Stainless steel exhaust ok?

[demonboy]

Wondered if anyone had any experience or opinions on stainless exhaust pipe parts? Looking to replace the rubber pipe in the lazarette but boatyard here wants to replace parts with stainless. Stainless tube with exhaust and salt water? Is rubber pipe better?

Opinions/experience appreciated, cheers.

 

[KellysEye]

I had a stainless exhaust pipe fitted which replaced a rusty steel one it worked fine with no sign of corrosion

 

[NormanS]

There can be problems with welds on stainless exhausts, if incorrect filler rods are used, but I can't see any problem with using plain lengths of stainless tube.

 

[macd]

Hi Demonboy.
I've recently redesigned a 25 year-old exhaust system in my current boat, which included several sections of SS. All were in A1 nick, including the gooseneck, which has been re-used. Exhaust injection elbows, of course, are often SS, and happily run much, much hotter than the rest of the exhaust system (which actually runs quite cool).

 

[vyv_cox]

When the correct grade of low carbon stainless steel, 316L, is welded with rods of the same grade it will last very well in hot seawater. What it doesn't like is drying situations where the chloride concentration is increased by evaporation. In conjunction with increased temperature this is a recipe for stress corrosion cracking. There have been exhaust traps manufactured in stainless steel, perfectly successful.

 

[Tranona]

Can't see any advantage in using stainless rather than the proper rubber exhaust hose. The latter is used because it is is long lasting, flexible and relatively cheap.

 

[macd]

Can't see any advantage in using stainless rather than the proper rubber exhaust hose. The latter is used because it is is long lasting, flexible and relatively cheap.

I'd certainly go along with that, for the resons you give. If the yard is proposing re-making the exhaust in all-steel, that's a nonsense. My earlier post was based on the assumption that they would only make certain elements (the gooseneck, say) in SS. And even bearing in mind that, Vetus hose isn't much cheaper than stainless...

 

[srm]

A previous boat had an all stainless steel exhaust, which was hot until the cooling water was injected just above the outlet in the lazeret. The engine was below the waterline and the previous owner who fitted the engine was concerned that the usual injection point could cause back flooding.
After a few years there were pin hole leaks where the cooling water was injected into the exhaust, These were patched with car body filler from time to time until I sold the boat.

 

[demonboy]

I'd certainly go along with that, for the resons you give. If the yard is proposing re-making the exhaust in all-steel, that's a nonsense. My earlier post was based on the assumption that they would only make certain elements (the gooseneck, say) in SS. And even bearing in mind that, Vetus hose isn't much cheaper than stainless...

No, only parts of it (goose neck, elbow). Here in Thailand I suspect the Vetus hose is more expensive than the stainless, but I'm concerned that I don't know enough about welding to make a judgement on whether the stainless parts are acceptable.

Thanks for the replies.

 

[rob2]

I've often thought of replacing the straight run of exhaust under the fuel tank with a stainless tube with hose either end for easier fitting and vibration absorbtion. If the tube is solid drawn, then there won't be a problem with pin holes as these accur where the welding has altered the structure of the alloy. As others have mentioned, after the water injection elbow, the exhaust isn't all that hot in metallurgical terms. In rough conditions on my mate's boat when it was difficult to check for water out of the exhaust, we would simply touch the pipe to check it wasn't getting hot - in cold weather people volunteered to check!

I wonder whether preformed bends (sleeve fitting) could be superglued on? Maybe better to rough up the surfaces and epoxy them together? It may fail if the water flow fails, but so does hose.

Rob.

 

[demonboy]

I've told the yard I don't want the stainless except at the elbow. The next quandary, however, is sourcing the rubber exhaust hose. I should be able to get Vetus or equivalent but it'll be at a premium, so I was wondering what special properties a marine exhaust has over a dry exhaust. I can get hold of any exhaust size locally but it will be for land-based machinery. Does marine exhaust have special properties that normal exhaust pipe doesn't?

 

[macd]

I've told the yard I don't want the stainless except at the elbow. The next quandary, however, is sourcing the rubber exhaust hose. I should be able to get Vetus or equivalent but it'll be at a premium, so I was wondering what special properties a marine exhaust has over a dry exhaust. I can get hold of any exhaust size locally but it will be for land-based machinery. Does marine exhaust have special properties that normal exhaust pipe doesn't?

I can't answer that directly, mate, but a friend speaks highly of this mob who probably can: http://www.lhss.co.uk/

The main difference between a wet and dry exhaust, I'd haver thought, is that the former runs a helluva lot cooler. Most of it's just tepid.

 

[demonboy]

I can't answer that directly, mate, but a friend speaks highly of this mob who probably can: http://www.lhss.co.uk/

The main difference between a wet and dry exhaust, I'd haver thought, is that the former runs a helluva lot cooler. Most of it's just tepid.

True enough. Just wondered if the salt water has an adverse effect on normal rubber and if marine exhaust is treated to counter the effects of warm, salty, smokey water.

Thanks for the link. I see their brightly coloured silicone marine hoses are SAE J2006 R3 approved, which is a Lloyd's registered requirement.

 

[macd]

Thanks for the link. I see their brightly coloured silicone marine hoses are SAE J2006 R3 approved, which is a Lloyd's registered requirement.

I didn't give the link with the thought they could supply you: might be a bit on the expensive side. But they could maybe advise on which more generic hose might be suitable. I'd have thought, apart from chemical properties, that it needs be wire-reinforced to prevent deformation and abrasion resistant.

 

[KenMcCulloch]

When the correct grade of low carbon stainless steel, 316L, is welded with rods of the same grade it will last very well in hot seawater. What it doesn't like is drying situations where the chloride concentration is increased by evaporation. In conjunction with increased temperature this is a recipe for stress corrosion cracking. There have been exhaust traps manufactured in stainless steel, perfectly successful.

We had a stainless steel exhaust waterlock in our boat which may well have been there from the original fitout. It began to leak and was temporarily and succesfully repaired by welding before being replaced by a GRP one.The boat was commisioned in 1981 and the repair done in 2012 so I think it's fair to say that SS exhaust parts on boat diesels will have a reasonable life.