PIPELINE TRANSPORTATION SYSTEMS FOR ASME B31.4-2006LIQUID HYDROCARBONS AND OTHER LIQUIDS

Table 434.6(a) Minimum Cover for Buried Pipelines

For Normal For Rock Excavation RequiringExcavation, Blasting or Removal by

Location in. (m) Equivalent Means, in. (m)

Cultivated, agricultural areas where plowing 48 (1.2) N/Aor subsurface ripping is common [Note (1)]

Industrial, commercial, and residential areas 48 (1.2) 30 (0.75)River and stream crossings 48 (1.2) 18 (0.45)Drainage ditches at roadways and railroads 48 (1.2) 30 (0.75)All other areas 36 (0.9) 18 (0.45)

NOTE:(1) Pipelines may require deeper burial to avoid damage from deep plowing; the designer is cautioned

to account for this possibility.

shall be treated as indicated in Fig. 434.8.6(a)-(2) or usea transition nipple not less than one-half pipe diameterin length with acceptable joint designs as illustrated inFig. 434.8.6(a)-(2).

434.8 Welding

434.8.1 General(a) Scope. Welding herein applies to the arc and gas

welding of pipe in both wrought and cast steel materialsas applied in pipelines and connections to apparatus orequipment. This includes butt joints in the installationof pipe, valves, flanges, fittings, and other equipment,and fillet welded joints in pipe branches, slip-on flanges,etc. It does not apply to the welding of longitudinal orspiral joints in the manufacture of pipe, fittings, andvalves, or to pressure vessels or assemblies manufac-tured in accordance with the ASME Boiler and PressureVessel Code, Section VIII, Division 1 or 2.

(b) Welding Terms. Definitions pertaining to weldingas used in this Code conform to the standard definitionsestablished by the American Welding Society and con-tained in ANSI/AWS A3.0, Section IX of the ASMEBoiler and Pressure Vessel Code, and API 1104.

(c) Safe Practices in Cutting and Welding. Prior to cut-ting and welding in areas in which the possible leakageor presence of vapor or flammable liquid constitutes ahazard of fire or explosion, a thorough check shall bemade to determine the presence of a combustible gasmixture or flammable liquid. Cutting and welding shallbegin only when safe conditions are indicated.

434.8.2 Welding Processes and Filler Metal(a) Welding shall be performed by a manual, semiau-

tomatic, or automatic process or combination of pro-cesses that have been demonstrated to produce soundwelds.

(b) Unless otherwise specified by the operating com-pany, welding electrodes and consumables shall complywith the following:

(1) Filler metal and consumables shall be selectedso that the strength of the completed weldment will

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equal or exceed the specified minimum tensile strengthof the materials being joined.

(2) If base metals of different tensile strengths areto be joined, the nominal tensile strength of the weldmetal shall equal or exceed the tensile strength of theweaker of the two.

(3) When filler metals of different strenghts areused in a single weld, the proportions shall be such thatthe completed weldment equals the specified minimumtensile strength of the base metal.

(4) For alloy steels, the nominal chemical analysisof the weld metal shall be the same as the nominalchemical analysis of the base metal. If base metals ofdifferent chemical analysis are being joined, the weldmetal shall be the same as eitehr base metal, or of inter-mediate composition, except as specified below.

(5) When austenitic steels are joined to ferriticsteels, the weld metal shall have an austenitic structure.

434.8.3 Welder and Welding Procedure Qualifica-tions

(a) Welder and welding procedure qualifications forcross country pipelines shall be performed in accordancewith API 1104. Welder and welding procedure qualifica-tions for alloy steel and for shop fabricated pipingassemblies, and welding at stations and terminals shallbe performed in accordance with API 1104 or SectionIX of the ASME Boiler and Pressure Vessel Code.

(b) Prior to any welding covered by this Code, a weld-ing procedure specification shal be established and qual-ified by testing to demonstrate that welds havingsuitable mechanical properties and soundness can beproduced. Welding procedure specifications shall bequalified as required by API 1104, or Section IX of theASME Boiler and Pressure Vessel Code, whichever isappropriate for the locations, materials, and type ofwelding to be performed except as modified by the fol-lowing:

(1) Standard Welding Procedures. Standard WeldingProcedure Specifications (SWPSs) published by theAmerican Welding Society and listed in Appendix E of

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ASME B31.4-2006 PIPELINE TRANSPORTATION SYSTEMS FORLIQUID HYDROCARBONS AND OTHER LIQUIDS

ASME Section IX are permitted for code constructionwithin the limitations established by Article V of ASMESection IX. The employer shall either demonstrate hisability to follow SWPSs as required by ASME SectionIX or he shall qualify one welder or welding operatorfollowing each SWPS.

