CHEVRON Pressure Vessel - Asme Codes

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200 ASME Codes

AbstractThe American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code is the basis for design, fabrication, and testing of all new boilers and pressure vessels throughout the Company. The “Code,” or “ASME Code,” is used exclu-sively in the United States and Canada. Most jurisdictions (primarily state govements) require equipment to be constructed according to the Code. Company pis to follow the ASME Code regardless of jurisdictional requirements.

This section is an introduction to and overview of the entire code, plus a more detailed summary of Section VIII, which specifically addresses pressure vesselIt clarifies the purpose and scope of the Code, and its application within the Company. It also outlines recommended practices that exceed Code requireme

Section VIII, Pressure Vessels, is divided into Division 1, which is most commoused, and Division 2, which requires more extensive design, fabrication, and intion requirements, but which may be the economic choice for thick-walled vessThe differences between Division 1 and Division 2 are summarized.

The information in this Section (and the entire manual) is not intended to be a substitute for the Code, but rather to clarify the requirements of, and to save time in using the Code. You must use a current Code when designing, fabri-cating, and testing new vessels.

Contents Page

210 Overview 200-3

211 Introduction

212 Brief History of the ASME Code

213 Organization of the ASME Code

214 Updating and Interpreting the Code

220 ASME Code Stamps 200-5

230 ASME Code, Section VIII, Division 1 Vs. Division 2 200-7

240 Design Criteria, ASME Code, Section VIII, Division 1 200-7

241 Scope, Division 1

242 Structure, Division 1

Chevron Corporation 200-1 April 2000

200 ASME Codes Pressure Vessel Manual

243 Allowable Stresses, Division 1

244 Material Specifications, Division 1

245 Inspection Openings, Division 1

246 Pressure Relief Devices, Division 1

247 Cryogenic and Low-temperature Vessels, Division 1

248 Testing, Inspection, and Stamping, Division 1

250 Design Criteria, ASME Code, Section VIII, Division 2 200-14

251 Scope, Division 2

252 Structure, Division 2

253 Allowable Stresses, Division 2

254 Materials and Tests, Division 2

255 Responsibilities, Division 2

260 Welding, ASME Code, Section IX 200-18

270 ASME Code, Section I, Power Boilers 200-18

271 Scope and Limitations, Boilers

272 Allowable Stresses, Boilers

273 Fabrication, Inspection and Tests, Boilers

280 Other Codes And Regulations 200-20

281 Other National Codes

290 Additional Company Recommendations 200-21

291 Model Specifications

April 2000 200-2 Chevron Corporation

Pressure Vessel Manual 200 ASME Codes

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210 Overview

211 IntroductionThe design and construction of pressure vessels is governed by jurisdictional author-ities of the site location. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code is recognized by most States as a safe and accept-able set of rules for design, fabrication, and testing of boilers and pressure vessels. The Code covers vessels made of metal, concrete, and composites for power, chem-ical, petroleum, and nuclear applications.

Note The Code does not directly apply to repairs or alterations, although the prin-ciples are generally applied. See Section 800 for information on commonly applied published standards for repair and alterations.

The Code is issued by ASME with the approval of the American National Standard Institute (ANSI). One or more of its sections have become legal requirements in most of the States and all of the Provinces of Canada. It is also used in many other countries around the world.

212 Brief History of the ASME CodeFrequent failures of boilers and pressure vessels at the beginning of the 20th Century showed the necessity of legislating rules and regulations for their construc-tion. The first legal code of rules for the construction of steam boilers was enacted in 1907 by Massachusetts after two catastrophic boiler explosions resulting in death, injuries, and extensive property damage. The following year, Ohio passed similar legislation, and other states soon followed.

Regulations differed from state to state and often conflicted with one another, and manufacturers began to find it difficult to build vessels that would be accepted in different states. Both manufacturers and users appealed to the Council of ASME in 1911 to correct the situation. After 3 years of meetings and public hearings, the first “ASME Rules for Construction of Stationary Boilers and for Allowable Working Pressures” was adopted in 1915. It ultimately became Section I, Power Boilersthe ASME Code.

The first Code for pressure vessels, “Rules for the Construction of Unfired PresVessels,” was issued in 1925. In 1934, a joint American Petroleum Institute (API)-ASME Committee issued the first pressure vessel code for the petroleumindustry, and two separate pressure vessel codes existed until 1951. In 1952 thcodes were consolidated into one, the ASME Unfired Pressure Vessel Code, SVIII. Subsequently, this became Section VIII, Division 1, in 1968 when Division “Alternative Rules for Pressure Vessels,” was issued.

213 Organization of the ASME CodeMany changes have been made to the ASME Code since 1915, and new sectioadded. At the present time, the Code includes the following sections:



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• Section I—Power Boilers. Covers fired steam boilers, electric, and high temperature water boilers. The rules of this section apply to the boiler and external piping, valves and fittings within certain specified limits. This sectiois briefly reviewed in Section 270.

• Section II—Material Specifications. Part A—Ferrous Materials, Part B—Nonferrous Materials, Part C—Welding Rods, Electrodes and Filler Metals.Materials listed in these specifications have “SA” and “SB” designations anare the only materials that can be used in the construction of Code vesselsMost “SA” and “SB” specifications are the same as “A” or “B” specificationsin ASTM standards.

• Section III—Division 1—Nuclear Power Plant Components, Division 2—Concrete Reactor Vessels and Containment. Division 1 divides nuclear plant components into four classes: 1,2,3, and MC. It allows a choice of rules providing different levels of structural integrity and quality according to the relative importance assigned to the individual components of a nuclear power plant.

