Stress corrosion cracking (SCC) occurs when a susceptible material is exposed to a corrosive environment and tensile stresses above a given threshold. Effective treatment of stress corrosion cracking requires one of these three contributors be alleviated before crack propagation begins and catastrophic failure ensues. The ability of Ultrasonic Impact Treatment to enhance surface quality while removing tensile stresses and fortifying susceptible metals on a granular level has made it the preferred method of treatment across various industries vulnerable to stress corrosion cracking.
Surface Quality and Stress Corrosion Cracking
One of the most troubling issues with stress corrosion cracking is that it can proceed unnoticed to the point of failure. The chemical environment that leads to SCC is often only mildly corrosive to the material otherwise. This commonly results in no visual symptoms of fatigue occurring while the metal is approaching the point of failure.
Understanding and recognizing chemicals that react corrosively when introduced to specific metals is key to preventing stress corrosion cracking prior to development. If the component is already in place and surface corrosion has begun, or is suspected to have begun and replacement is cost prohibitive (which is often the case), it’s vital to remove corrosion and restore the surface to its optimal condition.
Ultrasonic Impact Technology harnesses the power of ultrasonic energy to improve metal surface quality more effectively than past methods, such as grinding or peening, but ultrasonic treatment also improves corrosion resistance in susceptible metals, thereby extending their useable life greatly.
Metals Prone to Stress Corrosion Cracking
Stress corrosion cracking is more common in alloys than pure metals, but can occur in a variety of materials, including:
- Austenitic Stainless Steels & Aluminum Alloys
- Mild Steel
- Copper Alloys
A seemingly obvious solution is to replace the susceptible metal with a more SCC-resistant alloy. However, this method involves great cost and extensive time to achieve, and its success rate has proven marginal.
Ultrasonic Impact Technology on the other hand, quickly and effectively improves surface quality and alleviate tensile stresses in a multitude of vulnerable metals without the need or drawbacks of component replacement. This has led to its emergence as a preferred option in numerous industries.
Digging Deep to Prevent Stress Corrosion Cracking
Detrimental tensile stresses at or near a metal’s surface bring about the onset of miniscule cracks that propagate and spread to a critical level. Conventional methods, such as needle peening and cavitation peening were initially utilized to prevent stress corrosion cracking due to their ability to deliver compressive residual stresses into susceptible, fatigued metals. However, the depth to which tensile stresses are relieved via these methods, are relatively shallow and their application causes a considerable amount of cold working, which actually increases the risk of SCC.
By driving tensile stresses to a depth of 12mm (far beyond the capabilities of conventional peening methods) and introducing beneficial compressive stresses near the surface, Ultrasonic Impact Treatment drastically reduces the dangers inherent in tensile stresses and combats another component of stress corrosion cracking.
Preventing Stress Corrosion Cracking on All Levels
Stress corrosion cracking requires the “combination” of a vulnerable metal, tensile stresses, and a corrosive environment. Therefore, effective stress corrosion cracking treatment requires only 1 of the 3 ingredients be removed. As Ultrasonic Impact Treatment has been proven to improve the intergranular composition of susceptible metals, remove tensile stresses from the surface, and effectively restore surface quality; it provides lasting protection against the devastating financial, operational and life threatening impact of stress corrosion cracking.