(2) Procedure Qualification by Others. In order toavoid duplication of effort and subject to the approvalof the owner, WPSs qualified by a technically competentgroup or agency may be used provided the followingare met:

(1) the WPSs meet the requirements of ASMESection IX or API 1104 and any additional qualificationrequirements of this Code

(2) the employer has qualified at least one welderor welding operator following each WPS

(3) the employer’s business name shall be shownon each WPS and on each qualification record. In addi-tion, qualification records shall be signed and dated bythe employer, thereby accepting responsibility for thequalifications performed by others.

The welding procedure specification shall be adheredto during welding performed under this Code.

(c) The welding procedure specifications shall at aminimum include the information required by API 1104or Section IX of the ASME Boiler and Pressure VesselCode. When materials, welding consumables, mechani-cal restraint, service conditions and/or weather condi-tions make more details necessary to produce a soundweld, such as preheat, interpass temperature, and post-weld heat treatment, such details shall be provided.When joining materials with notch-toughness require-ments, particularly for low temperature service, consid-eration shall be given to weld metal and heat-affectedzone toughness requirements in the welding procedurespecification. When applicable, the test method, temper-ature, specimen, and acceptance criteria shall be speci-fied in the welding procedure specification.

(d) API 1104 and Section IX of the ASME Boiler andPressure Vessel Code contain sections entitled “EssentialVariables” applicable to welding procedure specifica-tions, procedure qualification records, and welder quali-fications. The classification of base materials and weldfiller materials into groups does not imply that othermaterials within a particular group may be indiscrimi-nately substituted for the base material or weld fillermaterial used for the qualificaition test. Welding proce-dure qualification tests should be conducted with thehighest strength base metal to be welded in the essentialvariable groups identified in the procedure specification.

(e) Prior to any welding covered by this Code, eachwelder or welding operator shall be qualified as requiredby API 1104, or Section IX of the ASME Boiler andPressure Vessel Code, whichever is appropriate for thelocations, materials, and type of welding to be per-formed.

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In order to avoid duplication of effort and subject tothe approval of the owner, an employer may acceptthe performance qualification of a welder or weldingoperator made by a previous employer. This acceptanceis limited to performance qualifications that were madeon pipe or tube test coupons. The new employer shallhave the WPS that was followed during qualification oran equivalent WPS that is within the limits of the essen-tial variables. An employer accepting such qualificationtests shall obtain a copy of the performance qualificationtest record from the previous employer. The record shallshow the name of the employer by whom the weldersor welding operator was qualified and the date of thatqualification. A record showing use of the process orprocesses from the date of the welder’s qualificationshall be available. The new employer’s business nameshall be shown on the qualification record, and it shallbe signed and dated by the employer thereby acceptingresponsibility for the qualifications performed by others.

Welder requalification tests are required if there issome specific reason to question a welder’s ability or ifthe welder is not engaged in a given process of weldingfor a period of six months or more.

(f) The operating company shall be responsible forqualifications of procedures and welders. The prepara-tion of welding procedure specifications and/or per-formance of welding qualification tests may bedelegated to others; however, each company that per-forms welding activities is responsible for the weldingactivities performed by its employees and contractors.

(g) Qualification Records. The welding procedure fol-lowed during the qualifying tests shall be recorded indetail. Records of the tests that establish the qualificationof a welding procedure specification shall be retained aslong as that procedure is in use. A record of the weldersqualified, showing the date and results of the tests, shallbe retained during the construction involved and for sixmonths thereafter. These records shall be available to theowner or the owner’s agent and the inspector at the loca-tion where the welding is being done.

434.8.4 Welding Standards. All the welding doneunder this Code shall be performed under a specificationwhich embodies the minimum requirements of thisCode and shall encompass the requirements of API 1104except as provided in paras. 434.8.3(a) and (b).

434.8.5 Required Inspection and Acceptance Criteria(a) Required Inspection

(1) The quality of welding shall be checked byvisual inspection and supplemental nondestructivemethods or by removing completed welds as selectedand designated by the inspector for destructive testing.

