Stainless Steel 'corrosion'?

[alant]

Not a boaty situation, but a marine environment query.
Recently beach huts that were devastated in the valentine night storm some years ago, have been rebuilt to a much more pleasing appearance, enhancing the beach front. However, the stainless steel railings atop the huts, is already corroding after just 2 months, described by a council official as "tea staining". Some of the heaviest stain, is around welds & holes where s/s wire is threaded through posts, but even the s/s handrail is covered on almost all the surface with lighter "tea staining" over it.
The council claim, that the material has been certificated as 316, so should it start staining this quickly?
I accept that weld areas & where wire is routed through a hole may be different to tubing brightwork.
Why is it happening if the material is 316?

 

[Topcat47]

Definitely one for Vyv, I think, especiallly after reading his book.

 

[John the kiwi]

I am dealing with an issue in my job where 316 stamped fittings are degrading under chemical attack.
316 is the recommended grade for the chemical and we have used it in the past without problem.
The only thing to change is the suppliers source of fittings.
Anecdotally i have heard of other stainless steel users having similar issues with fittings sourced from China.
In your case their may be other issues such as:
- contamination of the stainless by carbon steel grinding dust and tools. The best stainless shops are kept scrupulously stainless steel only and kept clean to avoid this.
-dissimilar metal corrosion between weld filler wire and parent metal or wire and handrail.
- airbourne pollutants
etc
good luck.

 

[Kukri]

This is not a scientific response, but I would not trust any stainless steel item that is made in China and stamped "316". I lived in China for five years and all stainless steel cooking pots there seem to be stamped "316" although here in Britain we would use "304" stainless for such applications. I have a couple of "316" saucepans which are most definitely magnetic!

 

[William_H]

Good old oxalic acid would be a good thing to try to restore the clean look of the SS. olewill

 

[lpdsn]

Why is it happening if the material is 316?

I understood from a conversation with a yacht designer that 316 is not suitable for welding. Apparently Cr Carbide is produced which detracts from the corrosion resistance. Apparently there is a grade 316L that should be used.

Alternatively: I was once told by someone doing North Sea oil rig weld inspections that the wrong type of rod is often used by the welder.

 

[Neeves]

There is nothing wrong with stainless steel made in China - provided you buy it from a reputable supplier and to a specific specification and that specification is checked.

I'm buying, or involved in the buying of, lifting chain and components - we check every delivery. Bunzl who check the components also check shackles coming from China and if they find 2 shackles out of specification they sample again and if the find another 2 out of specification they send the whole container back to China, where they are destroyed.

The bendy anchors - made in China - were bendy because the the then NZ license operators thought less strong steel would be adequate - the Chinese operator caught some of the flak - but it had nothing at all to do with them. The company who set up the investment casting of the fluke (of the bendy anchors) specialises in cast stainless components for staircases, window fittings, balconies - they would be out of business if their components rusted. Despite the bendy anchors saga they are still going strong with a high reputation.

G30 Chinese, short link, metric, anchor chain has consistently been at or near G40 strength - though this might change. But over the recent past it has been excellent quality.

Its all about specification and quality control - if its cheap - there is usually a reason.

And Xenophobia has no place here.

 

[macd]

And Xenophobia has no place here.

On the contrary, Jonathan, it's hugely popular (and in the Lounge almost de rigueur).

 

[alant]

Good old oxalic acid would be a good thing to try to restore the clean look of the SS. olewill

Permanently?

 

[Neeves]

On the contrary, Jonathan, it's hugely popular (and in the Lounge almost de rigueur).

 

[vyv_cox]

Staining of 316 wire is common, caused by crevice corrosion. The crevice are tiny laps formed during the drawing process. They are unlikely to cause serious problems. The welding comments are correct, 316L should be used.

 

[Kukri]

There is nothing wrong with stainless steel made in China - provided you buy it from a reputable supplier and to a specific specification and that specification is checked.

You don't say!

I'm buying, or involved in the buying of, lifting chain and components - we check every delivery. Bunzl who check the components also check shackles coming from China and if they find 2 shackles out of specification they sample again and if the find another 2 out of specification they send the whole container back to China, where they are destroyed.

The late Mandy Rice-Davies had something to say about that...

