{"operation":"document","citation":"25-0066","title":"The Hartford Steam Boiler Inspection and Insurance Company — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2026-01-22","effective_on":null,"summary":"25-0066 response to The Hartford Steam Boiler Inspection and Insurance Company concerning 171.8, 178.337, 180.403, 180.413.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0066.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0066.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0066","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-01/250066.pdf","body":"<<<PAGE 1>>>\n\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nJanuary 22, 2026\nTimothy Nuoffer\nField Services Manager\nThe Hartford Steam Boiler\nInspection and Insurance Company\nOne State Street\nHartford, CT 06102\nReference No. 25-0066\nDear Mr. Nuoffer:\nThis letter is in response to your May 14, 2025 letter requesting clarification of the Hazardous\nMaterials Regulations (HMR; 49 CFR Parts 171-180) applicable to the repair and modification\nof MC 331 specification cargo tanks. You explain that your company has received questions\nregarding repairs to Department of Transportation (DOT) MC 331 specification cargo tanks that\nunderwent postweld heat treatment (PWHT) during their construction. You ask several questions\nand seek confirmation of your understanding as it relates to § 180.413, the Compressed Gas\nAssociation (CGA) Technical Bulletin TB-2, Guidelines for Inspection and Repair of MC 330\nand MC 331 Cargo Tanks, and the NB-23, National Board Inspection Code (NBIC), A Manual\nfor Boiler and Pressure Vessel Inspectors.\nWe have paraphrased and answered your questions as follows:\nQ1. What edition of the NBIC must be used for the repair or modification of an MC 331\nspecification cargo tank?\nA1. The 1992 edition of the NBIC—incorporated by reference in the HMR—is necessary to\nperform what makes up a “repair” for an MC 331 specification cargo tank\n(see § 180.413(b)(6)). By contrast, performing a “modification” on an MC 331\nspecification cargo tank is prescribed in § 180.413(a)(1) and (d). Please note if any\nmodification involves welding on the cargo tank wall, it must meet all requirements for\n“repair,” as defined in § 180.403 and the use of the 1992 edition of the NBIC.\nQ2. For instances where PWHT is required for “non-minor” weld repairs, the 1992 edition of\nNBIC NB-23 states that alternative methods for PWHT may be used if it involves a\n“special welding method” that is acceptable to the inspector. It also emphasizes that,\n\n<<<PAGE 2>>>\n\nwhere necessary, competent technical advice should be obtained from the manufacturer\nof the object or from another qualified source. You ask, since the 1992 edition of NBIC\nNB-23 does not provide examples of “special welding” methods for P-No 11A and P-No\n11B materials, may the alternative welding methods without PWHT, as described in the\n2023 edition of NBIC NB-23 Part 3, Repairs and Alterations—which includes methods\nfor P-No 11A and 11B materials—be considered as “another qualified source” per the\n1992 Edition and not require a special permit?\nA2. Yes. Welding methods authorized by the applicable edition of the NBIC may be used for\nan MC 331 specification cargo tank weld repair, provided the requirements of\n§ 180.413(b)(6) are met. Section 180.413(b)(6) requires that each cargo tank having\ncracks or other defects requiring welded repairs must meet all inspection, test, and heat\ntreatment requirements of § 178.337-16 in effect at the time of the repair, except that\nPWHT is not required after minor weld repairs. Accordingly, MC 331 specification cargo\ntanks undergoing non-minor weld repairs remain subject to the applicable heat treatment\nrequirements. Please note that alternative welding methods described in external\npublications (i.e., reference materials) do not replace or waive the requirements;\ntherefore, waiving any HMR mandated heat treatment requirement would require\nissuance of a special permit.\nQ3. As it relates to § 180.413(b)(6), which references minor weld repair, the CGA TB-2\nappears to describe a “minor repair” in section 3.4. What is the definition of “minor\nrepair”?\nA3. A “minor weld repair” as referenced in § 180.413(b)(6) is not defined in either § 171.8 or\n§ 180.403 of the HMR. However, CGA TB-2 describes what constitutes a “minor repair”\nin section 3.4. Additionally, section 3.7 of CGA TB-2 states that no PWHT is required\nafter a minor repair, which is referenced in § 180.413(b)(6) for “minor weld repairs.”\nThus, it is the opinion of this Office that, in this context, weld repairs as described in\nCGA TB-2 and performed in accordance with requirements of § 180.413(b)(6) and CGA\nTB-2 may be considered a “minor repair.”\nQ4. Does PHMSA permit a repair facility to forgo PWHT or any alternative methods on an\nMC 331 specification cargo tank after performing a non-minor welded repair?\nA4. No. A repair facility is not allowed to forgo PWHT on an MC 331 cargo tank after\nmaking a non-minor welded repair. PWHT is excepted only for minor weld repairs, as\nreferenced in § 180.413(b)(6).\n\n<<<PAGE 3>>>\n\nQ5. If a repair facility is adding non-pressure retaining and non-structural pads to the inside of\nan MC 331 specification cargo tank that is welded directly to the shell or head by fillet\nwelds, would PWHT be required?\nA5. Yes. Direct welding to the shell or head(s) of a cargo tank would affect the structural\nintegrity by introducing uneven heating and cooling, as well as residual stress. Therefore,\ninstallation of mounting pads by welding would be considered a modification. Note,\n§ 180.413(b)(6) of the HMR requires non-minor weld repairs to an MC 331 specification\ncargo tank be accompanied by PWHT.