A lesson remembered - too late

Driving home this morning having collected a load of nuts and bolts from an electroplaters a very odd thing happened. I'd been asking him what it was that he 'pickled' stuff in to get the rust off because, as some of you may have read, my experiment with molasses wasn't a great success. He uses Hydrochloric acid - great, I'll get some and do everything else with it.

Anyway going through the lovely countryside and out of nowhere I think 'Hydrogen embrittlement'. As you do. Don't think that it was covered in my eng course, so must have picked it up from somewhere along the way.

Long and short - never 'pickle' important bolts in any acid with Hydrogen in it. Weakens them horrifically, and the harder the steel the better the Hydrogen creeps into it.

Given that my bucket of bolts contains mainly quite important axle, suspension and brake bolts you can see that I'm a bit disappointed that I've not only thrown £40 on plating, I've now got to buy a new set.



I hope that you read this and avoid making the same mistake.

I'll torque a few and see where and when they break - usually the head comes off, next most likely is the start of the thread and then the point where it meets the nut/hole.

boguing said:

Driving home this morning having collected a load of nuts and bolts from an electroplaters a very odd thing happened. I'd been asking him what it was that he 'pickled' stuff in to get the rust off because, as some of you may have read, my experiment with molasses wasn't a great success. He uses Hydrochloric acid - great, I'll get some and do everything else with it.

Anyway going through the lovely countryside and out of nowhere I think 'Hydrogen embrittlement'. As you do. Don't think that it was covered in my eng course, so must have picked it up from somewhere along the way.

Long and short - never 'pickle' important bolts in any acid with Hydrogen in it. Weakens them horrifically, and the harder the steel the better the Hydrogen creeps into it.

Given that my bucket of bolts contains mainly quite important axle, suspension and brake bolts you can see that I'm a bit disappointed that I've not only thrown £40 on plating, I've now got to buy a new set.

I hope that you read this and avoid making the same mistake.

I'll torque a few and see where and when they break - usually the head comes off, next most likely is the start of the thread and then the point where it meets the nut/hole.

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i dont know how the bolts were cleaned though it was acid dip of some sort by the platers that did all the bolts from the reconditioners i worked at ,but there was never an issue with the bolts,unless a poor bolt had been sent for plating by mistake

The torque at which they fail will tell James! From the sound of what this chap told me, Hydochloric is the weapon of choice with platers, but there's Hydrogen in all the acids that I can think of.

I normally bite my tongue when I read of people fitting stainless bolts on important parts, but thought that a heads up on this worthwhile.

worth trying a couple against a couple of unplated botls to see, we never found issues but then most of the bolts that were plated wernt critical like head bolts or con rod studs etc

Just read this to remind myself...

http://www.fera.org.uk/pdf/Fera activity listing - hydrogen - march 06.pdf

In my case the bolts got two days in acid because a few were quite rusty. That's very bad. If you read the article you'll see that embrittlement is:-

Random. Some fasteners will get it, other identical ones won't.

It's doesn't cause instant failure, it can take months, so my torquing experiment may not be conclusive.

There are means of reducing the chances, listed towards the end of the document. Baking post plating might have helped (again random) but it's way too late for mine.

seems to be an issue ,i can only say it doesnt seem to have shown up in my experience,though most bolts you plate arent under a lot of stress

I wish... The bucket has bolts for all the vital axle stuff, and even the diff studs aren't worth using - if one head comes off it'll inevitably be a top one which will fall straight into the diff.

Looking on the bright side, the drain and level plugs'll look smart. And the M6 stuff for the swivel seals will be fine.

boguing said:

I wish... The bucket has bolts for all the vital axle stuff, and even the diff studs aren't worth using - if one head comes off it'll inevitably be a top one which will fall straight into the diff.

Looking on the bright side, the drain and level plugs'll look smart. And the M6 stuff for the swivel seals will be fine.