• Section IV—Heating Boilers. Covers fired steam heating boilers, fired hot water heating boilers, and fired hot water supply boilers. The rules of this section, as in the case of Section I, apply also to external piping, valves and fittings within certain limits.

• Section V—Nondestructive Examinations. Covers requirements and methods for nondestructive examination required by other Code Sections, including radiographic, ultrasonic, liquid penetrant, eddy current, visual examination, and leak testing.

• Section VI—Recommended Rules for Care and Operation of Heating Boilers.

• Section VII—Recommended Rules for Care of Power Boilers.

• Section VIII—Division 1—Pressure Vessels, Division 2 —Pressure Vessels—Alternative Rules. This section is discussed in the following text.

• Section IX—Welding and Brazing Qualifications. Covers requirements for qualifications of welding procedures and welding operators.

• Section X—Fiberglass-Reinforced Plastic (FRP) Pressure Vessels.

• Section XI—Rules for Inservice Inspection of Nuclear Power Plant Components.

214 Updating and Interpreting the CodeIn order to keep up with the constant growth and progress of the industry, constant revisions of the Code have been required. Each new material, design, fabrication method, and protective device brings new problems to the Code Committee, requiring the technical advice of many subcommittees, in order to expedite proper additions and revisions to the Code.



Semiannually, on January 1st and July 1st, a new addendum to the Code is issued. An addendum becomes mandatory 6 months after the date of issuance. Every 3 years, on July 1st, a new edition of the Code is issued, incorporating all addenda to the previous edition. It becomes mandatory on the date of issuance.

Since the Code does not cover all the details of design, construction, and materials, pressure vessel manufacturers sometimes have difficulties in the interpretation of a certain rule, in order to meet specific customer requirements. In such cases, the inspector’s office is consulted, and if he is not able to give the proper interpretation of the intent of the Code, or has doubts or questions about it, the question is referred to the Authorized Inspector’s office. If they are not able to provide a ruling, the manufacturer may request the assistance of the ASME Boiler and Pressure Vessel Committee, which meets regularly to consider inquiries of this nature. After a deci-sion has been reached, it is forwarded to the inquiring party and also published in the Mechanical Engineering magazine. If no further criticism is received, the deci-sion may be formally adopted as a Code Interpretation. Every 6 months, Code Interpretations are published in the form of questions and replies, and they may be included in the next addendum.

Code Cases are also issued periodically. They contain rules for materials and special constructions that have not been sufficiently developed for inclusion in the Code itself.

220 ASME Code StampsUsers of pressure vessels prefer to order ASME Code vessels because they know that such vessels will be designed, fabricated, and inspected in accordance with an approved quality control system and in compliance with a safe standard.

It is Chevron’s policy to order vessels that conform to ASME Code require-ments, whether or not the jurisdiction where the vessel will be installed requires its use.

Company Specifications have been prepared that supplement the Code with addi-tional recommendations that are considered advisable, to provide additional safety and reliability under the process conditions and environments in which the vessels will be used. Note that the Code assigns to users the responsibility of assuring that the vessel is satisfactory for the intended service conditions. The Company Specifi-cations help fulfill this requirement.

Pressure vessel manufacturers must obtain Certificates of Authorization from ASME to enable them to bid for and manufacture ASME Code vessels. These manufacturers obligate themselves with respect to quality of fabrication and docu-mentation. The issuance by ASME of a Certificate of Authorization is based on periodic surveys of the shop regarding its ability to design and fabricate pressure vessels and its quality control system. ASME Code, Section VIII, Division 1, requires the manufacturer to have a contract or agreement with a qualified inspec-tion agency employing authorized inspectors.



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ASME Code, Section VIII, Division 1, provides two stamps for vessels built according to its requirements: “U” and “UM” (Figure 200-1).

Division 2 of Section VIII provides the “U2” stamp for vessels built according to requirements.

Vessels stamped with the “UM” symbol are vessels that are exempt from inspecby authorized inspectors, the manufacturer being responsible for design, fabriction, inspection, and testing of the vessel. However, these vessels are limited inand design pressure to 5 cubic feet volume and 250 psi, or 1.5 cubic feet and 600 psi. The Certificate of Authorization for using the “UM” stamp must be renewed annually. Some local jurisdictions do not recognize the “UM” stamp anrequire inspection by an authorized inspector.

Vessels built to the provisions of ASME Code, Section VIII, and accepted by anauthorized inspector have their name plates stamped with the “U” symbol. The Certificate of Authorization for using the “U” symbol is renewable every 3 years

Some classes of vessels (see Section 241) are excluded from the scope of SecVIII, but even these, if built in accordance with the provisions of the ASME CodSection VIII, may be stamped with the “U” symbol.

Other sections of the Code use different stamps according to the type of equipmunder their jurisdiction: e.g., “N” for nuclear vessels (Section III), “S” for power boilers, “E” for electric boilers (Section I).

In order to satisfy state and local authorities that all their requirements are met,allowing manufacturers to build vessels that will be accepted anywhere in the United States and Canada, the National Board of Boiler and Pressure Vessel Intors has been formed. Its members are authorized inspectors recognized by stalocal authorities and responsible for enforcing and administrating the ASME Boand Pressure Vessel Code.

Acceptance of a vessel by an inspector holding a National Board Commission sfies that the vessel complies with the ASME Code and meets State and local retions as well.

The National Board also issues Certificates of Authorization for the use of the “symbol stamp (repair) to be applied to ASME Code and National Board stampeboilers and pressure vessels where repairs have been made (see Section 800)board also carries out certification of safety valves; a “V” symbol stamp is placeon Code-stamped vessels. Most states and all Canadian Provinces require boiand pressure vessels to be inspected during fabrication by an inspector holding

Fig. 200-1 UG-116 Official Symbols “U” “UM”



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230 ASME Code, Section VIII, Division 1 Vs. Division 2The ASME Code, Section VIII, is presently divided into Division 1 and 2.

