Hydrogen Embrittlement from a Novice…

I noticed recently that I picked up a follow from Milos Djukic, a very interesting name may i add, and I took a look at his blog.  It seems like this guy knows his stuff about hydrogen embrittlement mechanisms of metallic materials. I wanted to use this post to try and process this and explain, in a very basic way, what the studies are about. I don’t totally understand

So first of all, Im fairly sure what hydrogen is. The element near the start of the periodic table with one proton and one electron. A metallic material is a material that has a lattice of a crystalline arrangement of ions surrounded by a cloud of free/valence electrons.

Very interestingly, despite hydrogen induced cracks being a common issue in industry, there is no practical model that will predict these. This phenonomen was first documented  in 1875.

steel-with-hydrogen-induced-cracks-01

This is a picture of a crack as a result of hydrogen induced cracking.

So. Now I understand that hydrogen is bad and it causes cracks. Why and where does this happen?  Apparently hydrogen can just straight up diffuse into metals. The hotter the conditions the more likely hydrogen atoms are to diffuse. I am thinking of this like sugar into tea, the hotter the tea the more sugar you will dissolve. Hydrogen atoms find each other again, bond into molecules, which causes internal pressure for the materials (normally steel) Steel is used in loads of stuff making this an issue… An example where this happened is in 2013 before the opening of the Oakland Bay Bridge about a third of 96 10 foot bolts failed – and it was attributed to hydrogen embrittlement.

How do we sort this mess out. Like I said previously, scientists are not totally sure of the exact mechanism that controls this phenomena however it is known that hydrogen passes down the concentration gradient of hydrogen into the metal. Therefore if the metal gets ‘baked’ – no marijuana involved – in the absence of hydrogen there will be a tendency for the hydrogen to leave.There are many more methods to prevent the issue: Reducing corrosion rate, Proper welding (minimise water which is a source of hydrogen), Using alloys with Nickel also helps.

 

Thanks for reading. Please tell me what I have got wrong or how I have misunderstood, I am trying to learn!

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