalizing and tempering heat treatments.

– Fine grain practice is defined as the procedures necessary to obtain a fine austenitic grain size as described in SA-20.

3. The first edition of the API Code for Unfired Pressure Vessels (discontinued in 1956) included these ASTM carbon steel plate specifica-tions. These specifications were variously designated for structural steel for bridges, locomotives, and rail cars or for boilers and firebox steel for locomotives and stationary service. ASTM A 149 and A 150 were applicable to high-tensile-strength carbon steel plates for pres-sure vessels.

4. The 1934 edition of Section VIII of the ASME Code listed a series of ASME steel specifications, including S1 and S2 for forge welding; S26 and S27 for carbon steel plates; and S25 for open-hearth iron. The titles of some of these specifications are similar to the ASTM specifica-tions listed in the 1934 edition of the API Code for Unfired Pressure Vessels.

5. These two steels were replaced in strength grades by the four grades specified in ASTM A 515 and the four grades specified in ASTM A 516. Steel in accordance with ASTM A 212 was made only in strength grades the same as Grades 65 and 70 and has accounted for several known brittle failures. Steels in conformance with ASTM A 201 and A 212 should be assigned to Curve A unless it can be estab-lished that the steel was produced by fine-grain practice, which may have enhanced the toughness properties.

6. No attempt has been made to make a list of obsolete specifications for tubes, pipes, forgings, bars and castings. Unless specific informa-tion to the contrary is available, all of these product forms should be assigned to Curve A.

7. These assignments are from the draft of API Recommended Practice 579, except the items in italics are Chevron modifications.

Fig. 300-15 Assignment of Materials to the Curves in Figure 300-14 (2 of 2)

Curve Material (1, 2, 6)



Fig. 300-16 Typical Vessel Details Showing the Governing Thicknesses (1 of 3)




ld

gy f the

n 0.5". ks s

brittle

uch as the

well below freezing, should consider reviewing their systems. Contact MEE for help.

2. For temperatures above about 750°F for low alloy piping (1Cr, 1.25Cr, 2.25Cr) we must consider the effects of temper embrittlement. See the comments above in Section 345.

3. For pump cases, valves, and other cast components, Chevron has historically not been concerned with determining an MDMT/MAT. Because these compo-nents are typically highly over-designed, stress levels are not high enough to lead to brittle fracture. At this time, we would recommend against determining MDMT’s for such components. We will revisit this issue if the industry shoutake another approach in the future.

Some Comments for Tanks. Use API Standard 650 and the Tank Manual (along with API RP 579) for guidance in establishing MDMTs for tanks. The methodolois the same, but the curves and some of the materials employed are different. Itank material is unknown, then API RP 579 provides some help in that we can consider the tank safe to use at any temperature for metal thicknesses less thaAlso, metal temperatures above 60°F are safe regardless of the thickness. For tanwith metal temperatures less than 60°F, and thicknesses greater than 0.5", contactMEE for help. Also contact MEE for help with atmospheric or low pressure tankdealing with a refrigerated product.

Level 2 Assessments (These are from RP 579, Contact MEE for help)

Pressure Vessels, Method A: This method takes advantage of the fact that if the operating pressures/stresses are well below the design values, then the risk of fracture is much less. The method in effect involves calculating the ratio of the actual vs. the design stresses, then going to a curve to gain reductions of as m100F or even more in the MDMT/MAT. The ASME Code Divisions 1 and 2 use same methodology for new construction.




to at low

isfac-

(a s, to

-by-

ing and ed.

era-upon little on

may , the

g not .

t

s ou

stic e the . e

Pressure Vessels, Method B: For both Division 1 and 2 vessels, a reduction in MDMT can be taken based upon a combination of the actual metal temperature during a hydrotest, and the ratio of the operating pressure to the hydrotest pressure.

Pressure Vessels, Method C: This is essentially a “grandfather” set of guidelines consider a vessel safe for continued use based upon past experience operatingtemperatures (there is no Code equivalent, because the Code is only for new construction).

Piping, Method A: This method uses the same methodology as described for vessels, Method A above.

Piping, Method B: Seamless piping can be considered suitable to as low as -50°F (or possibly even lower), if a series of guideline questions can be answered sattorily, with special emphasis to avoid “shock chilling” (very rapid cooling of the metal).

Tanks: A Level 2 assessment for tanks involves answering a series of questionsdecision tree), including such factors as past operating conditions in some casedetermine the suitability for future service.

