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Thread: Hot Dipped Galvanized and hydrogen embrittlement

  1. #1
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    Default Hot Dipped Galvanized and hydrogen embrittlement

    Is this something I need to worry about in real life?

    In my quest for Grade 8 bolts for an angle iron ledger board, I came across the issue of hydrogen embrittlement set forth below.

    It looks like the easy answer is to stay away from high strength steel (stay below 170 ksi/170,000 psi tensile strength). Or stay away from HDG.

    The latter seems unwise from a maintenance/safety standpoint. Especially when the bolts will be mounted permanently without the realistic probability of inspection.

    However, Grade 8 is close at around 150,000 psi. This leads me to think that Grade 5 might be a safer choice.

    Is this something to worry about in real life?

    Any insight appreciated.

    Thanks

    Tom



    Hydrogen embrittlement occurs when steel cracks due to hydrogen that is trapped between the grains of the steel. Although steel commonly absorbs hydrogen during the hot-dip galvanizing process, it is usually expelled due to the temperature of the zinc in the galvanizing kettle. In some cases, however, the grain size of the steel is too small to allow release of atomic hydrogen. This can later cause cracking due to increased stress at the location of the hydrogen between the grains. Grains of steels with a tensile strength below 170 ksi (170,000 psi) are usually big enough to allow escape of hydrogen, but for steels having a tensile strength of 170 ksi or greater, there is a potential for hydrogen to remain trapped between grains leading to hydrogen embrittlement.

    https://galvanizeit.org/knowledgebas...-embrittlement
    Last edited by bluedog225; 02-25-2020 at 11:03 PM.

  2. #2
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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    There are all sorts of grade 8 bolts, not all the same alloy.
    I wouldn't use grade 8 in that application (because fire)
    Is Stainless out of reach? 18-8 stainless is relatively inexpensive, no embrittlement, no corrosion issues, and ductile.


    "Mechanical properties of low carbon-boron steel fasteners are shown to be generally equivalent to mechanical properties of higher carbon steel fasteners with two notable exceptions: The ductility of the low carbon steel fasteners is higher than that of the higher carbon steel fasteners at all strength levels, and the heat resistance of the low carbon-boron steels is considerably lower than that of the higher carbon steels." https://www.jstor.org/stable/44565080?seq=1

  3. #3
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    Default

    I dunno what a ledger board is. But heck, go to the hardware shop and get twice as many big assed bolts as you think you need and call it good.

    Sent from my CPH1851 using Tapatalk

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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Does harder steel not rust faster?

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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    I had not thought of stainless. Similar strength to Grade 5. Will look into it.

    I’m not sure about the relationship between corrosion and hardness.

    The bolt store did have some zinc bolts (yellow). I don’t think they suffer from the same issue. And I am in a pretty low corrosion environment.

    Can you tell me more about the issue with Grade 8 and fire? Not seeing it with quick google searches.

    Thanks

  6. #6
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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Quote Originally Posted by wizbang 13 View Post
    Does harder steel not rust faster?
    I don't think hardness impacts corrosion in steel, unless the material begins to develop surface cracks (fatigue cracks)

  7. #7
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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Some comments covering statements & questions in this and it's previous thread:

    1.) I would not use stainless steel in an anaerobic environment, especially in such a mix of materials.
    2.) When you consider shear strength of a bolt, make sure that you are considering the root diameter of the threads, not the gross diameter. This is moot if you used a shouldered bolt.
    3.) Be careful when considering high-strength steel; lower-grade steel will deform before shearing, giving advance warning of imminent failure, high-grade steel just breaks suddenly without warning. This is important if the bolts are supporting a live load, such as people.
    4.) I would not worry about hydrogen embrittlement from HDG unless this is a critically-stressed structure.

    Finally, a question: Unless I missed it, you have not said what this ledger beam is going to be supporting - what are you building?
    Hope for the best, but plan for the worst.

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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Quote Originally Posted by bluedog225 View Post
    I had not thought of stainless. Similar strength to Grade 5. Will look into it.

    I’m not sure about the relationship between corrosion and hardness.


    Can you tell me more about the issue with Grade 8 and fire? Not seeing it with quick google searches.

    Thanks

    Grade 8 bolts can be made of various steels to meet the specified requirements. The addition of boron to low carbon steel is usually adequate for use at moderate temperatures. As the temperature goes up the strength of boron steel goes down rather dramatically compared to high carbon steels (as I understand it) Grade 8 spec bolts can be made more economically using low carbon steel.
    I included a Linky thing that explains it better than I ever could.
    There were some notable helicopter failures in the late 70's early 80's because of these bolts. The publicity associated with that alerted me to the issue.

    My own empirical experience with stainless vs grade 8 was pretty dramatic. There was an single engine mounting bolt (5/8 x5") on a good sized tractor we had that was spec'd with gr 8. This bolt used to break about once a month and I generally kept spares on hand, but one day, out in the woods, it broke so I rummaged through my kit and found a bolt that fit and it happened to be stainless (probably 316). When the machine came back into the shop and we went to change the bolt it still looked good so we left it as an experiment. Well, that bolt is probably still in the tractor today, problem solved. Better ductility was the only logic I could come up with. I have since done some bending to break tests with stainless and generally they were not scientific but still convincing.

    Edit; As I understand it crevice corrosion in Stainless requires the presence of an electrolyte

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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    This is a galvanized steel landing from an old airport. It’s pretty stout.

    I’d like to attach it to a concrete wall supported by (and bolted to) 4 inch angle iron bolted through the wall and posts on piers on the outside.

    The wall is pretty robust. The floor of the landing will be 12 feet up so I am doing a little research to make sure it is safe.

    1838BD74-339C-4C27-BD9D-7659558BD2CE.jpg

  10. #10
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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Grade 5 or 6 5/8" UNC HDG steel shoulder bolts. That is the material we used when we built aerial transformer platforms on telephone poles. I see that the one that I built in Digby in 1979 to hold two tons of transformers is still standing after forty-one years and three hurricanes.

    That's my story, and I'm sticking to it.
    Hope for the best, but plan for the worst.

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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    I like the 5/8"...
    Why not just use hot dipped 5/8" bolts? Even grade 2 would be "adequate"

  12. #12
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    Default Re: Hot Dipped Galvanized and hydrogen embrittlement

    Yes. 5/8 UNC HDG shoulder bolts Grade 5 is probably where I am headed. I got a little lost in the rabbit hole researching. Though I will check into stainless.

    Thanks all.

  13. #13
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    Bolt the top of the railing to the wall and you'll be good. A brace against all that leverage.

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