Ask X3What does 49 CFR 178.36 (Specification 3A and 3AX seamless steel cylinders) require?
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As a motor-carrier owner, to comply with 49 CFR 178.36 for Specification 3A and 3AX seamless steel cylinders, you must ensure your cylinders meet the following practical and specific requirements:
* Type and Size:
* DOT-3A: A seamless steel cylinder with a nominal water capacity of no more than 1,000 pounds and a service pressure of at least 150 psig.
* DOT-3AX: A seamless steel cylinder with a water capacity of at least 1,000 pounds and a service pressure of at least 500 psig (with specific horizontal bending and hydrostatic test stress calculations not to exceed 80% of the minimum yield strength of the steel).
* Steel Material: Must be made of open-hearth or electric steel of uniform quality with maximum chemical content percentages of: Carbon, 0.55; phosphorus, 0.045; and sulphur, 0.050. Material must be suitably identified (plates and billets for hot-drawn cylinders must be marked with the heat number).
* Manufacture and Finish: Must be produced using adequate equipment and processes free of weakening fissures or defects (though surfaces may be machined or treated to eliminate defects). The thickness of cylinder bottoms welded or formed by spinning must be at least two times the minimum wall thickness of the cylindrical shell.
* Welding and Brazing: Generally prohibited except for attaching non-pressure neckrings and footrings on cylinders with a service pressure of 500 psig or less (using weldable steel with a carbon content not exceeding 0.25%, or 4130X steel), or for cylinders used solely in anhydrous ammonia service (which may have a 1/2-inch diameter bar welded in their concave bottoms).
* Wall Thickness: For cylinders with a service pressure under 900 psig, wall stress cannot exceed 24,000 psig. Any cylinder with an outside diameter over 5 inches requires a minimum wall thickness of 0.100 inch.
* Heat Treatment: Completed cylinders must be uniformly and properly heat-treated prior to testing.
* Openings and Connections: Openings require clean-cut, even, gauge-compliant threads. Taper threads must meet American Standard taper pipe length requirements; straight threads require at least 6 engaged threads, a tight fit, adequate sealing gaskets, and a calculated shear strength of at least 10 times the cylinder's test pressure.
* Pressure Testing: Each cylinder must successfully pass a water-jacket or direct expansion pressure test to a minimum of 5/3 times its service pressure, maintained for at least 30 seconds. Permanent volumetric expansion cannot exceed 10 percent of the total expansion at test pressure.
* Flattening Test: Must be performed on one randomly selected cylinder from each lot of 200 or less using wedge-shaped knife edges (for lots of 30 or less, a ring cut from each cylinder may be tested).
* Physical Tests: Physical testing (checking yield strength, tensile strength, elongation, and reduction of area) must be conducted on two specimens cut from one randomly selected cylinder per lot of 200 or less (or on an 8-inch ring cut from each cylinder for lots of 30 or less). Yield strength in tension corresponds to a permanent strain of 0.2 percent of the gauge length.