The Pipeline and Hazardous Materials Safety Administration (“PHMSA”) addressed in a March 24th interpretive letter a clarification of the Hazardous Materials Regulations (“HMR”) applicable to the construction of specification MC 338 cargo tanks. See Reference No. 26-0011.
PHMSA was responding to a January 19th query from Chart Industries (“CI”).
CI asked for clarification on the postweld heat treatment (“PWHT”) requirements for MC 338 cargo tanks when constructed in accordance with Part UHT in Section VIII of the American Society of Mechanical Engineers (“ASME”) Code as prescribed in § 178.338-2(e). The company also asked whether what is described therein is absolute or conditional based on ASME Code allowances.
The March 24th interpretive letter first addresses what does the terminology “as a unit” mean, as referenced in § 178.338-2(e).
PHMSA responds that “as a unit” means the entire tank.
Second, PHMSA addresses the question of whether § 178.338-2(e) require all MC 338 cargo tanks constructed in accordance with Part UHT to undergo PWHT as a unit regardless of material type and thickness, even if exempted by ASME Code Section VIII, Table UHT-56?
PHMSA responds in the affirmative, stating that the requirements in § 178.338-2(e) specify that each tank constructed in accordance with Part UHT must be postweld heat treated as a unit after the completion of all welds to the shell and heads. It further states that jurisdictional requirements can supersede ASME Code requirements.
Finally, PHMSA addresses whether alternative methods such as local heating methods as specified in UW-40.3.2 or UW 40-40.3.5 can be used in lieu of postweld heat treating the entire tank?
PHMSA responds in the negative. However, it states that if CI wishes to use alternative methods such as local heating methods as specified in UW-40.3.2 or UW 40-40.3.5 in lieu of postweld heat treating the entire tank, it may apply for a special permit, in accordance with § 107.105.
A copy of the March 24th interpretive letter can be found here.
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