Common metal materials affected
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Common metal materials affected include those 300 series SS, which are all highly sensitive. Duplex stainless steel is more corrosion-resistant. Nickel-based alloys are highly corrosion-resistant. Main factors affecting corrosion: 1. Form and concentration of chlorides, pH, temperature, stress, presence and concentration of oxygen, alloy composition. 2. Affected equipment or apparatus: All 300 series SS pipes and pressure vessel components are sensitive to Cl-SCC. Water-containing and low-temperature areas in units such as atmospheric and vacuum distillation, FCC, coking, and hydrogenation, including: tower top systems, drain points, and hydrogenation reaction effluent systems with temperatures below 200°C ； The surface of the equipment pipelines beneath the damp insulating layer ； Measuring the resistance of materials to chloride corrosion: Pitting resistance index PREN; Critical pitting temperature CPT: Testing method: ASTM G48. Critical crevice corrosion temperature CCT: Testing method: ASTM G48. Resistance to stress corrosion: Carbon steel and low-alloy steel have low sensitivity to CL-SCC; order of sensitivity from high to low: 300-series austenitic stainless steels—duplex stainless steels—Ni-based alloys
Some 300 series stainless steels are highly sensitive to chloride stress corrosion cracking (Cl-SCC), whereas duplex stainless steels and nickel-based alloys exhibit better corrosion resistance. Factors affecting corrosion include the form and concentration of chlorides, pH value, temperature, stress, the presence and concentration of oxygen, as well as alloy composition. The affected devices or equipment are usually 300-series stainless steel pipes and pressure vessels in low-temperature, wet areas, such as tower top systems, drain outlets, hydrogenation reaction effluent systems at temperatures below 200°C, as well as the surfaces of equipment pipelines beneath damp insulation layers. The indicators used to measure a material’s resistance to chlorine corrosion include the pitting resistance index PREN, the critical pitting temperature CPT, and the critical crevice corrosion temperature CCT; the testing method is ASTM G48. In terms of stress corrosion resistance, carbon steel and low-alloy steel are less sensitive to Cl-SCC, while the order from highest to lowest sensitivity is: 300 series austenitic stainless steels, duplex stainless steels, and nickel-based alloys. .