Interpretation Response #26-0011
Below is the interpretation response detail and a list of regulations sections applicable to this response.
Interpretation Response Details
Response Publish Date:
Company Name: Chart Industries
Individual Name: Robert Real
Location State: MN Country: US
View the Interpretation Document
Response text:
March 24, 2026
Mr. Robert Real
Mechanical Engineer II
Chart Industries
407 Seventh Street NW
New Prague, MN 56071
Reference No. 26-0011
Dear Mr. Real:
This letter is in response to your January 19, 2026 email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the construction of specification MC 338 cargo tanks. Specifically, you seek clarification on the postweld heat treatment (PWHT) requirements for these 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) and whether what is described therein is absolute or conditional based on ASME Code allowances.
We have paraphrased and answered your questions as follows:
Q1. As referenced in § 178.338-2(e), what does the terminology “as a unit” mean?
A1. “As a unit” means the entire tank.
Q2. Does § 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?
A2. Yes. 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. Jurisdictional requirements can supersede ASME Code requirements.
Q3. May alternative methods such as local heating methods as specified in UW-40.3.2 or UW 40-40.3.5 be used in lieu of postweld heat treating the entire tank?
A3. No. However, if you wish 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, you may apply for a special permit, in accordance with § 107.105.
I hope this information is helpful. Please contact us if we can be of further assistance.
Sincerely,
Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division
Regulation Sections
| Section | Subject |
|---|---|
| 107.105 | Application for special permit |
| 178.338-2 | Material |