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Evaluation of the Potential for Liquid Metal Embrittlement of 304L Stainless Steel by Galvanized Fasteners in an Industrial Fire Scenario

Picture for Evaluation of the Potential for Liquid Metal Embrittlement of 304L Stainless Steel by Galvanized Fasteners in an Industrial Fire Scenario
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Transfer of Zn from hot-dipped and mechanically galvanized steel bolting to stainless steel by exposing a 304L stainless steel/Galvanized bolting assembly to temperatures in the range 205°C to 537°C for one hour to simulate an industrial fire scenario.

Product Number: 51317--9192-SG
ISBN: 9192 2017 CP
Author: Ramon Solo
Publication Date: 2017
Industry: Coatings and Linings
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Liquid Metal Embrittlement (LME) is a phenomenon that promotes a drastic loss of ductility in normally ductile materials in the presence of certain liquid metals. Zinc (Zn) is known to promote LME in austenitic stainless steels at temperatures above its melting point [752°F (400°C)]. Although LME of austenitic stainless steel (SS) is more likely when Zn is in the molten state occurrences of Zn induced LME of SS have been reported at temperatures below 752° F. Industry has adopted a number of practices to prevent LME of SS pressure-retaining equipment by reducing the probability of contact with Zn. However the use of mechanically galvanized low-alloy fasteners in SS flange joints is common. The potential risk for LME of 300-series SS flanges caused by galvanized fasteners during high temperature exposure (e.g. during an industrial fire scenario) has not been properly evaluated.This study examines the possibility of transfer of Zn from hot-dipped galvanized and mechanically galvanized steel bolting to stainless steel by exposing a 304L SS/Galvanized bolting assembly to temperatures in the range 400°F to 1000°F (537°C) for approximately one hour to simulate an industrial fire scenario. Exposed samples were examined using optical and scanning electron microscopy. SEM/EDS analysis shows evidence of Zn transfer to stainless steel surface beneath the fastener. However metallographic examination did not reveal any infiltration/diffusion of Zn into the SS matrix.

Key words: Galvanized Steel, Fasteners, Liquid Metal Embrittlement, Stainless Steel, Corrosion

 

Liquid Metal Embrittlement (LME) is a phenomenon that promotes a drastic loss of ductility in normally ductile materials in the presence of certain liquid metals. Zinc (Zn) is known to promote LME in austenitic stainless steels at temperatures above its melting point [752°F (400°C)]. Although LME of austenitic stainless steel (SS) is more likely when Zn is in the molten state occurrences of Zn induced LME of SS have been reported at temperatures below 752° F. Industry has adopted a number of practices to prevent LME of SS pressure-retaining equipment by reducing the probability of contact with Zn. However the use of mechanically galvanized low-alloy fasteners in SS flange joints is common. The potential risk for LME of 300-series SS flanges caused by galvanized fasteners during high temperature exposure (e.g. during an industrial fire scenario) has not been properly evaluated.This study examines the possibility of transfer of Zn from hot-dipped galvanized and mechanically galvanized steel bolting to stainless steel by exposing a 304L SS/Galvanized bolting assembly to temperatures in the range 400°F to 1000°F (537°C) for approximately one hour to simulate an industrial fire scenario. Exposed samples were examined using optical and scanning electron microscopy. SEM/EDS analysis shows evidence of Zn transfer to stainless steel surface beneath the fastener. However metallographic examination did not reveal any infiltration/diffusion of Zn into the SS matrix.

Key words: Galvanized Steel, Fasteners, Liquid Metal Embrittlement, Stainless Steel, Corrosion

 

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