Stress corrosion cracking of a high strength steel in organic salt drilling fluids

Abstract

Abstract Two round bar tensile samples (without notch and with notch) and two temperatures, namely 100 °C and 150 °C, have been used to observe the effect of notch and temperature on stress corrosion cracking in steel. The stress corrosion cracking sensitivity index of the tensile strength and elongation was calculated by means of data from a stress-strain curve. The fracture surface of the high strength steel was analyzed by scanning electron microscopy (SEM). In this way, the effect of notch and temperature on stress corrosion crack of the steel was determined. The results of a constant load tensile stress corrosion test show that at the same stress level and temperature, the stress corrosion cracking performance of an unnotched round bar tensile specimen was better than that of the notched specimen, and the unnotched steel had better corrosion resistance. Simultaneously, it was observed that the samples at 100 °C exhibited a lower stress corrosion cracking sensitivity index at the same stress level compared to the higher temperature (150 °C), which means that the steel showed a better corrosion resistance at a temperature of 100 °C. The fracture morphology analysis shows that the fracture surface of the unnotched round bar tensile samples had a dimple fracture, but the notched round bar tensile samples had a characteristic intergranular fracture due to the combined action of stress and the corrosive solution. Temperature increased the corrosion's velocity and the stress concentration in the notch causing an increase in dislocation after plastic deformation were the main reasons for the increase in stress corrosion sensitivity of the steel. It can be seen that these two factors, the temperature and the notch both increased the stress corrosion cracking sensitivity of the steel in organic salt drilling fluid, but the notch had a greater influence.