Martensitic Stainless Steel Pressure Vessel Failure Due to Stress Corrosion Cracking
摘要
This work investigated a premature failure of a pressure vessel manufactured in ASTM A743 CA6NM martensitic stainless steel. The pressure vessel operated with a NaCl solution (165,000 ppm) in a CO2 atmosphere at a constant temperature and pressure of 90 °C and 60 MPa. Leak test, liquid penetrant examination, and magnetic particle tests were carried out to investigate the size and position of the cracks, as well as the extent of damage along the pressure vessel. Several techniques were employed to characterize the failure and the material, including optical microscopy, scanning electron microscopy, quantitative chemical analysis by optical emission spectroscopy, and Vickers hardness. The chemical composition was in accordance with the material's specifications. The results showed several branched intergranular cracks, typically associated with stress corrosion cracks. The cracks were more concentrated at the cylindrical wall close to the bottom of the equipment, the region that had presented the worse surface finish. The exposure of the material to the acidic NaCl solution resulted in the nucleation of a crack in the internal region. The surface finishing was poor at the bottom of the pressure vessel, the fluid was rich in Cl, and the pressure vessel had an internal pressure; the synergy of those parameters favored a rapid stress corrosion process.