IWEX: New Horizons for Pipeline Girth-Weld AUT Inspection

Abstract

AUT inspections of pipeline girth-welds are increasingly performed in the context of strain or fatigue sensitive applications (such as arctic, deepwater or ultra deepwater applications) with increased O&G companies’ requirements in terms of reliability, sensitivity and accuracy. Commonly used ultrasonic girth weld solutions (based on the Zone Discrimination Technique) exhibits some weaknesses and limitations. The performance of the inspection (probability of detection “PoD” and sizing accuracy) strongly depends on geometric and metallurgical properties such as: - wall thickness variations, - UT probes positioning (as a result of band and scanner positioning), - surface conditions, - flaw type and orientation - pipe to pipe alignment - Geometry information (cap and root profiles) cannot effectively be extracted from AUT scans and defects interaction rules are very difficult to apply. To reach a high confidence level in AUT inspection PoD and sizing accuracy, extensive and time consuming qualification programs as well as project specific qualification tests are carried out. By way of consequence, from an operating O&G Company point of view, there is a strong interest to promote the development of new inspection methods with lower sensitivity to equipment settings and less operator dependency and possibly reduced qualification requirements. Inverse Wave Field Extrapolation (IWEX) is an image reconstruction process from UT propagated waves that, until now, was mainly used in seismic exploration. Recently, APPLUS RTD has pushed forward the technology to make it applicable to pipeline girth-weld inspection not only for onshore applications but also for an offshore lay barge context (e.g. with high productivity requirements). In this paper, the weaknesses of the zone discrimination technique are first described and the areas where IWEX should bring improvements are highlighted. The IWEX technology is then described and an IWEX technology qualification route, matching both expectations of an AUT solutions provider and an O&G Operating company, is proposed. The results of the qualification tests performed so far (including tests on defective welds) are detailed and the technology readiness level is discussed. Recommendations for next qualification and operational steps are given.