Failure analysis on synergistic effect of erosion and corrosion on failed fittings in specialty chemical plant. Part I: Elbows

Abstract

Elbow is widely considered as a vulnerable part in the whole steam pipelines due to the special geometry and complex flow property. In this study, unexpected leakages took place on two elbows utilized in the same steam system of a specialty chemical plant. However, these two failed elbows exhibited completely different morphologies, which indicated that they might have undergone different failure processes. A series of macroscopic and microscopic analysis methods were conducted to identify and differentiate the root causes of the failures. Totally four corrosion mechanisms were involved and the key factor that led to the different morphologies of these two elbows was discussed in detail. The results show that the failure of one elbow resulted from the synergistic effect of uniform corrosion and under‐deposit corrosion, while the failure of the other elbow was caused by the combined effect of pitting corrosion and erosion. Some effective countermeasures were proposed to avoid the similar failure occurring again.