Level 3 Assessments (From RP 579, Contact MEE for help)Level 3 assessments of pressure vessels, piping, and tanks are done on a casecase basis. They typically involve specialists from several disciplines including process, materials, mechanical, and inspection. Often stresses are analyzed usadvanced techniques such as finite element analysis, and considering localizedtransient conditions. Normally a maximum expected flaw size must be determin

347 AutorefrigerationOne must consider the potential for autorefrigeration occurring either during option or as a result of equipment failure. The effect of autorefrigeration depends the state of the process fluid; for example, the vessel contains all gas (typicallyeffect), all liquid (typically large effect), or a mixture. The effect also depends uphow the vessel may be vented. Autorefrigeration, caused by depressurization, also occur in a flowing system with a flashing liquid. As the pressure decreasestemperature will follow the vapor pressure curve.

In recent years, at least one catastrophic failure occurred when a unit processinLPG suddenly depressured, causing the equipment to cool. The equipment didfail upon the initial event, because the pressure was low as the contents ventedHowever, the unit was repressurized while the equipment was still cold—at thapoint the equipment failed.

Autorefrigeration is not considered as stressful to the equipment as is continuouoperation at cold temperatures. This is due to the principle explained above: if yare below 8 ksi stress, you will not have brittle fracture. Therefore, it is not reali(nor often economic) to select the materials based upon the coldest temperaturequipment could possibly reach under autorefrigeration (at near zero pressure)Instead, for ASME Section VIII Division I vessels we would typically consider th



ore-i-

ld

y

ick-

e

d her d tle trol-

k ler e

sures inst

temperature of the vessel contents when the vessel is at 40% of the Maximum Allowable Working Pressure.

When dealing with autorefrigeration, as with brittle fracture in general, it is the metal temperature that is important. In some cases this can help give us an extra margin of safety, but a more careful thermal analysis of the cooling effects would be required.

If a review of operating facilities determines that some equipment may be subject to temperatures below the MDMT while above 40% of the MAWP, we urge that CRTC be contacted for a closer review. In some cases a “Level 3” analysis may be needed—this analysis determines what flaw sizes could be tolerated under autfrigeration conditions. The final step of such an analysis would be to assure (typcally by thorough nondestructive examination) that no such flaws exist, nor couthey reasonably occur before the next inspection interval.

348 Notes on Hydrotest

Effects of MDMT on Hydrotesting of Pressure Vessels and Tanks

Hydrotesting of Pressure Vessels. In general, hydrotest of existing equipment mabe required following: alterations or major repairs, re-rating that increases the equipment’s design pressure or temperature, determination of significant wall thness loss due to corrosion, etc. If it is determined by the field engineer that a hydrotest is required on existing equipment, it is imperative that the hydrotest bdone at a warm enough temperature to avoid the risk of brittle fracture.

ASME Code guidelines suggest that the mean metal temperature of equipmentduring hydrotest be at least 30°F warmer than the MDMT for the vessel. This addemeasure of safety is due to the fact that the hydrotest exposes the vessel to higthan design pressure (1.50 times MAWP for Section VIII, Division 1 vessels, an1.25 times Design Pressure for Division 2 vessels), during which the risk of britfracture is increased. The mean metal temperature is typically controlled by conling the temperature of the hydrotest water.

Chevron practice agrees with the added 30°F margin, except when it would cause the hydrotest to be done at hotter than 120°F. We avoid hydrotesting with water warmer than 120°F to limit the chance for burns to personnel in the event of a leaor rupture. If there is a conflict between keeping the hydrotest temperature coothan 120°F, but warmer than 30°F above the MDMT, a materials engineer should bconsulted.

If at all possible, hydrotest should be done against blinded flanges, not against blocked valves. Hydrotest pressure shall be limited to a lower value against blocked-in valves than against blind flanges. Figure 300-19 lists hydrotest presfor ASME carbon steel and low-alloy pipe classes against blind flanges vs. agablocked-in valves.

Note Hydrotest pressures are lower for stainless steels than for carbon and low-alloy steels.



e ace-ll, e r

the MT

rotest ter

thick-s or is f om use

Hydrotesting of Tanks. Hydrotesting of existing tanks is covered by API Standard 653 “Tank Inspection, Repair, Alteration, and Reconstruction.” Tanks which havundergone major repairs or alterations, such as cutting, adding, removal or replment of a major portion of the shell, the annular plate ring, the concrete ring wathe shell plates below the design liquid level, or the shell-to-bottom weld, may bsubject to hydrotesting before being placed back in service. Refer to API 653 fomore information.

Although the Standard does not suggest that the hydrotest temperature exceedMDMT, wherever possible the hydrotest water should be warmed above the MDto avoid brittle fracture. Warming above MDMT is not as critical for tanks as for pressure vessels, since tanks are not typically pressured any higher during hydthan during normal operation. As with the pressure vessel testing, hydrotest wawould be kept to a maximum of 120°F, if possible, to avoid danger to personnel from leaking water.

349 Worked Examples

Equipment Fabricated to ASME Code Section VIII, Division 1

Note For Division 2 equipment, contact a metallurgist for help.