The bendy anchors - made in China - were bendy because the the then NZ license operators thought less strong steel would be adequate - the Chinese operator caught some of the flak - but it had nothing at all to do with them. The company who set up the investment casting of the fluke (of the bendy anchors) specialises in cast stainless components for staircases, window fittings, balconies - they would be out of business if their components rusted. Despite the bendy anchors saga they are still going strong with a high reputation.

A citation would be nice, here,

G30 Chinese, short link, metric, anchor chain has consistently been at or near G40 strength - though this might change. But over the recent past it has been excellent quality.

True. And as I think Vyv Cox has pointed out, this is simply because a higher tensile steel is used, possibly because mild steels are not as readily obtainable as higher tensiles in China.

It's all about specification and quality control - if its cheap - there is usually a reason.

You don't say!

And Xenophobia has no place here.

Nor do ad hominems and I rather doubt that I would have spent twenty years working for a Chinese company were I prone to it.

 

[alant]

Staining of 316 wire is common, caused by crevice corrosion. The crevice are tiny laps formed during the drawing process. They are unlikely to cause serious problems. The welding comments are correct, 316L should be used.

What about staining of 316 handrail tubing?

 

[vyv_cox]

What about staining of 316 handrail tubing?

Could very well be exactly the same cause. Wire and tube are manufactured using very similar processes. With wire it seems that these small defects may be due to poor lubrication during the drawing process.

 

[alant]

Could very well be exactly the same cause. Wire and tube are manufactured using very similar processes. With wire it seems that these small defects may be due to poor lubrication during the drawing process.

Substandard tubing?

Presumably this should also be 316 L grade.

The wire corrosion, is seen where it is threaded through holes in the upright stanchions, perhaps due to the wire rattling in the holes & any protective layer being continually eroded.

 

[Martin&Rene]

The oil & gas industry would not use 316 type stainless steels of any type in a seawater application and instead use the much more highly alloyed super duplex stainless steel or 6Mo austenitic stainless steels. The point that many people forget is that in this type of situation we are not looking at standard seawater at a temperature of around 15deg C. Evaporation of the water will mean that the solids content can increase significantly and heating by the sun can raise the temperature significantly. Hence the advice to rinse a yacht's stainless steel hardware on a regular basis with fresh water or British rain.

 

[Neeves]

Minn,

I'm not sure what citations you need but Vyv and I both wrote an article for YM, following an earlier one I wrote, on the bendy shanks - it covered the whole sorry saga in considerable detail. I'm sure if you go through the archives you will find it. But its history now, arguably the brouhaha has resulted in the brand being instantly recognised (but the reasoning lost) and there have been no issues at all since.

Jonathan

 

[Neeves]

The oil & gas industry would not use 316 type stainless steels of any type in a seawater application and instead use the much more highly alloyed super duplex stainless steel or 6Mo austenitic stainless steels. The point that many people forget is that in this type of situation we are not looking at standard seawater at a temperature of around 15deg C. Evaporation of the water will mean that the solids content can increase significantly and heating by the sun can raise the temperature significantly. Hence the advice to rinse a yacht's stainless steel hardware on a regular basis with fresh water or British rain.

I would agree - duplex is the way to go , except its eyewateringly expensive. If you get a quote for a single shackle, for example - you simply do not believe it. Good British rain seems a much cheaper option.

Jonathan

 

[Neeves]

Minn,

Bit of thread drift here:

You said:

True. And as I think Vyv Cox has pointed out, this is simply because a higher tensile steel is used, possibly because mild steels are not as readily obtainable as higher tensiles in China.

But the trend is true in America, Europe and Australia - all make chain far stronger than specification - whether it is G30 which is almost and sometimes better than G40; G40 or G43 which is near or exceeds G50 strength.

Some G30 chain could be sold as G40, it would meet specification - just (and evidence seems to suggest this is happening). People buy G40 - yet G30 is near G40 quality and has zero failures.

If the welcome and outstanding safety record of G30 over the recent past is as a result of G30 that we all use being 25% overs strength will we enjoy that same safety record if for some reason supply of 'real' G30 is re-established and strength (and yield) drops by 25%.

Jonathan

 

[vyv_cox]

I would agree - duplex is the way to go , except its eyewateringly expensive. If you get a quote for a single shackle, for example - you simply do not believe it. Good British rain seems a much cheaper option.

Jonathan

Unfortunately duplex as is just as susceptible to crevice corrosion as 316. We conducted trials on submersible seawater pumps trying various grades of SS but eventually reverted to bronze.