Hazard analysis of copper metal pollution on surface of steel pipe
ZENG Bing 1,LIU Rongfeng 2,YUAN Jie 2,LIANG Xiaodong 1
1. Chongqing Machinery Industry Physical and Chemical Measures Center, Chongqing 400020, China;
2. Petrochina Southwest Oil & Gas Field Materials Branch, Chengdu 610017, China
Abstract:The unqualified hardness was observed during the field test of base metal of steel pipe for natural gas transmission. Through macroscopic observation, scanning electron microscopy (SEM), metallographic analysis, and microhardness test, it was found that there was copper metal pollution on the surface of steel pipe. Copper metal pollution was essentially belonged to heterometallic inclusion, which was caused by improper smelting operation, incomplete melting of alloy material or falling of foreign metal into gating system. Because the structure and properties of such dissimilar metal inclusions were different from the matrix, there were obvious boundaries with the matrix structure, which would split the continuity of the matrix and reduce the mechanical properties of the material. It would become the stress concentration point in the process of stress, and consequently reduce the service life of the steel pipe.