Example 1: K.O. Drum

Suppose the shell and heads are all SA285 Grade C carbon steel with nominalness of 9/16" and they are double butt welded. Barring any unusual weld detailthick reinforcing pads, the governing thickness for both the shell and the headsassumed to be 9/16" (equal to the welded nominal thickness). In the absence ofabrication drawings, this assumption should be checked by field inspection. FrFigure 300-15, we see that A-285 Grade C steel is assigned to Curve A. (BecaGrade C of SA-285 is not specifically listed, you must assume it is assigned to

Fig. 300-19 Hydrotest Pressures for ASME Carbon Steel and Low-Alloy Pipe Classes Against Blind Flanges vs. Against Blocked-in Valves

Standard ASME Carbon Steel / Low-Alloy Hydrotest Pressure

Pipe Class By Flange Rating Against Blocked-in Valves

150 psig 425 psig 350 psig

300 1100 750

600 2175 1000

900 3250 2200

1500 5400 3600

2500 9000 6000

Note CAUTION! Often high pressure flanges do not limit the hydrotest. Be sure the pipe wall is sufficient.



ngitu-l. thick heet

Curve A.) Using Figure 300-15, for a 9/16" (0.5625") thick section on Curve A, we can read on the Y-axis of the plot an MDMT for this vessel of 40°F.

The curves thus allow us to assume that there are no heats of A285 Grade C steel which would be at risk of brittle fracture above 40°F as long as the wall thickness is only 9/16". If the wall thickness of the same vessel was 2", the MDMT would rise to nearly 100°F. At that thickness, the vessel would be susceptible to brittle fracture up to 100°F.

If this drum was located at Hawaii Refinery, where the critical exposure tempera-ture (CET) exceeds 40°F, this exercise would show that no risk of brittle fracture exists with the vessel, and that no special start-up and shutdown precautions are warranted at that location. On the other hand, if the drum was located in El Paso, where the lowest one-day mean temperature is about 10F, (see Figure 300-13), a risk of brittle fracture would exist. In the El Paso location, when the ambient temperature during start-up or shutdown was less than 40F, the internal drum pres-sure should be kept below 65 psig, which is 40% of the MAWP of 163 psig.

For overseas locations where historical weather information is not available, care will be required to keep pressure below 40% of MAWP (or 25% for Division 2 vessels) whenever ambient temperatures are near MDMT. For locations shown on the map in Figure 300-13, the same care is required, but the map can serve as a guide to alert the operator when a problem with brittle fracture may exist.

Example 2: Assume the Same Vessel was Fabricated from Different Material

Suppose the same vessel as in Example 1 was fabricated from grade A516 Grade 60 steel. In that case, Curve C would be used for the MDMT determination. For the 9/16" thick drum fabricated from SA516 Grade 60, the MDMT is -30°F. With this material, even the El Paso location would have no concern about brittle fracture with this drum.

This example shows that for some locations, use of a tougher steel allows a vessel to be run immediately at 100% of MAWP on cold start-up, rather than at 40% of MAWP, which can save valuable time. Conversely, if during fabrication of the vessel, the steel had been Charpy Impact tested at 10F, and passed the tests in accor-dance with UG-84 of ASME Section VIII, Division 1 (or AM0211 of Section VIII, Division 2 for Div. 2 vessels), then the vessel could be assumed to be immune to brittle fracture under all weather conditions at the El Paso location.

Typically, for a colder location, either a tougher steel will be used or Charpy impact testing will be done at the lowest one-day mean temperature for the location, so that start-up and shutdown schedules are not affected by the concern for MDMT.

Example 3: A Heat Exchanger

Assume that the shell material is SA516, Grade 70 carbon steel. The nominal thick-ness, and assumed governing thickness, of the shell is ½". It has double butt lodinal and girth weld seams. The channel forging is SA105, Grade II carbon steeThe governing thickness of the channel is 4¼". The nonwelded tubesheet is 6"SA105, Grade II carbon steel. The governing thickness of this nonwelded tubesis 1½" (6" divided by four).



uld

e s al-

.

ith a

for

e per-

on

t ot

es-or

a-

d

that s se, hich

Baffle and partition plate materials and thicknesses are not considered. It is Chevron’s philosophy that non-pressure containing components and welds shonot enter into MDMT determinations.

For the channel forging and tubesheet, it is possible that the materials were purchased in the normalized condition; however, there is no proof of such on thU-1 Form. Unless proof of normalizing can be found on available mill certificatefor this exchanger, the channel and tubesheet must be assumed to be not normized. In that case, the channel forging (SA105, Grade II steel) goes on Curve AWith a weld thickness of 4¼", the MDMT for the channel forging (using Figure 300-14 is 118°F.

