Corrosive wear failure analysis in a natural gas pipeline

Corrosive wear failure in gas pipelines can potentially cause substantial human and economic losses. This work presents the failure analysis of an API 5L X52 steel grade section of a pipeline used in an underground transportation, which is located next to a natural gas extraction plant. A T-shape section of this line, failed by perforation under unknown circumstances. Chemical and mechanical characterization of the steel pipe section was performed. Optical microscopy, electron microscopy and energy disperse spectroscopy were performed near the failure origin site in order to identify the composition of the corrosion products. Based on the microscopic and visual analyses, a corrosive wear sequence was identified as follows: the scales adhered to the inner wall of the pipe were easily loosened and detached in certain sites due to the turbulent gas stream. This resulted in the exposure of the fresh steel surface to the highly corrosive environment that prevails inside the pipeline. The unprotected areas acted as preferential sites for pitting corrosion of the steel until the final failure of the pipe was produced.