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Up Topic Welding Industry / Technical Discussions / Bolts
- - By swift (*) Date 04-08-2003 22:47
I was asked to look at some valves today that have B8 stainless bolts, but appear to be zinc coated. These are non-magnetic and I was able to "shave" some coating off with my pocket knife. Has anyone else had a simmilar experience? How can I readily determine that it is or is not zinc.
Parent - By colins (*) Date 04-09-2003 15:13
Send it to a metallurgical lab, they will be able to identify the material in question.

Parent - By G.S.Crisi (****) Date 04-09-2003 19:43
Colin is right. The only way to determine for sure whether or not the material is zinc is to run a chemical test.
Now, I'm asking myself a couple of questions.
1. If the material is stainless steel, it doesn't need to be zinc coated.
2. If the material is carbon steel, it would be magnetic.
The mistery is still on.
Giovanni S. Crisi
Sao Paulo - Brazil
Parent - - By TimGary (****) Date 04-09-2003 22:49
When burning/welding zinc coated material, I have always noticed yellow discoloration on the outside of the HAZ leading to a fluffy white crust and an un-mistakable odor.
Can you test one of these bolts with a torch?
I don't understand why a SS bolt would be zinc coated...
Parent - - By swift (*) Date 04-10-2003 00:04

Great idea, I may be able to scrape enough off to obtain a sample to test with heat.

The factory rep is coming to take a look as well. If I remember correctly, melting point of zinc is about 650 deg. F.


Parent - By jwright650 (*****) Date 04-10-2003 11:20
I too was curious why someone would galvanize a Stainless Steel bolt. I thought the reason SS was used is for corrosion resistance(rust), why the extra zinc on top of that?
Let us know what you find out,
John Wright
Parent - - By Lawrence (*****) Date 04-10-2003 18:03

Safety check!

Some stainless fasteners are Cadmium plated.. Cad plating is highly toxic in small doses (dust or fume,) so be well ventalated if your going to test them by burning..
Parent - - By CHGuilford (****) Date 04-11-2003 13:09
Stainless steel that is exposed to zinc, cadmium, and other similar metals can suffer from a phenomenon called Liquid Metal Embrittlement. This causes the stainless to severely crack. The higher the temperatures are while the two metals are in contact the more rapid the reaction.
So my questions are: Are you sure you are dealing with metal plated stainless steel bolts? If yes, are you sure they are being used in the right apllication?
It might be worth doing a little more research.
Chet Guilford
Parent - By kk_chiong (*) Date 04-11-2003 13:29
The topic discussed earlier inspire me that maybe the B8 Stainless Bolts are actually not from stainless steel materials. As other materials maybe used to fabricate the bolt. e.g. Copper or brass and galvanize with zinc. I suggest to check further on the materials of the bolt. Could it be too soon that we jump to the conclusion that the materials for bolts is a stainless steel base. Manganese are also non-magnetic or other iron base product with austenitic structure are non-magnetic as well. Please check the bolt base materials.
Parent - - By jon20013 (*****) Date 04-11-2003 14:41
I whole heartedly agree with Chet, better check to see what gives. Stainless steel and zinc are not a good combination!
Parent - - By BankerQC (*) Date 04-11-2003 19:21
I dont mean to be asking the obvious, but we always get material test reports with all of our bolts...might that not be a good place to start ???
Parent - By swift (*) Date 04-11-2003 22:40

I had a visit with the valve manufacturer today. They confirmed that what they use is a A193 B8 stainless steel bolts and that they are then Zinc Plated!! The bolts are used on their SA351 CF8M valves. They claim that it is to prevent the bolts from seizing up. I would think that nickel-ez would be more appopriate. Has anyone else checked their valves? Perhaps if the valve fails due to corrosion, they sell more valves?
Parent - By jwright650 (*****) Date 04-12-2003 12:34
Hello BankerQC,
Just a quick question, which "Banker Steel are you with? The reason I ask is there is one here in town and was wondering if you worked there.
John Wright
Up Topic Welding Industry / Technical Discussions / Bolts

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