The SA516, Grade 70 carbon steel (non-normalized) shell goes on Curve B. Wthickness of ½" governing thickness, the MDMT for the shell is -5°F.

The tubesheet is SA105, Grade II with governing thickness of 1½". The MDMTthe tubesheet is 85°F.

The MDMT for the exchanger is chosen to match the highest MDMT for any oncomponent. In this case, it is 118°F. The internal pressure in the exchanger shouldbe kept at 440 psig or below (40% of the 1100 psig MAWP) when the metal temature is below 118°F.

Equipment Fabricated to API Standard 650The following is an example of how to determine MDMT for piping using ASME/ANSI B31.3:

Example 1: What is the MDMT for non-normalized 24" Schedule 60, A106 carbsteel pipe?

The thickness of 24" Schedule 60 pipe is nominally 0.968". Since the pipe is nonormalized, Chevron takes exception to ASME/ANSI rules and uses Curve A (ncurve B) to determine MDMT. Figure 300-14 shows that for material on Curve Awhich is 0.968" thick, the MDMT is 68F.

With this MDMT, the piping in question should not be allowed to operate at a prsure higher than 40% of MAWP at a temperature below 68F. Typically, MAWP fthe piping will be the same as design pressure.

Example 2: What is the MDMT for 8" Standard weight, A106 carbon steel pipe?

The thickness of 8" Standard weight pipe is nominally 0.322". No MDMT calcultion is necessary since the pipe is <3/4" thick.

Example 3: What is the MDMT for 18" Schedule 80 pipe of unknown grade, butwith chemistry and mechanical properties which match API 5L Grades X-52 anX-56?

The nominal thickness of 18" Schedule 80 pipe is 0.937". Figure 300-15 showsfor X grades of API 5L material, Curve B can be used to determine MDMT if it iknown that the steel is normalized or quenched and tempered (Q&T). In this casince we do not know the steel heat treatment, we are forced to use Curve A, w



g,” is

low

not any

is more conservative. From Figure 300-14, for 0.937" thick material on Curve A, the MDMT is 65°F.

The piping in question should not be allowed to operate at a pressure higher than 40% of MAWP (or design pressure) at a temperature below 65°F.

350 Fatigue and Thermal FatigueFatigue is one of the most common type of mechanical failure mechanisms. It occurs when cyclic stress causes a crack to initiate and then propagate.

The source of fatigue stress can be mechanical (e.g., vibration of a pipe attached to a compressor) or thermal (e.g., cyclic heating of a restrained part). Fatigue is usually divided into two types-high-stress/low-cycle (<~103 cycles) and low-stress/high-cycle (>~103 cycles).

Thermal fatigue is often high stress/low cycle fatigue. Much of the fatigue life is used up in the crack initiation; after cracks form, crack growth can be relatively fast. This type of fatigue results in multiple initiation sites, which can join randomly to form the main crack. This crack appearance, often referred to as “craze crackinshown in Figure 300-20.

351 Endurance and Fatigue Limit Carbon, low alloy steels and titanium have endurance limits—a cyclic stress bewhich fatigue failure does not occur. The limit is about half the tensile strength. Conversely, 300 Series stainless steels, aluminum, copper, and nickel alloys dohave an endurance limit; given enough cycles, such materials eventually fail atcyclic stress range.

Fig. 300-20 “Craze Cracking”



You can use a material that does not have an endurance limit under cyclic loading conditions only if the number of cycles is limited to test data indications of what it can withstand without fracture. This is called the fatigue limit. Figure 300-21 is a schematic illustration of fatigue curves on a plot of stress versus number of cycles, showing both fatigue limits and endurance limits.

352 Factors Affecting Fatigue Life Stress concentration is an important factor in fatigue. Notches at sharp corners (such as shaft keyways) and rough weld surfaces, for example, greatly shorten fatigue life. Conversely, using generous radii in corners and grinding rough weld surfaces smooth can greatly increase fatigue life. The fact that the fatigue limit is about half the tensile strength would indicate that the higher the strength, the higher the fatigue strength. However, this assumption is true only for polished specimens. Because most structures have notches, there is rarely any advantage in using a higher strength material to solve a fatigue problem. The best solution to fatigue is proper design. Fatigue is not a metallurgical problem.

In other parts of this manual we discuss the various effects of hydrogen upon metals. One of the effects is to increase the tendency of cracks to grow. Therefore, it should be no surprise that fatigue cracks grow faster when the metal is exposed to hydrogen. What can be surprising is how much effect the hydrogen can have, even under low temperature and low pressure hydrogen conditions.

Certainly the message is that in almost all cases, if we find a crack in hydrogen plus fatigue service, we need to remove it-regardless of the size of the crack. This mech-anism also explains why it is so important to pay attention to details like bridge welding piping connections. In the 1960s and early 1970s we learned these lessons the hard way by having many small diameter piping failures in the early Isomax plants, especially around the reciprocating hydrogen booster compressors.

