Predicted and Actual Dig Outcome of Dry Gas Internal Corrosion Direct Assessment of Unpiggable Pipelines

摘要

Dry Gas Internal Corrosion Direct Assessment (DG-ICDA) specified in NACE SP0206-2006 was developed in an attempt to proactively prevent and predict locations susceptible to internal corrosion in natural gas pipelines normally transporting dry gas. The DG-ICDA inspection program is used for pipelines that are difficult or impossible to pig or inspect with inline inspection (ILI), as well as piggable pipelines, where it can be used as a supplement to ILI. This inspection program is suitable for natural gas pipelines that normally carry dry gas, but may suffer from infrequent short-term upsets of condensation of moisture as a result of a shift in process variables such as pressure and temperature. Research and industry experience have shown that predicting water accumulation points using water condensation is paramount to the success of DG-ICDA in unpiggable pipelines. As liquid water is necessary for internal corrosion to initiate, determining the existence of water in a pipeline would be vital to the success of any DG-ICDA inspection program. This paper illustrates how appropriate use of predictive flow models and pipeline inclination profiles, in conjunction with dew point analysis, improves the prediction of locations susceptible to internal corrosion. This paper also discuss methodologies that contribute to ensuring that the most susceptible locations for internal corrosion are accurately pinpointed and addressed. Several case studies from previous DG-ICDA digs are presented to compare the predicted and actual dig results.