A previously developed internal corrosion direct assessment methodology (ICDA) for gas transmission systems is described in terms of a four step process that is analogous the External Corrosion Direct Assessment (ECDA) approach. The ICDA method can be used to enhance the assessment of internal corrosion in pipelines and assist in verifying pipeline integrity. The ICDA method provides the greatest benefit for pipelines that cannot be in-line inspected since the process does not depend on access to the inside of the pipe. The method is applicable to gas transmission lines that normally carry dry gas but may suffer from short term upsets of wet gas or liquid water (or other electrolyte). The basis behind ICDA is that detailed examination of locations along a pipeline where an electrolyte such as water would first accumulate provides information about the remaining length of pipe. Validation efforts are underway to determine the level of confidence that can be expected for ICDA implementation. Sample field data is used to illustrate the application of ICDA, and the case where steady-state gas flow cannot be assumed is discussed.
Keywords: natural gas, pipeline, internal corrosion, direct assessment, inspection, integrity