Steam cylinder welding joint coefficient?
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The company has a steam cylinder with a design pressure of 1.76 MPa and a design temperature of 209°C; it is classified as a Class 2 vessel. X-ray inspection is required at 20% of the surface area. The cylinder body is made of seamless steel pipe with an outer diameter of Φ426. The end caps have no seams, and the entire vessel shell consists of only two weld seams (those between the end caps and the cylinder body). The welding joint coefficient indicated in the drawings is 1/0.85; it should actually be 0.85. What do you think? Is the value given in the drawings appropriate?
I don’t think it’s appropriate. The welding joint coefficient generally refers to seam A; for seamless steel tubes of the cylinder, this value is 1 by default, and the same applies when the head is manufactured as a single piece. The welding joint coefficient should be determined based on the type of weld in the butt joint and the proportion of length subject to non-destructive testing. Regarding the inspection ratio, the inspection for gap B is specified as 20%, with a minimum length of 250 mm; grade AB, level II, is considered acceptable.
Taking a welding joint coefficient of 1, along with 20% flaw detection, seems inappropriate. But I can’t think of a better way to express it either. This situation is indeed quite special!
20% refers to the circumferential welds; generally, it is the longitudinal welds that are taken into account in the calculations, as the maximum tensile stress experienced by longitudinal welds is twice that of circumferential welds. By verifying the strength of the longitudinal welds, the strength of the container can be ensured – if the strength of the longitudinal welds is satisfactory, then the strength of the circumferential welds will also be adequate.
It cannot be written this way; the cylinder does not have any longitudinal weld joints, so the weld joint coefficient is 1.0