Welding Parameters

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramco’s employees.Any material contained in this document which is not already in the publicdomain may not be copied, reproduced, sold, given, or disclosed to thirdparties, or otherwise used in whole, or in part, without the written permissionof the Vice President, Engineering Services, Saudi Aramco.

Chapter : Welding For additional information on this subject, contactFile Reference: COE11403 A.A. Omar

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Welding Parameters

Engineering Encyclopedia Welding

Welding Parameters

Saudi Aramco DeskTop Standards

Contents Pages

INTRODUCTION................................................................................................................ 1

COMMONLY USED BASE METALS IN THE OIL AND GAS INDUSTRY..................... 2

Base Metal Definition ............................................................................................... 2

Base Metal Types and Properties............................................................................... 2

Carbon Steels ................................................................................................ 3

Low Alloy Steels ........................................................................................... 3

Stainless Steels .............................................................................................. 4

Iron Carbon Reactions............................................................................................... 5

Fusion Zone................................................................................................... 5

Heat-Affected Zone (HAZ)............................................................................ 7

Base Metal..................................................................................................... 7

Melting Properties ......................................................................................... 7

Solidification Properties ................................................................................ 9

Thermal Cycles ............................................................................................11

Phase Transformations..................................................................................16

WELD JOINT DESIGNS AND SYMBOLS........................................................................18

Types of Weld Joints................................................................................................18

Fillet Weld Joint ...........................................................................................18

Butt Weld Joint ............................................................................................20

Partial Penetration Weld Joint.......................................................................23

Combination.................................................................................................24

Stud Weld Joint ............................................................................................25

AWS Weld Symbols ................................................................................................26

Elements of a Weld Symbol..........................................................................26

Fillet Weld Symbol.......................................................................................28

Butt Weld Symbol ........................................................................................31

Partial Penetration Weld Symbol ..................................................................33

Combination.................................................................................................34

Stud Weld Joint Symbol ...............................................................................36


Welding Parameters


WELDING CONSUMABLES ............................................................................................37

Types of Welding Consumables ...............................................................................37

Coated Electrodes.........................................................................................37

Bare Rods.....................................................................................................39

Bare Wires....................................................................................................39

Flux Cored Electrodes ..................................................................................39

AWS Classifications ................................................................................................41


Bare Rods and Wire......................................................................................46


Shielding Gasses and Fluxes.........................................................................48

Gases............................................................................................................48

Fluxes...........................................................................................................48

Storage and Handling Requirements.........................................................................50


Bare Rods and Wire......................................................................................51


HEAT INPUT EFFECTS ....................................................................................................52

Parameters ...............................................................................................................52

Current .........................................................................................................52

Voltage.........................................................................................................53

Travel Speed.................................................................................................53

Effects of Heat Input ................................................................................................53

HEAT TREATMENT EFFECTS ........................................................................................55

Preheat.....................................................................................................................55

Purpose ........................................................................................................55

Methods .......................................................................................................56

Determination...............................................................................................60

Postweld Heat Treatment .........................................................................................63

Purpose ........................................................................................................64

Methods .......................................................................................................64


Welding Parameters


Requirements................................................................................................66

GLOSSARY........................................................................................................................71

WORK AID 1: HOW TO IDENTIFY THE MOST COMMONLY.....................................73

WORK AID 2: HOW TO IDENTIFY WELD JOINT DESIGNS AND SYMBOLS ...........75

WORK AID 3: HOW TO IDENTIFY WELDING CONSUMABLES ................................76

WORK AID 4: HOW TO DESCRIBE HEAT INPUT EFFECTS .......................................78

WORK AID 5: HOW TO DESCRIBE HEAT TREATMENT EFFECTS ...........................80

BIBLIOGRAPHY ...............................................................................................................83


Welding Parameters

Saudi Aramco DeskTop Standards 1

INTRODUCTION

This Module provides information on several of the most important parameters that areassociated with welding operations. The emphasis on base metals and heat affects of welding isto introduce the Participant to the metallurgical properties of welding. The information on weldjoint designs, symbols, and welding consumables provides additional background on weldingparameters and operations.

This Module contains the following topics:

• Commonly Used Base Metals in the Oil and Gas Industry

• Weld Joint Designs and Symbols

• Identifying Welding Consumables

• Heat Input Effects

• Heat Treatment Effects


Welding Parameters


COMMONLY USED BASE METALS IN THE OIL AND GAS INDUSTRY

This section contains a discussion of the most commonly used base metals in the oil and gasindustry and, specifically, in Saudi Aramco. The information in this section providesbackground on welding-related base metal considerations and includes the following topics:

• Base Metal Definition

• Base Metal Types and Properties

• Iron Carbon Reactions

Base Metal Definition

A base metal is the metal or metals that are to be welded. More specifically, the term base metalrefers to the portion of the weld joint that has not been affected by the welding thermal cycles.Welding joins two pieces of metal to provide a single piece with mechanical properties that areequivalent to the mechanical properties of the original pieces. However, the two pieces of basemetal that are joined are not always the same material. In some cases, the two base metals havecompletely different chemical and mechanical properties. In other cases, the base metals are ofdifferent product forms such as a forging and a seamless pipe.

Base Metal Types and Properties

The most common types of base metals that are used in the oil and gas industry are broadlyclassified as follows:

• Carbon steels

• Low alloy steels

• Stainless steels

Each of these common types of base metal have numerous sub-classifications that are calledalloys, types, or grades. The American Society for Testing and Materials (ASTM) and theAmerican Iron and Steel Institute (AISI) have classified all types of base metals to help identifythe huge number of base metals that are available to the oil and gas industry, as well as otherindustries. This classification system uniquely identifies the chemical composition, mechanicalproperties, and product form of the base metal. Each of the three common base metals that areused in Saudi Aramco will be discussed in greater detail in the sections that follow.


Welding Parameters


Carbon Steels

Carbon steels are alloys of iron and carbon in which the carbon content is less than 1 percent, themanganese content is less than 1.65 percent, and the copper and silicon content are each less than0.60 percent. Normally, other alloy agents are only present in residual amounts. The propertiesand weldability of carbon steels mainly depend on the carbon content. Other elements have alimited effect on the properties and weldability of carbon steels. Increased carbon content in acarbon steel leads to increased hardness and strength.

There are three types of carbon steel base metals as follows:

• Low-carbon

• Medium-carbon

• High-carbon

Low-carbon Steels –0.10 to 0.25% carbon ( c ), and 0.25 to 1.5 % magnesium (Mn). Low-carbon steels are widely used for industrial fabrication and construction. These steels are easilywelded with all of the gas and arc welding processes.

Medium-carbon Steels –0.25 to 0.50% c, and 0.60 to 1.65% Mn. Medium-carbon steels arereadily weldable if proper preheat (300°F to 500°F) and postweld heat treatment is applied to theweldment. These steels are easily welded with all of the gas and arc welding processes.

High-carbon Steels –0.50 to 1.03% c, and 0.30 to 1.00% Mn. High-carbon steels are readilyweldable if proper preheat (400°F to 600°F) and postweld heat treatment is applied to theweldment. These steels are easily welded with all gas and arc welding processes.

Low Alloy Steels

Low alloy steels are designed to provide a combination of higher strength, better corrosionresistance, or improved notch toughness compared to conventional carbon steels. Inaccordance with the American Iron and Steel Institute, steel is considered to be a low-alloy steelwhen any of the following conditions exist:

• The amount of manganese is greater than 1.65 percent.

• The amount of silicon is greater than 0.60 percent.

• The amount of copper is greater than 0.60 percent.

• A definite minimum quantity of any of the following elements is specified orrequired in alloy steels: aluminum, boron, chromium up to 3.99 percent, cobalt,columbium, molybdenum, nickel, titanium, tungsten, vanadium, or zirconium.

• Any other alloying agent is added to obtain a desired alloying effect.


Welding Parameters


Low alloy steels are readily weldable if proper preheat and postweld heat treatment are appliedto the weldment. Low alloy steels are easily welded with all of the arc welding processes.

Stainless Steels

Stainless steels iron-base alloys with excellent corrosion resistance. Stainless steels do not rust,and they strongly resist attack by a great many liquids, gases, and chemicals. All stainless steelscontain iron as the main element and chromium in amounts that vary from about 11 percent to 30percent. The chromium provides the corrosion resistance. A thin film of chromium-oxide formson the surface of the metal when the metal is exposed to the oxygen in the atmosphere. Thischromium-oxide film acts as a barrier to further oxidation. In general, stainless steels have alower melting temperature and higher coefficient of thermal expansion than carbon steels.

Stainless steels are divided into the five following groups:

• Austenitic

• Chromium Martensitic

• Chromium Ferritic

• Duplex

• Precipitation-hardened

Austenitic Stainless Steels – are the most commonly used welded stainless steel in SaudiAramco facilities. Austenitic stainless steels provide excellent corrosion resistance and are notmagnetic. Among stainless steel groups, austenitic stainless steels are the easiest to weldbecause preheat and postweld heat treatments are not required.

Chromium Martensitic Stainless Steels – are magnetic steels that contain 12 to 14 percentchromium and up to 0.35 percent carbon. Low carbon chromium martensitic stainless steels arereadily welded. Welding of the higher carbon alloys generally requires preheat and postweldheat treatment.

Chromium Ferritic Stainless steels – are also magnetic and readily welded; however, the gaswelding processes are not recommended.

Duplex (ferritic-austenitic) Stainless Steel – combine the corrosion resistance properties ofaustenitic S. S. grade, especially stress corrosion cracking (SCC), and the mechanical propertiesof the ferritic stainless steel grades. However, welding duplex stainless steels requires carefulcontrol over the selection of welding wires/electrodes, heat input, and interpass temperature inorder to ensure a weld joint with similar metallurgical, corrosion resistance, mechanicalproperties as that of the base metal.


Welding Parameters


Precipitation-hardened Stainless Steels – can develop high strength with reasonably simpleheat treatments; however, not all of the precipitation-hardened stainless steels are readilyweldable. Precipitation-hardened stainless steels that are readily welded require no preheat orsolution annealing heat treatment.

Iron Carbon Reactions

Although an in-depth review of the metallurgy of a weld is not practical in this introductorycourse, several key topics must be addressed. The heat of welding changes both the structure ofthe base metal and the weld metal itself. Some of these changes occur while welding; otherchanges occur after the metal has cooled. The following discussions will present informationabout the properties and metallurgical transformations of iron carbon reactions that occur whilewelding carbon steels.

Fusion Zone

Figure 1 shows a full penetration weld joint and a typical metallographic cross-section of amultipass welded joint with topical areas pointed out. The fusion zone in Figure 1 represents thearea of base metal that was melted while welding. The boundaries of the fusion zone arebetween the original weld bevel surface and the fusion line. The actual fusion zone can only bedetermined through removal of a cross-section of the weld to examine the metallurgical structureof the base metal. The depth of the fusion zone depends on the amount of heat applied to theweld joint while welding. When more heat is applied to the weld joint while welding, the fusionzone will be wider. When less heat is applied to the weld joint while welding, the fusion zone isnarrower. The heat applied to the weld joint is controlled by the welding voltage, current, andthe electrode travel speed.


Welding Parameters


Use Word 6.0c or later to

view Macintosh picture.

