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Hydrogen in Steels: A Critical Review and Recommended Practices

A summary of hydrogen bakeout history to remove hydrogen from a component. Existing recommendations regarding hydrogen bakeout in codes and standards. Results from an industry survey of energy producers. Proposed methodology for selecting bakeout parameters.

 

 

Product Number: 51317--9548-SG
ISBN: 9548 2017 CP
Author: Mark Sadowski
Publication Date: 2017
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Hydrogen the smallest element on the periodic table can produce extensive damage to welded steel structures if its deleterious effects are not mitigated. In steels hydrogen damage may manifest as hydrogen induced cracking blistering stress oriented hydrogen cracking welding cracking etc. While the exact mechanisms of hydrogen damage are not well understood its effects are pronounced and often a contributing factor in cracking or failure of the component. Hydrogen can be introduced to the component during fabrication welding operational service and welded repairs. Repair welds are often the most susceptible to hydrogen-related damage due to pre-existing hydrogen in the component from service.To reduce the ruinous effects of hydrogen during welding a common industry practice is to drive as much hydrogen as possible out of steel prior to welding. This process is commonly called “hydrogen bakeout”. There is currently no industry-wide guideline/code governing this procedure. Instead each user currently has to determine a workable procedure from experience or by trial and error – a very expensive approach. The current authors have compiled and analysed data on hydrogen bakeout practices from various industry sources and are currently preparing a guide towards the selection of appropriate hydrogen bakeout time and temperature.This communication will review hydrogen-related damage mechanisms report the result of a recent industry survey on hydrogen bakeout practices present a simple model for selecting hydrogen bakeout parameters and provide guidance for reducing the harmful effect of occluded hydrogen on welded repairs through thermal treatments.

Keywords: Hydrogen bakeout, diffusible hydrogen concentration, delayed cracking, hydrogen embrittlement

Hydrogen the smallest element on the periodic table can produce extensive damage to welded steel structures if its deleterious effects are not mitigated. In steels hydrogen damage may manifest as hydrogen induced cracking blistering stress oriented hydrogen cracking welding cracking etc. While the exact mechanisms of hydrogen damage are not well understood its effects are pronounced and often a contributing factor in cracking or failure of the component. Hydrogen can be introduced to the component during fabrication welding operational service and welded repairs. Repair welds are often the most susceptible to hydrogen-related damage due to pre-existing hydrogen in the component from service.To reduce the ruinous effects of hydrogen during welding a common industry practice is to drive as much hydrogen as possible out of steel prior to welding. This process is commonly called “hydrogen bakeout”. There is currently no industry-wide guideline/code governing this procedure. Instead each user currently has to determine a workable procedure from experience or by trial and error – a very expensive approach. The current authors have compiled and analysed data on hydrogen bakeout practices from various industry sources and are currently preparing a guide towards the selection of appropriate hydrogen bakeout time and temperature.This communication will review hydrogen-related damage mechanisms report the result of a recent industry survey on hydrogen bakeout practices present a simple model for selecting hydrogen bakeout parameters and provide guidance for reducing the harmful effect of occluded hydrogen on welded repairs through thermal treatments.

Keywords: Hydrogen bakeout, diffusible hydrogen concentration, delayed cracking, hydrogen embrittlement

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