Overview of Hydrogen Bake-Outs
A Hydrogen Bake-out is an essential, yet oftentimes undervalued procedure in petroleum refining. Under certain conditions, atomic hydrogen can diffuse into steel equipment. Hydrogen Bake-outs are used to drive this hydrogen out of the steel, as trapped hydrogen can cause cracking in a weld or an entire vessel, including delayed cracking, cold cracking, hydrogen assisted cracking, hydrogen induced cracking, or hydrogen embrittlement.
Hydrogen cracking in ferritic steels only occurs when a critical combination of four basic factors is exceeded. These factors are:
- Hydrogen content,
- Susceptible microstructure,
- Stress, and
- Temperature.
Hydrogen uptake by steel can occur at specific conditions at both low temperature as well as high temperatures. At low temperatures, atomic hydrogen forms as a result of corrosion involving hydrogen promoters, such as H2S and hydrofluoric acid (HFA), or cleaning & pickling. At high temperatures, atomic hydrogen forms as a result of welding - when wet electrodes charge the steel with hydrogen, and service at high temperatures - when a small amount of hydrogen gas can dissociate to form atomic hydrogen and diffuse into the steel.
Hydrogen bake-outs involve heating the steel to an elevated temperature and allowing time for the hydrogen to diffuse out of the steel, leaving it hydrogen-free and weldable. There is some uncertainty though over the exact time and temperature needed to effectively "bake out" the hydrogen to a safe level, and there are several disagreeing opinions on the subject.
Hydrogen bake-outs should be used on all steel equipment to remove molecular hydrogen from equipment to prevent it from becoming brittle and cracking during or after welding. It cannot be overstated how important this process is before welding, as failing to do so can lead to expensive and dangerous problems.
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November/December 2017 Inspectioneering JournalBy Marc McConnell, P.E. at Pro-Surve Technical Services, and David A. Hansen, PhD, PE at Metallurgical Consulting, Inc.
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BlogNovember 10, 2014 By Nick Schmoyer at Inspectioneering
One of the more insidious problems within the industry is the issue of atomic hydrogen dissolving into steel equipment. This can happen to some steel components under certain circumstances and can cause weld failure, or what is known as “hydrogen...
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January/February 2014 Inspectioneering JournalBy Marc McConnell, P.E. at Pro-Surve Technical Services, Josh Yoakam at Holly Frontier Companies, and Frank Dean at Ion Science, Ltd.
This is the second of two articles published in Inspectioneering Journal discussing the value of hydrogen bake-outs. Our first article was published in the May/June 2013 issue and received a great response from the Inspectioneering community. In...
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BlogJanuary 6, 2014 By Nick Schmoyer at Inspectioneering
In 2013 Inspectioneering published content covering a wide array of topics, from risk-based inspection, to advanced nondestructive testing methods, to pipeline integrity management systems. Last year, we published more content than any year prior;...
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BlogJuly 29, 2013 By Greg Alvarado at Inspectioneering Journal
In the last issue of Inspectioneering Journal, Marc McConnell at PinnacleAIS submitted an article discussing hydrogen bake-outs. This article was extremely popular among our readers, both of the printed copy of the Journal and our online users.
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May/June 2006 Inspectioneering JournalBy John Reynolds at Intertek
As noted in the discussion on delayed cracking, when the steel contains hydrogen as a result of service exposure (or corrosion, or high temperature - high pressure hydrogen processing) then a hydrogen bake out may be needed to avoid cracking...
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