Figure 1. Full Penetration Weld Joint


Welding Parameters


Heat-Affected Zone (HAZ)

The heat-affected zone (HAZ) in Figure 1 shows the portion of the base metal that was notmelted but whose mechanical properties or microstructure were altered by the heat of welding.The alteration of the microstructure can be increased grain size as illustrated in themetallographic inset of Figure 1.

The boundaries of the HAZ are between the fusion line and some point in the base metal. Whenheat is applied to a weldment from the electrode, the heat also transfers into the adjacent basemetal. As the heat travels through the base metal, the heat dissipates as it gets further from theweld. Even though the temperature may not be great enough to melt the base metal that is in theHAZ, the temperature is sufficient to alter the microstructure and physical properties of the basemetal in the HAZ.

Base Metal

The base metal in Figure 1 shows the material to be welded; and the base metal is shown as platematerial. The boundaries of the base metal include all of the material up to the HAZ. Althoughthe base metal is heated while welding, the amount of heat is not sufficient to change themicrostructure and physical properties of the base metal. However, the heat can distort the basemetal, which could result in improper alignment of welded components.

Melting Properties

Metals are crystalline solids whose atoms are arranged into distinct structures. The mostcommon crystalline structures that are found in metals are face centered cubic (FCC), bodycentered cubic (BCC), and hexagonal close packed (HCP). These structures are shown in Figure2. When metal is in a liquid state (e.g., molten weld metal), the metal loses its crystallinity andhas no distinct structure or orderly arrangement of atoms. The individual atoms move freelywithin the liquid. The mobility of the atoms allows the liquid metal to yield to the slightestpressure and to conform to the shape of the weld joint. As heat is applied to the metal duringwelding, the thermal energy increases the kinetic energy of the individual atoms. When thekinetic energy of the atoms increases to a certain level (the melting point temperature), the atomsovercome the bonding energy in the crystalline structure and the atoms can move freely.


Welding Parameters




Figure 2. Common Crystal Structures in Metals


Welding Parameters


Solidification Properties

Crystalline solids are usually produced when a liquid metal solidifies. Figure 3 illustrates thesolidification process of liquid weld metal on a solid base metal. This figure shows the initialcrystal formation, continued solidification, and complete solidification. When molten weldmetal starts to cool to its solidification temperature, solid particles begin to form small initialcrystals, which are called dendrites. These small initial crystals are already arranged in thespecific atomic structure that is characteristic of the particular metal. This dendritic growth is aresult of the hotter, solid material growing into the cooler, liquid, weld metal and more readilydissipating the latent heat of solidification. Solidification proceeds by the growth of thedendrites into larger solid particles that are called solid grains. As the amount of solid particlesincreases, the amount of liquid weld metal decreases. As the grains grow, the individual grainsultimately meet. The junction at the individual grains is a random arrangement of the atoms,which is called the grain boundary. The overall arrangement of grains and grain boundaries in ametal makes up the unique microstructure of that metal.


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Figure 3. Process of Solidification


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Thermal Cycles

The most important physical characteristic of a normal arc weld is the weld's thermal behavior,which is the way in which the temperatures change in the weld and in the heat-affected zone.Welding is a dynamic process that causes rapid temperature changes. These rapid temperaturechanges result in a complex temperature environment that produces a wide variety of heattreatments in a weld. Because the various heat treatments can change some of the properties ofmetals, engineers need to understand how temperatures change at and near a fusion weld.Engineers also need to understand how a metal behaves during and after welding.

In a butt weld, the electrode moves along the weld joint and applies heat to a specific point.Because the base metal is cold when welding is initiated, heat continually flows into the basemetal and away from the region that is heated by the welding arc. The rate of heat flow into thesurrounding base metal is governed by many factors that include the physical properties of thebase metal and the rate of applied heat that is produced by the welding arc. Figure 4 shows aplate groove weld in-process with the base metal, solidified weld metal, and molten weld metalidentified. To see the effects of heat flow while welding, a thermal "picture" of the weld puddleand plate at any given instant must be examined.

Figure 4. In-Process Plate Groove Weld


Welding Parameters


Figure 5 is a thermal picture of a weld puddle and plate that illustrates the effect of heat flowwhile welding and a graphic illustration of the isothermal lines in the plate for a specificdirection of welding. Figure 5 also shows the temperature profiles in a mild steel plate at a giveninstant while welding. In the figure, the W represents molten weld metal; the shaded area is themetal that is in the mushy stage and is bounded by the liquidus temperature (2,795°F) and thesolidus temperature (2,714°F). The numbers 1 through 5 are reference points at various locationsfrom the centerline of the weld. As the welding arc moves, the isotherms (lines of constanttemperature) move along with the welding arc and do not change. The temperatures, 400°Fthrough 2550°F, in Figure 5 are arbitrary temperatures that are used to indicate the temperaturedifferences of the isothermal lines. As the welding arc moves, a wave of temperature is createdthat moves along with the welding arc. The line W n-n' marks the location of the peaktemperatures at any distance from the centerline of the weld at a given instant in time.


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Figure 5. Weld Temperature Profiles


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Figure 6 shows the thermal cycles that occur in the five reference locations (from Figure 5) on anarbitrary scale of temperature versus time (in seconds) to show relative temperature effects. TM

represents the melting point of the metal that is being welded, and line n-n' marks the location ofthe peak temperatures at any distance from the centerline of the weld at a given instant in time.

Figure 6 shows that each reference point is rapidly heated to an elevated temperature, dwellsmomentarily, and then rapidly cools. The shape of these curves will vary based on the travelspeed during the welding process. The following are the general characteristics of thermalcycles:

• The peak temperature that is reached decreases as the distance from the centerlineof the weld increases.

• The time that is required to reach the peak temperature increases as the distancefrom the centerline of the weld increases.

• The heating and cooling rates decrease as the distances from the centerline of theweld increases.

Figure 6. Thermal Cycles


Welding Parameters



Welding Parameters


Phase Transformations

Temperature differences cause the atoms of many metals to vary their crystallographic structure.For example, the crystalline structure of iron at temperatures below 1,670°F is body centeredcubic (BCC); at temperatures between 1,670°F and 2,540°F, the crystalline structure of iron isface centered cubic (FCC); and at temperatures between 2,535°F and 2,795°F (the temperature atwhich iron melts), the crystalline structure of iron is again BBC. The change in crystallinestructure is formally called a phase transformation. However, steel is primarily an alloy of ironand carbon. The presence of carbon alters the temperature at which freezing and other phasetransformations occur. Iron-carbon alloys freeze over a range of temperatures. Differentliquidus and solidus temperatures exist for each unique composition. As the carbon content ofsteel increases up to 4.3% carbon, the liquidus and solidus temperatures decrease.

Phase changes and solidification are best shown through use of a phase diagram or anequilibrium diagram. A brief explanation of the iron-carbon phase diagram provides insight intothe behavior of steels during welding thermal cycles and heat treatment. Figure 7 shows an iron-carbon alloy phase diagram with 0 to 5% carbon content. As previously mentioned, iron exhibitstwo different crystalline structures (BCC and FCC). Above 2,795°F, pure iron (0% carbon) is ina liquid state and no crystalline structure exists. Below 2,795°F, pure iron solidifies and has aBCC structure that is called "delta iron". As the temperature is further reduced below 2,540°F, atransformation occurs and the crystalline structure changes to an FCC structure that is called"gamma iron". As much as 2.1% carbon can be held in solution in gamma iron at a specifictemperature, which establishes a dividing point on the phase diagram; the alloys of iron andcarbon that contain less than 2.1% carbon are called steels, and the alloys that contain more than2.1% carbon are referred to as cast irons. Below, 1670°F, the iron transforms back to the BCCstructure that is called "alpha iron".

To better understand the iron-carbon phase diagram, consider a steel with a composition of0.25% carbon. This steel is indicated on Figure 7 by drawing a vertical line midway between the0.0 and 0.5% carbon line. Above approximately 2,768°F, the 0.25% carbon steel is molten. Asthe temperature decreases, delta iron starts to form in the liquid. At just below 2,732°F, the deltairon transforms to austenite (a solid solution of carbon in gamma iron) and molten metal. Atabout 2,696°F, all of the liquid metal solidifies and the composition is austenite. Atapproximately 1,500°F, the austenite breaks down and forms a new phase at the grainboundaries. This new phase is almost pure iron or ferrite. Ferrite formation continues until atemperature of 1,340°F is reached.


Welding Parameters


Figure 7. Iron-Carbon Alloy Phase Diagram


Welding Parameters


WELD JOINT DESIGNS AND SYMBOLS

The following section identifies several of the most common weld joints and associated weldsymbols that are used at Saudi Aramco. Welds are made at the junction of at least two members.These weld junctions, which are called weld joints, are the location at which two or moremembers are joined. The placement of these members defines the weld joint design. TheAmerican Welding Society (AWS) has developed a set of standard weld symbols to represent allthe different types of weld joint designs that join members together. The information in thissection provides some background on several types of welds and weld symbols. Thisinformation includes the following topics:

• Types of Weld Joints

• AWS Weld Symbols

Types of Weld Joints

As was noted in Module COE 114.01, the five basic types of weld joints are butt, corner, tee, lap,and edge. In some instances, several types of weld joints may be used in combination tocomplete a weldment. The specific weld joints designs described in this Module include fillet,butt, partial penetration, and stud. Several illustrations of each type of weld joint will bepresented in the following sections.

Fillet Weld Joint

A fillet weld joint is a joint between two members that are at right angles to each other. Theweld that joins fillet joints is called a fillet weld and it has an approximately triangular cross-section. Figure 8 shows a lap joint, a tee joint, and a corner joint with fillet welds. Figure 8 alsoshows the nomenclature of fillet welds including base metal, face of fillet weld, root of filletweld, toe of fillet weld, throat of fillet weld, equal leg fillet weld, unequal leg fillet weld, and theleg and size of fillet weld.


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Figure 8. Fillet Welds


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Butt Weld Joint

A butt weld joint is a joint between two members that are aligned approximately in the sameplane. The weld that joins butt joints is called a groove weld. Figure 9 identifies thenomenclature of complete penetration butt welds including base metal, face of weld, toe of weld,root of weld, external weld reinforcement, and root reinforcement.



Figure 9. Complete Penetration Butt Weld Nomenclature


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Figure 10 shows single-groove butt welds, including a single-square groove weld, a single-bevelgroove weld, a single-V groove weld, and a single-U groove weld with complete penetration.



Figure 10. Single-Groove Butt Welds


Welding Parameters


Figure 11 shows double-groove butt welds including a double-square groove weld, a double-bevel groove weld, a double-V groove weld, and a double-U groove weld.



Figure 11. Double-Groove Butt Welds


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Partial Penetration Weld Joint

A partial penetration weld joint is any joint design between two members in which completeweld penetration is not possible. Figure 12 shows a partial penetration single-square grooveweld, a partial penetration single-V groove weld, and a partial penetration double-V grooveweld. Figure 12 also shows the unique nomenclature of partial penetration welds including rootpenetration and joint penetration (also called the effective throat). Joint penetration of a partialpenetration weld is the minimum distance (less any reinforcement) from the root of a weld to theface of the weld.



Figure 12. Partial Penetration Welds


Welding Parameters


Combination

A combination weld joint is any joint with more than one joint design. The welds that joincombination joints are known by their individual names such as butt weld and fillet weld. Figure13 shows the most common type of combination weld, a single-V groove weld with a fillet weldcover. A single-V grove weld is used almost exclusively to weld pipe nozzles to pressurevessels. Figure 13 also shows the nomenclature of a combination weld including base metal,root of weld, face of weld, single-V-groove weld, and fillet weld.



