Ask X3What does 49 CFR 178.57 (Specification 4L welded insulated cylinders) require?
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As a motor-carrier owner, here is what you need to know about 49 CFR 178.57 for Specification 4L welded insulated cylinders:
* Basic Design & Pressure: A DOT 4L cylinder is a fusion-welded insulated cylinder with a nominal water capacity of no more than 1,000 pounds and a service pressure between 40 and 500 psig. For liquefied hydrogen service, they must be designed to stand vertically on end.
* Design Service Temperatures: Cylinders must be suitable for the coldest temperature of the specific cryogenic liquid they carry (e.g., minus 320 °F or colder for Argon, Nitrogen, and Oxygen; minus 423 °F for Hydrogen; minus 411 °F for Neon; and minus 452 °F for Helium).
* Materials & Manufacture: Inner containment vessels must use authorized steels, while outer jackets can be steel or aluminum. Cylinders must be free of weakening defects with a smooth, uniform surface. Heads must be seamless, concave to the pressure, and meet specific thickness rules.
* Insulation: The cylinder surface must have fire-resistant insulation. Non-evacuated jackets require a steel jacket (at least 0.060-inch thick) or an aluminum jacket (at least 0.070-inch thick) to keep moisture out. Evacuated jackets must handle a minimum collapsing pressure of 30 psig differential, and total heat transfer must meet strict limits.
* Welding & Testing: All seams must be fusion-welded (butt or joggle butt joints with complete penetration). Welding procedures and operators must qualify using CGA Pamphlet C-3, including weld impact tests.
* Openings & Pressure Testing: Openings are only allowed in the heads, must be circular (3 inches or less, or one-third the cylinder diameter), and must have fusion-welded fittings, bosses, or pads. Before being insulated and jacketed, each cylinder must pass a pressure test (proof pressure, water-jacket, or direct expansion method) to at least two times its service pressure for a minimum of 30 seconds with no leakage or visible distortion.
* Physical Tests: Physical tests are required to determine yield strength, tensile strength, and elongation on specimens from each heat of material.
*(Note: Heat treatment is not permitted.)*