The use of advanced non-destructive techniques like ToFD and Phased Array to perform maintenance inspections of pressure vessels enables the characterization of numerous defects not detectable during the construction, as planar defects, whose detection by radiography is highly dependent on its orientation. These techniques lead to a substantial increase in reliability of equipments, since, the early detection of defects under development allows the planning of interventions, reducing down times, or non-productive times, and the number of unscheduled shutdowns. The deficiencies of fabrication are usually identified in maintenance inspections, because the techniques used are more sensitive and the tested areas are more extensive than required after construction. Some defects can be easily classified as manufacturing defects, but some are indistinguishable from the ones related to service conditions. Regarding its origin, the critical decision to take is to assess if future evolution is likely to occur, based on the application, material, service conditions and size of defect. This study envisages a proposal of a methodology for technical evaluation based on a large amount of industrial cases, aiming to assist personnel in decision steps in maintenance, inspection and repair of weld defects detected on pressure vessels from process.
pressure vessels; NDT; maintenance; repair; fitness for service methodologies; risk based inspection