Figure 13. Combination Weld


Welding Parameters


Stud Weld Joint

A stud weld joint is a joint between a metal stud (of any shape) and a base metal. The weld thatjoins a metal stud to base metal is called a stud weld. Stud welds have essentially the sameconfiguration as a fillet weld. Figure 14 shows stud joints with different stud shapes and the studwelds. Figure 14 also identifies the nomenclature of stud welds including base metal, stud, studweld, toe of weld, and size of weld.



Figure 14. Stud Weld


Welding Parameters


AWS Weld Symbols

The American Welding Society (AWS) Standard A2.4, Standard Symbols for Welding, Brazing,and Nondestructive Examination, is the standard for weld symbols in Saudi Aramco. A weldsymbol represents the weld joint on a drawing so that the details of the weld joint do not have tobe shown. The specific weld symbols described in this Module include fillet, butt, partialpenetration, combination, and stud. To aid in the understanding of these weld symbols, eachweld symbol will include an illustration of the desired weld detail that matches the weld symbol.

Elements of a Weld Symbol

Figure 15 shows the basic components of a weld symbol including the reference line, arrowleader, tail, arrow side of the reference line, other side of the reference line, weld-all-aroundsymbol, and field weld symbol. The reference line is the horizontal line from which all elementsof a weld symbol are positioned. The arrow leader points to the joint to be welded. The tail isused only if additional reference information needs to be included. Weld symbols below thereference line are on the "arrow side", and the weld is made on the same side of the joint wherethe arrow leader points. Weld symbols above the reference line are on the "other side", and theweld is made on the opposite side of the joint from where the arrow leader points. Weld symbolsthat are placed both above and below the reference line are considered to be "both side", and theweld is made on both sides of the joint where the arrow leader points." The weld-all-aroundsymbol means that a weld that extends around a series of connected joints must be completelywelded around the entire series of connected joints. The weld-all-around symbol is not requiredfor circumferential butt welds. The field weld symbol identifies those welds that must be madein the field.



Figure 15. Components of a Weld Symbol


Welding Parameters


Additional elements can be added to this basic weld symbol to provide more weld jointinformation. To establish uniformity among all possible weld symbols, the AWS hasstandardized the location of these elements on a weld symbol. Figure 16 shows the standardlocation of elements for any weld symbol that includes the finish symbol, contour symbol, rootopening, groove weld size, depth of penetration, welding procedure specification (or otherreference), basic weld symbol, number of spot, stud, or projection welds, pitch, length of weld,and groove angle.

TS L-P

FAR(E)

(N)(BO

TH

SID

ES

)

Finish Symbol

Groove Weld Size

Depth of Bevel: Size orStrength for Certain Welds

Specification, Process,or other Reference

Contour Symbol

Length of Welds

Pitch (Center-To-CenterSpacing) of Welds

Groove Angle; IncludedAngle of Counter Sinkfor Plug Welds

Number of Spot, Stud,or Projection Welds

Basic Weld Symbolor Detail Reference

Root Opening; Depth of FillingFor Plug and Slot Welds

Figure 16. Standard Location of Elements on a Weld Symbol


Welding Parameters


Fillet Weld Symbol

The dimensions of fillet welds are always shown on the same side of the reference line as theweld symbol, and they generally identify the size of the weld, the length of the weld, and thepitch of the weld. Figure 17 shows a weld symbol for a 5/16" fillet weld on the arrow side of thejoint. Figure 17 also shows the desired weld.

Figure 17. Arrow Side Fillet Weld Symbol

Figure 18 shows a weld symbol for a 1/2" fillet weld on the arrow side of the joint and a 1/4"fillet weld on the other side of the joint. Figure 18 also shows the desired weld.



Figure 18. Both Side Fillet Weld Symbol


Welding Parameters


Figure 19 shows a weld symbol for a 1/4" (Member A) by 1/2" (Member B) fillet weld (unequalleg) on the arrow side of the joint. Figure 19 also shows the desired weld. Because the weldsymbol convention does not provide sufficient detail, a note is required when it is necessary toaccurately locate the 1/2" leg.



Figure 19. Unequal Leg Fillet Weld Symbol

Figure 20 shows a weld symbol for a 1/4" intermittent fillet weld on both sides of the joint that is2" long with a pitch of 5". Figure 20 also shows the desired weld.



Figure 20. Intermittent Fillet Weld Symbol


Welding Parameters


Figure 21 shows a weld symbol for a 3/8" staggered intermittent fillet weld that is staggered onboth sides of the joint and that is 3" long with a pitch of 10". Figure 21 also shows the desiredweld.

Figure 21. Staggered Intermittent Fillet Weld Symbol


Welding Parameters


Butt Weld Symbol

The dimensions of butt welds are also shown on the same side of the reference line as the weldsymbol. Butt weld symbols generally identify the root opening, groove angle, contour symbol,and finish symbol. Figure 22 shows a weld symbol for a single-V groove weld with zero rootopening, a reference to WPS 16, a 60° included bevel on the arrow side of the joint, and thedesired weld.



Figure 22. Single-V Groove Weld Symbol


Welding Parameters


Figure 23 shows a weld symbol for a double-V groove weld with a 1/8" root opening, a 60°included angle, a 3/4" depth of preparation, a ground convex face. Figure 23 also shows thedesired weld.



Figure 23. Double-V Groove Weld Symbol

Figure 24 shows a weld symbol for a single-U groove with a 1/16" root opening, a 40° includedangle, and a 7/8" depth of preparation on the other side of the joint. Figure 24 also shows thedesired weld.

Figure 24. Single-U Groove Weld Symbol


Welding Parameters


Partial Penetration Weld Symbol

The dimensions of partial penetration welds generally identify the root opening, groove angle,depth of preparation, groove weld size, contour symbol, and finish symbol. Figure 25 shows aweld symbol for a single-V groove weld with zero root opening, a 60° included angle on thearrow side of the joint, a depth of preparation of 1/4" and a weld size of 3/8". Figure 25 alsoshows the desired weld.



Figure 25. Partial Penetration Single-V Groove Weld Symbol

Figure 26 shows a weld symbol for a double-V groove weld with a zero root opening, a 60°included angle, a depth of preparation of 1/4" and a weld size of 7/16". Figure 26 also shows thedesired weld.



Figure 26. Partial Penetration Double-V Groove Weld Symbol


Welding Parameters


Combination

The dimensions of combination welds may include the root opening, groove angle, depth ofpreparation, groove weld size, contour symbol, finish symbol, fillet weld size, the length of theweld, and the pitch of the weld. Figure 27shows a weld symbol for a square groove weld (bothsides) with zero root opening, a weld size of 3/8", and a 1/4" fillet weld (both sides). Figure 27also shows the desired weld.



Figure 27. Combination Square Groove/Fillet Weld Symbol


Welding Parameters


Figure 28 shows a weld symbol for a single-V groove weld (both sides) with a zero root opening,a 60° included angle, a depth of preparation of 1/4", a weld size of 9/16", and a 3/8" fillet weld(both sides). Figure 28 also shows the desired weld.



Figure 28. Combination Single-V Groove/Fillet Weld Symbol


Welding Parameters


Stud Weld Joint Symbol

The symbol for a stud weld is a circle with a cross in the center. Figure 29 shows a stud weldsymbol with a 0.25" stud diameter, a pitch of 1", and five stud welds. The stud weld symboldoes not indicate the welding of a joint in the ordinary sense; therefore, it has no arrow or otherside significance. The stud weld symbol must be placed below the reference line and an arrowmust clearly point to the surface to which the stud is to be welded. As with other weld symbols,the dimensions must be placed on the same side of the reference line as the stud weld symbol.Because a stud weld symbol cannot locate the first and last stud weld, the drawing must alsospecify the exact location of the first and last stud welds that are in a single line. In Figure 29,the first and last studs are positioned 3/4" from the edges of the plate.

Figure 29. Stud Weld Symbol


Welding Parameters


WELDING CONSUMABLES

The following section will describe the identification standards for welding consumables.Because there are so many types of welding consumables, each type has been assigned a uniqueclassification number by the American Welding Society (AWS). The information in this sectionprovides some background on welding consumable identification and includes the followingtopics:

• Types of Welding Consumables

• AWS Classifications

• Storage and Handling Requirements

• Shielding Gases and Fluxes

Types of Welding Consumables

Several types of welding consumables, generally referred to as "filler metal," are available fordifferent welding processes and materials. During welding, the filler metal melts in the heat ofthe welding arc and is consumed in the finished weld. The following basic types of weldingconsumables are described in this Module:

• Coated Electrodes

• Bare Rods

• Bare Wires

• Flux Cored Electrodes

Coated Electrodes

Coated electrodes are the most popular type of filler metal that is used in arc welding. Coatedelectrodes are also readily adaptable to field welding applications that use the shielded metal arcwelding (SMAW) process. Coated electrodes have a solid metal rod as core and the electrodeshave a coating of baked-on flux. The solid metal rod is made of various materials such as carbonsteel, low carbon alloys, stainless steel, and nickel alloys. The formulation of the electrode fluxis very complex. The flux determines the usability of the electrode, the composition of thedeposited weld metal, and the specification of the coated electrode. The original purpose of theflux was to shield the welding arc from atmospheric oxygen and nitrogen. Researchersdetermined that ionizing agents that are added to the flux to help stabilize the arc to make theelectrodes suitable for alternating current. Researchers also found that silicates and metal oxideshelped to form slag. Slag improves the weld bead shape due to the reaction at the surface of theweld metal. In addition, alloy agents that are added to the flux improve the strength and providespecific weld metal deposit composition. Most recently, iron powder has been added to the fluxto improve the weld metal deposition rate.


Welding Parameters


Today, the flux on a coated electrode is designed to achieve the following desirablecharacteristics. It is designed to:

• Provide a specific composition and enhance mechanical properties of the depositedweld metal

• Reduce weld metal porosity

• Reduce weld metal cracking

• Provide a desirable weld deposit contour

• Provide a desirable weld metal surface finish (e.g., smooth with even edges)

• Reduce undercut adjacent to the weld

• Reduce spatter adjacent to the weld

• Control slag in all positions of welding

• Provide a stable welding arc

• Provide penetration control (e.g., deep or shallow)

• Provide for immediate arc initiation and re-initiation capabilities

• Reduce electrode overheating while welding

Two common types of coated electrodes are the cellulosic and low hydrogen-iron powder.When burned in the electric welding arc, the flux coating on a cellulose-sodium coated electrode(e.g., E6010 and E7010) produces both CO2 and hydrogen. The solid metal rod of the cellulosicelectrode must contain sufficient deoxidizers to counteract the effects of oxygen from the flux.The cellulosic-coated electrodes tend to have an arc that produces deep penetration into the basemetal. The weld deposit is somewhat rough and the spatter is at a higher level than other coatedelectrodes. Cellulosic-coated electrodes are one of the earliest types of coated electrodes thatwere developed. Cellulosic-coated electrodes are widely used for welding cross-countrypipelines, using the downhill welding technique.

The low hydrogen-iron powder-coated electrodes do not use cellulose, clays, asbestos, or otherminerals that contain combined water. These components are not used to ensure the lowestpossible hydrogen content in the arc atmosphere. The low hydrogen-iron powder coatedelectrodes provide superior weld metal properties, such as resistance to cracking, better beadappearance, and improved strength with moderate penetration.


