Some Observations on the Role of Inclusions in the Hydrogen Induced Blister Cracking of Linepipe Steels in Sulfide Environments

Abstract

A scanning electron microscope investigation has been conducted on selected line-pipe steels that had been exposed to the hydrogen sulfide in the British Petroleum test. The results show that: (1) Hydrogen induced blister cracking initiates at elongated manganese sulfide inclusions confirming the findings of other workers. In addition, glassy silicate inclusions or massive columbium carbonitride precipitates can also act as initiation sites. (2) Hydrogen induced blister cracking is dependent on the hydrogen input fugacity of the corrosive environment. Qualitative experiments indicate a threshold fugacity below which no cracking will initiate, between 104 and 105 atmospheres. (3) Propagation of hydrogen induced blister cracking occurs by hydrogen assisted fracture of the matrix surrounding the initiating inclusion. (4) Step wise hydrogen induced blister crack propagation occurs by hydrogen assisted fracture between interconnecting planes.