Internal pitting corrosion in bronze toilet seacock

[jbweston]

I have just dismantled the two Blakes seacocks fitted to the toilet inlet and discharge on my boat. The inlet one was in perfect condition, but the outlet one had some pitting corrosion. This is on the tapered plug in line with the outboard end of the toilet discharge pipe when the cock is closed - i.e. it seems to have been caused by something lying in the pipe against the closed cock.

Has anyone else had this problem and do you know what might have caused it? I'm interested to know whether it occurs with just the sewage, or whether the vinegar and occasional 'Toilet Duck' I use can eat through the bronze.

I've had the boat for just over a year and don't know if the pitting occurred while I have had her, or (perhaps more likely) in the 17 years of her previous ownership. It's always possible someone in the past has used stronger chemicals, for example of the drain cleaner type.

If vinegar or Toilet Duck can do it, then I'll be even more careful to flush them through, although I thought I was doing that already.

The rest of the seacock seems in good condition. This is not general corrosion, and I can't see how it can be electolytic in that position.

Any wisdom appreciated.

 

[BrendanS]

Sit tight and wait for Headmistress to post. There is almost nothing she doesn't know on the subject of marine toilets.

 

[Bilgediver]

This is quite normal and happens on many sea cocks of one sort or another and is usually a slight electrolytic reaction between the plug and the material around the hole in the inlet. So long as there is no pinkness things should be fine.

John

 

[VicS]

Before Headmistress replies try to establish what "Toilet Duck" contains as I think that is brand name not found in the US (even if it was it may not have the same formulataion).

Our favourite flavour of toilet cleaner seems to be Harpic which, according to the label, contains hydrochloric acid.

It might not be wise to leave HCl in the seacocks!

 

[BrendanS]

She has also commented previously on corrosiveness of urine etc, which is one of reasons I haven't jumped in, as she has seen all these problems before, and can probably give a more definitive answer.

 

[VicMallows]

I have the same corrosion on my 24yr old Blakes seacocks, both on the outlet and to a much lesser extent on the inlet. The pitting on the outlet cock is too severe to be cleared by grinding/emery. To achieve a seal, I now turn the lever nearly 180deg from the 'on' position so as to use a 'new' part of the cone, but some pitting is now starting to show there (after about 6yrs). I guess the ideal solution would be to get the cone machined down a little, taking care to retain the existing taper.

Vic

 

[Poignard]

I'll be replacing my 40-year old heads seacock [Blakes] this winter because of deep pitting. However, I first noticed it when I bought the boat in 1997 and I filled the pits with a mixture of epoxy and graphite powder which has lasted since then without problems, but I think the time has come to treat her to a new seacock.

 

[samwise]

As I understand it the only "proper" solution when your Blakes seacocks develop permanent pitting that cannot be cured by grinding and lapping is to fit a whole new unit, including skin fitting because Blakes insist that each seacock is unique and you can't just buy the bit with the handle because it won't fit the barrel properly. Both my last two boats have had Blakes seacocks and in both cases had suffered fairly badly from "fit and forget" syndrome. In one case, the cocks had been turned on and never turned off for a year or more. They took a bit of robust activity with a piece of wood and a hammer to budge them, followed by some hard work with valve grinding paste. You can go too far with the grinding work to the extent that you can destroy the fit and end up with a wasp-waisted plug that will never seal properly. My maintenance regime always includes withdrawal and inspection at every haul out, gently grinding with fine grade past if needs be, but generally just a clean up and liberal application of seacock grease before refitting.

 

[Birdseye]

[ QUOTE ]
As I understand it the only "proper" solution when your Blakes seacocks develop permanent pitting that cannot be cured by grinding and lapping is to fit a whole new unit, including skin fitting because Blakes insist that each seacock is unique and you can't just buy the bit with the handle because it won't fit the barrel properly. Both my last two boats have had Blakes seacocks and in both cases had suffered fairly badly from "fit and forget" syndrome. In one case, the cocks had been turned on and never turned off for a year or more. They took a bit of robust activity with a piece of wood and a hammer to budge them, followed by some hard work with valve grinding paste. You can go too far with the grinding work to the extent that you can destroy the fit and end up with a wasp-waisted plug that will never seal properly. My maintenance regime always includes withdrawal and inspection at every haul out, gently grinding with fine grade past if needs be, but generally just a clean up and liberal application of seacock grease before refitting.

