Stainless Corrosion

[Guest red7]

Anybody know anything about Stainless steel corrosion?

 

I am a Draughtsman, the other day I was called to a power station, to take a look at some stainless panels.

 

The Engineer took me over to the boilers, the bottom panels were badly corroded and he needed drawings to get replacements made. They were 316L stainless steel the same stuff as our cars, I think.

The boiler panels had been in contact with sea water from the cooling system, this had accelerated their corrosion considerably.

 

I need to talk to someone technical to hear what grade of stainless they recommend for the job.

 

This job got me thinking about our cars and winter driving.

 

Has anyone seen corrosion in their stainless Robin Hoods?

[Guest Jim Poole]

Somebody correct me if I'm wrong but 316L is subject to pitting and crevice corrosion in warn chloride environments. So basically for your hood, don't get it covered in salt water and leave it in the sun. Although, I wouldn't have thught that the stuff supplied by RHSC is this grade as it would be too expensive. It's more likely to be 304.

 

This is probably why parts of your boiler are corroded, as its warm and in contact with seawater (warm & high chlorides >1000mg/l). If the boiler gets above 60 deg C it will also be susceptable to stress corrosion cracking. Go for 22Cr SS or even better titanium.

[Guest chris brown]

Has anyone seen corrosion in their stainless Robin Hoods

Yes I spent yesterday afternoon cleaning the rust from my roll bar and around the edge of panels particularly the stone guards and rear wings all close to the cut edges it is just surface and cleans up with a bit of elbow grease

PS my car lives outside and does tend to get used in most weathers

[Guest Charles B]

The chassis of the hood is made of 409 grade stainless. It's a ferritic stainless, welds well, and doesn't fracture like some stainless, particularly with stress.It's actually made for exhaust tubing as it's very resistant to atmosphere and hot exhaust gasses. The down side is that it forms an oxide layer, which doesn't look to good. but protects the metal. So don't clean it off unless it's on a bit you really want to look shiny like the roll bar. It will only reform again anyway.

I'm not positive about the body panels, but they are probably a 304 grade of some sort, though they must be a low grade as a magnet will stick to them.

316 grade stainless is specially made for it's high resistants to pitting and chloride attack, so it would be the usual choice for boiler use. There are some higher grades, but it all gets very expensive, and very difficult to form and weld.

For more info, check out some of the stockholders web sites, they have loads of details.

[Guest Jim Poole]

Sorry Chris, have to disagree with you there.

 

316 SS should not be used for boiler applications with sea water, where the temperature can rise above 60C. As a precaution I wouldn't use 316 anywhere that can rise above 40C. You need something with a larger PREN (eg 22Cr Duplex)

 

As for your RH, the time which it is subjected to salt water is only small and therefore this needn't be worried about.

[Guest chris brown]

Sorry Chris, have to disagree with you there

Why me???? I didn’t say anything :boohoo: :boohoo: :boohoo: I blame Charles

[Guest Charles B]

Jim, yes you are right for standard 316L. 316H or 316Ti would be fine. 904L or even 2205 would be even better. From what Steve said I assume he is just talking about the outer panels, so non structural. So I suppose the cost may become a problem with these high grades.

[Guest red7]

Hey Lads!

Thanks for the info. Some clever RH owners out there.

[Guest Cantbearsed]

D'ahhh, who cares anyway? get the gasboard to do it...

[Guest Charles B]

Just thought, another problem you can get with some stainless (particularly duplex) is galvanic action. Might be worth checking what metal the panels are bolted to, if the corrosion is along where the panels are fixed

[Guest red7]

Gas Board? It's as big as a block of flats! This boiler is making steam for a 390 Megawatt power station. It's using one million tonnes of imported coal each year.

[swan]

red

 

Which station was that?

 

Swan

[Guest Jim Poole]

Sorry Chris... God knows where that came from.

 

Charles... I don't agree with you on the 316H and 316Ti. 316H has a higher carbon content and is therefore stronger at higher temperature (>500C), but has the same resistance to corrosion as all 316 SS. 316Ti is stabilised form due to the addition of titanium and is stronger at even higher temperatures (>800C). For all 316 SS the PREN is the same due to the same chrome, moly and nitrogen content. All are also still susceptible to SSCC. I definitely agree with the 904L and 2205 though, but if this was installed our electricity bill would go up due to the cost of it! Inconel 625 would be an option!

[Guest V8K]

D'ahhh, who cares anyway? get the gasboard to do it...

 

to do what

[Guest graham dockerill]

I think we will call that a draw?