Welding Parameters


Bare Rods

Bare rods are typically manufactured in 36" straight lengths with diameters that range from0.045" to 3/16". Bare rods were first used with oxyacetylene welding to add filler metal to theweld joint. Today, bare rods are predominantly used with the gas tungsten arc welding (GTAW)process and the torch brazing process. Bare rods are similar to the coated electrode in that barerods are made of various materials such as carbon steel, low carbon alloys, stainless steel, nickelalloys, and aluminum alloys.

Bare Wires

Bare wire electrodes are similar to bare rods except that bare wire is manufactured in continuouslengths with diameters that range from 0.020" to 1/8." The solid bare wire was developed foruse with automatic and semi-automatic welding processes such as gas metal arc welding(GMAW), GTAW, and submerged arc welding (SAW). The bare wire is wound onto spools thatrange from 4" to 30" in diameter; however, for high volume applications, the bare wire may evenbe provided in large drums. Bare wire is similar to bare rods in that bare wire is made of variousmaterials such as carbon steel, low carbon alloys, stainless steel, nickel alloys, and aluminumalloys. The carbon and low alloy steel wires are also coated with a thin layer of copper toprevent rusting and to improve the current pick-up between the contact tip and the electrode.

Flux Cored Electrodes

Flux cored electrodes consist of tubular wire that is manufactured in continuous lengths withdiameters that range from 0.045" to 5/32." The tubular wire is actually a metal sheath that isfilled with a flux material and alloying compounds. Figure 30 shows several different types offlux cored electrodes. As with coated electrodes, the flux inside the electrodes improves thewelding characteristics of the electrode. The majority of flux cored electrodes are carbon steel;however, some low carbon alloys, stainless steel, and chromium-nickel alloys are alsomanufactured and used in flux cored arc welding (FCAW) applications.


Welding Parameters




Figure 30. Various Types of Flux Cored Electrodes


Welding Parameters


AWS Classifications

The American Welding Society (AWS) has established specifications for filler metals and fluxes.Each specification contains information about the chemical and physical properties of the fillermetal such as manufacturing, packaging, and identification requirements; testing requirementsand acceptance criteria; and additional information about the use of welding consumables.Currently, 30 specifications in the AWS A5.x series prescribe the requirements for filler metalsand fluxes. These welding material specifications are identical to the specifications in Section II,Part C of the ASME B&PV Code, Specifications for Welding Rods, Electrodes, and FillerMetals.

Each AWS specification covers numerous types of metallurgically similar filler metals. Toreadily identify each type of filler metal, the AWS has developed a unique filler metalclassification system. The AWS classification system provides a unique identification for allstandard filler metals including coated electrodes, bare rods, bare wires, and flux coredelectrodes. Due to the large number of AWS classifications and variations within theclassification system, only the most common types of filler metal classifications will bedescribed in this module.

Coated Electrodes

The AWS classifications for carbon and low alloy steel coated electrodes are based on an "E"(electrode) prefix with a four or five digit number (EXXXXX). The first two digits (or threedigits in a five digit number) indicate the minimum required tensile strength in the “asdeposited” weld metal (not stress relieved) in thousands of pounds per square inch. For example,60 = 60,000 psi and 100 = 100,000 psi. The next to the last digit indicates the weldingposition(s) in which the coated electrode can make satisfactory welds: 1 = all positions and 2 =flat and horizontal fillet welds.

Table 1 is a tabulation of AWS/ASME Section II, Part C classification of E6XXX and E70XXcarbon steel electrodes which shows type of electrode coating, welding position , and type ofwelding current and polarity. A tabulation of typical welding current ranges for these carbonsteel electrodes is shown in Table 2.


Welding Parameters


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Table 1. AWS/ASME, Section II, Part C Classification of Coated Carbon SteelWelding Electrodes

AWSCLASSIFI

CATION

TYPE OF COVERING SATISFACTORYWELDINGPOSITIONS(a)

TYPE OFCURRENT(b)

E60 Series Electrodes

E6010 High cellulose sodium (Organic) F, V, OH, H DCEP

E6011 High cellulose potassium (Organic) F, V, OH, H AC or DCEP

E6012 High titania sodium (Rutile) F, V, OH, H AC or DCEN

E6013 High titania potassium (Rutile) F, V, OH, H AC or DCeither polarity

E6020 High iron oxide H-fillets AC or DCEN

E6022( c ) High iron oxide F AC or DCeither polarity

E6027 High iron oxide, iron powder H-fillets, F AC or DCEN


Welding Parameters


E70 Series Electrodes

E7014 Iron powder, titania F, V, OH, H AC or DCeither polarity

E7015 Low hydrogen sodium F, V, OH, H DCEP

E7016 Low hydrogen potassium F, V, OH, H AC or DCEP

E7018 Low hydrogen potassium, iron powder F, V, OH, H AC or DCEP

E7024 Iron powder, titania H-fillets, F AC or DCeither polarity

E7027 High iron oxide, iron powder H-fillets, F AC or DCEN

E7028 Low hydrogen potassium, iron powder H-fillets, F AC or DCEP

E7048 Low hydrogen potassium, iron powder F, OH, H, V-down

AC or DCEP

a. The abbreviations, F, V, V-down, OH, H, AND H-fillets indicate the welding positionsas follows:

F = FlatH= HorizontalH-fillets = Horizontal filletsV-down = Vertical down*V = Vertical*OH = Overhead

*Note: For electrodes 3/16in.(4.8mm) and under, except 5/32 in. (4.0 mm) and underfor classifications E7014, E7015, E7016. And E7018

b. The term DCEP refers to direct current, electrode positive (DC reverse polarity).The term DCEN refers to direct current, electrode negative (DC straight polarity).

c. Electrodes of the E6022 classification are for single-pass welds.


Welding Parameters


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Welding Parameters


Table 2. Typical Welding Current Ranges For Mild Carbon Steel Electrodes

Electrodediameter

in. mm

E6010andE6011

E6012 E6013 E6020 E6022 E6027 andE7027

E7014 E7015,E7016,andE7016-1

E7018 andE7018-1

E7024-1,E7024, andE7028

E7048

1/16 1.6 — 20 to 40 20 to 40 — — — — — — — —

5/64 25 to 60 25 to 60 — — — — — — — — —

3/32a

2.4 a 40 to 80 35 to 85 45 to 90 — — — 80 to 125 65 to 110 70 to 100 100 to 145 —

1/8 3.2 75 to 125 80 to 140 80 t0 130 100 to150

110 to160

125 to 185 110 to 160 100 to 150 115 to 165 140 to 190 80 to 140

5/32 4.0 110 to170

110 to190

105 to 180 130 to190

140 to190

160 to 240 150 to 210 140 to 200 150 to 200 180 to 250 150 to 220

3/16 4.8 140 to215

140 to240

150 to 230 175 to250

170 to400

210 to 300 200 to 275 180 to 255 200 to 275 230 to 305 210 to 270

7/32 5.6 170 to250

200 to320

210 to 300 225 to310

370 to520

250 to 350 260 to 340 240 to 320 260 to 340 275 to 365 —

¼ 6.4 210 to320

250 to400

250 to 350 275 to375

— 300 to 420 330 to 415 300 to 390 315 to 400 335 to 430 —

5/16a

8.0 a 275 to425

300 to500

320 to 430 340 to450

— 375 to 475 390to 500 375 to 475 375 to 470 400 to 525 —

a. These diameters are not manufactured in the E7028 classification

Engineering Encyclopedia


The AWS classifications for stainless steel coated electrodes are also based on an "E" prefix withonly a three digit number and a two digit suffix (EXXX-XX). The first three digits represent theAmerican Iron and Steel Institute's (AISI) numbering system for stainless steels.

The 300 series designates austenitic stainless steels and the 400 series designates martensitic andferritic stainless steels. The two digits in the suffix indicate the type of current and the type ofcoating for the electrode. These two digits are similar to the final two digits of carbon and lowalloy steel coated electrodes that were shown in Table 1. Most stainless steel coated electrodeshave suffixes of either 15 (lime coating) or 16 (titania coating).

For example, an E308-15 coated electrode is a 308 stainless steel material that can be welded inall positions with dc+ (reverse polarity) only whenE308-16 can operate on AC or dc+. E308-15coated electrodes have a low hydrogen coating. In the AWS classification E308L-15, the "L"represents a low carbon version of the filler metal with a maximum of 0.03% C and a minimumof 0.08% C for conventional grades.

Bare Rods and Wire

The AWS classifications for carbon and low alloy steel bare rods and wire have an "ER" prefixwith a two or three digit number and a one or two digit suffix (ERXXXS-XX). The "E"indicates an electrode, and the "R" indicates a welding rod; therefore, "ER" indicates either anelectrode or a welding rod. The first three digits "XXX" indicate the minimum required tensilestrength in thousands of pounds per square inch. These three digits are similar to the first threedigits of the carbon coated electrodes. The "S" indicates a solid electrode or rod. The one or twodigits in the suffix indicate the chemical composition of the deposited weld metal.

The AWS classifications for stainless steel bare rods and wire have an "ER" prefix with a threedigit number (ERXXX). The first three digits represent the American Iron and Steel Institute's(AISI) numbering system for stainless steels. The 300 series designates austenitic stainlesssteels, and the 400 series designates the martensitic and ferritic stainless steels. In the AWSclassification ER308L, the "L" represents a low carbon version of the filler metal.


The AWS classifications for carbon and low alloy steel flux cored electrodes have an "E" prefixwith a two digit number "XX and a one digit suffix (EXXT-X). The "E" indicates an electrodeand the "T" indicates a tubular electrode. The first two digits indicate the minimum requiredtensile strength in thousands of pounds per square inch. These first two digits are similar to thefirst two digits of the carbon coated electrodes. The one digit suffix indicates the chemicalcomposition of the deposited weld metal, gas type, and usability factor. For example, an E70T-1flux cored electrode has a 70,000 psi tensile strength and it uses CO2 shielding gas for flatposition welding. The method of classification of carbon steel and stainless steel electrodes forflux-cored arc welding is illustrated in Figure 31.



EXXT-X

Designates an electrode.

Indicates the minimum tensile strength of thedeposite weld metal in a test weld made withthe electrode and in accordance with specifiedwelding conditions.

Indicates the primary welding position for whichthe electrode is designed:

Indicates usability and performance capabilities.

Indicates a flux cored electrode.

Note:The letter " X " as used in this figure and in electrode classifications this specification substitutes for specific designations indicated by this figure.

0-flat and horizontal positions

1-all positions

(A) Carbon Steel flux-cored electrodes such as E70T-1

EXXXT-X

Indicates an electrode.

Designates a flux cored electrode

Designates the external shielding medium to be employed during welding (SeeNotes)

Designate classification according to compposition

(B) Stainless steel flux-cored electrodes such as E316T-3.

EXXXT-1 – designates an electrode using carbon dioxide shielding plus a flux system.EXXXT-2 – designates an electrode using a mixture of argon with 2% oxygen plus a flux system.

EXXXT-3 – designates an electrode using no external shielding gas wherein shielding is provided by the fluxsystem contained in the electrode core (self-shielding).EXXXT-G – indicates an electrode with unspecified method of shielding, no requirements being imposed except asagreed between purchaser and supplier. Each producer of an EXXXT-G electrode shall specify the chemicalcomposition and mechanical property requirements for his electrode.

Figure 31. Classification Method of Carbon Steel and Stainless Steel Flux-CoredElectrodes.



