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Electrodes that require "Diffusable Hydrogen Testing"

Electrodes that require "Diffusable Hydrogen Testing"

Electrodes that require "Diffusable Hydrogen Testing"

Happy New Year to the almighty Welding Engineers:

It is my hope that one of you good people will either inform me of a good reference or explain what the subject language precisely refers to, especially in regards to flux-cored welding consumables.

What IS a Diffusable Hydrogen Test, and, are there "good" and "bad" results, or, are there simply only results that can be used on a comparative basis with "competing" welding consumables that could be selected for a welding process?

Stating this in another way...having undergone a Diffusable Hydrogen Test, is there a descriptive system that will comparatively identify one consumable as having a tendency to diffuse either more, or less, hydrogen when compared with another consumable? How does this help with the selection of a welding consumable for an application?

If the answers to the aforementioned questions are taken into consideration, then, is it possible to distinguish between flux-cored wires and "bare" solid GMAW wires in their propensity to "diffuse" hydrogen into the welded area?

Thank you very much, in advance, for providing me with the information that I am in need of.

RE: Electrodes that require "Diffusable Hydrogen Testing"

The AWS designation of a consumable (like E71T-1) can include a hydrogen designation at the end (E71T-1H4).  The number is the ppm of hydrogen, based on how much mass was lost when the specimen was heated.   (Post-heating lets the hydrogen escape.)  The test method is given in ANSI/AWS A4.3.

The lower the number, the better the result.

Most major brand welding electrodes for structural steel are probably H16 or so, even if there's no designation on the certificate (but if you really *need* the H16, make sure it's on the cert).  If you really need controls on the hydrogen (generally in crack-sensitive applications like fatigue or seismic), then you look for whatever's required--often H8, sometimes even H4.

Both FCAW and GMAW electrodes can be purchased with specified hydrogen levels, so it shouldn't be used as a means of distinguishing between the two processes.

If you don't store the electrode properly, the flux in the cored wire could absorb all kinds of moisture, and your H designation becomes irrelevant.  But it's easy enough to treat FCAW wire right that that in itself should not be the basis for choosing between FCAW and GMAW.

What's your application?  How did this come up?  Typically if there's a diffusible hydrogen requirement it should be in the specs & codes governing the manufacture of the product.  If you're trying to choose between FCAW and GMAW, that selection has a lot more to do with what the welders are comfortable working with and how appropriate the various GMAW transfer modes might be to your application than with diffusible hydrogen.


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