Division 1. Division 1 has relatively low maximum allowable design stresses that are consistent with simplified design methods generally referred to as “design brules.” It is the most frequently used Code in the world, and provides the most economic design and construction for the majority of vessels used in the petrolindustry.

Division 2. Division 2 was developed to take advantage of the technological advancements made in design methods, materials, and nondestructive examinHigher design stresses are permitted because: (1) the combined stresses undeoperating loads must be calculated more accurately; (2) the materials of constrtion must be tested more extensively; and (3) the nondestructive examination owelded joints is more thorough.

Division 2 vessels will consequently have thinner walls than Division 1 vessels the same design conditions. Division 2 can be more economical for high-pressuheavy-wall vessels greater than approximately 2 inches thick, when the reductimaterial and fabrication costs exceeds the increase in design and inspection coThe specifications in this manual have been revised to facilitate obtaining comptive Division 1 and Division 2 bids for vessels 2 inches thick and greater.

240 Design Criteria, ASME Code, Section VIII, Division 1

241 Scope, Division 1For the scope of the Code, pressure vessels are defined as “containers for the containment of pressure, either internal or external. This pressure may be obtafrom an external source, or by the application of heat from a direct or indirect source, or any combination thereof.”

Excluded from the scope of ASME Code, Section VIII, Division 1, are piping anpiping components, fired process tubular heaters, and pressure containers whiintegral parts or components of rotating or reciprocating mechanical devices, suas pumps, compressors, turbines, generators, engines, and hydraulic or pneumcylinders. Also excluded are vessels of any size with an operating pressure of lthan 15 psia and vessels with an inside diameter, width, height or cross-sectiononal under 6 inches. (However, it is often desirable to have these vessels desigand fabricated in accordance with Code rules to assure their basic integrity, andwhen this is done, a Code stamp can be applied to the nameplate as permanenfication of Code compliance.)

For pressures over 3000 psia, in order to meet the design and construction reqments, additions and deviations from Code rules may be necessary. If the vess



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complies with all the requirements of Division 1, it may be stamped with the appli-cable Code stamp.

The ASME Code jurisdiction terminates at one of the following piping connections:

• The first circumferential welded joint in welded-end connections• The face of the first flange in bolted flange connections• The first threaded joint

242 Structure, Division 1Section VIII, Division 1, of the ASME Code has three subsections (A, B, and C)plus mandatory and nonmandatory appendices:

• Subsection A consists of part UG covering general requirements applicableall pressure vessels.

• Subsection B covers specific requirements related to the various methods uin the fabrication of pressure vessels. It consists of parts UW, UF and UB, dealing with welded, forged and brazed fabrication.

• Subsection C covers specific requirements applicable to classes of materialused in pressure vessel construction: parts UCS (carbon and low-alloy steeUCF (nonferrous metals), UHA (high-alloy steels), UCI (cast iron), UCL (integral cladding, weld metal overlay cladding or applied linings), UCD (caductile iron), UHT (ferritic steels with tensile properties enhanced by heat trment), ULW (layered construction), and ULT (materials having higher allowable stresses at low temperature).

• Mandatory appendices address specific subjects not covered elsewhere, antheir requirements are mandatory.

• Nonmandatory appendices provide information and recommended practices

243 Allowable Stresses, Division 1ASME Code, Section VIII, Division 1, is based on the maximum-stress theory of failure, one of the most conservative methods available. Only the primary membrane and bending stresses need be considered for design according to Dsion 1 rules. Detailed analyses of discontinuity, thermal, and fatigue stresses arnecessary, and no design stress limits are imposed for them.

This simplified approach is compensated for by using: (1) a safety factor of 4, wmeans the allowable tensile stress, at temperature, is one-fourth of the specifieminimum tensile strength for the material; and (2) special Code-approved desigrules, such as for the cone-to-cylinder junction.

In addition, Code allowable stresses are generally used for the design of the imtant nonpressure parts, such as support skirts or supports for important vessel nals. Allowable stresses for less-important nonpressure structural parts may behigher than Code stresses.



Division 1, ASME Code, Section VIII, provides the necessary equations for calcula-tion of the required thicknesses of the basic vessel components due to internal and external pressure. Code requirements represent only minimum construction stan-dards, and for more complicated vessels or more severe services, higher-quality requirements are necessary. These requirements are usually defined in specifica-tions written for typical vessels. Company practices are discussed in Section 290 below and the Specifications section of this manual.

Please note that in 1999, the allowable stresses for Division 1 vessels were increased. For Division 1 vessels built before 1999, refer to the older code allow-able stresses. For Division 1 vessels built in 1999 and later, refer to the newer code allowables.

244 Material Specifications, Division 1The selection of construction materials for Code pressure vessels has to be made from Code-approved material specifications. Most Company vessels are constructed of ferrous and nonferrous alloys (described below).

The ASME Code, Section VIII, Division 1, gives tables with the maximum allow-able stress in tension at different temperatures for all the various materials of construction. These values are used for determining the thickness of various pres-sure vessel parts using Code equations and calculation procedures.

When allowable stresses are requested for a new material not listed in the Code, the evaluation is based upon an evaluation of test data for this material. Appendix P (mandatory) lists the information required for determining the properties of a new material. Appendix R (mandatory) describes the basis and criteria used to deter-mine allowable stresses and charts for external pressure for a new material.

The following is a general discussion of common vessel materials approved by the Code. For a more detailed description, and guidelines for material selection, see Section 500 of this manual. Also see the Corrosion Prevention and Metallurgy Manual.

