Hydrogen Bake-outs

Last update: Jan 13, 2017

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:

  1. Hydrogen content,
  2. Susceptible microstructure,
  3. Stress, and
  4. 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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The Hydrogen bake-out process: an introduction and helpful resources
November 10, 2014

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 cracking.” These cracks can occur during the welding process itself, but sometimes they can occur up to 48 hours later.

A Discussion on Hydrogen Bake-Outs: Part II
January/February 2014 Inspectioneering Journal
By Marc McConnell, P.E. at Versa Integrity Group, Josh Yoakam at Holly Refining and Marketing - Tulsa, LLC, 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 this piece, we will continue the discussion and touch on some new technologies used to enhance the bake-out process.

July 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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The Hype about Hydrogen Bake-Outs!
May/June 2013 Inspectioneering Journal
By Marc McConnell, P.E. at Versa Integrity Group

With 30 years of refinery experience, I have been through many turnarounds and been involved with a lot of repairs. When I started in the business, we would have inspectors that “owned” their specific pieces of equipment.

May/June 2006 Inspectioneering Journal
By 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 problems during or after welding.