Stress Corrosion (Environmental) Cracking Repair
Stress-corrosion cracks in a pressure vessel can be repaired in a manner similar to fatigue cracks (see Section 744). However, the repairs to the vessel can be very extensive, because large numbers of cracks can occur in susceptible vessels.
The depth of stress-corrosion cracks should be determined by ultrasonic examination (UT) using shear wave procedures before repairs begin. The cracks may be superficial and possibly dormant, in which case immediate repairs may not be necessary if the vessel satisfies fitness-for-service criteria (see Section 750). Determining the crack depth by UT examination may be very difficult due to the form and structure of the crack (see Section 736). Very specialized shear wave procedures may be required. If the depth of the cracks cannot be determined by UT examination, grinding to the minimum depth for their complete removal at selected locations can be substituted. Use of this method could also be considered to verify the accuracy of UT examination depth measurements.
It is essential to reexamine during the next scheduled inspection any stresscorrosion cracks that are allowed to remain in a pressure vessel. A pressure vessel or materials engineer should be consulted to determine the maximum interval advisable before the next examination.
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