In-Service Inspection Data Analysis

The information obtained from the inspection of a pressure vessel must be interpreted and evaluated to determine if the vessel has sufficient integrity for continued service, or if repairs or replacement are required. The judgment of experienced pressure vessel or materials engineers may be required to properly determine the disposition of a vessel after in-service inspection.

A very important concept to understand is that detected flaws do not necessarily have to meet the ASME Code acceptance standards for the vessel to be suitable for continued service without repair. The ASME Code acceptance criteria have been established to assure owner/users that vessels receiving the Code symbol have been manufactured to a high level of quality that can be obtained with good workmanship. These acceptance criteria have no direct relationship to the requirements for safe operation. This is because some flaws occurring in service, though larger than those acceptable to ASME Code at time of vessel manufacture, are too small to cause vessel failure at its design temperature and pressure. Because of the various forms of deterioration that may occur during the operation of a vessel, in-service inspection can detect flaws that the ASME Code would not accept, but this does not always mean that the vessel has to be repaired or replaced.

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