Medium Range Guided Wave Inspection of the Triple Point in Lined Pipes by EMATs

摘要

The advent of mechanically lined pipes represented a new turning point for the oil industry in terms of performance and cost for fluids transportation. However, the implementation of this technology demanded the development of new improvements such as reel-lay techniques and joining methods to ensure the reliable and safe operation of the pipeline. It also posed new challenges for inspection and flaw assessment by non-destructive testing (NDT) methods, especially of the joining region formed at the pipe termination by the interface between liner, steel substrate and the weld overlay used for sealing of the assembly. This region, commonly referred to as the triple point, is formed by a dissimilar weld joint with high metallurgical complexity. As a consequence, many conventional NDT techniques have failed in providing trustworthy indications of the defects. Thus, in order to find an alternative for NDT inspection to fulfil the international security standards, this paper reports the use of guided waves generated by an electromagnetic acoustic transducer (EMAT) to interrogate the integrity of the triple point. The present research focused on the performance evaluation of shear horizontal waves to interrogate a test piece simulating a lined pipe structure which had artificially inserted discontinuities at the triple point region. The findings documented in this paper were achieved by the means of finite element analysis (FEA) and experimental validation of a transducer design and wave propagation in the triple point area.