{"operation":"document","citation":"26-0011","title":"Chart Industries — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2026-03-24","effective_on":null,"summary":"26-0011 response to Chart Industries concerning 178.338.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-26-0011.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-26-0011.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-26-0011","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2026-03/260011.pdf","body":"<<<PAGE 1>>>\n\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nMarch 24, 2026\nMr. Robert Real\nMechanical Engineer II\nChart Industries\n407 Seventh Street NW\nNew Prague, MN 56071\nReference No. 26-0011\nDear Mr. Real:\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nThis letter is in response to your January 19, 2026 email requesting clarification of the\nHazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the construction\nof specification MC 338 cargo tanks. Specifically, you seek clarification on the postweld heat\ntreatment (PWHT) requirements for these cargo tanks when constructed in accordance with Part\nUHT in Section VIII of the American Society of Mechanical Engineers (ASME) Code as\nprescribed in § 178.338-2(e) and whether what is described therein is absolute or conditional\nbased on ASME Code allowances.\nWe have paraphrased and answered your questions as follows:\nQ1. As referenced in § 178.338-2(e), what does the terminology “as a unit” mean?\nA1. “As a unit” means the entire tank.\nQ2. Does § 178.338-2(e) require all MC 338 cargo tanks constructed in accordance with Part\nUHT to undergo PWHT as a unit regardless of material type and thickness, even if\nexempted by ASME Code Section VIII, Table UHT-56?\nA2. Yes. The requirements in § 178.338-2(e) specify that each tank constructed in accordance\nwith Part UHT must be postweld heat treated as a unit after the completion of all welds to\nthe shell and heads. Jurisdictional requirements can supersede ASME Code requirements.\n\n<<<PAGE 2>>>\n\nQ3. May alternative methods such as local heating methods as specified in UW-40.3.2 or UW\n40-40.3.5 be used in lieu of postweld heat treating the entire tank?\nA3. No. However, if you wish to use alternative methods such as local heating methods as\nspecified in UW-40.3.2 or UW 40-40.3.5 in lieu of postweld heat treating the entire tank,\nyou may apply for a special permit, in accordance with § 107.105.\nI hope this information is helpful. Please contact us if we can be of further assistance.\nSincerely,\nDirk Der Kinderen\nChief, Standards Development Branch\nStandards and Rulemaking Division\n\n<<<PAGE 3>>>\n\nCardez, E.\n26-0011\nFrom: INFOCNTR (PHMSA)\nTo: Baker, Yul (PHMSA)\nCc: Hazmat Interps\nSubject: Letter of Interpretation Request - FW: UHT question on 178.338-2 (e)\nDate: Tuesday, January 20, 2026 11:41:21\nHi Yul,\nPlease see the below interpretation request.\nLet us know if you need anything.\nThanks,\nJanaye\nFrom: Real, Robert <Robert.Real@chartindustries.com>\nSent: Monday, January 19, 2026 9:43 AM\nTo: PHMSA HM InfoCenter <PHMSAHMInfoCenter@dot.gov>\nSubject: UHT question on 178.338-2 (e)\nYou don't often get email from robert.real@chartindustries.com. Learn why this is important\nCAUTION: This email originated from outside of the Department of Transportation (DOT). Do\nnot click on links or open attachments unless you recognize the sender and know the content\nis safe.\nDear PHMSA Team,\nI am requesting clarification on the requirements in 49 CFR §178.338-2(e) regarding\npostweld heat treatment (PWHT) for tanks constructed under ASME Section VIII,\nDivision 1, Part UHT.\nThe regulation states:\n“Each tank constructed in accordance with part UHT in Section VIII of the ASME Code\nmust be postweld heat treated as a unit after completion of all welds to the shell and\nheads. Other tanks must be postweld heat treated as required in Section VIII of the\nASME Code. For all tanks the method must be as prescribed in the ASME Code.\nWelded attachments to pads may be made after postweld heat treatment.”\nMy questions are as follows:\n1. Scope of PWHT for UHT Tanks:\nDoes this language mean that all tanks built to ASME Part UHT must undergo full-unit\nPWHT, regardless of material type and thickness, even if it would be exempted by ASME\nSection VIII Table UHT-56, and that this requirement is over and above what is\n\n<<<PAGE 4>>>\n\nprescribed by ASME? Or is the intent that for tanks built to ASME Part UHT, PWHT is only\nrequired when ASME Table UHT-56 prescribes it, and when required, it must undergo\nfull-unit PWHT.\n2. Acceptable Method:\nWhen PWHT is required, does the clause “as a unit” mean the only acceptable methods\nare ones where the entire tank is heated up at once to keep thermal gradients down like\nwhat is described in UW40.3.1 or UW 40.3.4, or are all methods described in UW40.3\nacceptable as long as all weld joints receive PWHT.\nSpecifically are methods that address the whole vessel in sections such as UW\n40.3.5 which allows for local heating of weld joints, or 40.3.2 which allows for\nheating part of the vessel in an oven smaller than the vessel itself acceptable, or\ndoes the entire vessel need to be brought up to temp and cooled down uniformly\nas a single unit.\nUnderstanding whether the DOT requirement is absolute for all UHT tanks or conditional\nbased on ASME material/thickness rules is critical for design compliance.\nThank you for your assistance. Please let me know if additional details are needed.\nSincerely,\n-Robert Real\nMechanical Engineer II\nChart Industries\nRobert Real\nDesign Engineer II– Hydrogen and Road Mobiles | D&S West\n407 Seventh Street NW │ New Prague, MN │ 56071 │ USA\nDirect: +1 651 332 0033\nrobert.real@chartindustries.com│www.chartindustries.com\nThis e-mail message, including any attachment (collectively the \"e-mail\"), may contain\nPRIVILEGED AND CONFIDENTIAL INFORMATION. If you are not the intended\nrecipient, then please (i) do not read this e-mail, (ii) do not forward, print, copy or\notherwise disseminate this e-mail, (iii) notify us of the error by a reply to this e-mail,\nand (iv) delete this e-mail from your computer. Thank you.","truncated":false,"body_characters":5658}