(2) All welds shall be visually inspected.(3) When the pipeline is to be operated at a hoop

stress of more than 20% of the specified minimum yieldstrength of the pipe, the welds shall be inspected. Aminimum of 10% of the girth welds and 10% of the other

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PIPELINE TRANSPORTATION SYSTEMS FOR ASME B31.4-2006LIQUID HYDROCARBONS AND OTHER LIQUIDS

welds completed each day shall be randomly selected bythe operating company and nondestructively inspected.The inspection of girth welds shall be by radiographicor other accepted volumetric methods. Nonvolumetricmethods, such as dye penetrant or magnetic particle,may be used for other welds. Each weld inspected shallbe inspected completely with the selected method. Inthe following locations or conditions, all welds in thepipe shall be completely inspected; however, if some ofthe welds are inaccessible, a minimum of 90% of thewelds are to be inspected:

(a) within populated areas such as residentialsubdivisions, shopping centers, and designated com-mercial and industrial areas

(b) river, lake, and stream crossings within thearea subject to frequent inundation; and river, lake, andstream crossings on bridges

(c) railroad or public highway rights-of-way,including tunnels, bridges, and overhead railroad androad crossings

(d) offshore and inland coastal waters(e) old girth welds in used pipe(f) tie-in girth welds not hydrostatically tested

in accordance with para. 437.4.1(b) Inspection Methods and Acceptance Standards

(1) Nondestructive inspection shall consist ofvisual inspection and radiographic examination or otheracceptable nondestructive methods, and shall be inaccordance with API 1104. The methods used shall becapable of producing indications of potential defectsthat can be accurately interpreted and evaluated. Weldsshall meet the acceptance standards for discontinuitiescontained in API 1104, or the alternate acceptance stan-dards for girth welds in Appendix A of API 1104.

(2) Completed welds which have been removed fordestructive examination shall meet the requirements ofAPI 1104 for Welder Qualification by Destructive Test-ing. Trepanning methods of testing shall not be used.

434.8.6 Types of Welds, Joint Designs, and TransitionNipples

(a) Butt Welds. Butt welded joints may be of the singlevee, double vee, or other suitable type of groove. Jointdesigns shown in Fig. 434.8.6(a)-(1) or applicable combi-nations of these joint design details are recommendedfor ends of equal thickness. The transition between endsof unequal thickness may be accomplished by taper orwelding as shown in Fig. 434.8.6(a)-(2), or by means ofa prefabricated transition nipple not less than one-halfpipe diameter in length with acceptable joint designs asillustrated in Fig. 434.8.6(a)-(2).

(b) Fillet Welds. Fillet welds may be concave toslightly convex. The size of a fillet weld is stated as aleg length of the largest inscribed right isosceles triangleas shown in Fig. 434.8.6(b) covering recommendedattachment details of flanges.

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(c) Tack Welds. Tack welding shall be done by quali-fied welders, the same as all other welds.

434.8.7 Removal or Repair of Defects(a) Arc Burns. Arc burns can cause serious stress con-

centrations in pipelines and shall be prevented,removed, or repaired. The metallurgical notch causedby arc burns shall be removed by grinding, provided thegrinding does not reduce the remaining wall thicknessto less than the minimum permitted by the materialspecifications. Complete removal of the metallurgicalnotch created by an arc burn can be determined as fol-lows. After visible evidence of the arc burn has beenremoved by grinding, swab the ground area with a mini-mum 10% solution of ammonium persulfate or a 5%solution of nital. A darkened spot is evidence of a metal-lurgical notch and indicates that additional grinding isnecessary. If the resulting wall thickness after grindingis less than that permitted by the material specification,the portion of pipe containing the arc burn shall beremoved or repaired in accordance with para. 451.6.Insert patching is prohibited.

(b) Weld Defects. Authorization for repair of welds,removal and repair of weld defects, and testing of weldrepairs shall be in accordance with API 1104.

(c) Pipe Defects. Laminations, split ends, or otherdefects in the pipe shall be repaired or removed in accor-dance with para. 434.5(b).

434.8.8 Preheating and Interpass Temperature(a) The welding procedure specification shall specify

the minimum preheat temperature. When the weldingprocedure specification specifies preheating aboveambient temperatures, the method of heating shall bespecified. For heat treated and other high strength mate-rials and impact tested materials, control of interpasstemperatures may be necessary. The operating companyshall determine when interpass temperature limits arenecessary, and, when required, the interpass tempera-tures shall be provided in the welding procedure specifi-cation.

(b) When welding dissimilar materials having differ-ent preheating requirements, the material requiring thehigher preheat shall govern.

(c) The preheating temperature shall be checked bythe use of temperature indicating crayons, thermocouplepyrometers, or other suitable method to assure that therequired temperature is attained prior to and maintainedduring the welding operation.

434.8.9 Stress Relieving(a) Welds shall be stress relieved when the effective

weld throat [see Fig. 434.8.6(a)-(2)] exceeds 11⁄4 in.(32 mm), unless it can be demonstrated by welding pro-cedure qualification tests, using materials of the samespecification, type, and grade with an effective weldthroat that is equal to or greater than the productionweld, that stress relieving is not necessary.

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