technical insight
processes such as welding, cutting, and forming. In this case, additional stresses would be induced by the operational load of the heated water. • A corrosive environment - Chloride ions are a common culprit, and their effect can be exacerbated in acidic water or at elevated temperatures. Temperatures above 50°C significantly increase the risk of SCC in Grade 316. Given that the water in this application is expected to be chloride-rich, and the vessel is exposed to continuous tensile stress and heat, all three conditions for SCC are likely to be met. While the pitting resistance of Grade 316 is suitable, its vulnerability to SCC makes it less than ideal for this specific use. Failure due to SCC can be unpredictable, irreversible, and costly, with consequences ranging from operational downtime to serious safety risks. A Viable Alternative: Ferritic Grade 444 An alternative that warrants consideration is Grade 444, a ferritic stainless steel that shares several corrosion- resistant features with Grade 316 but offers key advantages in this application. Grade 444 contains approximately 18% chromium and 1.8 to 2.5% molybdenum, matching Grade 316 in general corrosion protection and pitting resistance. In fact, thanks to its chemical composition, Grade 444 offers a higher Pitting Resistance Equivalent Number (PReN) than Grade 316, providing superior performance in chloride-bearing environments. Crucially, being a ferritic steel, Grade 444 is immune to SCC, eliminating one of the major risks posed by the use of Austenitics in high-chloride, high-temperature environments. In addition, it does not contain nickel, which not only reduces the likelihood of SCC but also lowers material costs, making it a more economical and stable option in price-sensitive applications. From a fabrication standpoint, 2.5 mm material thickness is suitable for use with Ferritics and falls within the weldable gauge range, simplifying construction and assembly.
The Hidden Threat of Stress Corrosion Cracking SCC is an insidious form of corrosion that can cause sudden, catastrophic failure without significant warning. It occurs when three key factors are present simultaneously:• • A susceptible material - Austenitic stainless steels, especially those containing between 5% and 20% nickel (such as Grade 316), are inherently prone to SCC.• Unnecessary costs, associated with removing, re- cutting, or treating affected products by taking proactive measures immediately after cutting. • Tensile stress - This can be introduced through residual stresses in flat-rolled products, or through fabrication
18
Issue 2 – 2025
Made with FlippingBook - professional solution for displaying marketing and sales documents online