Internal pipeline corrosion can be a major risk factor for pipeline operations. To facilitate the monitoring
of Shallow Internal Corrosion (SIC), an In-Line Inspection (ILI) tool based on Eddy Current (EC)
technology has been developed.
Several cases exist where the prevalent growth of internal metal loss corrosion is the major risk for
pipeline operation. One important example is Top of the Line Corrosion (TLC) in wet gas pipelines due
to high water condensation rate. Heavy wall pipelines, which are common in offshore applications, are
often used to allow a specified maximum corrosion growth rate over the life time of the pipelines. A
good approximation even of marginal corrosion growth rates to monitor the degradation process is
thereby required. This estimation can be subsequently used to predict pressure that causes failures
and shorten pipeline lifetimes in the context of limited state design guidelines.
The presented EC technique gives a depth measurement of metal loss defects in terms of absolute
figures that complements relative wall loss measurements of Magnetic Flux Leakage (MFL) tools. By
inspection of heavy wall pipelines in offshore applications, SIC tool measurement results can
outperform MFL depth sizing of shallow internal corrosion, or likewise assist MFL defect identification or
depth sizing e.g. by increased distinction of individual pits in dense clusters due to its high lateral
resolution of defect surface measurement.
Key Words: Top of line corrosion, eddy current technology, magnetic flux leakage, wet gas pipeline