Abstract
The effect on corrosion performance of duplex stainless steels after cold bending with and without heat treatment have been widely studied and documented within the refining industry and material producers. Current recommendations exists regarding the minimum bend radiuses allowed for both regular duplex and super duplex stainless steels without the need to perform stress relieve heat treatment that could be detrimental to the material performance if not performed properly. While these recommendations are generalized for refinery services, they are based on conclusions drawn from strain calculations and possible resulting residual stresses found when bending 22% chrome duplex stainless steels or, in the case of 25% chrome duplex stainless steels, the recommendations are based on corrosion data for pitting resistance and chloride stress corrosion cracking testing. However, existing data does not address the suitability of either alloy for sour services in the refining industry in the as-bent condition.
This study evaluates the suitability of as-bent super duplex stainless steel UNS-S32750 tubing for refinery sour services by presenting data about the impact of work hardening by u-bending and evaluating these results against current hardness limits per NACE standard MR0103 for super duplex stainless steels. Several seamless .75” diameter super duplex tube samples with two different wall thickness were u-bent to bend radius of 1.5, 2, 3, 4, and 5 times the tube diameter. Hardness data as well as corrosion testing per ASTM G48 method A and NACE TM0177 were recorded and will be presented in order to demonstrate the material’s performance despite residual stresses.