Ferrous AlloysFerrous alloys are those having more than 50% iron. They include carbon and low-alloy steels, stainless steels, cast iron, wrought iron, and quenched and tempered steels. ASME designates ferrous alloys with the prefix SA. Iron alloys with carbon content of less than 2% are called steels, those with more than 2% carbon are called cast iron. Most steels used in pressure vessel applications have less than 0.4% carbon. A higher carbon content will make the steel very brittle and difficult to weld. Cast iron is very brittle, and because it cannot be rolled, drawn or welded, its use in pressure vessels is very limited.

The ASME Code, Section VIII, Division 1, lists the following categories of steels:

• Carbon steels• Low-alloy steels• High-alloy steels



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Carbon Steels. Moderate in yield and tensile strength, carbon steels have the proper combination of strength, ductility, toughness, and weldability to perform satisfacto-rily in structural applications, including pressure vessels. The carbon content is rarely over 0.25% (above this level, toughness and weldability are reduced), or below 0.15% for reasons of strength. Besides carbon, the most significant alloying element is manganese, used to increase yield and tensile strength without reducing ductility. The use of carbon steels is limited to tempera-tures under 1000°F. The most widely used carbon steels are SA 36, SA 285 Graand SA 515 and 516 Grade 70.

Low-alloy Steels. Main alloying elements in low-alloy steels are chromium (up to10%), molybdenum, and nickel. Low-alloy steels are not as easily welded as casteel, and although low-alloy steels are somewhat more expensive, their superstrength and toughness makes them attractive in cases where carbon steel worequire much heavier plates for the same load-carrying capacity, for high-tempeture applications, or in hydrogen service. The most common low-alloy steels fopressure vessel applications are SA 387 Grades 11 and 22.

High-alloy Steels. Usually called stainless steels, high-alloy steels are known fortheir high levels of corrosion resistance. Based on their metallurgical microstructure, stainless steels used for pressure vessels and piping construction can be dinto three groups:

1. Austenitic stainless steels are chromium-nickel (300 series), or chromium-nickel-manganese (200 series) steels. They are nonmagnetic, highly corrosresistant, and hardenable only by cold working; their strength and hardnessbe increased at the expense of ductility. These are the only steels assignedallowable stresses in the Code for temperatures above 1200°F, up to 1500The typical and most commonly used are Grades 304 and 316. For weldedconstruction, low carbon Grades 304L and 316L, or stabilized Grades 321 347 are usually specified. Higher chromium content steels, Grades 309 and310, are resistant to oxidation and sulfur attack up to 2000°F.

2. Ferritic stainless steels are straight chromium stainless steels with a minimof 10% chromium. They are nonhardenable by heat treatment, and seldomin vessel construction except for corrosion-resistant lining or cladding or internal trays for less-corrosive environments. Common grades are Grade and 430.

3. Martensitic stainless steels contain 11% to 16% chromium, with sufficient carbon to be hardenable (less than 1%). They are hardenable by heat treatthe least corrosion resistant of the stainless steels, are difficult to form, andrequire heat treatment after welding. They are rarely used as construction mrials for pressure vessel parts, with the exception of internal linings and traybecause of poor weldability.

Nonferrous AlloysNonferrous alloys are designated in the ASME Code by the prefix SB, and are used in corrosive environments or at high temperatures where ferrous alloys arunsuitable.



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Section VIII, Division 1, has five categories of nonferrous materials:

• Aluminum alloys• Copper and copper alloys• Nickel and high-nickel alloys• Titanium and titanium alloys• Zirconium

Aluminum Alloys. Aluminum alloys have excellent corrosion resistance, are lighweight, easy to form, and have a very good strength-to-weight ratio. Major alloyelements are silicon, magnesium, and copper. They are used for storage tankscryogenic vessels. Copper containing alloys (7xxx and 2xxx series alloys) may have good corrosion resistance, depending on the service.

Copper and Copper Alloys. Copper and copper alloys have good corrosion resistance and machinability. They are not susceptible to heat treatment, and their strength can be altered only by cold working.

Nickel and High-nickel Alloys. Nickel and high-nickel alloys have excellent corrosion resistance and are used in high-temperature applications in corrosive enviments. The main alloying element is chromium; others are molybdenum, tungsaluminum, columbium, and titanium. Products are usually referred to by their commercial names rather than by their ASME designation numbers: Monel, Inconel, Incoloy, or Hastelloy.

Titanium and Titanium Alloys. Titanium and titanium alloys are used in vesselssubject to severe environments. They have high strength-to-weight ratios, highmelting points, excellent corrosion resistance, and can be hot-worked by standsteel mill equipment. Welding can be done only with helium or argon shielding.

Zirconium. Similar in properties and use to titanium.

245 Inspection Openings, Division 1Regular internal inspections are very important to the safety and reliability of a vessel. Code Paragraph UG-46 requires inspection openings in all vessels subinternal corrosion, or having internal surfaces subject to erosion or mechanical sion, so that these surfaces may be examined for defects.

Removable heads or cover plates may be used in place of inspection openingsprovided they are large enough to permit entry or a view of the interior.

246 Pressure Relief Devices, Division 1Paragraph UG-125 states that all pressure vessels must be provided with meanprotection against overpressure. When the source of pressure is external to thevessel, the protective device can be installed elsewhere in the system if it can control the pressure in such a manner that it will not exceed the maximum allowable working pressure in the vessel, at the operating temperature.



Pressure relief devices do not have to be provided by the vessel manufacturer, but they must be installed before the vessel is placed in service or tested for service. However, the number, size and location of the pressure relief devices have to be listed on the manufacturer’s data report.