Fig. 300-21 Schematic Illustration of the Fatigue Behavior of Ferrous and Non Ferrous Alloys



Stress relieving a structure does not usually affect fatigue life; however, shot peening a part to put residual compressive stresses on the surface increases fatigue life.

Following are some common locations where fatigue failures occur in our facilities:

• Heat ExchangersTube vibration as a result of flow patterns is a common cause of fatigue fail-ures. Many such failures have occurred on alloy tubes, which are usually purchased with thinner wall thickness. Failures typically initiate at tube-to-tube sheet joints or baffles. Fatigue failures, although rare, can be found in the middle between two baffles. There are also typical patterns on the tube sheet layout, depending on the baffle location and other factors, where fatigue fail-ures occur.

• Branch and Screwed ConnectionsBecause failure of valved branch connections on large lines is common in refin-eries, such connections should be designed properly and regularly inspected.

Screwed connections on cyclic service should be seal-welded, and valves at branch connections should be “bridge-welded”—see Section 600 of the Piping Manual.

• Reciprocating Pumps and CompressorsReciprocating pumps and compressors are significant sources of alternating stresses and, therefore, a common area for fatigue to develop.



anual300 M

etallurgy


February 2000

3

F ry Materials Engineering Web Site)

Tubes(Heat Exchgr) Castings

A48

A126

A278

A351, A352 - Code

A395

A536 Gr. 60-40-18

A436

60 Reference Tables

ig. 300-22 Common Chevron Refinery Alloy Material Specifications and Applications (Adapted from the Richmond Refine(1 of 8)

Alloy TypeProcess Envi-

ronmentsRichmond Pipe Class

Common UNS Equivalent Plate Pipe

Forgings& Fittings(Includes

Bars)

Gray Cast Iron Fresh Water, Cooling Water, BFW,

Depends on grade

Ductile Cast Iron

Depends on grade

Ni Resist Sour Water, Caustic


anual300 M

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A161-LC, C-1/2 Mo

A179 (Smls, Cold Drawn) - acidic svc., UNS K03503

A192 (Smls, Hi Press) - Boiler, UNS K01201

A214 (ERW) - non-acidic svc., UNS K01807

A27

A216-WCB (UNS J03002) - WCA, -WCC

A352

A27



Code Carbon Steel

General Hydrocarbon, steam and water service, to 800F, w/ H2, w/H2S, cyclic, MEA, Caustic, Sulfuric >85%

AA6,AA7, AA9, ABO, AB1, AB2, AB4, AB6, AB7, AB8, AF1, AF2, AF3, AF4, AF5, AF6, AF7, AF8, AF9, AF10, AF11, AG2, AJ1, AJ2, AJ4, AK1, AL1, BB1, BF1, BJ2, BL1, DK1, DK2, DK4, DL1, DL4, DP1, DP2, DP4, DP5, DR1, DR4

Depends on grade and product form.

A285 Gr. C (UNS K0281

A515

A516

A53

A106

A333

A671

A672

A691

A234-WPB

A181

A105

Non-Code Carbon Steel (Structural)

Depends on grade and product form.

A36 (UNS K02600)

A131

A283

A120

API 5L

A134 EFW

A135 ERW

High Str. Steel Depends on grade.

A537, A737

Tank General Hydrocarbon steam and water service

Depends on grade.

A36, A131, A283, A285, A516, A573






Bars)


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February 2000

A161-T1

A209-T1 (UNS K11522)

A250

A692

A217-WCI

A356 Gr. 2

A199-T11 (UNS K11597)

A213-T11 (UNS K11597)

A200-T11

A217-WC6

A356 Gr. 6

A389 Gr. C23

A199-T22

A213-T22 A200-T22

A217-WC9

A356 Gr. 10

A199-T5

A213-T5 (UNS K21590)

A200-T5

A217-C5, C-12



C-1/2 Mo Steel

Formerly used in High temperature H2

A204 Gr. A - C

A302

A335-P1

A672 Gr. C

A182-F1

A234-WP1

A336 Gr. F1

1 Cr - ½ Mo High tempera-ture H2, Oxidation

A387-12

1 ¼ CR-1/2 Mo High tempera-ture H2, Oxidation, H2 w/ HC, H2 w/LPG,

Steam

RG1, RG4, RK1, RK2, RK3, RK4, RL1, RL2, RP3, RP4, RR4

A387-11 A335-P11 A182-F11

A234-WP11

A336-F11

A541 Cl 11c

2 ¼ Cr - 1 Mo High tempera-ture H2, Oxidation, H2 w/ HC

SP4, SR4 A387-22 A335-P22 A182-F22

A234-WP22A336-F22

A541 Cl 22b

5 Cr - ½ Mo High tempera-ture H2, Sulfi-dation, HC, Furnace Transfer

TF1, TF2 A387-5 A335-P5 A182-F5

A234-WP5






Bars)


anual300 M

etallurgy


February 2000

A199-T7

A213-T7

A200-T7

A217-C

A199-T9

A213-T9

A200-T9

A217-C12

A268-TP406, 410 (UNS 41500)

