Design of Welded Joints

The choice of weld design depends on a number of factors including:
• The conditions of welding. Accessibility has a definite influence on the type of weld joint. In small diameter vessels, the openings may have weld joints which are not accessible on both sides.
• The ASME code itself limits the design and use of weld joints based upon service, material, and location of weld.
• Company practices. Certain types of welds have been found through experience to be more reliable and less prone to failure than others. For example, the use of backup rings in circumferential welds leads to many problems, yet the Code allows this. The Company has found the following problems with backup rings: (1) they are difficult to check for weld quality by radiography; (2) they invariably contain root weld defects; (3) they greatly increase susceptibility to some form of fracture or cracking; and (4) they are not worth the savings that might be achieved.
• Economic considerations. If the previous three choices allow freedom to use different welds, then economic consideration may be the deciding factor; for example, V-edge preparation of a weld joint which can be made by flame cutting. This is usually more economical than J- or U-type edge preparation.

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