How to Prevent Intergranular Corrosion and Stress Cracking in Stainless Steel Reactors in Strong Acid and Alkali Media?
Publish Time: 2025-11-13
Stainless steel reactors are core equipment in industries such as chemical, pharmaceutical, food, and new material synthesis, widely used due to their excellent corrosion resistance, high strength, and good processing performance. However, when handling harsh media such as strong acids or alkalis, stainless steel reactors still face two major failure risks: intergranular corrosion and stress corrosion cracking. These two forms of corrosion are often highly concealed and develop rapidly, potentially leading to equipment perforation, leakage, or even safety accidents.1. Causes and Control Strategies of Intergranular CorrosionIntergranular corrosion in stainless steel reactors mainly occurs when chromium-containing stainless steel remains within the sensitization temperature range of 450–850℃. At this temperature, carbon combines with chromium to form chromium carbide, which precipitates at the grain boundaries, resulting in chromium depletion in the vicinity of the grain boundaries and loss of passivation ability. When exposed to strong acids or chloride ion-containing environments, the chromium-depleted areas are preferentially corroded, forming "tunnel-like" damage along the grain boundaries. To avoid this problem, the primary measure is to select ultra-low carbon stainless steel with a carbon content ≤0.03%, greatly reducing the possibility of chromium carbide precipitation. Secondly, solution treatment should be performed after welding or heat treatment to redissolve the carbides and restore a uniform austenitic structure. In addition, adding stabilizing elements such as titanium or niobium can preferentially combine with carbon, protecting chromium from consumption.2. Mechanism and Countermeasures of Stress Corrosion CrackingStress corrosion cracking is the result of the combined effects of tensile stress, specific corrosive media, and material sensitivity. In strongly alkaline environments, austenitic stainless steel is prone to "alkali embrittlement"; in acidic or neutral media containing chloride ions, it is prone to "chlorine-induced stress corrosion cracking." Cracks usually initiate from surface defects or residual stress concentrations in the weld, propagating transgranularly or intergranularly, and are highly sudden. The core of prevention and control lies in eliminating or reducing tensile stress: reducing geometrical abrupt changes through optimized structural design, replacing fillet welds with full-penetration butt joints; implementing stress-relief annealing after welding; and, more importantly, selecting duplex stainless steel or high-nickel alloys, whose microstructure or composition has natural resistance to SCC. For stainless steel reactors that must use 316L stainless steel, strict control of chloride ion concentration and operating temperature in the medium is also crucial.3. Synergistic Protection of Surface Treatment and Operation ManagementEven with reasonable materials and structure, the rough inner surface of a stainless steel reactor can still become a corrosion initiation point. Therefore, the inner wall of the reactor is often electrolytically polished, which not only improves smoothness and reduces material buildup and microbial growth, but also enriches the surface chromium content, enhancing the stability of the passivation film. Simultaneously, strict process control procedures must be established during operation: avoiding sudden temperature changes that cause thermal stress, preventing dry burning leading to localized overheating and sensitization, regularly monitoring the pH value and impurity content of the medium, and strictly prohibiting the mixing of materials with different properties that could create an unexpected corrosive environment.In summary, the reliability of the stainless steel reactor under strong acid and alkali conditions relies on a comprehensive protection system encompassing "material selection, structural optimization, strict process control, and meticulous operation and maintenance." Through scientific material selection, meticulous manufacturing, and intelligent management, not only can the risks of intergranular corrosion and stress cracking be effectively avoided, but the equipment lifespan can also be significantly extended, ensuring production safety and product quality, and providing solid equipment support for high-end chemical processes.
