Stress corrosion cracking is the formation and growth of cracks in components that are subjected to tensile stress and a corrosive environment. SCC requires that three factors be present: a susceptible material or material condition, an aggressive chemical environment, and a sufficiently high tensile stress. SCC can have serious consequences in terms of economic losses and personnel injury or loss of life. Onset of rapid fracture from SCC can occur in almost all materials with exposure to specific corrosive environments.
The material-environment combinations that lead to SCC cannot always be predicted. Corrosion fatigue can accelerate damage accumulation processes, which leads to premature failure. Some common and not-so-common material-environment combinations for SCC that Quest Reliability has observed include:
- Caustic SCC of carbon steels, caused by caustic cleaning solutions
- Polythionic acid SCC in austenitic stainless steels in refinery hydrotreaters
- Chloride SCC in austenitic stainless steel pressure vessels and piping
- SCC in duplex stainless steels
- Chloride/sulphide pitting, SCC and corrosion fatigue of a stainless alloy 321 compensator after long service in a geothermal steam pipeline
- Carbonate / bicarbonate SCC of buried and coated carbon steel under cathodic protection
- Pitting, SCC and corrosion fatigue of aluminium alloy compressor blades near marine environments
Fitness-for-service assessment of SCC is complex, due to the broad spectrum of material-environment conditions that may lead to SCC. Moreover, the crack growth rate in a given material-environment combination is highly sensitive to electrochemical conditions such as potential and pH level.
Quest reliability performs Level 3 FFS engineering assessments for SCC, including probabilistic remaining life predictions. Typically, we also develop ancillary information needed to extend equipment life and optimize process parameters. These may include:
- Selection or development of standards for replacement materials selection that minimize the risk of corrosion and cracking
- Development of guidelines for welding and weld repair of standard and non-standard grades of material
- Recommendations for heat treatments for minimizing residual stress.
- Characterization of kinetics for continuing cracking
- Process control and process changes for cracking minimization
For further information about Stress Corrosion Cracking, please contact us.