\nI hope this information is helpful. Please contact us if we can be of further assistance.\nSincerely,\nDirk DerKinderen\nChief, Standards Development Branch\nStandards and Rulemaking Division\n\n<<<PAGE 4>>>\n\nBaker, Y.\n25-0066\nStandards and Rulemaking Division\nPipeline and Hazardous Materials Safety Administration\nAttn: PHH-10\nUS Department of Transportation\nEast Building\n1200 New Jersey Avenue, SE\nWashington, DC 20590-0001\nTo whom it may concern:\nRepair/Modification of MC-331 Cargo Tanks\nIn the past year, HSB has received some questions regarding repairs to DOT MC-\n331 specification tanks where postweld heat treatment (PWHT) was performed\nduring construction of the tank. HSB has discussed these questions in the past with\nUS DOT and would like to receive a formal response. The questions are related to\nparagraph 49CFR180.413, CGA TB-2 and the National Board Inspection Code\n(NBIC). The repair organizations that HSB works with do have a National Board R\nstamp. HSB’s role is as the NBIC Repair Inspector. HSB is not the DOT Design\nCertifying Engineer(DCE) or the DOT Registered Inspector(RI).\nQuestion #1: Paragraph 180.413(a)(1) states the edition of the NBIC to be used for\nthe repair and modification should be the edition in effect at the time of the repair.\nFor a repair performed on tank in 2024, the repair would be performed to the 2023\nEdition of the NBIC. Paragraph 180.413(b)(6) refers to 171.7 for the NBIC to be\nused for repairs of MC-331 cargo tanks. Per 171.7 the edition of the NBIC\nincorporated by reference is 1992. What edition of the NBIC shall be used for the\nrepair and modifications of MC-331 cargo tanks?\nAnswer #1: 1992 Edition of the NBIC shall be used for repair and modifications of\nMC-331 cargo tanks.\nQuestion #2a: For repairs that are not considered “minor” per 49CFR180.413(b)(6),\nPWHT is required per the DOT specification requirements for the construction of the\ncargo tank at the time the repair is being performed. For MC-331 cargo tanks\nconstructed with ASME Section VIII Div. 1 Part UHT materials, PWHT would be\nrequired. The 1992 Edition of the NBIC paragraph R-303.2.2 is for alternative\nmethods for PWHT and states, “special welding method acceptable to the Inspector\nmay be used. Examples of special welding methods for P1 and P3 materials are\ndescribed in Supplement 3, page 55. Where deemed necessary, competent\ntechnical advice should be obtained from the manufacturer of the object or from\nanother qualified source.” The Part UHT materials used for construction are P-No\n11A or P-No 11B materials. Since the 1992 Edition does not provide examples of\nspecial welding methods for P-No 11A and P-No 11B materials, may the alternative\nwelding methods without PWHT as described in the 2023 Edition of the NBIC Part 3,\nwhich includes methods for P-No 11A and 11B materials, be considered as “another\nqualified source” per the 1992 Edition and not require special permit?\n14 May 2025\nTimothy J. Nuoffer\nField Services Manager\nCodes & Standards\nTel.: (618) 444-7628\nTimothy_Nuoffer@hsb.com\nThe Hartford Steam Boiler\nInspection and Insurance Co.\nOne State Street\nP.O. Box 5024\nHartford, CT 06102-5024\nwww.munichre.com/HSB\n\n<<<PAGE 5>>>\n\nPage 2 14 May 2025\nAnswer #2a: Yes.\nQuestion #2b: In reviewing 180.413(b)(6) and CGA TB-2:1980 paragraph 3.4, it\nseems the definition of “minor repair” is when a repair is made to remove cracks and\nthen the affected area built-up by welding. Other repairs that do not meet this\ndefinition would be considered a “major repair.” Is this correct the correct definition\nfor “minor repair”?\nAnswer #2a: Yes, provided the repair organization follows the procedure for\nperforming the minor repair in 180.413(b)(6) and CGA TB-2:1980 paragraph 3.4.\nQuestion #3: Is it permitted by US DOT for a repair organization to not perform any\nPWHT or any kind of alternative method on a MC-331 tank following a welded\nrepair, excluding “minor” repairs?\nAnswer #3: Yes. Only if a cargo tank is not constructed to Part UHT may postweld\nheat treatment not be performed. For all Part UHT cargo tank constructions, post\nweld heat treatment is required.\nQuestion #4: If a repair organization is adding a non-pressure retaining and non-\nstructural pad to the inside of a MC-331 cargo tank to be welded directly to the shell\nor head by fillet welds, would PWHT be required?\nAnswer #4: If the addition of the non-pressure/non-structural pad is not specifically\ncalled out in the design drawing, this would fall under a modification and would\nrequire a DCE. The DCE has authority to determine whether or not PWHT is\nrequired. If the non-pressure/non-structural pad is called out in the design drawing\nand was originally constructed to Part UHT, the welded attachments and pads may\nnot need PWHT provided that the design drawing does not require the welded\nattachments and pads to be PWHT. If the design drawing requires PWHT of the\nwelded attachments for these non-pressure and non-structural pads, the repair\norganization must PHWT.\nA reply as soon as possible would be appreciated. Should you have additional\nquestions or need to discuss, please call 618-444-7628.\nSincerely,\nTimothy J. Nuoffer\nField Services Manager\nCodes & Standards\nTel.: (618) 444-7628\nTimothy_Nuoffer@hsb.com\nThe Hartford Steam Boiler Inspection\nand Insurance Co.","truncated":false,"body_characters":10502}