Stress corrosion cracking, or SCC, causes the relatively rapid failure of components due to either trans- or inter-granular cracking occurring in susceptible alloy-environment combinations when static tensile stresses are present that exceed some threshold for SCC initiation. Stress corrosion cracking is a complex phenomenon not as yet fully understood. Mechanisms proposed include rapid crevice corrosion along grain boundaries and the wedging open of the cracks by oxide formation. SCC is more common in high strength materials, such as high strength aluminum aircraft structural alloys and steels. Susceptibility is affected by alloy segregation, as in the sensitized heat-affected zones of 304 stainless steel welds.
Conventional approaches to SCC mitigation are:
- substitution of a less susceptible alloy
- isolation of the alloy surface from the aggressive environment with plating or coatings
Unfortunately, stress corrosion cracking can be induced in environments like common seawater or very low concentrations of dissolved oxygen and chlorine, making isolation and control of these environments extremely difficult. Substitution of an “un-crackable” alloy is expensive, and projecting long-term performance with accelerated laboratory testing is difficult. Often the new alloy is again found to be cracked in service, and the substitution cycle is repeated. Mechanical suppression of SCC, by introducing a deep layer of surface compression to eliminate tensile stresses in contact with the environment, is the one approach which eliminates stress corrosion cracking at minimal cost.
LPB® has been demonstrated to completely eliminate stress corrosion cracking in high strength steels like 300M and 4340, structural aluminum alloys including 7075-T6, and 304 stainless steel welds with or without sensitization. By introducing a deep layer of stable high compression, the surface of the susceptible alloy that is in contact with the aggressive environment remains entirely in compression, well below the tensile threshold required for SCC. As a result, stress corrosion cracking is completely mitigated. LPB® has been repeatedly demonstrated to hinder SCC and its cyclic variant corrosion fatigue. General corrosion continues, but the risk of catastrophic failure caused by SCC driven cracks can be completely eliminated.