Under Deposit Corrosion Failure of a Compressor after Stage Cooler at an NGL Plant—A Case Study

Premature tube leaks were encountered at a compressor after-stage cooler operating at 100-130°F after three years in service due to under-deposit corrosion.  The damage encountered was confirmed by visual, metallurgical examination and chemical analysis of corrosion products.  The premature failure resulted from condensation of water containing dissolved carbon dioxide, hydrogen sulfide and possibly oxygen at the center bottom portion of the tube.  Moreover, the presence of pitting in the liquid phase area indicates that the injection of the oil soluble water dispersible corrosion inhibitor was not effective.  Chemical analysis of the deposits revealed that they comprised mainly of iron sulfide products.  Metallurgical examination revealed no manufacturing defects.  Mitigation measures of similar failures are discussed in terms of design and inhibition.

Keywords:  fin fan, corrosion inhibitor, hydrogen sulfide, failure analysis, Pourbaix diagram, mitigation