[/ QUOTE ]

That sounds like pretty poor quality control from Blakes - obviously old style British engineering where compnents needed to be "fitted". Made on modern machinery this should never be necessary

I had the same experience when I first put a holding tank into my old boat. The tank in this case was designed to empty by syphon started by a Henderson pump. So what I did was to leave the cock open and let the seawater flush the sewage away from the bronze.

As a long term solution, get a Marelon (?) sea cock. ie a re-inforced plastic one.

 

[gjeffery]

I have just bought a 1.25 inch ID bronze through hull skin fitting to use as a log tube. Apparently top quality (at the price, it should be!) and machined from a sand casting. The outside surfaces are machined, but I was disappointed to find that the inside finish is rough as cast. I have cleaned this up with carborundum paper, but some surface roughness remains.

 

[Poignard]

[ QUOTE ]
As a long term solution, get a Marelon (?) sea cock. ie a re-inforced plastic one.


[/ QUOTE ]

As mentioned above, my Blakes heads seacock is 40 years old. It still seals perfectly and is only being replaced because I feel the pitting has now reached the point where I feel it's time it was renewed. Seems to me that 40 years qualifies as "long term".

 

[VicS]

[ QUOTE ]
she has seen all these problems before

[/ QUOTE ] Brendan, the reason I chipped in was really only to make the suggestion that Julian should should establish what the constituents of "Toilet Duck" are as I know in the past Headsmistress has not always been familiar with UK brand names or variations in composition of brands between here and and the US. In this instance, as far as I can discover, S.C. Johnson do not have "Toilet Duck" in their range of products sold in the US.

Interesting to discover that the stuff we use contains HCl. I believed that they contained NaHSO4. I think that was in the powders of yesteryear anyway.
Not really necessary to use vinegar if you are already using something with HCl in it either.

 

[samwise]

I guess it depends what you mean by "long term." I would think that the Blakes bronze would outlast any plastic replacement and are not vulnerable to catastrophic failure i.e. the handle is unlikely to suddenly break off. The ever-cheerful Nigel Calder has recounted some doomy tales of plastic seacock failures. The ordinary metal ball valves are probably the best alternative.

 

[jerryat]

Agreed! I changed both of mine last year during a big refit only because there was minor pitting but no leaking, and access was then available.

They had been there for 23 years without a single problem. Dunno about the seacocks, but it feels long-term to me!!

 

[Steve_N]

I'm sure it will be due to the corrosive nature of the toilet effluent. I had to replace my heads outlet seacock last year, while all 12 others were in as new condition after 22 years in service.

Although the corrosion didn't look too bad it was bad enough to prevent a good seal being formed by the cone. Worryingly however, to remove the cock I had to 'tap' a pallet knife in under the internal flange to break the sealant bond: to my horror it continued straight through the metal of the cock itself which can only have been 0.5mm or so thick due to the corrosion..

 

[HeadMistress]

I'm familiar with Toilet Duck...it's one of a line of cleaning products made by SC Johnson, a US company. The MSDS for all the Toilet Duck products distributed in the UK are here: http://www.scjproducts.info/nqcontent.cfm?a_id=2699&brand=28&country_id2=2&archive=false

I don't see anything in 'em that would be damaging to marine toilets.

Urine is corrosive to all metals...however, if it takes 15-20 years for it to pit a bronze seacock enough to cause any concern, I don't think you have much to complain about. Steve, I suspect yours were so badly deteroriated because they weren't high quality bronze or they were subjected to either electrolysis or galvanic corrosions, or both.

Aside from that, I don't know what more I can contribute here, 'cuz seacocks aren't marine toilet components. All I can suggest is that you flush a litre of clean fresh water through the system to rinse any urine out before the boat is to sit.

 

[jbweston]

Many thanks to you all - very helpful.