See the Instrumentation and Control Manual for information on design and applica-tion of pressure relief valves.

247 Cryogenic and Low-temperature Vessels, Division 1Carbon steels and low-alloy steels exhibit a significant loss of toughness and ductility at cold temperatures. (See Section 500 for a discussion of toughness.) At low temperatures, the metal becomes brittle, and fracture can occur at stresses considerably below the yield point, and without prior noticeable deformation (brittle fracture).

Materials used for low-temperature applications must have a proven ability to safely resist brittle fracture. Code Division 1, Paragraph UCS-66, states whether an impact test is required to verify the toughness. The requirement is based on a combination of minimum design metal temperature and thickness. When the calculated stress in tension for a design condition is less than the maximum allowable design stress, the design temperature not requiring impact testing can be further lowered, based on the curve in Figure UCS-66.1. If impact testing is required, Code Paragraph UG-84 describes how it must be done. This method is discussed in more detail in Section 500.

Paragraph UHA-51 sets impact test requirements for stainless steels, and Paragraph UNF-65 covers nonferrous metals.

Whenever impact tests are necessary, every part of the vessel including welds must comply with Code requirements.

248 Testing, Inspection, and Stamping, Division 1The ASME Code has three quality levels based on the type and degree of examina-tion of the pressure vessel:

1. Visual examination of butt welds

2. Spot radiographic examination of butt welds

3. Full radiographic examination of butt welds

By applying joint efficiencies and stress multipliers (see Section 400), the Code compensates for a lower level of quality with an increased safety factor. For level (1), the theoretical factor of safety is 5; for level (2), between 4 and 5; and for level (3), it becomes 4.

The Code requires radiographing pressure vessels for certain design and service conditions, the type of radiography varying with materials, thicknesses, joint effi-ciency used for design calculations, and the design of weld joints. The Code



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requires employing a radiographic technique that will reveal the size of defects having a thickness equal to, or greater than 2% of the thickness of the base metal. Weld quality depends on several factors: design of the joint, welding procedures, fit-up of the parts, operator qualifications, supervision, and examination of the weld.

All methods of testing and inspecting welds can be grouped into two basic catego-ries: destructive and nondestructive.

Destructive. Destructive tests are methods of determining the properties of a weld where the weld itself is usually destroyed. Methods such as the bend test, impact test, tensile test, nick-break test, and etch test are used to determine a number of weld properties, including ductility, weld penetration, tensile strength, and fusion. Destructive tests are not considered a substitute for spot-radiographic examination, and permit no increase in joint efficiency.

Nondestructive. Nondestructive tests are methods provided to determine the suit-ability of a weld for the service conditions to which it will be subjected. They do not affect or alter the structure or appearance of the weld, and consequently are not as thorough as destructive tests in determining the properties of a weld.

Nondestructive Examination. Nondestructive examination (NDE) requires proce-dures that, like welding procedures, must satisfy the requirements of the Code and be acceptable to the authorized inspector. Various sections of the ASME Code refer to Section V, “Nondestructive examinations.”

Manufacturers' quality control manuals must include:

• A description of the manufacturer's system for assuming that all NDE persoare qualified in accordance with the applicable Code

• Written procedures to assure that NDE requirements are maintained in accdance with the Code

• If NDE is subcontracted, a statement of who is responsible for checking thesubcontractor's site, equipment and qualification of procedures to assure thare in conformance with the applicable Code

All completed pressure vessels must satisfactorily pass a hydrostatic test prescin Code Paragraph UG-99. The test must be at least 1.5 times the maximum alable working pressure to be marked on the vessel (multiplied by the lowest ratiothe stress value for the test temperature to the stress value for the design tempture). The water for hydrotest should be approximately room temperature, but nless than 60°F. If the temperature is lower, moisture in the air may condense onsurfaces, making proper testing difficult. Additional Company recommendationshydrotest are discussed in Section 431.

After the test, all joints and connections shall be inspected at a pressure not lestwo-thirds of the test pressure. The manufacturer's quality manual must containdescription of the system used for assuming that the gage measuring and testindevices are properly calibrated and controlled. All the gages shall be calibratedevery 6 months, or any time there is a reason to believe that they are in error. Tgages must always be used to provide a double check on the pressure. If only



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gage is used and it is incorrect, the vessel can be damaged by overpressure, or not properly tested, depending on the error. Paragraph UG-102 of the Code establishes requirements for the use of test gages.

Note that Paragraph UG-100 allows for pneumatic testing where vessels cannot be safely filled with water. Note also that pneumatic tests should be avoided when-ever possible; the energy stored in a pressurized vessel is much greater with a compressible gas than with a liquid.

The ASME Code requires inspection by an “Authorized Inspector,” who is authorized to perform Code inspections by the jurisdiction where the vessel will be usIt is the obligation of the manufacturer to see that the inspector has the opportuto perform his duties as required by the Code and the jurisdiction.

The inspector's duty starts with the review of the design documents submitted bmanufacturer. His first check of the fabrication is to verify that all materials to beused comply with the mill test reports and Code specifications. Dimensions andthicknesses must meet Code tolerances, and a thorough examination is made defects, such as laminations, pit marks, and surface scars.

For the whole fabrication process, the inspector will indicate “hold points” and discuss with the manager of quality control arrangements for additional inspectincluding the review of radiographs.

After witnessing the final hydrostatic or pneumatic test and carrying out the necsary examinations, the inspector will check the vessel data report sheets to masure they are properly filled out and signed by the manufacturer and that the mrial and quality of work in the vessel are accurately recorded. He will then allowthe Code Symbol to be applied in accordance with the Code and local or State requirements.

