A Case Study on Generation of Acceptance Criteria in Feedwater Supply Tube Bends Available to Purchase

Inspection of components utilizing advanced examination techniques is becoming standard practice in the power industry. One of the critical aspects during this type of inspection is to have on hand criteria for acceptance or rejection of flaws found during these inspections. The examinations typically include the use of advanced ultrasonic techniques such as Linear Phased Array (LPA), Focused Annular Phased Array (APA), and Time of Flight Diffraction. These techniques can detect and size flaws that are often “Fit for Service” for at least one additional outage cycle. However, schedule limitations during an outage often do not permit for extensive analysis time. Repair decisions need to be made immediately and having criteria available for these decisions are critical. The following is a case study for the generation of acceptance / rejection criteria for power boiler feedwater supply tube bends. The determination of “allowable flaw sizes” is needed to determine which of these supply tube bends need to be removed during the outage. The acceptance criteria in this work is based on the criteria of API 579-1 / ASME FFS-1 “Fitness for Service Standard” [1] to evaluate the rate of growth of the flaws found. Discussion is also made as to the sensitivity of the examination methods used to detect the flaws expected and how this relates to the acceptance criteria generated.