ASME Code, Section VIII, Division 1 (Paragraphs UW-11 and UCS-57), requires RT examination of longitudinal welds for shell components of carbon steel vessels exceeding 1¼-inches thick, for low-alloy 1¼ Cr—1 Mo vessels exceeding 5/8 inches, and for all low-alloy 2¼ Cr—1 Mo vessels regardless of thickness. Spot RT or VT (i.e., no RT) is permitted for components of vessels having thicknesses that are thinner than these limits, providing reduced weld joint efficiencies are used for the design (Paragraph UW-12). However, the pressure vessel specifications recommend spot RT as a minimum, and allow the option of full RT examination of vessels when not required by the Code. Full RT examination is recommended for the following conditions:
1. For service at low temperatures where undetected flaws could cause brittle fracture.
2. For service where cyclic pressures and/or temperatures are encountered, and undetected flaws could initiate fatigue cracks.
See the comments in PVM-MS-4750, Inspection Section, for additional guidance.
ASME Code, Section VIII, Division 2, requires full RT of all longitudinal welds regardless of thickness. The authorized inspector is obligated to review all radiographs that are required by the ASME Code, but the Company inspector will also review all radiographs, especially those that are specified exceeding Code requirements.
The pressure vessel specification PVM-MS-4749 recommends UT examination of all longitudinal welds in shell components 3-inches thick or greater, or when GMAW is employed, regardless of thickness, in addition to the RT examination required by the Code and/or the specification. The Company inspector should witness the UT examination performed by the fabricator to verify that the examinations are being performed properly, and that the results are being accurately recorded.
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