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Several grades of stainless steel are evaluated after 26 years of exposure in the marine atmosphere at Kure Beach, NC. The alloys evaluated include 1% Ni + 16% Mn, 5% Ni + Mn, 7 to 10% Ni, 12 to 13% Ni + Mo, 12Cr and 17Cr alloys. The test specimens are in the form of flat panels, with spot welds, arc weldments, and Erickson cup deformations.
An assessment is made of the degree of rust, rust stain, and pitting attack on the boldly exposed surface.
The materials exposed 25 m from the ocean have from 20% rust, 70% rust stain, (Type 316 stainless steel) to 100% rust (Type 410 stainless steel). Surface pitting is insignificant (<0.01 mm) on all material except Type 410 stainless steel, which has surface pits 0.06 mm in depth.
The materials exposed 250 m from the ocean have from 1% rust stain (Types 304 and 316 stainless steels) to 80% rust, 20% rust stain (Type 410 stainless steel), and surface pitting is insignificant.
The spot welded materials have a crevice area between the overlapped surfaces where significant pitting and intergranular corrosion occurs. The attack ranges between 0.08 to 0.17 mm in depth at the 25-m site, and between <0.01 to 0.10 mm in depth at the 250-m site. Spot weld failure caused by corrosion is found only on Type 430 stainless steel.
The arc welded materials show no evidence of weld failure. The weld and HAZ did have greater rust and rust stain cover than the panel surface.
The materials with Erickson cups show no evidence of stress corrosion failure. However, pitting is more severe in the stressed areas.
stainless steels, marine atmosphere, long term corrosion, spot weld, arc weld, Erickson cup, pitting, rust stain, intergranular corrosion
Senior research technologist, LaQue Center for Corrosion Technology, Inc., Wrightsville Beach, NC
Executive director, National Association of Corrosion Engineers, Houston, TX