Hydrogen Embrittlement of ASTM A320 L7 L43 Grade Carbon Alloy Steel Bolts in Subsea Environments

摘要

This paper reports an approach towards studying the susceptibility of materials to hydrogen embrittlement of several yield strength levels of ASTM(1)A320L7 & L43 grade carbon alloy material used for bolting1.The test method used is based on ASTM E1820 using pre-cracked compact tension(CT)specimens in a seawater environment and under cathodic protection2.The procedure has been to monitor the crack growth and the crack growth rate(CGR)at various constant stress intensity and at varying cathodic protection potentials.In this way these two parameters can be seen as representative of the susceptibility to hydrogen embrittlement cracking of the materials at the specific stress intensity levels and as a function of the varying CP levels.The results indicate the strong effect that both stress intensity factor and applied potential have on crack growth rates in environment and on the resulting susceptibility of the material to embrittlement.On the practical operational level,the results also highlight the importance of actively monitoring and controlling cathodic protection potential levels as a means of increasing the allowable margin of error of the intersection between material quality,design factors and the effect of the challenging environments of Oil & Gas subsea drilling and production operations.