Inspectioneering Journal

A Discussion on Hydrogen Bake-Outs

Part 2

By Marc McConnell, P.E. at Pro-Surve Technical Services, Josh Yoakam at Holly Refining and Marketing - Tulsa, LLC, and Frank Dean at Ion Science, Ltd.. This article appears in the January/February 2014 issue of Inspectioneering Journal
This article is part 2 of a 2-part series.
Part 1Part 2


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.

Managing the Bake-out

In the refining and process industries a bake-out is used to drive hydrogen out of steel, as trapped hydrogen can cause cracking in a weld. Typically, the time to perform a hydrogen bake-out happens during a maintenance turnaround, prior to welding, and as such, the need for the bake-out is frequently challenged by an effort to save time and money. The time and temperature needed to bake out the hydrogen to an acceptable level for successful weld repair is widely disputed, and when discussing with metallurgists or corrosion engineers, you will frequently find varying degrees of opinion ranging from none to some. There are rules-of-thumb for “in-house” delay times prior to weld inspection, e.g. between 16 to 48 hours in various standards, but there is no firm basis for these times. There is good reason for delaying the weld inspection after welding, as delayed hydrogen cracking can occur. Furthermore, there is generally no discrimination between different materials, joint geometries, or welding conditions. Due to a lack of detailed knowledge and for simplicity, most adopt a single delay time for all circumstances.

In a hydrogen bake-out, the user heats the steel to an elevated temperature and allows time for the hydrogen to diffuse out of the steel, leaving it hydrogen free and weldable. Several key issues play a role in the success of the hydrogen bake-out, including:

  1. Bake-out temperature;
  2. The amount of hydrogen trapped in the steel;
  3. The solubility and diffusivity of hydrogen in the alloy;
  4. Steel thickness; and
  5. The alloy’s susceptibility to hydrogen embrittlement (hardness).

The time and cost to remove cracks from delayed cracking, due to inadequate hydrogen bake-outs, and typically leading to multiple repairs, will always be more than the time and cost of performing the hydrogen bake-outs. And, not every attempt in outgassing meets with success.

It is quite well known that cracking can occur immediately during welding, or there can be some delay between the completion of the weld and the formation of hydrogen cracks, but it is usually within 48 hours. Therefore, if traditional inspection is carried out too soon after welding susceptible material, these cracks may not be detected and as a result, a faulty weld is put into service. On the other hand, excessive delays after welding prior to inspection can seriously impact project planning and delay the return of equipment to service.

This content is available to registered users and subscribers

Register today to unlock this article for free.

Create your free account and get access to:

  • Unlock one premium article of your choosing per month
  • Exclusive online content, videos, and downloads
  • Insightful and actionable webinars
Interested in unlimited access? VIEW OUR SUBSCRIPTION OPTIONS

Current subscribers and registered users can log in now.

Comments and Discussion

Posted by Harold Babuik on April 4, 2017
Do you ever do a hydrogen bake out on austenitic... Log in or register to read the rest of this comment.

Posted by Marc McConnell on April 5, 2017
Good question. The answer is no, you don't have... Log in or register to read the rest of this comment.

Posted by Sanooj Khaleed on September 15, 2017
I just want to know that a restricted heating and... Log in or register to read the rest of this comment.

Posted by Kamarul Ariffin on January 28, 2018
I just want to know, is there any standard that... Log in or register to read the rest of this comment.

Posted by Marc McConnell on January 28, 2018
Kamarul, you have asked a question that many... Log in or register to read the rest of this comment.

Posted by Rabin Pokharel on March 14, 2018
I am assuming you do bake-out if you are not... Log in or register to read the rest of this comment.

Posted by Marc McConnell on March 15, 2018
I'm glad that you asked that question, because a... Log in or register to read the rest of this comment.

Add a Comment

Please log in or register to participate in comments and discussions.

Stay up-to-date with the latest in industry — for free. Join thousands
of others
Join thousands
of others

Inspectioneering Journal

Explore over 20 years of articles written by our team of subject matter experts.

Company Directory

Find relevant products, services, and technologies.

Job Postings

Discover job opportunities that match your skillset.

Case Studies

Learn from the experience of others in the industry.

Event Calendar

Find upcoming conferences, training sessions, online events, and more.

Industry News

Stay up-to-date with the latest inspection and asset integrity management news.


Read short articles and insights authored by industry experts.


Commonly used asset integrity management and inspection acronyms.

Asset Intelligence Reports

Download brief primers on various asset integrity management topics.


Watch educational and informative videos directly related to your profession.

Expert Interviews

Inspectioneering's archive of interviews with industry subject matter experts.