• Carbon Steel, Low Alloy Steels• 0.05-1% C• <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

• 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