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As we all know, when calculating the strength of pressure-bearing plates for boilers and pressure vessels, it is necessary to use a value for the weld joint factor. But how is the value of the welding joint coefficient determined? By combining the requirements of the Code for Fixed Pressure Vessels and Pressure Vessels, the welding joint coefficient can be determined. Requirements for welded joints in the Code for Fixed Pressure Vessels: 1. For Class A and B butt joints of pressure vessels manufactured by welding methods for shell joint design, full-thickness penetration welding shall be employed. 2. Welded joints between nozzles and the shell: For the design of welded joints between nozzles (flanges) and the shell of pressure vessels, as well as those of jacketed pressure vessels, a fully penetrated structure shall be adopted in any of the following cases: (1) Pressure vessels with explosive media or those posing an extremely high or high level of toxicity; (2) Pressure vessels that require pneumatic testing or combined gas-liquid pressure testing; (3) Class III pressure vessels; (4) Cryogenic pressure vessels; (5) Pressure vessels subjected to fatigue analysis; (6) Pressure vessels exposed directly to flame heating; (7) When the designer deems it necessary. For the \"Code for Fixed Pressure Vessels\" and \"Pressure Vessels\", the value of the welding joint coefficient is set at 1. Principles for determining the welding joint coefficient: (1) For pressure vessels manufactured by welding, the welding joint coefficient shall be selected in accordance with product standards, based on the type of welding joint and the proportion of non-destructive testing required; (2) Except for simple pressure vessels, it is not allowed to reduce the welding joint coefficient as a means to waive the need for non-destructive testing on such pressure vessel products. 2. The welding joint factors for steel pressure vessels are specified as follows: (1) Double-sided welded butt joints and butt joints with full penetration equivalent to double-sided welding a) Full non-destructive testing, φ=1.0; b) Partial non-destructive testing, φ=0.85. (2) Single-sided welded butt joint (with gussets in close contact with the base metal along the entire length of the weld root): a) Full non-destructive testing, take φ=0.9; b) Local non-destructive testing, take φ=0.8.