Susceptibility to Corrosion Fatigue of Type 4145 Steel in Drilling Muds

Drill pipe tool joints are subjected in service to moderately aggressive environments (a wide range of drilling muds) and to a combination of high-static and dynamic loads. Under such service conditions, the high-strength, low-alloy, quenched and tempered steels that are used to fabricate the joints are susceptible to various forms of environmental cracking, particularly to hydrogen embrittlement (HE) and corrosion fatigue. Compact tension specimens were used to examine the susceptibility of type 4145 (UNS G41450) steel to corrosion fatigue in a water-based drilling mud. Environmental variables investigated included potential, pH, temperature, and the presence of zinc- and copper-containing lubricants. These tests were supported by detailed electron fractography and hydrogen measurements. Under all environmental conditions, a good correlation was observed between the enhancement in corrosion fatigue crack growth rate (CGR) with respect to that in air and the steady-state hydrogen permeation current density (iH).