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Hydrogen Bake-Outs

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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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Articles about Hydrogen Bake-Outs
November/December 2020 Inspectioneering Journal

Heat treatment has been used by mankind for centuries. This article details reasons to heat treat, the types of heat treating available, methods of heat treating to achieve specific material properties, and the role of MI in heat treating.

Authors: Ben Osborne
November/December 2017 Inspectioneering Journal

Hydrogen is a common culprit of equipment damage in the process industries. As hydrogen-induced damage can occur in multiple forms, it’s critical to identify the specific damage mechanism you’re dealing with before undertaking measures to...

Blog

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...

Authors: Nick Schmoyer
January/February 2014 Inspectioneering Journal

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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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;...

Authors: Nick Schmoyer
Partner Content

Traditional pressure vessel inspections often require taking assets out of service. However, MISTRAS’ Non-Intrusive Inspection (NII) programs provide data as good or better than internal inspections, while assets remain in service. NII is...

Blog

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.

Authors: Greg Alvarado
May/June 2013 Inspectioneering Journal

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

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...

Authors: John Reynolds
    Downloads & Resources related to Hydrogen Bake-Outs
      Asset Intelligence Report

      This Asset Intelligence Report on the hydrogen bake-out process serves as a primer to increase your familiarity with this technique used to drive hydrogen out of equipment prior to welding.

      News related to Hydrogen Bake-Outs
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        Becht’s industry-leading Corrosion and Metallurgical experts are here to help with significant owner-operator experience covering the refining, petrochemical and chemical industries. This expertise is leveraged to help our clients become more...


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