Carbon Steel, Low Alloy Steels <2% other elements (Cu, Ni, Si, Cr) Low corrosion resistance Tanks, Pipes, Buried structure, Concrete, ship hulls, piers, offshore structures Passive in alkaline pH Coating, cathodic protection Subject to hydrogen cracking in petroleum indutry

Stainless Steel at least 10.5% Cr Classification Ferritic Austenitic Duplex Martensitic Precipitation Hardening

Ferritic Cr + Mo (sometimes) Cr stabilizes ferrite Susceptible to IGC Immune to Chloride SCC Used in thin wall tubes-heat exchanger tubes Example SS405, SS 409, SS 430 ( architectural, automobile trimming) Elevated temp applications

Austenitic Steel Cr + Ni Cr-rich passive layer Chloride attack causes pitting, crevice and SCC SS 304, SS 316, SS317 Can handle H2S containing environments Used in valves, pumps, fasteners, screens, Process vessels, piping, etc

Martensitic and Precipitation Hardening SS Duplex Cr-Mo Alloys with Austenitic stabilizers like Ni and N Mixture of Ferritic and Austenitic Steels Mo strengthens the passive layer formed by Cr. Martensitic and Precipitation Hardening SS Good mechanical strength Lower corrosion resistance Susceptible to HIC and SCC

Designing to Prevent Corrosion Design Philosophy Process Variables Corrosion Data New Materials and Equipment Design