A487-Gr CA15 type B-D

A487-CA6NM

A217-CA15

A743-CA15

A743-CA6MM



7 Cr – 1 Mo High tempera-ture H2, Sulfi-dation

A387-9 A335-P7 A182-F7

A234-WP7

9 Cr - 1 Mo High tempera-ture H2, Sulfi-dation, Furnace Tubes

A387-9 A335-P9 A182-F9

A234-WP9

12 Cr Sulfidation UNS S04100 A240-405, 410, 410S

A176-410

(Commonly manufac-tured from sheet or plate)

A182-F6

A479-405, 410S (bars)






Bars)


anual300 M

etallurgy


February 2000

A213-TP3XX

A271-TP3XX

A351 CF3, CF3A, CF3M, CF8

A743 CF3, CF3A

A744 CF3, CF3A

A789

UNS S31803 (preferred), UNS S32205 (acceptable)

A789

UNS S32750



18 Cr - 8 Ni (3XX Series Stainless)

Demineral-ized Water, Lean/Rich (flashing) DEA, H2 w/ HC, Napthenic, Acid, Dilute Phosphoric Acid Weak to strong acids, Dilute Sulfuric acid, BFW Chemicals, low tempera-ture sulfur, sulfidation, ammonium bisulfide, high temperature.

GB!, GB6, GB7, GF1, GF6, GJ1, GJ6, GM1, GP6, GQ6, JB3, JF1, JF2, JK3, KF1, KF2, KK4, KL4, KL5, KP4, KP5, KR4, KR5, KR6,

Depends on alloy (and product form)

A240-3XX

A167-3XX

A312-3XX

A358-3XX

A182-F3XX

A403-WP3XX

2205 Duplex Stainless Steel

Chloride, H2S environments

UNS S32205 A240 A790 A182, A815

2507 Duplex Stainless Steel

Chloride, H2S environments

UNS S32750 A240 A790 A182, A815






Bars)


anual300 M

etallurgy


February 2000

B676 A744 CN3MN, UNS J94651

B468 (Welded Tube)

A351-CN7M, UNS N08007

B163-

B165

A494 Gr M . . .

B163, B167 (seamless)

B516 (Welded Tube)

B444 (seam-less)

B622 (tubing)

B494

B163, B407 (seamless)

B515 (welded)



Super Stain-less Steel AL6XN

UNS N08367 B688 B675

Alloy 20 Cb-3 Dilute Sulfuric acid

MB2 (UNS N08020) B-463 B464

B474 (EFW)

B462 (forg-ings)

B472, B473 (bars)

Monel 400 Acid Environ-ments – HCl, HF, and Caustic, Chlo-rine

UB2, UB6 UNS04400 B127 B165 B164

B564 (Forg-ings)

Alloy 600 UNS N06600 B168 B517 (welded)

B167 (Seam-less)

B166 (bars)

B366

B564 (Forg-ings)

Alloy 625 High tempera-ture, High hydrogen, High chloride

UNS N06625 B168

B443

B444 (Seam-less Tube)

B705 (Welded)

B446

B626

B564 (Forg-ings)

B574 (Rod)

Alloy 800/H/HT (Fe-32Ni-21Cr)

High tempera-ture hydrogen

UNS N08800, N08810, N08811

B409 B407 (Seam-less)

B514 (Welded)

B366

B408

B464 (Forg-ings)






Bars)


anual300 M

etallurgy


February 2000

B163

B423 (Seam-less)

B-468

B704

A297

B626B622 (Seamless)

B619 (Welded)

A494

Gr.Cw-12MW

B111 (A. B, C) B584

B111



Alloy 825 High velocity, high pres-sure, high temperature ammonium bisulfide, Sour Water.

XP6, XR6 UNS NO8825 B424 B423 (Seam-less)

B-468

B705 (welded)

B366

B425

B564 (Forg-ings)

HP Modified, HK-40

Hydrogen furnace tubes, furnace tube hangers

Hastelloy C-276

Acid UNS N10002

UNS N10276

(UNS N06022)

B575 (C-22 & C-276

B619 (Welded)

B622 (Seam-less)

B366

B574 (Rod)

B564 (Forg-ings)

Admiralty Brass (Inhib-ited)

General steam and cooling water service, to 140F

UNS C44300 (Arsenic), C44400 (Anti-mony),C44500 (Phosphorus)

B171 (A. B, C)

70-30 Cu-Ni Slightly higher temp steam and cooling water service, >140F.

