Evaluation of indication detected in high-thickness welds: comparison between traditional methods and new technologies

摘要

In the field of advanced ultrasonic techniques, the potential of new technologies in terms of sensitivity and accuracy in locating and sizing of indications has opened up new horizons in the inspection of high-thickness pressure vessels. The relevance of these new technologies is that now we can obtain more precise information on the weld defects that will allow the acceptance of flaws larger than those permitted applying traditional inspection criteria and that will permit flaws to be monitored in subsequent inspections with a high level of confidence. This progress in detection and measure systems should not tempt us into neglecting traditional methodologies: Code Case 2235 still considers PT, MT or ET inspection to be more effective in detecting surface flaws, and manual ultrasonic techniques appear necessary to provide information about the type of internal indications. Regarding the latter, although Code Case 2235 acceptance criteria do not require characterisation of the indication, we believe that knowledge of the type discontinuity (for example distinguishing planar from volumetric flaws) is necessary, especially for planning periodic inspections over the life of the pressure vessel.