When construction of a Code vessel is completed in the field, some organizatiomust take responsibility for the entire vessel, including the issuing of data sheethe parts fabricated in the shop and in the field, and the application of the Codestamp. It can be the vessel manufacturer (most of the time), or a separate assewhich should also have the required ASME Certification of Authorization and CSymbol stamp.

The stamp can be applied directly on the vessel, but is usually applied to a namplate. The nameplate should be located in a conspicuous place, preferably neamanhole or handhole opening. Paragraph UG-116 states what information shoumarked on each Code-built pressure vessel.

250 Design Criteria, ASME Code, Section VIII, Division 2

251 Scope, Division 2Pressure vessels subject to direct firing but not within the scope of Sections I, IIV of the Code can be built in accordance with the general rules of Division 2. InDivision 2, the requirements of Section VIII have been upgraded. A very detaile



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stress analysis of the vessel, generally referred to as “design by analysis,” is required. There are many restrictions in the choice of materials, and some common design details are prohibited. More thorough materials certification annondestructive examination are required because design stresses are higher ththose allowed in Division 1.

All these restrictions allow the use of a theoretical design factor of safety of 3, compared to 4 for Division 1 (see Section 243). There is no pressure limitation the scope, but as in the case of Division 1, at very high pressures, additions andeviations from Code rules may be necessary in order to meet design and constion requirements. Classes of vessels outside the scope of Division 2 and limitsjurisdiction over piping are the same as for Division 1 (see Section 241).

252 Structure, Division 2Section VIII, Division 2, of ASME Code has a different organization than Divisio1. It is divided in eight parts, plus mandatory and nonmandatory appendices:

• Part AG—“General Requirements” gives the scope of the Division, establisits jurisdiction, and states the responsibilities of the user, manufacturer, andduties of the inspector.

• Part AM—“Material Requirements” lists the materials which may be utilizedspecial requirements, and information concerning materials properties andmaximum design stress intensity values (allowable stresses).

• Part AD—“Design Requirements”

• Part AF—“Fabrication Requirements”

• Part AI—“Inspection and Radiography”

• Part AT—“Testing”

• Part AS—“Marking, Stamping, Reports and Records”

253 Allowable Stresses, Division 2Division 2 employs the maximum shear stress theory of failure, which is knownbe more accurate for predicting the failure of a pressure vessel by ductile yieldithan the maximum stress theory utilized by Division 1. It is assumed yielding ofvessel at any location is determined by the maximum shear stress resulting fromcombination of the three principal stresses developed by all of the loads acting the vessel at the location.

All categories of stress (i.e., primary, secondary, and peak) must be added togeto determine the stress intensity when designing a component, but the maximustress intensity permitted for design depends upon the particular categories of s(The different categories of stress are discussed in Section 100.) Appendix 4 ofDivision 2 gives the details for determining the maximum stress intensity permifor design with various combinations of stress in the different categories.



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In general the criteria for determining maximum stress intensities for design are the following:

1. The primary membrane stress cannot exceed the design stress for the material of construction at the design temperature.

2. Local primary membrane stresses are permitted to reach 1.5 times the design stress.

3. Primary membrane plus primary bending stresses are permitted to reach 1.5 times the design stress.

4. Primary membrane plus secondary and peak stresses are permitted to reach 3 times the design stress.

5. An additional 20% increase in stress is permitted for 1, 2, and 3 above for adding intermittent loads such as wind and earthquake loads.

Part AD of Division 2 provides simplified “rules” for the design of most of the commonly used components. These are consistent with the “design by analysisconcept incorporating the maximum shear stress theory of failure. Whenever thrules can be applied, the actual design procedure is not much more complicatethat required by Division 1.

Appendix 4 of Division 2 details the stress analysis procedures that must be usecomponents that do not conform to the simplified rules in Part AD. It is the respsibility of the designer to determine when the simplified rules of Part AD can beused and when a stress analysis conforming to Appendix 4 must be performed

Appendix 5 (Mandatory), “Design based on fatigue analysis,” provides the methof design for cyclic loading. Figure 5-100.1 presents fatigue curves for the typematerials permitted by Division 2, which will give an allowable number of cyclesfor certain values of stress intensities. Two different loading cases are considerdepending on whether the direction of the principal stress changes. If theoreticastress analysis for a part of a pressure vessel proves to be inadequate, Append(Mandatory), “Experimental Stress Analysis,” provides the procedure for tests trun in order to determine governing stresses, collapse load, or the adequacy ofcomponent for cyclic loading.

254 Materials and Tests, Division 2Division 2 is more restrictive than Division 1 in the choice of materials that can used. Special inspection and testing requirements add to the reliability of the mrials and permit the use of higher allowable stress values. For example, plate aforgings over 4 inches thick require ultrasonic examination (Paragraph AM-203cut edges of base materials over 1½ inches thick also must be inspected for deby liquid penetrant or magnetic particle methods. Because of the higher stress allowed, and for protection against brittle fracture of some steels like SA-285, thnesses over 1 inch will be limited to 65°F or above, unless they are impact test(Paragraph AM-211). In Division 1, those commonly used plate steels allow temperatures as low as -20°F without impact test.



Under Article F-2, Part AF, only some welding processes are allowed, and special precautions have to be taken before and during welding.

Division 2 provides for only one quality vessel: with all longitudinal and circumfer-ential seams butt-welded and 100% radiographic. It also requires more nondestruc-tive examinations than Division 1. Radiographers and ultrasonic examiners must be qualified (Paragraph AI-501 and Appendix 9-3) and their qualifications docu-mented as required.

