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ASME B31.3 Quality Factors

Quality factors are used in pressure design and, in addition for castings, design for occasional loads and displacement stress range. They are applied at longitudinal and spiral weld joints, and for castings.

The quality factors for weld joints are provided in Table A-1B of the Code, and vary from 0.6 to 1.0. The basis for these factors is summarized in Figure 3.2. The quality factor for furnace butt weld pipe is the lowest, at 0.60. Note that this quality factor does not generally effect the thickness of furnace butt weld pipe, since it is only permitted for Category D Fluid Service, and furnace butt welded pipe comes in standard wall, with a maximum diameter of DN 100 (NPS 4).

Electric resistance welded pipe has a quality factor of 0.85. This cannot be improved with additional examination.

The quality factor for electric fusion welded pipe varies from 0.80 to 1.0, depending upon whether it is a single or double sided weld, and the degree of radiographic examination (none, spot, or 100%). The quality factor for API 5L spiral weld pipe is 0.95; the welds are 100% UT examined per the specification.

The quality factors for castings are described in para. 302.2.3 of the Code. Due to the conservative stress basis, the casting quality factor for gray and malleable iron is 1.0. The casting quality factor for other castings is 0.8, unless supplemental requirements are met. These supplemental requirements involve additional examination and/or machining of surfaces to enhance examination. Compliance with these supplemental requirements can increase the quality factor to 0.85 to 1.0, depending upon which supplemental examinations are performed. #Little_PEng

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