Author Topic: Stainless Steel Studs In Boilers Advise Wanted  (Read 4069 times)

Offline sbwhart

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Stainless Steel Studs In Boilers Advise Wanted
« on: January 10, 2014, 01:59:52 PM »
Have we any mythologists who can advice on this email I had from a friend.

Quote
                     I am a little concerned about the use of stainless steel for studs in pressure vessels some years ago I built a steam fire engine and to make what I thought would be a good job I went to the trouble of making all the boiler stunds from the recommended grade of stainless. To properly clean the brass work I have to remove some of the fittings to my horror I found all the studs had corroded not rusted but corroded to almost dust the model is fairly delicate and not steamed so the electrolysis was due to contact with bronze  I was still working for ICI at the time and was in a position to ask the lab for their advice the answer was that I ought to have known better they advised either en8 or bronze pb102 I have since only used pb102 with no trouble whatsoever.
                     Wondered what you think I think it is fairly important.
                                                                 


Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline Pete W.

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Re: Stainless Steel Studs In Boilers Advise Wanted
« Reply #1 on: January 10, 2014, 05:30:03 PM »
Hi there, Stew,

I must start by stressing that I am no metallurgist.  However, I used to work with a team, some of whose members had to choose materials for long term immersion in sea water. 
When they deserved it, I used to tease them by reminding them that aluminium is never found in nature in its metallic form.   :lol:   :lol:   :lol: 

I remember it being said that stainless steel can be either anodic or cathodic, depending on the environment.  Also, stainless steel depends upon there being available oxygen to maintain its protective surface patina.  Stainless screws in blind holes were treated with a yellow chromate gap-filler to 'fool' the stainless into thinking that it was in an oxygen-rich environment.

Maybe that's all been so scrambled in my memory (it's been a long time!) that it's garbage. 
Still, maybe it will provoke some proper metallurgists to give you the real answer to your question.   :nrocks:   :nrocks:   :nrocks: 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline David Jupp

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Re: Stainless Steel Studs In Boilers Advise Wanted
« Reply #2 on: January 11, 2014, 05:04:24 AM »
Austenitic stainless in hot water with chlorides present can lead to Stress Corrosion Cracking (metal will just fall apart).  This is a big issue where there are welds or other causes of residual stress.

Some grades of austenitic stainless will suffer pitting corrosion in presence of chlorides (can perforate) - this is why tap water is normally not used for pressure testing stainless pressure vessels (even minor traces left behind can lead to disaster).

So yes, there could be issues with stainless items in a boiler.

Pete is correct about sufficient oxygen being needed to maintain the oxide layer - 316SS impellors in sea water pumps have been known to disappear if the pump is not operated occasionally to renew the water (and oxygen present in it).

Offline chipenter

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Re: Stainless Steel Studs In Boilers Advise Wanted
« Reply #3 on: January 11, 2014, 11:49:12 AM »
I would just stick to bronze or gun metal with copper slip so you can get it apart , had some success with Colphos free cutting bronze and the finish is realy good .
Jeff