Feeler Pig: a Simple Way to Detect and Size Internal Corrosion

摘要

Submarine pipeline inspection traditionally employs the same technologies used for onshore pipelines. One of such technologies is the instrumented pig, which usually runs under the same parameters and procedures as those used for onshore inspections. However, it is very common to find submarine pipelines with many kinds of obstacles that may prevent the use of conventional instrumented pigs, like magnetic flux leakage (MFL) and ultrasonic pigs. The relevant factors that make the inspection difficult are the different diameters along the pipeline, small radius bends, equipment installed in the pipeline (such as manifolds and valves), increased wall thickness, multiphase fluids, etc.rnCurrently available techniques to inspect these pipelines have limitations. For ultrasonic pigs, the need of a homogeneous fluid, with good acoustic properties, to serve as sonic wave coupling is a relevant factor. On crude oil pipelines, this homogeneous fluid is not always available, as these lines carry multi-phase products. For magnetic pigs, it may not be possible to fully magnetize the heavy wall thickness pipe needed in offshore applications for structural reasons.rnFocusing on this context, a new tool was developed to detect and size reductions of wall thickness associated to internal corrosion. This tool, called Feeler Pig, was designed to be able to overcome diverse limitations that conventional pigs have. The Feeler Pig performs the direct dimensional measurement of pipeline internal corrosion by contact, with no practical limit of wall thickness to inspect and no need of homogeneous fluid during the inspection job. The system has been tested in field and had the performance compared to a standard ultrasonic instrumented pig. Excellent defectrncorrelation was observed between the Ultrasonic and Feeler Pig data, not only in length and width but also in depths of internal corrosion. With this high confidence, other prototypes of Feeler Pigs were developed. One of them, named Feeler Snake Pig, was built with the installation of feeler nails into a flexible polyurethane support yielding tool with ultra high tolerance to geometric restrictions and is able to navigate through sharp bends and geometric accessories. The excellent results of the prototype and its robustness against line geometric restrictions immediately open a wide range of opportunities for the Feeler Snake Pig technology in field applications.