Mechanism of Hydrogen Induced Cracking in Pipeline Steels

摘要

The metallurgical parameters controlling hydrogen induced cracking (HIC) in pipeline steels were investigated. Twenty-nine commercial linepipe and fittings steels were studied using small scale immersion tests in NACE solution and optical and scanning electron microscopy. The roles of nonmetallic inclusions, manganese segregation and microstructure are described and a method of predicting HIC susceptibility is developed. It is concluded that pipeline steels for sour gas/oil service should have a low sulfur content ( 0.002% for heavily sour conditions), effective nonmetallic inclusion shape control by REM or calcium treatement and low levels of manganese segregation (via the use of improved steel-making practices and a reduction in the bulk manganese content to the minimum possible level).