Surface Chemistry Improvement on 316L Stainless Steel Weld Zones Using a Gelled Citric Acid-Based Passivation Agent

By Daryl L. Roll & Brent J. Ekstrand

Materials Passivation Stainless Steal Welding

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Abstract

This article examines a studya to determine the efficacy of a gel-based citric acid chelant passivation agent on welds and heat-affected zones. Questions regarding this type of passivation arise from data developed in experiments using commercially available citric acid solutions, which demonstrate that elevated temperatures are necessary for adequate passivation of weld areas to occur when citric acid is the primary passivation agent. Citric acid gel passivation processes use ambient temperatures for practical reasons (such as the tendency for the gel to liquefy at elevated temperatures). As elevated temperatures are not seen in the citric acid gel-based processes, some in the pharmaceutical industry question the efficacy of these citric acid gel-based passivation procedures, as the process temperatures seen conflict with the data developed from citric acid solution experiments, which indicate that elevated temperatures are necessary. In this study, we compared the original weld surface chemistry to the passivated weld surface chemistry after treatment with a gelled citric acid-based passivation agent for 2 and 4 hours as well as to the passivated weld surface chemistry obtained after treatment with a standard solution-based nitric acid treatment.

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