Effect of ammonium bisulphite and chloride on the pitting and stress corrosion cracking resistance of super duplex stainless steel pipes under combined internal pressure and axial tension

The oil and gas industry, like many others is constantly looking at ways to keep
costs of well completion down based on cost effective solutions that do not
compromise safety. This combined with the desire to develop new oil and gas
fields that are very challenging in terms of operating pressures, temperatures, and corrosivity of the environment may result in the need to utilize materials closer to their mechanical loading limit in a corrosive environment. Modern alloys of high strength and corrosion resistance are often more susceptible to cracking. With a move toward higher production pressures, and temperature, production tubing for downhole use may become a limiting factor for exploration of future oil and gas wells. Typically, materials and corrosion test samples are usually set up to examine material behavior under single mode loading (e.g., tensile sample) and not combined loads experienced by a production tubing in a well completion. A novel test set-up was developed to simulate stresses in a production tubing string with the potential to define combined load conditions in a corrosive environment once mechanical load limit is determined. In small scale tests cold worked super duplex stainless steel mini pipes were subjected to combined load, that is, axial stress simulating weight of the tubing string and internal pressure (from the reservoir). The mechanical load limit (failure envelope) was determined in the absence of a corrosive environment thereafter the mini pipes were subjected to load conditions below mechanical limit in a corrosive environment to determine load and environment conditions that would not lead to crack initiation. The potential pipe load limit when in the corrosive environment is below the corrosion test load condition to avoid crack initiation and failure.