51313-02078-Hydrogen Embrittlement in Titanium and Superferritic Stainless Steel Steam Surface Condenser Tubing

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Product Number: 51313-02078-SG

ISBN: 02078 2013 CP

Author: Dennis Schumerth

Publication Date: 2013

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Abstract
Embrittlement or hydriding of titanium and superferritic stainless steel steam surface condenser tubing can occur when solubility limits of nascent hydrogen are exceeded. The results of such an excursion can in the case of titanium induce the formation of brittle hydrides or in the case of superferritic stainless steels which typically do not form stable hydrides result in reduced ductility and subsequent fracture attack. In either case both corrosion events can ultimately lead to a loss of structural integrity of the material. Additional contributing factors may include elevated temperature pH extremes and other parameter anomalies. However since the typical powerplant steam surface condenser tube/tubesheet interface is continually passivated by circulating water (CIRH20) and the operating temperatures remain relatively low the solubility limit of hydrogen is rarely threatened. Indeed the mere existence of hydrogen embrittlement in a surface condenser environment has been infrequent reportedly occurring only several times over the past 40+ years of powerplant condenser tube service. Conversely industries such as the CPI (chemical process industry) which can expose the heat exchanger to elevated temperatures pH extremes and high levels of hydrogen charging without the benefit of passivation have reported hydrogen embrittlement damage.

Notwithstanding the infrequency of this form of corrosion in powerplant condenser service recently identified activity has surfaced that warrants further investigation of this phenomenon related to both stainless steel & titanium tubing. As a result of these recent events the paper will identify and research several case studies associated with hydrogen embrittlement. An in-depth investigation of each will provide a practical benchmark for future lessons learned operating experience. Since there appears to be a common denominator to most if not all of the reported hydrogen damage the paper will attempt to clear the air in terms of apparent confusion surrounding merely the innocuous hydrogen charging of certain materials vs. actual embrittlement damage.