Abstract
The fatigue life of 40Cr steel (SAE 5140) in drilling mud and inhibited mud was studied with a self-made, rotating bending corrosion fatigue testing apparatus. A significant improvement was found in the inhibited drilling fluids. As expected, 40Cr steel was susceptible to rapid failure through H embrittlement in drilling muds containing H2S, but chemical control with corrosion inhibitors resulted in a desirable improvement in corrosion fatigue life. Fractographic studies by scanning electron microscopy showed that the toughness of 40Cr was increased by the addition of corrosion inhibitors. In H2S-free drilling mud, the fatigue life increased almost 400% after adding corrosion inhibitors and an O2 scavenger. The mechanism of corrosion inhibition on pure iron and 40Cr has been studied by measuring polarization curves and hydrogen permeation rates.
