08676 SCC Initiation in Alloy 600 Heat Affected Zones Exposed to High Temperature Water

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Product Number: 51300-08676-SG

ISBN: 08676 2008 CP

Author: Edward Richey, David Morton, and Robert Etien

Publication Date: 2008

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Studies have shown that grain boundary chromium carbides improve the stress corrosion cracking (SCC) resistance of nickel based alloys exposed to high temperature, high purity water. However, thermal cycles from welding can significantly alter the microstructure of the base material near the fusion line. In particular, the heat of welding can solutionize grain boundary carbides and produce locally high residual stresses and strains, reducing the SCC resistance of the Alloy 600 type material in the heat affected zone (HAZ). Testing has shown that the SCC growth rate in Alloy 600 heat affected zone specimens can be ~ 30x faster than observed in the Alloy 600 base material under identical testing conditions due to fewer intergranular chromium rich carbides and increased plastic strain in the HAZ.1, 2 Stress corrosion crack initiation tests were conducted on Alloy 600 HAZ specimens at 360°C in hydrogenated, deaerated water to determine if these microstructural differences significantly affect the SCC initiation resistance of Alloy 600 heat affected zones compared to the Alloy 600 base material. Alloy 600 to EN82H to Alloy 600 HAZ specimens were fabricated from an Alloy 600 to Alloy 600 narrow groove weld with EN82H filler metal.