SS ball corrosion

[KeithW]

List,

I've just been preparing my rebuilt Merchant Navy in anticipation for the coming season. I always check the three safety valves by confirming that they behave properly when tested with compressed air at 80psi.
Today, all three proved unsatisfactory either not lifting at 80psi or not shutting down when the compressor was switched off.
When I examined the stainless steel balls, 5/16 inch diameter, I found they appeared to be corroded, or at least partly coated with a very hard brown deposit.
This loco was last run in Autumn of last year and there was no problem with the safety valves.
My concern is that either the SS balls are not as corrosion resistant as one should expect, or that the hard brown deposit originates from our local water. (Glos/Brisol).
I find it worrying if the former is the case since the balls were purchased from one of our regular and reliable suppliers, and if the latter, does anyone in my area have similar problems?
Keith

[Phil Sutton]

Hi Keith.The only thing I can say regarding water in the Bristol area is,that when my brother lived at Yate?Chipping Sodbury,you had to use a tea strainer on the boiling water from the kettle if you wanted tea or coffee,as there was no end of scum,which deffinately didn't add to the flavour!Maybe this is the cause of the brown stains on your s/s balls(!) .Can't say as I've ever come across rust on Stainless,we had a sheet as a wind sheild for the boiler flue on the wall outside.Never a trace of rust,and it was there for over 10 years.

Phil

[burnettsj]

Being a Bristol member - I've never heard of the water rusting S/S balls. It doesn't like brass though (de-zincification), which is why fittings below the waterline should be bronze.

How long have you had your balls (if that's not too personal)? How many steamings have they seen?

Are they magnetic (most S/S isn't)?

Were they S/S or "rustless" - I'm not a metallurgist, but I believe some balls are rustless rather than S/S, which possibly are not suited to steam applications? Anyone with any knowledge on these?

Stephen

[ron]

SS will also rust if it comes in contact with rusty mild steel [don't know the scientific reason?], but I would be more inclined to think you're problem is down to the water quality.
Ron

[SteveW]

Guys,

The version I heard was that stainless didn't rust because of an oxide like skin that gets created on the surface. It's one of the alloying constituents that does the trick but I forget which.

Maybe chatter of the SS ball on the valve seat gets through the protecting layer aggravated by any dissimilar metals effects.

[burnettsj]

Here's some metallurgy/chemist that I do remember!

All metals corrode - however some, such as Al, develop a thin layer of oxide (corrosion - rust is technically Iron Oxide), which inhibits further corrosion.

Other materials such as iron produce an oxide which doesn't inhibit (forget the technically term) - and so over time the material will corrode away.

S/S is an alloy of steel, with Chromium as added which produces the corrosion reducing property.

S/S will corrode quite badly in chloride environments. Thus in the marine industry, where corrosion resistant pipework which is in contact with salt water is required - Monel is used in preference to S/S.

On a side issue - why when I am writing this are the adverts at the top of the page: Mini Gay Luxury Cruise, Gay Travel and Retreats, Exotic Luxury Honeymoon, and Adult only luxury holidays?

[KeithW]

Thanks for all the comments. The balls are non-magnetic (austenitic) and were replaced last Spring and had seen only a few hours steaming.
A close examination with a glass has shown a hard, brown deposit which is very difficult to remove, but beneath it, the surface of the ball is smooth with no evidence of pitting corrosion. The deposit, as suggested in some replies must originate from the water/steam. It is a niusance but I guess, since changing the water source isn't an option, I'm going to have to replace the balls on a regular basis.
Keith

[ron]

Keith
On another thread I posted that I use distilled water in my stationary boiler [actually dehumidifier drain water] it might be worth your while exploring a source of cheap distilled water.
Ron

[chris vine]

Hi, Can you operate the locomotive from rain water?

I use a water butt which collects the water from the workshop roof. The boiler stays completely clean inside.

Some people talk about acid rain but it seems a bit far fetched to me.

Does any one else have an opinion on rain water?
Chris

[greasemonkey]

Hi Keith
Sounds like water impurities. Just a thought but if the balls are looking like that what about the rest of the boiler? I think I would descale it myself.

Andy

[houstonceng]

Guys

Regarding rain-water. Down at the WDMES (Falconwood), we have no running water on site so have to catch and store rain-water for use in boilers. No problems so far.

Regarding "Stainless Steel". As you probably all know, there are as many "Stainless Steels" as the customer desires. Each with it's own Characteristics. Same goes for any Alloy including ordinary carbon steels.

I was always told that S/S was "Stainless", but not "Rustless". It would oxidise and, having done so, would remain "Stainless" if, and only if, continually exposed to the atmosphere. The terms used are not scientific since "rust" is Iron Oxide (Can't remember from my School days if it's Ferric or Ferrous Oxide). The oxide on S/S isn't Iron Oxide.

Anyway. I've seen what happens to S/S Wire Cables when it was "parcelled and served" like ordinary Galvanised wire "Rope" would have been. Turned into a white powder. I've also noticed that some cheap S/S cutlery we have has developed stained spots (rust ?) after a few sessions in the dishwasher. A few years back, a stainless-steel butter dish was left in a damp enamelled steel sink for two weeks whilst we were on holiday. It developed definite rust - probably some form of electrolytic action. I've had S/S balls go black and have since only used bronze balls in clacks.

My conclusions are, therefore, that some types of S/S can and will "rust" in the wrong environments.

Andy