Design for Inspection
The requirements for future in-service inspections should be considered when new
pressure vessels are designed and constructed. In particular, weld joints should be
designed with configurations and geometries that permit nondestructive
examinations for deterioration.
Selection of the most appropriate design details for weld joints requires a thorough evaluation of the various forms of deterioration that may occur during service, and the nondestructive examination procedures that can be used to detect the deterioration. Furthermore, inspection during fabrication of the vessel may have to be more comprehensive than required by the ASME Code, to provide baseline data for the in-service inspections. It is often very difficult to distinguish pre-existing fabrication flaws from those that may have subsequently developed during service, and requires a highly skilled NDE examiner. Although nondestructive examination procedures are better now at identifying various flaw types, lack of appropriate baseline data can complicate in-service inspection.
Designing for in-service inspection can exceed the requirements for assuring the integrity of a new pressure vessel as constructed, but the modification of design details and additional inspections during fabrication can frequently be obtained with minimal additional cost. Nevertheless, additional initial expense for vessels that may be susceptible to some form of deterioration during service may be justified by the ability to properly assure through in-service inspection their integrity and reliability after a long service history.
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