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Evaluation Of The Suitability Of As Bent Super Duplex Stainless Steel UNS-S32750 Tubing For Refinery Sour Services

Product Number: 51321-16850-SG
Author: Yong-Joo Kim; Karen Picker
Publication Date: 2021
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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 bothregular duplex and super duplex stainless steels without the need to perform stress relieve heattreatment that could be detrimental to the material performance if not performed properly. While theserecommendations are generalized for refinery services, they are based on conclusions drawn fromstrain calculations and possible resulting residual stresses found when bending 22% chrome duplexstainless steels or, in the case of 25% chrome duplex stainless steels, the recommendations are basedon corrosion data for pitting resistance and chloride stress corrosion cracking testing. However, existingdata does not address the suitability of either alloy for sour services in the refining industry in the asbentcondition.
This study evaluates the suitability of as-bent super duplex stainless steel UNS-S32750 tubing forrefinery sour services by presenting data about the impact of work hardening by u-bending andevaluating these results against current hardness limits per NACE standard MR0103 for super duplex stainless steels. Several seamless .75" diameter super duplex tub 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 aswell as corrosion testing per ASTM G48 method A and NACE TM0177 were recorded and will be presented in order to demionstrate the material's performance despite residual stresses.

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 bothregular duplex and super duplex stainless steels without the need to perform stress relieve heattreatment that could be detrimental to the material performance if not performed properly. While theserecommendations are generalized for refinery services, they are based on conclusions drawn fromstrain calculations and possible resulting residual stresses found when bending 22% chrome duplexstainless steels or, in the case of 25% chrome duplex stainless steels, the recommendations are basedon corrosion data for pitting resistance and chloride stress corrosion cracking testing. However, existingdata does not address the suitability of either alloy for sour services in the refining industry in the asbentcondition.
This study evaluates the suitability of as-bent super duplex stainless steel UNS-S32750 tubing forrefinery sour services by presenting data about the impact of work hardening by u-bending andevaluating these results against current hardness limits per NACE standard MR0103 for super duplex stainless steels. Several seamless .75" diameter super duplex tub 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 aswell as corrosion testing per ASTM G48 method A and NACE TM0177 were recorded and will be presented in order to demionstrate the material's performance despite residual stresses.

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