electrolysis on Stainless waterlock

[davidmh]

I have a stainless waterlock on my boat, it normally lasts about 7 years before the corrosion from the exhaust gases causes a leak. It is not possible to fit a Vetus type plastic waterlock they are all to tall to give sufficient fall from the engine. The current one has just failed and the guy I use for welding up a new one thinks that there is some electrolysis going on and suspects a reinforcement wire on the exhaust hose from the engine may be touching the engine and passing on the voltage. I cannot find any connection but it would be easy to run a wire from the silencer to the boats hull pear anode. Would this be detrimental?

David MH

 

[Plum]

I have a stainless waterlock on my boat, it normally lasts about 7 years before the corrosion from the exhaust gases causes a leak. It is not possible to fit a Vetus type plastic waterlock they are all to tall to give sufficient fall from the engine. The current one has just failed and the guy I use for welding up a new one thinks that there is some electrolysis going on and suspects a reinforcement wire on the exhaust hose from the engine may be touching the engine and passing on the voltage. I cannot find any connection but it would be easy to run a wire from the silencer to the boats hull pear anode. Would this be detrimental?

David MH

I think electoysis is a red herring and is not causing the corrosion and an anode will not help at all. A non metalic waterlock is the way to go. Vetus do a big range and if you have a height problem they do a very low one Rotatable waterlock/muffler type NLPH45 - Vetus

 

[rogerthebodger]

It may be possible to fabricate a plastic water lock in the shape you wish using HDPE as used in fabricated tanks.

I have a stainless steel waterlock and I have had no issues for over 10 years. I made mine my self from 3 mm thick 316 if that helps

 

[penfold]

Is there room above the engine to fit a taller water injection elbow? That would allow use of standard plastic waterlocks.

 

[B27]

To do any good, the anode would need to be in the water that's doing the corrosion, i.e. inside the water lock just as you have an anode inside a heat exchanger.
You could get a boss welded on and use a screw in anode like this:
BETA MARINE ZINC ANODE, 209-61840, GENIUNE PARTS, boat, | eBay

I don't buy the reinforcing wire thing, but you could isolate it surely?

Hot sea water is nasty stuff, a GRP waterlock might be better?

 

[RivalRedwing]

GRP ones by Centek are another option, ASAP (for example) supply them

 

[Tranona]

It is more likely crevice corrosion in the weld. Very common in the stainless end caps of the Volvo rubber muffler. The lower part of the waterlock, particularly around the outlet spigot spends most of its life in perfect conditions for crevice corrosion - oxygen starved water. Slightest inclusion in the weld gives a start to the corrosion. One solution is to weld doublers on the outside of all the welds. That is how I had one end cap repaired and the welder had done several in the past that had extended the life.

Another supplier of moulded ones here

halyard.eu.com/wp-content/uploads/2022/07/T2966-Halyard-Product-Range-Brochure-Issue-7.pdf#page=4

 

[vyv_cox]

Where is the failure - in the welds, immediately alongside the welds, at the inlet nozzle or all over? The cause of each location is different, diagnosis is impossible without this information.

 

[pandos]

Have you opened it up? if so what is inside?

Reason I ask is that I have one and this morning whilst thinking about positioning a heater in the engine bay, I began to realise in the 20 years i have the boat that I never really looked at mine, as the engine is out it would be a good time to have a look and renew any parts that need to be be renewed.

 

[B27]

Is the welder filling the waterlock with argon before welding it?

 

[Tranona]

Have you opened it up? if so what is inside?

Reason I ask is that I have one and this morning whilst thinking about positioning a heater in the engine bay, I began to realise in the 20 years i have the boat that I never really looked at mine, as the engine is out it would be a good time to have a look and renew any parts that need to be be renewed.

Don't think the OP has a Volvo muffler but a custom made stainless one.

If you do have a Volvo one as per your other thread, they are very simple. Large diameter reinforced rubber tube with end caps in stainless. The forward input end cap has a 45mm tube welded in towards the top to take the exhaust and water. The aft cap has the outlet welded through at an angle so that inside is always under the water - that is what creates the waterlock. The lower part of the inside weld is the weak point, not only is it difficult to get a good clean weld because of the angle but it is also under water. First indicator of failure is pin pricks in the cap below the outer tube and a fine spray when the engine is running, or rusty water in the bilge. Caps are not available on their own and a new assembly is over £400. Although I replaced my failed one, I also had the old one repaired with a doubler on the cap round the tube. cost about £50.

 

[rogerthebodger]

Is the welder filling the waterlock with argon before welding it?

I did not when I welded mine/

The one issue when welding stainless steel is chromium migration from the weld zone

 

[vyv_cox]

I did not when I welded mine/

The one issue when welding stainless steel is chromium migration from the weld zone

Exactly, hence my question.

 

[davidmh]

Thanks for all the replies.
Tranona - The halyard link was good, they have so good cylindrical waterlocks at a reasonable price but none quite small enough in diameter to enable me to achieve an acceptable drop from the engine. The also do "cuffed" exhaust hose, anyone tried it?
Vyv - The corrosion is very limited, there is a small pitted area in the inlet and and outlet pipe. There are a couple of patches of more general corrosion on the base of the cylinder one patch near the end plate weld and the very slight pinholes in the area ringed on the photo. Two photos attached, how it works
David

 

[vyv_cox]

Thanks for all the replies.
Tranona - The halyard link was good, they have so good cylindrical waterlocks at a reasonable price but none quite small enough in diameter to enable me to achieve an acceptable drop from the engine. The also do "cuffed" exhaust hose, anyone tried it?
Vyv - The corrosion is very limited, there is a small pitted area in the inlet and and outlet pipe. There are a couple of patches of more general corrosion on the base of the cylinder one patch near the end plate weld and the very slight pinholes in the area ringed on the photo. Two photos attached, how it works
David

Your photos suggest the pitting is on the outside of the trap, in one case beneath the hose. Is this correct?

 

[davidmh]

Vyv - yes beneath the hose. the other areas are on the outside of the case, it is clamped to to stainless shoe which does make contact with the area of the corrosion, there is no leak from this area. The area circled looks different it is very small pin holes and a slight discoloration almost as if the corrosion on the inside is about to break through, this is where the leak is.

David

 

[penfold]

A taller water injection elbow will give you more choice of waterlock, assuming the engine compartment has space to accommodate one.

Thanks for all the replies.
Tranona - The halyard link was good, they have so good cylindrical waterlocks at a reasonable price but none quite small enough in diameter to enable me to achieve an acceptable drop from the engine.

 

[vyv_cox]

Vyv - yes beneath the hose. the other areas are on the outside of the case, it is clamped to to stainless shoe which does make contact with the area of the corrosion, there is no leak from this area. The area circled looks different it is very small pin holes and a slight discoloration almost as if the corrosion on the inside is about to break through, this is where the leak is.

David

Definitely not electrolytic, looks nothing like it. It seems to be crevice corrosion due to water between the trap and hose/bracket/support. The hose one is easy, use some sealant. This may arrest the leak that is causing the rest.

I had a central heating tank that failed like this. Corroded through from outside where the tank was in contact with its stand, rainwater accumulation.