Electrolyisis in SS exhaust?

[thruska]

Send it back to the manufacturer for refund. Go to home depot for a copper or bronze fitting of substantial build. Stainless is not the best for all marine applications. Who knows where the ss came from? Could be bad material, wrong filler rod? Yes, homedepot could be chinese crap too.its a crapshoot sometimes. ?..

[Streetcar]

Response from Paguro Genset agent and manufacturer (based on the same information and pictures) is that it is definitely electrolytic corrosion. So there you are, according to them almost everyone else is wrong.

[Neptune's Gear]

What I said yesterday. Take it off and clean it, both sides. Take pics of the damaged area, post here.... Then we can make a better diag... and perhaps it might be worth pointing out this thread to the dealer/manufacturer. What are your rights as a consumer where you are? Here in NZ some talk of the Sale of Goods act, and fit for purpose come to mind.

[Cheechako]

Originally Posted by Cheechako

Pretty much par for the course for SS. Hot salty water, enclosed ... perfect for corrosion. I once replaced a corroded SS one with iron pipe fittings... actually lasted longer.
If welded assembly, they could improve it's life by solution heat treating after selding. But most manufacturers would pay for that. Are those droplets at the weld line?

Sorry about the nonsense... having trouble with my keyboard. Should read:

Pretty much par for the course for SS. Hot salty water, enclosed ... perfect for corrosion. I once replaced a corroded SS one with iron pipe fittings... actually lasted longer.
If welded assembly, they could improve it's life by solution heat treating after welding. But most manufacturers wouldnt pay for that. Are those droplets at the weld line?

[Tingum]

Cheechako has nailed it. Poor material to use in the first place. You would be better off with iron or aluminum.

[Cheechako]

Yeah, the one in question was on an old Volvo MD2B. It had an elbow that was pipe threaded into a flange on the exhaust. When it failed I tried the Iron pipe. All I needed was a 45degree elbow , a couple nipples, and a tap to thread a hole I drilled into the pipe for the water cooling hose/nipple. One of the few "jerry rigged" things I did that actually worked!
If I were making one out of comon SS, I would probably use 316L (low carbon), after welding I would have it Solution Heat Treated. The SHT returns the structure of the metal around the welding to the same state as the rest. Then it doesnt corrode near as much. Untreated welded SS is an invitation to corrosion.

[boatpoker]

Originally Posted by Streetcar

Response from Paguro Genset agent and manufacturer (based on the same information and pictures) is that it is definitely electrolytic corrosion. So there you are, according to them almost everyone else is wrong.

You might want to point out to them that the galvanic scale (pretty sure it's widely accepted in scientific circle ) does not agree.

[Andrew Troup]

Boatpoker

Electrolytic corrosion is not the same thing as galvanic corrosion

Refer post #10 if you would like a small amount of clarification

[boatpoker]

Originally Posted by Andrew Troup

Boatpoker

Electrolytic corrosion is not the same thing as galvanic corrosion

Refer post #10 if you would like a small amount of clarification

Sorry but you are incorrect. Electrolytic corrosion refers to any type of corrosion involving electricity. There are two basic types under the electrolytic umbrella.

a. Stray current corrosion caused by leaking current whether AC or DC although the corrosive effects of AC leaks are minimal although electric shock drowning is a serious concern.

b. Galvanic corrosion caused by the differing voltage potential of metals whereby the least noble metal in a galvanic cell with corrode first.

[Cheechako]

Not sure why we have such a big focus on defintitions, but doesnt surprise me. Both types of corrosion involve electricity. Where it comes from is what's different.

[boatpoker]

Originally Posted by Cheechako

Not sure why we have such a big focus on defintitions, but doesnt surprise me. Both types of corrosion involve electricity. Where it comes from is what's different.

The difference is important because AC stray current can kill. DC current can corrode ..... a significant difference. Misuse of the terms indicates a lack of understanding of the processes involved and makes resolution of any problems near impossible.

eg. Electrolysis is a term that's thrown around quite a bit but actually refers to chemical changes in the electrolyte and not corrosion. Do you really want to take advice on these issues from someone who does not understand the words they are using ?

[Andrew Troup]

Boatpoker.

The "Paguro Genset agent and manufacturer's claim" is that it is definitely electrolytic corrosion, not electrolysis

Even your broader definition of electrolytic corrosion (which is arguable, in the sense that you can justifiably argue for it) it does not support your proposition that the galvanic scale "does not agree" with their claim.

( I do not agree with their claim either, but that's a different matter)

[Andrew Troup]

FWIW, I stand by my assertion that electrolytic corrosion is not the same thing as galvanic.

According to some definitions, it includes it.

But to say that makes them the same thing is like saying humans are the same thing as females.

[boatpoker]

Originally Posted by Andrew Troup

FWIW, I stand by my assertion that electrolytic corrosion is not the same thing as galvanic.

According to some definitions, it includes it.

But to say that makes them the same thing is like saying humans are the same thing as females.

Please show me where anyone said they were the same thing. My post clearly stated that there were two different types under the umbrella of "electrolytic"

[boatpoker]

Let me make one more effort to make this clear.

"ELectrolytic Corrrosion" an umbrella term that refers to any corrosion involving electricity and an electrolyte (seawater) and covers both stray and galvanic corrosion.

"Stray Current Corrosion" - AC or DC corrosion caused by AC of DC current leaking through an electrolyte (sea water). AC stray current has minimal corrosive effects and may take years to cause noticeable corrosion. DC stray current at it's worst can act extremely quickly and destroy metals in a matter of days.

"Galvanic Corrosion" - is corrosion that occurs in the presence of an electrolyte whereby a galvanic cell is created by the differing voltage of any two metals in contact. The closer these metals are on the galvanic scale the slower the corrosion. The farther apart they are on that scale the faster the corrosion. The lower metal on the scale will corrode and this is how anodes work.

This is not my position this is simply established chemistry. The stainless elbow with not corrode because it is connected to a less noble metal ie. the iron exhaust manifold. There is a bit of a caveat here. The stainless can become anode/cathode within itself due to working and welding but this would put the fault on manufacture and not any electrolytic action emanating from your boat. So it is possible (likely) that there is some electrolytic corrosion here but it is the elbow acting on itself.

Suggest you pick up Everett Colliers excellent "Boat Owners Guide To Corrosion". ABYC also runs a very good "Marine Corrosion Analysis" course and if you really want to spend a few bucks and learn from the best, Captain David Rifkin USN Ret'd nuclear sub commander and consultant to the USN and BoatUS on marine corrosion runs an amazing marine electrical/corrosion seminar.