Shielding Gasses and Fluxes

All welding processes require some protection for the molten weld metal while welding. Thisprotection is called weld shielding and it takes the form of either shielding gas or flux. Theprimary purpose of the shielding gas or flux is to protect the molten weld metal fromcontamination by the oxygen and nitrogen in the atmosphere.

Gases

Weld shielding gases are considered consumables and are mostly used with the GTAW,GMAW,and the FCAW welding processes. The quality of commercial shielding gases are governed byspecifications that were developed by the Compressed Gas Association. Although argon andhelium are the only two inert gases that are available in sufficient quantities to support weldingoperations, the inert gases argon, helium, neon, krypton, and xenon are commercially available.

Argon – is an inert gas that is most widely used by Saudi Aramco with the GTAW process.Because it is heavier than air, argon forms a protective blanket over the weld area.

Helium – because it is lighter than air, i6t does not make a good shielding gas when weldingoutdoors. If it is used, helium must be highly controlled to ensure that the shielding gas canactually protect the molten weld metal and not rise from the weld and disperse. When buttwelding the stainless and nickel alloy steels, a purge gas must also be used to protect the moltenweld metal that is at the root of the weld.

Carbon Dioxide (CO2)– This gas is most widely used by Saudi Aramco to weld carbon and lowalloy steels with the GMAW and FCAW processes. Because CO2 contains oxygen, the fillermetals must contain sufficient deoxidizers to counteract the effects of oxygen from the shieldinggas. CO2 is a used mainly because of its relative low cost.

Fluxes

Fluxes are also considered consumables and are used mostly with the SMAW, FCAW, and theSAW processes. The coatings on carbon and low alloy steel electrodes may have from 6 to 12 ofthe following ingredients:

• Cellulose - to provide a gaseous shield with a reducing agent. The gas shield thatsurrounds the are is produced by the disintegration of the cellulose.

• Metal Carbonates - to adjust the basicity of the slag and to provide a reducingatmosphere.

• Titanium Dioxide - to help form a highly fluid but quick-freezing slag and toprovide ionization for the welding arc.



• Ferromanganese and Ferrosilicon - to help oxidize the molten weld metal and tosupplement the manganese and silicone content of the deposited weld metals.

• Clays and Gums - to provide the elasticity for extruding the plastic coating materialand to help provide strength to the coating.

• Calcium Fluoride - to provide shielding gas to protect the welding arc, to adjust thebasicity of the slag, and to provide fluidity and solubility of the metal oxides.

• Mineral Silicates - to provide slag and to give strength to the electrode.

• Alloying Metals -to provide alloy content, (such as, nickel molybdenum, andchromium) to the deposited weld metal.

• Iron or Magnesium Oxide - to adjust the fluidity and other properties of the slag.

• Iron Powder - to increase the productivity by providing additional metal to bedeposited in the weld.

Through combinations of various amounts of the above ingredients, an infinite variety ofelectrode coatings are possible.

The flux in flux cored electrodes is essentially the same as the flux on coated electrodes,however, to do the same job, more flux is required on the coated electrodes than in flux coredelectrodes. When electrodes are manufactured, binders (other ingredients) are added to keep thecoating intact. The binders allow for the extrusion f the coating. Because the flux on a coatedelectrode contains additional binders a greater volume of flux is required.

The flux that is used with the submerged arc welding (SAW) process is separate from the fillermetal. The flux is a granular form that is made up of may of the same ingredients that werelisted previously for the SMAW coated electrodes. Three type of SAW fluxes used are asfollows:

• Fused Flux - the ingredients are dry mixed, melted in a furnace at approximately2,900°F, and quenched to form a glassy material This material is then driedcrushed, sized, and packaged.

• Agglomerated Flux - - ingredients are wet mixed and dried in a rotary kiln atapproximately 1,800°F to form small balls of flux. After the flux balls are cooledthe balls of flux are sized and packaged.

• Bonded Fluxes - are very similar to the agglomerated fluxes with the exception thatthe flux mixture is bonded at a lower temperature. When alloy materials are notadded to the flux, the flux is considered “neutral”.

In accordance with the Saudi Aramco standards, agglomerated fluxes and bonded fluxes shouldnot be used because of their high affinity for moisture. Welds that are made by using thesefluxes are know to develop weld metal hydrogen delay cracks.



Storage and Handling Requirements

The proper storage and handling of filler metals is crucial to maintain the cleanliness and qualityof the filler metal. The storage of filler metal includes not only the packaging requirements ofthe filler metal but also the interim storage requirements of the packages until the filler metal isactually used. The handling of filler metals refers to the following movements:

• Movement of the filler metal from the receipt location to the storage location

• Movement of the filler metal from the storage location to the issuance location

• Movement of the filler metal from the issuance location to the work location

Coated Electrodes

Because of the flux coating, coated electrodes can be easily damaged when improperly stored orhandled. Rough handling in shipment or in storage can cause a portion of the flux coating tocrack loose from the solid metal rod, which can make the electrode unsuitable for welding.When most coated electrodes are bent, the flux coating will crack loose from the solid metal rod.When opening a sealed container of coated electrodes, the container must be inspected forevidence of damage. A dented or punctured container can indicate possible damage to thecoating of the electrodes. When the solid metal rod is exposed, coated electrodes should not beused.

Although coated electrodes may look similar, not all coated electrodes have the same packagingand storage requirements. When the flux coating is exposed to moisture for an extended periodof time, some coated electrodes may become unusable. The popular low hydrogen coatedelectrodes are extremely sensitive to moisture (e.g., rain, humidity). The cellulosic-coatedelectrodes are less sensitive to moisture pick-up and actually require moisture levels of three toseven percent to maintain the flux coating. Today, the majority of coated electrodes arepackaged in hermetically-sealed metal containers to prevent excessive moisture intrusion.

Coated electrode containers must be stored in a clean, dry area. Coated electrode containersshould be stored separately by AWS classification. Once the low hydrogen coated electrodes areremoved from the container, the coated electrodes must be placed in storage ovens atapproximately 250°F to ensure that the coated electrodes do not absorb any moisture. When thelow hydrogen coated electrodes are required to be taken into the field (for more than four hours)to perform welding, the low hydrogen coated electrodes must be placed in small portable storageovens at approximately 150°F. SAES-W-001 specifies storage temperatures for types of L.H.electrodes. The lids on the portable storage ovens must remain closed at all times except whenelectrodes are removed.



When the low hydrogen coated electrodes are used in the field for less than four hours, the lowhydrogen coated electrodes must be kept dry but they do not need to be stored in a heated oven.All low hydrogen coated electrodes that are exposed to the atmosphere must be rebaked for aperiod of at least four hours. Saudi Aramco procedures SAES-W-001 and SADP-W-001 specifythe proper rebake temperature for a variety of coated electrodes. The cellulosic-coatedelectrodes do not require storage in heated ovens, but they must be kept in a dry environment.Coated electrodes should never be placed directly on cold concrete or steel that can draw heat outof the coated electrode and allow moisture to enter the coating. Coated electrodes that becomewet should never be used for welding and must be discarded.

Bare Rods and Wire

Bare rods and wire must be stored in sealed containers, which must be placed in a clean, dryenvironment. Any bare rods or wires with visible rusting or contamination must not be used forwelding and must be discarded. After removal from the sealed containers, bare rods and wiresmust remain dry and clean in the field. Contamination on bare wire can cause porosity in theweld or operation difficulties in the wire feed mechanism.


Flux cored electrodes must also be stored in sealed containers in a clean, dry environment. Anyflux cored electrodes with visible rusting or contamination must not be used for welding andmust be discarded. After removal from the sealed containers, flux cored electrodes must remaindry and clean in the field.

Contamination on flux cored electrode wire can cause porosity in the weld or operationdifficulties in the wire feed mechanism. Consideration must be given to the storage of flux coredelectrodes in heated ovens based on the type of flux and the electrode manufacturer'srecommendations.



HEAT INPUT EFFECTS

The following section introduces the relation of heat input to welding. Heat input will bedescribed in terms of the welding process variables that contribute to variations in the amount ofheat input to a weld. This section includes the following topics:

• Parameters

• Effects of Heat Input

Parameters

Heat is required for all welding processes to melt the surface of the metal to be welded and thefiller metal that is added to the weldment so that coalescence can occur. The most common heatsource for welding is the electric arc.

The three key welding parameters affect the amount of heat input to a weld are:

• The welding current

• The welding arc voltage

• The travel speed of the welding process

Preheat and interpass temperatures are additional variable that can affect the amount of heatinput to a weldment. Because preheat is not directly associated with a welding process, preheatwill be described in the next section. Each of the three welding parameters is described below.

Current

The current in a welding circuit is the amount of electric charge that flows through the weldingcable in one second. The amount of electric per second that flows through the welding cable iscalled an ampere and it is designated by the letter "I". High welding current results in greaterbase metal penetration, and a lower welding current results in shallow base metal penetration.An increase in the welding current increases the heat input to the weld. An increase in thewelding current also increases the melt-off rate of the electrode and improves productivitybecause more weld metal is deposited.



Voltage

Voltage is the force that causes a current to flow. The measure of electrical pressure is the volt.The difference in potential or voltage causes the current to flow in an electric circuit. AsEquation 1 shows, both current and voltage affect the heat input to a weld. The letter "V" is usedto designate voltage. High welding voltage results in greater base metal penetration, while lowerwelding voltage is indicative of shallow base metal penetration. An increase in the weldingvoltage increases the heat input to the weld.

Travel Speed

The rate that a welding electrode progresses along a weld joint while welding is called the travelspeed. The letter "S" designates the travel speed. Several welding variables affect the travelspeed, such as, the welding process, the position of the weld, the welder, and the wire feed speed.Slow travel speeds make wide weld beads with deep base metal penetration. Fast travel speedsmake narrow weld beads and shallow base metal penetration. A decrease in the travel speedincreases the heat input to the weld.

Effects of Heat Input

The electric arc welding process uses a high temperature heat source that can melt the basemetals. An extensive difference in temperature between a high temperature heat source and thebase metal can cause thermal expansion and contraction between the base metal and the weldmetal. The following are some of the disadvantages of excessive heat input that can affect weldquality:

• Warpage and distortion caused by high residual differential shrinkage stresses

• Cracks caused by a reduction of ductility or a degree of hardening

• Premature failure caused by the deterioration of the toughness properties of theweld joint

• Premature failure caused by the loss of strength of certain work hardened,quenched, and tempered materials

Even though the electric welding arc is a heat source that moves continuously, steady stateconditions are established and the temperature distribution relative to the heat source is relativelystable.



Because many variables are involved, the heat input-time-temperature relationship (the thermalcycle of a weld) cannot be precisely determined. However, fairly accurate estimates can predictthe effects of heat input from a specific welding process. The total heat input to a weldmentmust be balanced to produce the desired weld properties. Extra heat is required, over and abovethe heat that is needed to melt the base metal and filler metal, to compensate for the heat that isconducted away from the weld and into the adjacent base metal. The heat input to a weldment(in joules per inch of weld) by a welding process can be estimated with Equation 1, located inWork Aid 4

EXAMPLE:

If a weld is to be made with the SMAW process and a 1/8" coated electrode at 145 amperes, 22volts, and a travel speed of ten (10) inches per minute, the amount of heat input to the weld couldbe estimated as follows:

( )( )Heat Input joules per inch=

×=

145 22 60

1019 140,

If a 5/32" coated electrode is used at 210 amperes and 24 volts with a travel speed of only six (6)inches per minute, the heat input is significantly increased.

