Creep and Stress-Rupture Repair

Stress-rupture cracks can be repaired by grinding for removal and then restoring the ground area to the minimum required thickness with weld build-up, similar to that for fatigue cracks (see Section 744). However, this method may not always serve as a permanent repair, because the shell material adjacent to the repair might have undergone sufficient creep for additional stress-rupture cracks to develop after a relatively short period of additional operation. Therefore, it may be more realistic to plan for replacement of the components of the vessel exhibiting the cracks. It is unlikely that all components of a vessel will begin to develop stress-rupture cracks at the same time, and, therefore, it will not usually be necessary to replace the entire vessel. Consult a specialist for guidance.

Stress-rupture cracks tend to propagate relatively slowly, and if the stress-rupture cracks in a pressure vessel are relatively small when they are first detected, it may be acceptable to return the vessel to service until the replacement materials and components are obtained. Fitness-for-service analysis (see Section 750) can be used to help evaluate if the vessel has sufficient integrity and reliability for limited continued service.

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