Pressure Vessel from a High-Pressure Vibratory Autoclave Burst by Explosion

A forged pressure vessel made from high temperature austenitic steel X8Cr-Ni-MoVNb 16 13 K (DIN 1.4988) failed. The widest part of the burst had fine cracks on the internal wall running longitudinally. When the internal wall was cleaned, numerous even finer cracks were exposed. On the fracture surfaces in this region an irregularly formed zone was visible in the direction of the internal wall and a fibrous oriented fracture zone towards the external wall. The fracture was typical of stress-corrosion cracking in austenitic steels. Vanadium trichloride was present and tensile stresses were of necessity set up by the internal pressure. Stress-corrosion cracking does not occur if one of the basic requirements is lacking. Because the chloride agent and tensile stresses were inevitably present, the only possible way to prevent future reoccurrence is to forge the entire pressure vessel from a material immune to stress-corrosion cracking or to use interchangeable linings of such a material. A nickel alloy could be considered.