Unlike Division 1, for hydrostatic testing, Division 2 establishes an upper limit on the test pressure: it should be no less than 1.25 times the design pressure at every point in the vessel, but if at any point this pressure (including static head) is exceeded by more than 6%, the upper limit shall be established so that the calcu-lated stress intensities, using all the loadings that may exist during the test, do not exceed certain limits given in Paragraph AD-151.1.

If a pneumatic test is used, the minimum test pressure is 1.15 times the design pressure.

255 Responsibilities, Division 2A feature of Division 2 is that the user of the vessel, or a representative agent, must provide the manufacturer with design specifications giving detailed information about the intended operating conditions (Paragraph AG-301). This information should constitute the basis for selecting materials and designing, fabricating and inspecting the vessel as required.

The User’s Design Specification should include the method of supporting the vessel. It should also list the amount of corrosion allowance to be provided and informa-tion on whether or not a fatigue analysis of the vessel shall be made for cyclic service, and if it is required, to provide enough information so that an analysis can be carried out.

The User’s Design Specification must be certified by a registered professional engi-neer experienced in pressure vessel design. The vessel manufacturer is required to prepare a Manufacturer’s Design Report establishing the conformance with the rules of Division 2 for the design conditions specified in the User’s Design Specification. This conformance should also be certified by a registered professional engineer.

Division 2 does not hold the inspector responsible for approving design calcula-tions, but he has to verify the existence of the User’s Design Specification and the Manufacturer’s Design Reports, and that they have been certified by a registered professional engineer (Paragraph AG-303). It is also the authorized inspector’s duty to review the design with respect to materials used, to see that the manufacturer has qualified welding procedures and welders, and to review the vessel geometry, weld details, nozzle attachment details, and nondestructive testing requirements.



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260 Welding, ASME Code, Section IXThe ASME Code does not dictate welding methods to the manufacturer, but it does require proof that the welding is sound (Section IX, Paragraph QW-201) and that operators are qualified in accordance with the ASME Code, Section IX, “Weldinand Brazing Qualifications” (Paragraph QW-301). For additional information onwelding, see Sections 400 and 600, and the Specification Section in this manuaand the Welding Manual.

Welding Procedure Specifications (WPS) and Procedure Qualification Records(PQR) are required by Section IX, and are the most important factors in the achment of sound welding. If they have been properly established, welders need odemonstrate their ability to make a weld that will pass root and face or side bentests in the position to be welded, in order to gain qualification.

ASME Code, Section IX, requires fabricators to have written Welding ProcedureSpecifications (Paragraph QW-201.1) and properly completed records of qualiftions of the welders working on the vessel (Paragraph QW-301.2).

The Code requires postweld heat treatment (PWHT) of some pressure vesselsdependent upon the materials of construction and shell thickness. Paragraph Udescribes the procedure to be followed for postweld heat treatment, when requIt must be done before hydrostatic testing and after any welded repairs.

In his quality control manual, the manufacturer must describe the welding preheand interpass temperature control methods, and for postweld heat treatment dehow the furnace is loaded, how and where the thermocouples are placed, the ttemperature recording system, methods used for heating and cooling, metal tematures and how they are controlled, and the methods of supporting the vessel dpostweld heat treatment. These precautions are important to help ensure that tentire vessel gets an adequate PWHT, and to prevent deformation of the vessetemperatures beyond its design.

270 ASME Code, Section I, Power BoilersPower boilers are not in the scope of this manual. The provisions of Section I abriefly discussed below for comparison.

271 Scope and Limitations, BoilersASME Code, Section I, covers rules for construction of power boilers, electric boilers, miniature boilers, and high-temperature water boilers to be used in stationary service, and includes power boilers used in locomotive, traction, andportable service. The scope and jurisdiction of Section I apply to the boiler and external piping. Superheaters, economizers, and other pressure parts connectedirectly to the boiler without intervening valves shall be considered as part of thboiler and are included within the scope of Section I.

Fired steam boilers are pressure vessels in which steam is generated by the aption of heat resulting from the combustion of fuel. They shall be constructed un



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the provisions of Section I. Also included are unfired pressure vessels in which steam is generated, with the following exceptions:

• Evaporators

• Heat exchangers

• Vessels in which vapor is generated incidental to the operation of a processsystem, containing a number of pressure vessels, such as used in chemicapetroleum manufacture

Boilers covered by Section I are those in which steam or other vapor is generata pressure of more than 15 psig. High-temperature water boilers within the scoSection I are intended for operation at pressures exceeding 160 psig and/or temtures exceeding 250°F. For services below those specified, the rules of Section“Heating Boilers,” apply; however, if all applicable requirements of Section I aremet, these boilers can still be stamped in accordance with Section I.

272 Allowable Stresses, BoilersGenerally, materials and allowable design stresses for Section I are the same aSection VIII, Division 1, pressure vessels. However, not all pressure vessel marials are suitable for the construction of boilers. For example, nonferrous materare limited to copper and nickel alloys.

Section I is less definitive than Section VIII, Division 1, concerning the loadingsnecessary to consider, and what shall be included in a design specification or purchase order. PG-22 of Section I states that loadings that cause stresses to ghigher than 10% over those caused by internal design pressure and static headshould be considered. Section I uses a safety factor of 4 for determining the allable stresses.

273 Fabrication, Inspection and Tests, BoilersSection I requires all welds in pressure parts to be full penetration butt-welds, afully radiographed (except for pipe material under 10-inch nominal pipe size, or1-1/8-inch wall thickness having only circumferential welded butt joints). Weld procedures and welders must be qualified according to Section IX of the Code.Carbon steel parts over ¾ inch thick require postweld heat treatment. Inspectioan authorized inspector is required.

Hydrostatic test is required at a pressure not less than 1.5 times the maximum able working pressure.

