{"operation":"document","citation":"25-0050","title":"Fleener Consulting LLC — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2025-08-07","effective_on":null,"summary":"25-0050 response to Fleener Consulting LLC concerning 178.337, 180.407.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0050.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0050.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-25-0050","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/2025-08/250050.pdf","body":"<<<PAGE 1>>>\n\n1200 New Jersey Avenue, SE\nWashington, DC 20590\nU.S. Department\nof Transportation\nPipeline and Hazardous\nMaterials Safety\nAdministration\nAugust 7, 2025\nArt Fleener\nFleener Consulting LLC\n3741 Mathews Road\nAmes, IA 50014\nReference No. 25-0050\nDear Mr. Fleener:\nThis letter is in response to your April 23, 2025 email requesting clarification of the Hazardous\nMaterials Regulations (HMR; 49 CFR Parts 171-180) applicable to the minimum thickness for\nDepartment of Transportation (DOT) specification Motor Carrier (MC) 331 cargo tanks. You\nexplain that Pipeline and Hazardous Materials Administration (PHMSA) previously issued a\nmemo to the Federal Motor Carrier Safety Administration’s (FMCSA) Hazardous Materials\nDivision, providing clarification on the minimum thickness requirements for cargo tanks under\nthe HMR, including those for MC 331 cargo tanks. You ask questions regarding the minimum\nshell thickness requirements.\nWe have paraphrased and answered your questions as follows:\nQ1. Is the memo from PHMSA to FMCSA, as referenced in your incoming email, regarding\nthe minimum shell thickness of an MC 331 specification cargo tank still valid?\nA1. Yes, this memo remains valid for the specific scenario that it addressed at the time it was\ndrafted. Please keep in mind that an interagency memo, like the one referenced in your\nincoming email, is intended for “internal use only.” This memo is not meant to be shared\noutside of the agency, as it serves as internal guidance for specific situations.\nQ2. For an MC 331 specification cargo tank, what thickness is considered below the\nminimum requirement?\nA2. In accordance with § 178.337-3(e), the minimum thickness of the tank shell and head\nshall be determined using structural design requirements in Section VIII of the American\nSociety of Mechanical Engineers (ASME) Code1 or 25% of the tensile strength of the\n1 ASME BPVC.VIII.1-2017, Section VIII—Rules for Construction of Pressure Vessels Division 1.\n\n<<<PAGE 2>>>\n\nmaterial used. Additionally, the minimum required thickness for an MC 331 cargo tank\nconstructed before October 1, 2003, is determined by the thickness indicated on the U-1A\nform2 minus any corrosion allowance, as required in § 180.407(i)(9). If no corrosion\nallowance is indicated on the U-1A form, then the thickness of the tank shall be the\nthickness of the material of construction indicated on the U-1A form with no corrosion\nallowance. For an MC 331 cargo tank constructed after October 1, 2003, the required\nminimum thickness is the value that has been marked on the cargo tank, as required by\n§§ 180.407(i)(9) and 178.337-17(b).\nIncidentally, § 180.407(i)(9) states that the minimum thickness for an MC 331 cargo tank\nconstructed after October 1, 2003, can be found on the specification plate, but this is incorrect.\nHowever, the minimum thickness markings can be found on the name plate in accordance with\n§ 178.337-17(b) and this will be corrected in a future rulemaking.\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\n2 Form U-1A\n\n<<<PAGE 3>>>\n\nBaker, Y\n25-0050\nFrom: Dodd, Alice (PHMSA)\nTo: Baker, Yul (PHMSA)\nSubject: FW: interp request\nDate: Thursday, April 24, 2025 11:53:46\nAttachments: under mill tollerance with .0004.pdf\ninterp thickness.pdf\nFrom: Kelley, Shane (PHMSA) <shane.kelley@dot.gov>\nSent: Wednesday, April 23, 2025 3:19 PM\nTo: Hazmat Interps <hazmatinterps@dot.gov>\nCc: art fleener <fleenerconsulting@yahoo.com>\nSubject: Fw: interp request\nPlease process and thank you\nFrom: art fleener <fleenerconsulting@yahoo.com>\nSent: Wednesday, April 23, 2025 3:09:48 PM\nTo: Kelley, Shane (PHMSA) <shane.kelley@dot.gov>\nSubject: interp request\nYou don't often get email from fleenerconsulting@yahoo.com. Learn why this\nis 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.