Ask X3What does 49 CFR 178.61 (Specification 4BW welded steel cylinders with electric-arc welded seam) require?
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As Ask X3, your fleet-compliance assistant, here is what 49 CFR 178.61 requires for DOT 4BW welded steel cylinders with electric-arc welded seams:
* Design & Capacity: Cylinders must have a spherical or cylindrical design, a water capacity of 1,000 pounds or less, and a service pressure range of 225 to 500 psig. Closures made by the spinning process are not allowed.
* Materials & Construction: The steel used must comply with specific standards (table 1 of appendix A), and manufacturers must keep records of intentionally added alloying elements. Heads must be concave to pressure, have a minimum thickness of at least 90 percent of the sidewall thickness, and meet specific shape and chemical composition limits.
* Welding Requirements:
* Circumferential seams must use electric-arc welding (butt joints with an offset/joggle butt or lap joint with a minimum overlap of 4 times the sheet thickness).
* Longitudinal seams must be butt-welded using an automatic machine process, complete penetration, and strict limits on misalignment.
* Welding procedures and operators must be qualified in accordance with CGA C-3.
* Welds must undergo radioscopic or radiographic examination (with joint efficiencies varying based on whether seams are fully examined, spot-examined, or unexamined).
* Attachments: Welded attachments to the top and bottom (such as neckrings, footrings, handles, bosses, pads, and valve protection rings) must be made of weldable steel with a carbon content of 0.25 percent or less. Exposed bottom welds on cylinders over 18 inches long must be protected by footrings.
* Wall Thickness: For outside diameters over 6 inches, the minimum wall thickness must be 0.078 inch, and the resulting wall stress (calculated using the formula in the regulation) cannot exceed specified stress limits.
* Heat Treatment: Each cylinder must be uniformly and properly heat treated prior to testing, accomplished after all forming and welding operations (with specific exceptions for certain attachment welds).
* Openings: All openings must be located in the heads or bases, be securely attached by fusion welding/welding, and meet strict thread standards if threads are used.
* Pressure Testing: At least one cylinder randomly selected from each lot of 200 or fewer must successfully withstand a pressure test (water-jacket or direct expansion method).