Effects of Residual Stress on Stress-Corrosion Cracking of Non-Macnetic Drill Collars

Abstract

Abstract Non-magnetic drill collars (NMDC’s) are known to crack, especially when used in drilling fluids with a high concentration of chlorides. The cause is stress corrosion cracking driven by residual tensile stresses on the collar I.D. Residual stress measurements and subsequent stress corrosion tests show that generally chrome-manganese (Cr-Mn) austenitic stainless steel NMDC’s have greater residual hoop tensile stress on the I.D. than the material can tolerate in chloride bearing drilling fluids. These data are presented. A realistic solution is to specify controlled residual stresses for Cr-Mn collars, since Cr-Mn austenitic stainless steel is the most economical material for NMDC’s. A number of such NMDC’s are in service and their performance is briefly presented and discussed.