( )( )Heat Input joules per inch=

×=

210 24 60

1030 240,

This heat input equation is used to calculate the heat that is developed in an electric arc and canbe used to compare welding procedures when heat input is a consideration. The base metaltemperature changes in an arc welding operation are much quicker and more abrupt than formost metallurgical processes (e.g., heat treatments). The metallurgical reactions from weldingheat input do not follow the normal heat treating relationships due to the short time duration attemperature. More specifically, in the arc welding process, melting and solidification occur withrelative quickness; and equilibrium is not achieved as it is achieved in direct treatment processes.



HEAT TREATMENT EFFECTS

With some welding processes and materials, heat must be applied to a weld prior to welding(preheat treatment). Other welding processes and materials require the use of heat after thewelding is complete (postweld treatment). The information in this section provides backgroundon the heat treatment of welds and includes the following topics:

• Preheat

• Postweld Heat Treatment

Preheat

Preheat is defined as the heat that is applied to the base metals of a weld joint immediately beforewelding. The construction standards that are associated with systems and components at SaudiAramco facilities identify the required preheat temperatures for the various base metals.However, the preheat temperature depends on many factors such as the composition of the basemetal, the ambient temperature, and the welding procedure. Several methods of preheatdetermination and application, along with typical preheat requirements for commonly usedmaterials, are described in more detail below.

Purpose

The main purpose of preheat is to reduce the rate at which a weld cools. The preheat ofweldments has the following advantages:

• Reduces shrinkage stresses in the weld and heat-affected zone that lead to cracks

• A slower rate at which the weld metal cools through the critical temperature range(approximately 1,600°F to 1,330°F), which prevents excessive hardening and lossof ductility of both the weld metal and the heat-affected zone

• A slower rate at which the weld metal cools through the 400°F range, which allowsmore time for any hydrogen that is present to diffuse away from the weld andadjacent base metal to avoid underbead cracking

• Maintains sufficient heat at the weld area on highly conductive or thick base metals

• Removes moisture from the weld joint



Figure 32 is a graph of temperature versus time that shows the effect of preheat on a plate buttweld. As the graph shows, a greater temperature drop in one second exists at a giventemperature (T1) when the initial temperature (To) of the plate is 70°F than when To is 300°F. Inother words, the cooling rate (°F/sec) is slower when preheat is used. Preheat should also beconsidered before thermal cutting (i.e., oxyacetylene cutting). Thermal cutting tasks may includethe preparation of weld joint bevels, the removal of attachments, or the removal of defectivematerial. For thick carbon and low alloy steels, preheat ensures that the base metal cools at aslower rate and prevents excessive hardening and loss of ductility in the base metal.



Figure 32. Effect of Preheat on Cooling Rate

Methods

Several methods are available for preheat treatment. The most common tools are oxyacetylenetorches and electric resistance heaters. The choice of the preheat tools depends on factors suchas the following:

• The preheat temperature

• The duration of the preheat cycle

• The size and shape of the weldment

• The need for a one-of-a-kind or a continuous production preheat operation



For the majority of pipe welds, an oxyacetylene torch provides sufficient preheat to support thewelding operation. Oxyacetylene torches are usually limited to small weldments orcircumferential pipe welds that are less than 12" in diameter and that are less than 3/4" thick. Forsmall weldments or circumferential pipe welds, actual preheat temperature is measured with atemperature indicating crayon. When an oxyacetylene torch is used to preheat a weld, thesurface of the base metal is generally much hotter than the average temperature in the base metal.When possible, temperature measurements should be made on both sides of the weld joint.Because the welder must constantly switch between the welding process and the preheat process,the use of an oxyacetylene torch is not the most productive tool to apply preheat.When preheat for a single weld or for multiple welds that are in close proximity is required for along period of time, electric resistance heaters are often more convenient to use thanoxyacetylene torches. Gas burners are more effectively and more widely used in pressurevessels (and in building industries in general) than handheld torches. The resistance heaterelements are commonly available in either rope, rope pads, or ceramic pads. Figure 33 shows atypical arrangement for rope resistance heaters and the power connections that provide preheatfor a circumferential butt weld in pipe.



Figure 33. Typical Arrangement of Rope Resistance Heaters



Figure 34 shows a typical arrangement for resistance heating pads and the power connectionsthat provide preheat for a circumferential butt weld in pipe.



Figure 34. Typical Arrangement of Resistance Heating Pads

Figure 35 shows a typical arrangement for ceramic resistance heater pads and the powerconnections that provide preheat for a circumferential butt weld in pipe. The limitations ofelectric resistance heaters include the inability to adapt to small intricate parts and to adequatelyheat materials greater than six inches thick.



Figure 35. Typical Arrangement of Ceramic Resistance Heater Pads



Figure 36 shows an electric resistance heater system that consists of a power supply, atemperature controller, a temperature recorder, resistance heating wires, power cables,thermocouples, and thermocouple signal cables. In electric resistance heaters, thermocouplesattach directly to the base metal that is adjacent to the weld to measure the exact preheattemperature of the weld. The thermocouples provide signals to the temperature controller thatregulates the electrical power that is required for the preheat. The temperature recorder makes apermanent record of the exact preheat temperature throughout the preheat and welding operation.



Figure 36. Electric Resistance Heater System



Determination

The necessity to preheat weld joints and the temperature requirements should be established byEngineering and should be demonstrated by a welding procedure specification (WPS). Thepreheat temperature depends upon these factors:

• Type of base metal and its composition

• Joint thickness degree of restraint

• Type and composition of filler metal

The interpass temperature should also be considered. The interpass temperature is the highesttemperature in the weld joint immediately prior to welding. Usually, the minimum interpasstemperature will be the same as the preheat temperature.

The weldment temperature should never be allowed to become lower than the preheat or theinterpass temperature. When welding is interrupted for any reason, the preheat temperature mustbe attained before welding is started again. Preheat and interpass temperatures must bemaintained through the entire thickness of the welding area. The interpass temperature is usuallyspecified as a maximum temperature to prevent excessive heat input to a weldment.

When welds are made on a small weldment, the interpass temperature increases due to the heatinput from welding. Under certain conditions, allowing the interpass temperature to exceed aspecific temperature is usually not desirable; therefore, a maximum interpass temperature isspecified. When the heat build up becomes excessive, the weldment must be allowed to cool butmust not cool below the minimum preheat temperature. Otherwise, distortion and loweredductibility of the weld joint can result.

The temperature of the welding area must be maintained within the minimum preheat and themaximum interpass temperature.

Higher preheat temperatures should be considered when the base metal has a carbon content inexcess of 0.30%, when the base metal is thick (over 1-1/2"), or when the weld joint is highlyrestrained (e.g., a piping closure weld).

Carbon Equivalent (CE) – While the material thickness, the type of base metal to be welded,the degree of joint restraint, and the filler metal are taken into account when preheatrequirements are determined, some adjustment may be needed for specific material composition.Generally, as the carbon content of a material increases, the necessity for preheat also increasesbut the critical cooling rate decreases. However, carbon is not the only element that influencesthe critical cooling rate.



Other elements in steel materials are responsible for the hardness and the loss of ductility thatoccur with rapid cooling. The determination of preheat requirements must account for the totalhardenability of a material. This total hardenability can be represented by a "carbon equivalent".This common measure of the effects of carbon and other alloy elements on hardening is the basisfor preheat and interpass temperature estimates.

CE empirical values that represent the sum of the effects of various elements on thehardenability. One of the most widely used carbon equivalent formulas is shown in Equation 2,Work Aid 5.

For carbon steels (all ASME p-No.2 materials, including API pipe grades up to and includingX60), the minimum preheat is calculated using Standard Drawing AE-036451. For carbon steelpiping and pipeline welds, the minimum preheat requirements are listed in the preheat tables ofSAES-W-011 and SAES-W-012. For all other materials, the minimum preheat shall be no lessthan what is listed or specified in the applicable codes and standards, such as ASME/ANSIB31.3, B31.4, B31.8, and AWS D1.1, Structural Welding Code.

Metal Thickness –As previously stated, the thickness of the material to be welded also affectsthe required amount of preheat. In general, thicker materials require more preheat. The requiredamount of preheat can be determined through review of the applicable construction standards orindustry guidelines that are based on carbon equivalency. The preheat requirements ofapplicable construction standards will be discussed in the following paragraphs.

The ASME standards present the minimum preheat temperature based upon the applicable PNumber (from ASME Section IX) of the materials to be welded. When materials of twodifferent P Numbers are welded together, the preheat temperature is normally the highest preheattemperature that is recommended for either of the materials. The AWS D1.1 standard alsopresents the preheat temperature requirements based on similar material (specific to structuralconstruction) groups. The API standards provide more generic preheat temperature information.The preheat temperature information that is presented below is based on the applicableconstruction standards. Table 3 summarizes the ASME preheat requirements for the followingmaterials:

• P Number 1 (carbon steel)

• P Number 3 (low-alloy steels)

• P Number 4 (1-1/4 chrome-moly steels)


• P Number 8 (stainless steels)



Table 3. ASME Construction Standard Preheat Temperature Requirements



Where:C = carbon contentCr = chromium contentt = material temperatureTp = preheat temperatureTs = minimum specified tensile strength



The AWS D1.1 standard categorizes structural steel base materials into four main groups thatare, for the most part, considered carbon steels. Slight differences exist between each of thecategories, and base metal thickness is the primary determinant of the minimum preheattemperatures. Table 4 shows the preheat temperature ranges have been developed and are basedupon the four standard thickness ranges that are listed in AWS D1.1.

Table 4. Preheat Temperature Ranges for the Four Thicknesses Ranges Listed InAWS D1.1.

Thickness of Thickest Partat Point of Welding (Inches

Preheat Temperature (°F) Range

???????? ?????????Up to 3/4 None 50Over 3/4 through 1-1/2 50 150Over 1-1/2 through 2-1/2 150 225Over 2-1/2 225 300

API 620 and 650 do not specifically require preheat treatment when welding tanks. However,both construction standards do acknowledge the benefit of preheat and suggest that all preheattreatments be qualified with the welding procedure specification prior to production welding.

Filler Metal Coating Type and Composition – Minimum preheat temperature is also affected bythe type of electrode coating (low versus non -low hydrogen) types as well as its chemicalcomposition. When used to weld materials of the same thickness and chemical composition, theminimum preheat temperature is much higher with the non-low hydrogen electrodes than thoseof the low hydrogen type. Similarly, welding electrodes containing alloys are elements thatcontribute to the weld ????????? such as Cr, Mo, etc. will require higher preheat than those thatdon’t contain these elements. The difference in preheat temperatures levels as a function ofwelding electrode types is shown by preheat tables of AWS D1.1 structural welding and SaudiAramco piping and pipeline standards SAES-W-011 and -012.

Postweld Heat Treatment

A number of postweld heat treatments exist for weldments but stress relief is the most widelyused postweld heat treatment. Some other postweld heat treatments include annealing andnormalizing. For the purposes of this Module, postweld heat treatment will be synonymous withstress relief. Postweld heat treatment is any heat treatment that is applied to a weld or weldmentafter welding to reduce residual stresses. The construction standards for systems andcomponents at Saudi Aramco facilities identify the required postweld heat treatments for thevarious base metals. However, the postweld heat treatment depends on many factors such as the

*composition* of the base metal joint thickness and type of service. Several methods ofpostweld heat treatment temperature determination and application, along with typical postweldheat treatment requirements for commonly used materials are described in more detail below.