(UNS C71500) B171 B466

90-10 Cu-Ni Seawater, steam

UNS 70600






Bars)


anual300 M

etallurgy


February 2000

n steel, including “obsolete” grades still

B338 Gr. 1, 2, 12

B367



Note that Section 315 further discusses the most common ASTM grades of carbocommonly found in our facilities.

Titanium Alloys

H2S, waste water treater HEX <180F

Gr. 2 UNS R50400

Gr. 12 UNS R53400

B265 Gr. 1, 2, 12

B337 Gr. 1, 2, 12

B381 F-1, 2

AISI 4130

AISI 4140 A193 B7, B7M (bolts)

AISI 4340






Bars)


Fig. 300-23 Corrosion Resistance and Mechanical Properties for Common Steel Product Forms (1)

Typical Alloy Typical ChemistryAmbient Temp. Yield & Tensile Strengths Comments

Low and Medium Carbon Steels

Fe-1Mn-0.2C Y = 25-40 ksi

UTS = 50-80 ksi

Adequate strength and corrosion resistance for many applications.

Low-Alloys 1¼Cr-½Mo;2¼Cr-1Mo;9Cr-1Mo5Cr-½Mo

Y = 25-60 ksiUTS = 60-110 ksi

Strength and creep resistance > 900ºF.Hydrogen attack resistance > 450ºF.H2S resistance to 650ºF for the higher Cr alloys.

“12-Chrome” (e.g., 410) and “17-4PH”

12-13Cr17Cr-4Ni

Y = 40-100 ksiUTS = 60-200 ksi

Very high hardness and strength.H2S resistance to 800ºF.Susceptible to sulfide stress cracking.

304SS, 304L, 304H

18Cr-8Ni Y = 25-40 ksiUTS = 65-80 ksi

Good high temperature corrosion resistance. Weld with “L” grade.H2S resistance > 800ºF; H2/H2S > 550ºF.304H has creep resistance to 1500ºF.All sensitize after long-term service above 700ºF.

316SS, 316L, 317SS, 317L

18Cr-12Ni-2Mo(317/L: 3%Mo)

Y = 25-40 ksiUTS = 70-90 ksi

Better aqueous corrosion resistance than 18-8SS., Type 317 resists naphthenic acid corrosion.All will sensitize after long-term service above 700ºF.

321SS, 347SS 18Cr-10Ni Y = 25-40 ksiUTS = 70-90 ksi

Stabilized grades can be welded without sensitization.Type 321 will not sensitize below about 850ºF.Type 347 will not sensitize below about 900ºF.

Alloy 20 20Cr-33Ni-2Mo-3.5Cu(Cb3 adds <1% Nb)

Y = 35-50 ksiUTS = 80-95 ksi

Acid corrosion resistance especially sulfuric. May contain Cb for sensitization resistance (Alloy 20Cb3).Cast pump cases in sulfuric acid plants.

Incoloy 825 21Cr-42Ni-3Mo-2.3Cu-1Ti

Y = 35-45 ksiUTS = 85-95 ksi

Corrosion and SCC resistant.Will not sensitize on welding or in operation.For effluent air coolers in aqueous NH4Cl.

Inconel 625 21Cr-61Ni-9Mo-4Nb-4Fe

Y = 60-80 ksiUTS = 120-140 ksi

Excellent in strong acids.High temp. strength and oxidation resistance.

Hastelloy C-276

15Cr-57Ni-15Mo-4V-5.5Fe

Y = 40-190 ksiUTS = 100-200 ksi

Excellent in strong acids (esp. hydrochloric, nitric, and sulfuric) and in acids contaminated with chlorides.Resists SCC and pitting in severe environments.

Monel 66Ni-31Cu Y = 25-35 ksiUTS = 60-80 ksi

Best for hydrofluoric acid.

Titanium Grades 2, 7, 12 Y = 40-60 ksiUTS = 50-70 ksi

Seawater exchangers and aqueous streams containing H2S and chlorides.

(1) Also see Appendix A of the Welding Manual.



