Testing Requirements for DOT 4E Cylinders
Pipeline and Hazardous Materials Safety Administration · Apr 15, 1998 · Reference No. 98-0551
This is in response to your inquiry requesting clarification of the testing requirements for DOT 4E specification cylinders. Your questions are paraphrased below, followed by our answers.
Q1: Are weld tensile specimens tested per 49 CFR § 178.68-17(a) (now § 178.68(1)(1)) required to meet both apparent and actual breaking stress requirements?
A1: Yes. The specimen must meet both requirements to pass the test.
Q2: What are the minimum wall thickness requirements of 49 CFR 178.68-10 (now § 178.68(f))?
A2: The absolute minimum wall thickness is 0.140. In addition, the minimum wall thickness must be such that the calculated wall stress at twice the service pressure is less than 20,000 psi or 1/2 the minimum tensile strength, whichever is less. The minimum tensile strength is determined in accordance with § 178.680).
Q3: Where should the thickness of tensile coupons be measured?
A3: According to ASTME8, paragraph 7.1.1: "For referee testing of specimens under 3/16 in. in their least dimension, measure the dimensions where the least cross-sectional area is found".
A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.