In Follow Up to the Inspectioneering Journal Article on Hydrogen Bake-Outs

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.

Due to the tremendous feedback received, Marc is working on a follow-up article on this subject. More specifically, his next article will include more specific details about the grades of ferritic materials, hydrogen bake-out procedure, and conditions needed for an effective bake-out. In preparation of this second article, we do have two comments in follow up. The follow-up article was published in the January/February 2014 issue of Inspectioneering Journal.

First, in the conclusion of the hydrogen bake-out article, the author said, “when in doubt, run a test bead.” Many readers posed questions regarding this statement. The fundamental concept the author was trying to get across is that, if time allows, simply run a test bead on your material and wait to see if it cracks. If it does not crack, proceed on without that bake-out.

The second comment refers to hydrogen flux monitoring. Others have reported good experiences using hydrogen flux monitoring to determine when a bake-out is necessary, and how long it should last. These probes can be used on-stream to see how much hydrogen is diffusing through the steel while on-stream, which helps determine hydrogen bake-out guidelines and even whether a bake-out is necessary in the first place.

Rather than relying on the old 'rule of thumb' of a prescribed bake-out time for a particular thickness, during the bake-out process, use the hydrogen flux monitors to determine when the flux rate through the steel drops below a certain "trigger." When the rate is below this point, the material is baked-out and the process can be stopped.

Using this method of control, experience has shown cases in which bake-outs can be terminated in much shorter times than were traditionally thought necessary. There have also been cases where bake-outs have been extended for longer than expected due to the high levels of hydrogen charging noticed by flux monitoring.

If you have any additional feedback that we haven’t covered, email us at admin@inspectioneering.com, or visit the Inspectioneering LinkedIn Group for more great discussions.

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