\nShane\nSee the below and the attached files.\nThanks\nart\nFleener Consulting LLC.\n515 291 9208\nfleenerconsulting.com\nOn April 18, 2014, PHMSA issued a Memorandum, REF: 13-0216 that addressed\nminimum thickness of various specification cargo tanks. (see attached file). This\nmemo appears to no longer be available as a PHMSA interpretation (interp) when a\nsearch is made on PHMSA's website.\n\n<<<PAGE 4>>>\n\nThis interp amongst other things answers questions on when a MC331 cargo tank is\nbelow the minimum thickness. This interp tells us based on ASME code that the\nUSDOT will allow .014” below the minimum thickness as shown on the specification\nplate. So, if a tanks minimum thickness as shown on the specification plate is .250”,\nthis tank would not be too thin until it is more then .014” below .250” or once the tank\nwent below .236” for thickness.\nPHMSA determined the .014” in the April 18, 2014, memo by using the ASME code\nfor mill under tolerance for .01”. The .004” is based on a ASME interpretation for\nrounding rules for a combination total of .014”. (see attached file)\nBelow are the 49 CFR regulations for determining minimum thickness of specification\ncargo tanks.\nQuestions:\n1.\nIs the April 18, 2014, Memorandum, REF: 13-0216 that addressed minimum\nthickness of various specification cargo tanks still accurate for when a MC 331 cargo\ntank is too thin and allowing .014” below the minimum thickness as shown on the\nspecification plate before the tank is too thin.\n2.\nIf as described in question #1 is no longer allowed by the USDOT for a MC331\ncargo tank when would a MC331 cargo tank that has a minimum thickness of .250”\nbe below the minimum thickness?\nIf you have any questions, please let me know.\nThank you.\nArt Fleener\nFleener Consulting LLC\n§ 180.407 Requirements for test and inspection of specification cargo tanks.\n(i) Thickness testing.\n(5) Minimum thicknesses for MC 300, MC 301, MC 302, MC 303, MC 304, MC\n305, MC 306, MC 307, MC 310, MC 311, and MC 312 cargo tanks are determined\nbased on the definition of minimum thickness found in § 178.320(a) of this\nsubchapter. The following Tables I and II identify the “In-Service Minimum\nThickness” values to be used to determine the minimum thickness for the\nreferenced cargo tanks. The column headed “Minimum Manufactured Thickness”\nindicates the minimum values required for new construction of DOT 400 series\ncargo tanks, found in Tables I and II of §§ 178.346-2, 178.347-2, and 178.348-2 of\nthis subchapter. In-Service Minimum Thicknesses for MC 300, MC 301, MC 302,\n\n<<<PAGE 5>>>\n\nMC 303, MC 304, MC 305, MC 306, MC 307, MC 310, MC 311, and MC 312\ncargo tanks are based on 90 percent of the manufactured thickness specified in\nthe DOT specification, rounded to three places.\n§ 178.320 General requirements applicable to all DOT specification cargo tank\nmotor vehicles.\nMinimum thickness means the minimum required shell and head (and baffle and\nbulkhead when used as tank reinforcement) thickness needed to meet the\nspecification. The minimum thickness is the greatest of the following values:\n(1)\n(i) For MC 330, MC 331, and MC 338 cargo tanks, the specified minimum thickness\nfound the applicable specification(s); or\n(ii) For DOT 406, DOT 407 and DOT 412 cargo tanks, the specified minimum\nthickness found in Tables I and II of the applicable specification(s); or\n(iii) For MC 300, MC 301, MC 302, MC 303, MC 304, MC 305, MC 306, MC 307, MC\n310, MC 311, and MC 312 cargo tanks, the in-service minimum thickness prescribed\nin Tables I and II of § 180.407(i)(5) of this subchapter, for the minimum thickness\nspecified by Tables I and II of the applicable specification(s); or\n(2) The thickness necessary to meet with the structural integrity and accident damage\nrequirements of the applicable specification(s); or\n(3) The thickness as computed per the ASME Code requirements (if applicable).","truncated":false,"body_characters":7935}