Purpose

The purpose of postweld heat treatments is to reduce the residual stresses that are withinweldments. The following are the advantages of postweld heat treatment of weldments:

• Reduce residual stresses that are inherent to any weldment, casting, or forging

• Soften hardened weld zones

• Improve resistance to corrosion and caustic embrittlement

• Improve dimensional stability of the weldment when machined

• Increase service life of the weldment

Methods

With the exception of welding torches, similar methods as that utilized for preheat are used foruse for postweld heat treatment (PWHT) of welds Electric resistance heaters are the mostpopular method of PWHT for field applications. Postweld heat treating furnaces are generallyvery large permanent structures that can accommodate an entire pressure vessel. Furnaces aregenerally used by manufacturers of large components that require PWHT. Temporary furnacesare also used and are usually built around a field constructed component such as a pressurevessel. The choice of the PWHT methods is similar to preheat treatment methods and dependson factors such as the following:

• The postweld heat treatment temperature

• The duration of the postweld heat treatment cycle

• The size and shape of the weldment or component

• The need for a one-of-a-kind or a continuous production postweld heat treatmentoperation

Electric Resistance Heaters – For most pipe welds, electric resistance heaters suffice forpostweld heat treatment operations. These resistance heaters are identical to the preheat devicesthat were described earlier in this Module. Figure 36 showed an electric resistance heater systemthat consisted of a power supply, a temperature controller, a temperature recorder, resistanceheating wires, power cables, thermocouples, and thermocouple signal cables. As with preheatingoperations, thermocouples directly attach to the base metal adjacent to the weld to measure theexact PWHT weldment temperature. The thermocouples provide signals to the temperaturecontroller to regulate the electrical power that is required for the PWHT. The number andlocation of thermocouples that should be attached to the weldment and other PWHTrequirements are outlined in SAES-W-010, SAES-W-0011, and SAES-W-012.





Figure 36. Electric Resistance Heater System

To reduce the time that is necessary to get the weldment up to the PWHT temperature and toprovide a slower cooling down period, welds that require PWHT are usually well insulated. Aswith preheat, the temperature recorder provides a permanent record of the exact PWHTtemperature throughout the PWHT.

The major limitations of electric resistance heaters include the inability to adapt to small intricateparts and the inability to adequately heat very thick materials.

Furnace PWHTs – When using the furnace PWHT, the following factors must be consider:

• The support requirement of the component to be heat treated

• Freedom of the material to expand and contract

• The placement of sufficient thermocouples to verify the accuracy of the PWHT

• The type of heat source



The heat source for furnaces is either natural gas or fuel oil. For uniform application of heat, thecomponent to be treated is carefully and strategically surrounded by heating nozzles. Toexpedite the heating process, heating nozzles may also be arranged inside the component toimprove the heat-up rate and thorough heat soak of the component. The component's location inthe furnace must also be considered to avoid hot or cold spots. The location of severetemperature gradients depends upon the arrangement of the furnace and the location of the heatsource.

The duration of a PWHT cycle includes the heating time to maximum temperature (ramp up), theholding time at the specified maximum temperature (soak), and the cooling time to ambienttemperature (ramp down). A typical soak time that is specified in the construction standards isone hour per inch of material thickness. In some cases, obtaining the required maximum PWHTtemperature or soak time is not possible. In these cases, the construction standards haveprovisions for alternate temperatures and soak times.

Regardless of the PWHT method that is employed, the heating and subsequent cooling rates arecritical to the success of the operation. When the heating rate is too high, the temperatures ofthin sections of material increase faster than thick sections. Similarly, when the cooling rate istoo low, the temperatures of thin sections of material decrease faster than thick sections.Nonuniform heating and cooling can cause distortion, residual stresses, and cracks. For thisreason, the heating and cooling rates are specified by the applicable construction standards.

Requirements

The majority of postweld heat treatment applications in Saudi Aramco must be in accordancewith ASME Section VIII, Division 1, Paragraph UCS-56. All construction standards that wereaddressed in earlier Modules contain mandatory PWHT requirements for specific types ofmaterials. When a PWHT temperature must be determined for a particular welding operation,the applicable construction standard is the first place to look. Typically, the constructionstandards require that the heating rate must not exceed 300°F to 400°F per hour when the basemetal of the weld or component is above 800°F. While the weld or component is ramping up intemperature, the heating rate is not critical below 800°F. The cooling rate must not exceed400°F to 500°F per hour when the base metal of the weld or component is above 800°F. Whilethe weld or component is ramping down in temperature, the cooling rate is not critical below800°F.



The postweld heat treatment temperature information presented below is based on the applicableconstruction standards. This information has been greatly simplified because the constructionstandards provide many exemptions from the mandatory PWHT requirements. The PWHTtemperature requirements for materials that are covered by ASME construction standards aresimilar to each other but care must be taken because the differences are very subtle. SpecificPWHT requirements must be directly derived from the applicable construction standards. Figure39 summarizes the ASME PWHT requirements for the following materials:

• P Number 1 (carbon steel)

• P Number 3 (low-alloy steels)



Carbon Steels – The PWHT temperature requirements for mild carbon steels (P Number 1) thatare covered by ASME Section I, Section VIII, B31.1, and B31.3 are similar. The PWHTtemperature for materials with a thickness that exceeds 3/4" is generally between 1,100°F and1,200°F. ASME Section VIII is the only exception in that PWHT is not required until thematerial thickness (t) exceeds 1-1/2". Materials between 1-1/4" and 1-1/2" in thickness alsorequire PWHT per Section VIII when the preheat temperature (T

p) is less than 200°F. Table 5

summarizes the ASME preheat requirements for P Number 1 materials.



Table 5. ASME Construction Standard PWHT Temperature Requirements



Where:C = carbon contentCr = chromium contentO.D. = outside diameterNPS = nominal pipe sizet = material temperatureTp = preheat temperatureTs = minimum specified tensile strength



The AWS D1.1 construction standard does not specifically require PWHTs of weldments. AWSD1.1 acknowledges that the need for PWHT must be identified on the contract drawings orspecifications. However, AWS D1.1 does provide guidelines for PWHT temperature between1,100°F and 1,200°F for most carbon steels and heating and cooling rates that are similar tothose previously discussed.

Because the size and weight of field erected tanks do not permit adequate support at PWHTtemperatures, API 620 does not specifically require the use of PWHT when welding tanks. API650 does describe PWHT for all flush-type cleanout fittings and shell connections. In general,the PWHT temperatures are between 1,100°F and 1,200°F. Variations in the PWHTrequirements are based on the diameter of the opening, the material group, and the thickness ofthe tank shell material.

Low Alloy Steels – The postweld heat treatment temperature requirement for low alloy steels (PNumber 3) in ASME Section I and B31.1 is 1,100°F when the material thickness (t) is in excessof 5/8" and the carbon content (C) is in excess of 0.25%. ASME Section VIII requires PWHT at1,100°F for all P Number 3, Group Number 3, materials. Group Number 1 and 2 materialsrequire PWHT at 1,100°F when the material thickness exceeds 1/2" and the carbon contentexceeds 0.25%. ASME B31.1 requires PWHT at temperatures between 1,100°F and 1,200°Fwhen the material thickness exceeds 5/8" and the carbon content exceeds 0.25%. ASME B31.3requires PWHT at temperatures between 1,100°F and 1,200°F when the material thicknessexceeds 3/4" or the minimum specified tensile strength (T

s) exceeds 71 ksi. Figure 39

summarizes the ASME PWHT requirements for P Number 3 materials.

The postweld heat treatment temperature requirement for low alloy steels (PNumber 4) in ASMESection I and VIII is 1,100°F when the outside diameter (O.D.) is greater than 4", when thematerial thickness (t) is greater than 5/8", or when the carbon content (C) is greater than 0.15%,when the minimum preheat temperature(T

p) is less than 250°F. ASME B31.1 requires PWHT at

temperatures between 1,300°F and 1,375°F when the nominal pipe size (NPS) is greater than 4",the material thickness (t) is greater than of 1/2", the carbon content (C) is greater than 0.15%, orthe minimum preheat temperature(T

p) is less than 250°F. ASME B31.3 requires PWHT at

temperatures between 1,300°F and 1,375°F when the material thickness (t) is greater than 1/2" orthe minimum specified tensile strength (Ts) exceeds 71 ksi. Figure 39 summarizes the ASMEPWHT requirements for P Number 4 materials.



The postweld heat treatment temperature requirement for low alloy steels (PNumber 5) in ASMESection I and VIII is 1,250°F when the chromium content is greater than 3.0%, when the outsidediameter (O.D.) is greater than 4", when the material thickness (t) is greater than 5/8", when thecarbon content (C) is greater than 0.15%, or when the minimum preheat temperature(Tp) is lessthan 300°F. ASME B31.1 requires PWHT at temperatures between 1,300°F and 1,400°F whenthe nominal pipe size (NPS) is greater than 4", when the material thickness (t) is greater than1/2", when the chromium content is greater than 3.0%, when the carbon content (C) is greaterthan 0.15%, or when the minimum preheat temperature(Tp) is less than 300o F. ASME B31.3requires PWHT at temperatures between 1,300°F and 1,400°F when the material thickness (t) isgreater than 1/2", the chromium content is greater than 3.0%, or the carbon content is greaterthan 0.15%. Figure 39 summarizes the ASME PWHT requirements for P Number 5 materials.



GLOSSARY

acidity A chemical term relating to the quality or condition of beingacidic in composition.

annealing A heat treatment that increases the temperature of steel abovethe critical temperature and then is slowly cooled to removeinternal stresses that result in a steel of lower strength andhigher ductility.

basicity A chemical term relating to the quality or condition of beingbasic in composition.

coalescence The growing together or growth into one body of the materialsbeing welded.

interpass temperature The highest temperature in the weld joint immediately prior towelding, or, in the case of multiple pass welds, the highesttemperature that is in the section of the previously depositedweld metal immediately before the next pass is started.

liquidus temperature The lowest temperature at which a metal or alloy is completelyliquid, i.e., the temperature at which freezing starts.

normalizing A heat treatment that increases the temperature of steel abovethe critical temperature and is then air cooled to removeinternal stresses that result in a steel of higher strength andlower ductility than annealing.

postweld heat treatment For stress relieving applications, any heat treatment that isapplied to a weld or weldment subsequent to welding in orderto reduce stresses or to alter the weld structure.

preheat Heat that is applied to the base metals of a weld jointimmediately before welding.

reducing agent A material that adds hydrogen to an element or compound.

reducing treatmentatmosphere

An atmosphere of hydrogen (or other substances that readilyprovide electrons) surrounding a chemical reaction or physicaldevice. The effect is the opposite to that of an oxidizingatmosphere.

root penetration The depth of fusion that is obtained with the root pass.



solidification temperature Synonymous with solidus temperature.

solidus temperature The highest temperature at which a metal or alloy iscompletely solid, i.e., the temperature at which melting starts.

temperature indicatingcrayon

A temperature measuring device that is made from a chalk-likematerial and that is formulated to melt at specific temperatureswith a ± 1% accuracy

thermocouple A thermoelectric device that measures temperature differences.

weldment An assembly of component parts that is joined by welding.