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it would be interesting to know whether the plated bolts we used ever gave any problems ,as it was done for cosmetic reasons internal and vital bolts didnt usually get plated,we just presumed it was ok ,though it did give me a skill in identifying bolts and threads,sorting through the returned plated bolts

Best not to think about that before bed James!

Is it just the concentrated stuff that causes the problem? Plenty threads on here about using various vinegars.

Just stamp the heads with Chinese writing

Phosphoric Acid is what a lot of places use for rust removal.

Peter

Maybe I'm missing the point here, why not use stainless steel bolts etc...is there a reason or am I being obtuse

stew laws said:

Maybe I'm missing the point here, why not use stainless steel bolts etc...is there a reason or am I being obtuse

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Stainless is a comparatively soft metal and can shear / distort / stretch / wear a lot more than 'regular' fasteners and shouldn't be used on anything that has structural implications such as steering / suspension / towing

Kwakerman said:

Stainless is a comparatively soft metal and can shear / distort / stretch / wear a lot more than 'regular' fasteners and shouldn't be used on anything that has structural implications such as steering / suspension / towing

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Ok .. my thought process always thought it was a superior product .. but thats me being simplistic. Lol

listerdiesel said:

Phosphoric Acid is what a lot of places use for rust removal.

Peter

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Phosphoric is named in the article along with Hydrochloric because they are the two most common in pickling, and is just as bad as any acid. Which doesn't stop 'phosphating' being a good treatment for mild steels.

I think that any plater worth his salt should be pointing this out to people, and am a bit disappointed with the guy I used.

The thing to remember is that it's fine for anything that doesn't compromise safety - for two reasons. One is the obvious one, but also that the unimportant fasteners are made of softer metals, which don't suffer from the problem.

Kwakerman said:

Stainless is a comparatively soft metal and can shear / distort / stretch / wear a lot more than 'regular' fasteners and shouldn't be used on anything that has structural implications such as steering / suspension / towing

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There are 5 main types of stainless and umpteen grades within that. Many of which easily exceed the 8.8 metric spec. The trouble is one ss bolt is not the same as another, so a bag from screwfix will, as you say, be soft and prone to shear.
Buy a reasonable bolt and there will be no problem. Having said that, average price bolts could be more prone to stress failure so may not be a good idea for suspension. But many high stress applications demand 10.9 or 12.9 bolts so ordinary steel bolts would not be suitable either.

SpringDon said:

There are 5 main types of stainless and umpteen grades within that. Many of which easily exceed the 8.8 metric spec. The trouble is one ss bolt is not the same as another, so a bag from screwfix will, as you say, be soft and prone to shear.
Buy a reasonable bolt and there will be no problem. Having said that, average price bolts could be more prone to stress failure so may not be a good idea for suspension. But many high stress applications demand 10.9 or 12.9 bolts so ordinary steel bolts would not be suitable either.

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Yea, well aware of the differences in SS as I'm an aircraft engineer and also do a lot of my own machining (CNC Mill & Lathe). I was generalising as many will not realise the implications of using SS fasteners. Trouble is you wont have any comeback except on yourself if something were to go significantly wrong with a major component and cause an accident and you were found out to be using non approved / non standard parts. If a garage fitted them without your express permission then they would be on the hook but knowing how insurance companies like to wriggle out of big-buck payouts I wouldn't take the risk.

Al2O3 said:

Is it just the concentrated stuff that causes the problem?

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In the article I showed the link for you'll see that it mentions time as factor. That's half the story - because concentration is just as important. Bottom line is that it takes a certain amount of time vs. concentration to remove the rust, and that can be too much exposure for high tensile stuff. It goes on to mention baking as a way to improve the probability of avoiding embrittlement, but that takes skill and knowledge which won't necessarily be available in a small electroplating business.

Hmmmm interesting thread......I know about the use and where not to use stainless.....
But the effects acid can have on steel is enlightening.....although logical.....