Fig. 300-24 Conversion Table for Hardness Numbers for Steel (Non-austenitic)—Approximate (1 of 2)

Conversion To Rockwell C Conversion To Rockwell B

Rockwell C

Hardness(1) Vickers

Hardness(1)

Brinell Hard-

ness(1),(2)

Tensile Strength (approx.) 1000 psi(3)

Rockwell B

Hardness(1)Vickers

Hardness(1)

Brinell Hard-

ness(1),(2)


68 940 — 100 240 240 116

67 900 — 99 234 234 114

66 865 — 98 228 228 111

65 832 — 97 222 222 107

64 800 — 96 216 216 105

63 772 — 95 210 210 101

62 746 — 94 205 205 100

61 720 — 93 200 200 98

60 697 — 92 195 195 95

59 674 — 91 190 190 92

58 653 — 90 185 185 90

57 633 — 89 180 180 88

56 613 — 88 176 176 84

55 595 — 87 172 172 83

54 577 — 86 169 169 82

53 560 — 85 165 165 80

52 544 500 265 84 162 162 79

51 528 487 83 159 159 78

50 513 475 252 82 156 156 76

49 498 464 245 81 153 153 75

48 484 451 236 80 150 150 73

47 471 442 229 79 147 147 72

46 458 432 225 78 144 144 71

45 446 421 216 77 141 141

44 434 409 76 139 139

43 423 400 201 75 137 137 67

42 412 390 192 74 135 135

41 402 381 73 132 132

40 392 371 72 130 130 65

39 382 362 177 71 127 127



38 372 353 172 70 125 125 63

37 363 344 166 69 123 123

36 354 336 68 121 121 60

35 345 327 157 67 119 119

34 336 319 66 117 117

33 327 311 149 65 116 116 58

32 318 301 146 64 114 114

31 310 294 142 63 112 112

30 302 286 138 62 110 110 56

29 294 279 135 61 108 108

28 286 271 131 60 107 107

27 279 264 127

26 272 258

25 266 253

24 260 247 120

23 254 243 116

22 248 237 114

21 243 231 110

20 238 226 108

(1) ASTM E140-86, Standard Hardness Conversion Tables for Metals(2) The Brinell hardness numbers in boldface type are outside the range recommended for Brinell hardness testing in 3.2.2 of ASTM Test

Method E10.(3) Tensile strength values given are approximate, and are provided for general reference only.

Fig. 300-24 Conversion Table for Hardness Numbers for Steel (Non-austenitic)—Approximate (2 of 2)

Conversion To Rockwell C Conversion To Rockwell B

Rockwell C

Hardness(1) Vickers

Hardness(1)

Brinell Hard-

ness(1),(2)


Rockwell B

Hardness(1)Vickers

Hardness(1)

Brinell Hard-

ness(1),(2)




Fig. 300-25 Temperature Color Scale Courtesy of Tempil Division, Air Liquide America Corp.(This Scale is in color (and easier to read) on the website: http://chevron.com/MEE/Metallurgy/)



r

,

rpose

-

370 References1. C. D. Buscemi and G. B. Kohut, “Brittle Fracture and MPT Determination fo

Upstream Equipment,” CRTC Upstream Portfolio Item PFS-19 memo 9/22/97.

2. C. D. Buscemi, et. al., “Temper Embrittlement in 2-¼ Cr-1Mo Steels After 75,000-Hour Isothermal Aging,” Journal of Engineering Materials and Technology, July 1991, vol. 113, p. 329.

3. R. A. Flinn and P. K. Trojan, Engineering Materials and Their Applications, Houghton Mifflin Company, Boston, second edition, 1981.

4. R. M. Brick, et. al., Structure and Properties of Engineering Materials, McGraw-Hill Company, New York, fourth edition, 1977.

5. R. W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials, John Wiley & Sons Company, New York, second edition, 1983.

6. W. T. Lankford, et.al, The Making, Shaping and Treating of Steel, ed. U.S. Steel Company with Association of Iron and Steel Engineers (AISE), 10th edition1985.

7. “Properties and Selection: Irons and Steels,” Metals Handbook, Volume 1, American Society for Metals (ASM), Metals Park, OH, first printing 1978.

8. “Properties and Selection: Stainless Steels, Tool Materials, and Special-PuMetals,” Metals Handbook, Volume 3, American Society for Metals (ASM), Metals Park, OH, first printing 1978.

9. “Heat Treatment,” Metals Handbook, Volume 4, American Society for Metals (ASM), Metals Park, OH, first printing 1978.

10. Source Book on Copper and Copper Alloys, American Society for Metals (ASM), Metals Park, OH, first printing 1979.

11. API Recommended Practice 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants, fifth edition, 1997.

12. Pressure Vessel Manual, Section 500 Materials, Volume 1, Engineering Guidelines, Chevron.

13. Welding Manual, Section 100 Welding Fundamentals, Chevron.

14. Welding Manual, Section 300 Welding Practices, Chevron.

15. Fired Heater and Waste Heat Boiler Manual, Section 700 Materials, Chevron.

16. API RP 579, Recommended Practice for Fitness-For-Service, Section 3, “Assessment of Equipment for Brittle Fracture” (Final Draft - Revision 33).


CPM300 Metallurgy

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introduction311 metallurgy

equipment subject

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upstream operations

transportation operations

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