WORK AID 1: HOW TO IDENTIFY THE MOST COMMONLY

The following Work Aid will assist you in identifying the most common metals used in the oil andgas industry.

TYPE OF METAL OR SUB-GROUP

DESCRIPTION

Carbon Steel (Three Types) Carbon content is less than 1 percent

Manganese content is less than 1.65 percent

Copper and silicon content are each less than 0.60 percent

(1). Low-carbon Steel – to 0.25% carbon ( c ) -0.25 to 1.5 %magnesium (Mn)

(2). Medium-carbon Steel –0.25 to 0.50% c, 0.60 to 1.65%Mn.

(3). High-carbon Steels –0.50 to 1.03% c,0.30 to 1.00% Mn.

• Low Alloy Steels The amount of manganese is greater than 1.65 percent.

The amount of silicon is greater than 0.60 percent.

The amount of copper is greater than 0.60 percent.

A definite minimum quantity of any of the followingelements is specified or required in alloy steels: aluminum,boron, chromium up to 3.99 percent, cobalt, columbium,molybdenum, nickel, titanium, tungsten, vanadium, orzirconium.

Any other alloying agent is added to obtain a desiredalloying effect.



• Stainless Steels (Fivegroups)

All stainless steels contain iron as the main element andchromium in amounts that vary from about 11 percent to 30percent. Chromium provides corrosion resistance

(1) Austenitic – most commonly used, corrosive resistant,easily welded, does not require pre or post heat.

(2) Chromium Martensitic – are magnetic steels thatcontain 12 to 14 percent chromium and up to 0.35percent carbon

(3) Chromium Ferritic – are also magnetic and readilywelded; however, the gas welding processes are notrecommended

(4) Duplex – combine the corrosion resistance properties ofaustenitic S. S. grade, especially stress corrosioncracking (SCC), and the mechanical properties of theferritic stainless steel grades

(5) Precipitation-hardened – can develop high strength withreasonably simple heat treatments; Precipitation-hardened stainless steels that are readily welded requireno preheat or solution annealing heat treatment.



WORK AID 2: HOW TO IDENTIFY WELD JOINT DESIGNS AND SYMBOLS

This Work Aid consists of Figure 8 through Figure 29 in the Information Section of this module.Use the Table of Contents for Figures to locate the page numbers.



WORK AID 3: HOW TO IDENTIFY WELDING CONSUMABLES

This Work Aid will assist you in identifying welding consumables.

Following is a synopsis of the four basic types of welding consumables:

1. Coated Electrodes

• Most popular type of filler metal for arc welding

• Also used in the SMAW welding process

• The AWS classifications for carbon and low alloy steel coated electrodes are based on an"E" (electrode) prefix with a four or five digit number (EXXXXX).

− The first two digits (or three digits in a five digit number) indicate the minimumrequired tensile strength in the “as deposited” weld metal (not stress relieved) inthousands of pounds per square inch.

− The next to the last digit indicates the welding position(s) in which the coatedelectrode can make satisfactory welds:

(a) – 1 = all positions(b) – 2 = flat and horizontal fillet welds

• The AWS classifications for stainless steel coated electrodes are also based on an "E"prefix with only a three digit number and a two digit suffix (EXXX-XX).

− The first three digits represent the American Iron and Steel Institute's (AISI)numbering system for stainless steels.

(a) – The 300 series designates austenitic stainless steels(b) – The 400 series designates martensitic and ferritic stainless steels

− The two digits in the suffix indicate the type of current and the type of coating for theelectrode.

2. Bare Rods and Wires

• Bare rods are typically manufactured in 36" straight lengths with diameters that rangefrom 0.045" to 3/16".

• Bare rods are predominantly used with the gas tungsten arc welding (GTAW) processand the torch brazing process.

• Bare wire electrodes are similar to bare rods except that bare wire is manufactured incontinuous lengths with diameters that range from 0.020" to 1/8."



• The AWS classifications for carbon and low alloy steel bare rods and wire have an"ER" prefix with a two or three digit number and a one or two digit suffix(ERXXXS-XX). The "E" indicates an electrode, and the "R" indicates a welding rod;therefore, "ER" indicates either an electrode or a welding rod.

− The first three digits "XXX" indicate the minimum required tensile strength inthousands of pounds per square inch.

− The "S" indicates a solid electrode or rod.

− The one or two digits in the suffix indicate the chemical composition of thedeposited weld metal.

• The AWS classifications for stainless steel bare rods and wire have an "ER" prefix with athree digit number (ERXXX).

− The first three digits represent the American Iron and Steel Institute's (AISI)numbering system for stainless steels.

− The 300 series designates austenitic stainless steels, and the 400 series designates themartensitic and ferritic stainless steels.

− In the AWS classification ER308L, the "L" represents a low carbon version of thefiller metal.

3. Flux cored Electrodes.

• Tubular wire that is manufactured in continuous lengths with diameters that rangefrom 0.045" to 5/32."

• The AWS classifications for carbon and low alloy steel flux cored electrodes have an"E" prefix with a two digit number "XX and a one digit suffix (EXXT-X).

− The "E" indicates an electrode and the "T" indicates a tubular electrode.

− The first two digits indicate the minimum required tensile strength in thousandsof pounds per square inch.

− The one digit suffix indicates the chemical composition of the deposited weldmetal, gas type, and usability factor. (Refer to Figure 31)

− Example, An E70T-1 flux cored electrode has a 70,000 psi tensile strength andit uses CO2 shielding gas for flat position welding.



WORK AID 4: HOW TO DESCRIBE HEAT INPUT EFFECTS

This Work is a synopsis of the effects of heat input.

1. Parameters of heat input

• The three key welding parameters affect the amount of heat input to a weld are:

− The welding current

(a) High welding current results in greater base metal penetration, and a lowerwelding current results in shallow base metal penetration.

(b) An increase in the welding current increases the heat input to the weld.(c) An increase in the welding current also increases the melt-off rate of the

electrode and improves productivity because more weld metal is deposited

− The welding arc voltage

(a) Voltage is the force that causes a current to flow.(b) The difference in potential or voltage causes the current to flow in an

electric circuit.(c) The letter "V" is used to designate voltage(d) High welding voltage results in greater base metal penetration, while lower

welding voltage is indicative of shallow base metal penetration.(e) An increase in the welding voltage increases the heat input to the weld

− The travel speed of the welding process.

(a) The rate that a welding electrode progresses along a weld joint whilewelding is called the travel speed.

(b) The letter "S" designates the travel speed.(c) Several welding variables affect the travel speed, such as, the welding

process, the position of the weld, the welder, and the wire feed speed.(d) Slow travel speeds make wide weld beads with deep base metal penetration.(e) Fast travel speeds make narrow weld beads and shallow base metal

penetration(f) A decrease in the travel speed increases the heat input to the weld



2. Disadvantages of excessive heat input that can affect weld quality.

• Warpage and distortion caused by high residual differential shrinkage stresses

• Cracks caused by a reduction of ductility or a degree of hardening

• Premature failure caused by the deterioration of the toughness properties of the weldjoint

• Premature failure caused by the loss of strength of certain work hardened, quenched,and tempered materials

3. Use the following equation to determine heat input.

Equation 1. Heat Input

Where:I = the welding current in amperesV = the arc voltage in voltsS = the travel speed in inches per minute



WORK AID 5: HOW TO DESCRIBE HEAT TREATMENT EFFECTS

This Work Aid is a synopsis of the effects of heat treatment.

1. Preheat

• Heat that is applied to the base metals of a weld joint immediately before welding.

• Preheat temperature depends on many factors such as the composition of the basemetal, the ambient temperature, and the welding procedure.

• The main purpose of preheat is to reduce the rate at which a weld cools.

• Preheating the weld has these advantages:

− Reduces shrinkage stresses in the weld and heat-affected zone that lead to cracks

− A slower rate at which the weld metal cools through the critical temperature range(approximately 1,600°F to 1,330°F), which prevents excessive hardening and lossof ductility of both the weld metal and the heat-affected zone

− A slower rate at which the weld metal cools through the 400°F range, whichallows more time for any hydrogen that is present to diffuse away from the weldand adjacent base metal to avoid underbead cracking

− Maintains sufficient heat at the weld area on highly conductive or thick basemetals

− Removes moisture from the weld joint

• The choice of the preheat tools depends on factors such as the following:

− The preheat temperature

− The duration of the preheat cycle

− The size and shape of the weldment

− The need for a one-of-a-kind or a continuous production preheat operation

• For the majority of pipe welds, an oxyacetylene torch provides sufficient preheat tosupport the welding operation

• When preheat for a single weld or for multiple welds that are in close proximity isrequired for a long period of time, electric resistance heaters are often more convenient.

• Gas burners are more effectively and more widely used in pressure vessels (and inbuilding industries in general) than handheld torches.

• The necessity to preheat weld joints and the temperature requirements should beestablished by Engineering and should be demonstrated by a welding procedurespecification (WPS).



• The preheat temperature depends upon these factors:

− Type of base metal and its composition

− Joint thickness degree of restraint

− Type and composition of filler metal

• The interpass temperature should also be considered. The interpass temperature is thehighest temperature in the weld joint immediately prior to welding.

• The weldment temperature should never be allowed to become lower than the preheator the interpass temperature.

Use the following formula to determine carbon equivalent of base metals

Equation 2. Carbon Equivalent Formula

CE = %C + (%Mn/6) + ( Er Mo v5

= + ) + ( Ni Cu1.5+ )

Where:%C = Percent of Carbon%Mn = Percent of Manganese%Ni = Percent of Nickel%Mo = Percent of Molybdenum%Cr = Percent of Chromium%Cu = Percent of Copper

2. Postweld Heat Treatment

• A number of postweld heat treatments exist for weldments but stress relief is the mostwidely used postweld heat treatment..

• Postweld heat treatment is any heat treatment that is applied to a weld or weldmentafter welding to reduce residual stresses.

• Advantages of postweld heat treatment of weldments:

− Reduce residual stresses that are inherent to any weldment, casting, or forging

− Soften hardened weld zones

− Improve resistance to corrosion and caustic embrittlement

− Improve dimensional stability of the weldment when machined

− Increase service life of the weldment



• Similar methods as that utilized for preheat are used for use for postweld heat treatment(PWHT) of welds. T he choice of the PWHT methods is similar to preheat treatmentmethods and depends on factors such as the following:

− The postweld heat treatment temperature

− The duration of the postweld heat treatment cycle

− The size and shape of the weldment or component

− The need for a one-of-a-kind or a continuous production postweld heat treatmentoperation

• The majority of postweld heat treatment applications in Saudi Aramco must be inaccordance with ASME Section VIII, Division 1, Paragraph UCS-56.

• Typically, the construction standards require that the heating rate must not exceed300°F to 400°F per hour when the base metal of the weld or component is above 800°F.

• The cooling rate must not exceed 400°F to 500°F per hour when the base metal of theweld or component is above 800°F



BIBLIOGRAPHY

AWS A5.x series, 1991

ASME Section I, Rules for Construction of Power Boilers, 1966

ASME Section II, Part C, Specifications for Welding Rods, Electrodes, and Filler Metals, 1966

ASME Section VIII, Pressure Vessels, 1966

ASME Section IX, Qualification Standards for Welding, 1966

ASME/ANSI B31.3, Process Piping, 1966

ASME/ANSI B31.4, Liquid Transportation of Hydrocarbons, 1992

AWS D1.1, Structural Welding Code, 1996

Welding Parameters

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