Mitigation of Sulfide Stress Cracking in Downhole P110 Components via Low Plasticity Burnishing

Sulfide stress corrosion cracking (SSC) along with hydrogen embrittlement (HE) prevents the use of less expensive carbon steel alloys in the recovery of fossil fuels in H₂S containing ‘sour’ service environments that are commonly seen in deep well fossil fuel recovery efforts. High magnitude tensile stresses are generated from the internal fit-up of down hole tubular components. When subject to service loads the stresses are increased further providing the high tensile stresses necessary for SSC initiation. Because these alloys are not suited for sour service environments, the current solution is to use or develop much more expensive alloys with increased corrosion resistance.

Introduction of stable, high magnitude compressive residual stresses into less expensive carbon steel alloys can alleviate the tensile stresses and dramatically reduce SSC while also improving fatigue strength. This would allow less expensive alloys to be used in sour environments. Low plasticity burnishing (LPB) is a proven reproducible process of producing deep, high magnitude compressive residual stresses in complex geometric components without altering the geometry, design or chemistry.             The LPB process can be employed to treat components to provide a substantial increase in service life through SSC mitigation. The benefits of LPB have been evaluated on full size specimens of uni-axial hoop stress loaded coupling stock as well as NACE A tensile and C-ring specimens manufactured from quench and tempered API P110 grade. Specimens were exposed to NACE A solution per NACE TM0177 in both the LPB treated and untreated condition. The time to crack initiation was documented along with the increase in life resulting from LPB treatment. LPB was successful in completely mitigating SSC in each test; LPB specimens greatly exceeded the 720-hour exposure time defined in NACE TM0177 at applied stresses of up to 85% of SMYS. LPB processing of down hole tubulars is an economical means of SSC mitigation providing an increase in productivity and greatly reducing risk of component failure in sour environments.