Section I provides for six Code Symbol stamps, defined as follows:

• S—power boilers• M—miniature boilers• E—electric boilers• A—boiler assemblies



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280 Other Codes And RegulationsIn addition to the ASME Boiler and Pressure Vessel Code, there are other codestandards commonly used for the design of process equipment in the United S

Pressure piping is regulated by standard ANSI B31. It is divided into many sectaccording to the applications, and some of the sections are related to sections ASME Code:

• B31.1 —Power Piping (related to Section I)• B31.2 —Fuel Gas Piping (related to Section VIII)• B31.3—Chemical Plant and Petroleum Refinery Piping (related to Section VI• B31.4—Liquid Petroleum Transporting Piping (related to Section VIII)• B31.5—Refrigeration Piping (related to Section VIII)• B31.8—Gas Transmission and Distribution Piping Systems (related to Section V

In addition to all these codes and standards, users and manufacturers also havcomply with State and local regulations where the vessel will be in operation. Nthat some States and cities do not require ASME construction for pressure vesalthough this is a Company requirement.

The Uniform Boiler and Pressure Vessel Laws Society is a nonpolitical, noncommercial, and nonprofit technical society, whose objective is to secure uniformitythe laws, rules, and regulations that affect the boiler and pressure vessel indusinspection agencies, and users. The society cooperates with all the organizationofficials charged with the enforcement of boiler and pressure vessel inspection and regulations. It publishes a “Synopsis of Boiler and Pressure Vessel Laws, Rand Regulations,” which gives a summary of applicable laws of States, cities, cties and provinces in the United States and Canada, and has proved valuable toand manufacturers of boilers and pressure vessels. Members of the Society areinformed by bulletins about the actions of governmental bodies adopting or revcodes and regulations for the construction, installation, and inspection of boilerspressure vessels.

Also note that API has a “Digest of State Boiler and Pressure Vessel Rules andRegulations.” This document is a catalog of applicable jurisdictional requiremenincluding various laws and addresses of officials.

Various other countries have adopted their own pressure vessel codes with prosions that differ from the ASME Code, and difficulties often occur when a vessedesigned in one country and built and/or installed in a different one.

281 Other National CodesSeveral other national codes have been issued throughout the world for the deand construction of pressure vessels. They differ from ASME Code, Section VII



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Division 1, mainly with regard to the maximum allowable design stresses that are permitted for the various materials of construction. Many other national codes permit significantly higher design stresses, and justify these by increased require-ments for nondestructive examination and by not permitting the use of some design details that the ASME Code accepts along with its lower design stresses. On the other hand, the ASME Code requires a higher hydrotest pressure than most of the other codes. The hydrotest is considered the ultimate proof of the integrity of design and fabrication. The design criteria (i.e., stress theories and equations) used by the ASME Code and all of the other national codes are very similar.

The other national codes are rarely used outside of the country of their origin. The ASME Code is the most widely used code in the world, and in this sense is the “universal” code. ASME does not claim that its Code is technically superior to thother national codes, but no other code has a better safety record for regulatingdesign and construction of as many vessels of diverse design and operation.

A major benefit derived from using the ASME Code for international projects, inlieu of the other national codes, is that virtually every manufacturer providing vessels to the world market is familiar with the ASME Code and has used it for design and construction. No manufacturer can acquire the detailed understandevery national code that is required to become proficient in their use. It is usualvery difficult for a manufacturer to design and fabricate vessels to specificationsbased upon other national codes, unless the manufacturer resides in the code's“home” country. Therefore, basing specifications upon other national codes canactually hamper the procurement of vessels in the international market. Some competent manufacturers may choose not to bid or may increase their bid pricebecause they lack familiarity with the other national codes. Moreover, confusionabout complex technical details that are not thoroughly understood could resultmistakes in design and fabrication. Therefore, use of the ASME Code for interntional projects facilitates the procurement of technically comparable vessels fromanufacturers throughout the world, on the most economically competitive bas

The higher maximum allowable design stresses permitted by other national codmay lead to lower vessel costs, but this is usually an advantage only if the vessare both procured and installed in the same country where the code originated.Generally the disadvantages of using the other national codes outside their homcountry outweigh possible advantages. A preferred alternate is to use Division ASME Code, Section VIII. Although Division 2 also allows for higher design stresses, although not as high as many other national codes allow, Division 2 hadvantage of being universally accepted.

290 Additional Company Recommendations

291 Model SpecificationsThe rules provided by the ASME Code are minimum requirements for the constrtion of pressure vessels. Because of the extremely wide scope of Section VIII, efor the simplest of vessels for noncritical service, higher requirements are recom



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mended in the Company model specifications PVM-MS-4749 and PVM-MS-4750. These specifications define the higher quality considered justified for typical process plants and other critical services. These specifications restrict the use of some design details permitted by the Code (especially for nozzles and weld joints), specify more materials testing to assure adequate toughness to resist brittle fracture, and specify more thorough inspection to assure the integrity of fabrication.

The significant provisions in these specifications, above the minimum Code require-ments, include the following:

1. Nozzle welds are recommended to be full penetration welds that receive either ultrasonic or magnetic particle inspection.

2. Flange welds are recommended to be full penetration welds.

3. Integral reinforced nozzles are recommended for shell components over 2 inches thick, design temperatures over 650°F, and for low temperature servwhen CV-impact testing is required.

4. Longitudinal and girth welds should be double-V butt welds or an acceptabequivalent.

5. Hydrotest pressure should stress all longitudinal welds to at least 1.5 timesdesign pressure, and the design pressure cannot be limited by flanges, nozor reinforcing pads.

6. Postweld heat treatment is recommended for some process environments exceed ASME Code requirements.
