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Interpretation Response #06-0020 ([Trinity Industries, Inc.] [Mr. Greg McRae])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: Trinity Industries, Inc.

Individual Name: Mr. Greg McRae

Location State: TX Country: US

View the Interpretation Document

Response text:

Aug 29, 2007

Mr. Greg McRae                                 Reference No. 06-0020

Engineering and Technical Director

Trinity Industries, Inc.

P.O. Box 56887

2525 Stemmons Freeway

Dallas, TX 75356

Dear Mr. McRae:

This responds to your letter regarding the repair of MC 331 cargo tanks under the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180). I apologize for the delay in responding and for any inconvenience it may have caused. Specifically, you inquire whether a dye penetrant examination is an acceptable alternative to a radiographed examination. Your questions are paraphrased and answered below.

Q1. Is a dye penetrant (liquid penetrant, PT) examination of a welded joint containing a backing bar in the shell or hemispherical head of an MC 331 cargo tank an acceptable alternative to Radiographic (RT) examination of a full penetration weld?

Al. No. The basis for this determination is the original construction requirements for an MC 331 cargo tank under § 178.337-1. This section mandates that the design, construction and certification of an MC 331 cargo tank be in accordance with the ASME Code which in turn requires radiographic examination of this type of weld. See ASME Section VIII, Div 1, Part UW-11; UW-l2: Table UW-12. Further, because this action is considered a repair, the requirements for such a repair are mandated by § 180.413 and the National Board Inspection Code (NBIC). See NBIC RC 1090 and RD 2060. NBIC requires welding to be performed in accordance with the original code of construction, that is, if the original pressure vessel received an RT examination, the repaired pressure vessel would also need an RT examination. Any deviation from this requirement would be subject to the approval of the Inspector. Additional guidance is provided in RD 1020, which allows for welding methods as alternatives to post-weld heat treatment. In addition, this guidance specifies that if it is not practical to RT the weld, a successful (defect free) PT examination must be conducted and the maximum allowable working pressure (MAWP) of the pressure vessel must be re-evaluated by the jurisdiction.

Q2. If a repaired MC 331 cargo tank was fully radiographed when originally constructed and the repair weld is not radiographed, should the MAWP of the cargo tank be reduced based on lower joint efficiency?

A2. Yes, provided prior agreement is obtained from all parties involved. See reasoning in Al above.

I trust this satisfies your inquiry. Please contact us if we cam be of further assistance.


Hattie L. Mitchell

Chief, Regulatory Review and Reinvention

Office of Hazardous Materials Standards


Regulation Sections

Section Subject
180.407 Requirements for test and inspection of specification cargo tanks