Soldered plumbing joints/seawater OK?

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paulsmith

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For practical reasons of access etc I would like to solder a short length of 22mm copper tube onto the heads basin seacock to then attatch the hose. As a plumber I am happy about the integrity of the joint itself, but are there any corrosion issues with the seawater and the solder? the ball valve itself is a DZR one and I assume the through hull flange is bronze. There are no electrical connections to anodes etc.
Paul
 
Soft solder is an alloy of lead and tin. Whilst tin is a noble metal, and fairly well up the scale in terms of electrolytic action, lead is low down. Therefore if in contact with seawater a soft solder joint may be eroded away. I am not too certain of the level of risk, but just as brass can become weakened and porous through de-zinkification, there has to be some risk of soft solder going the same way as it is about 60% lead. If you can do it, I would prefer silver solder, but that will require a lot of heat. As an aside I once saw someone silver braze a copper pipe to a "bronze" fitting using an oxy-acetylene torch. The fitting however proved to be brass instead of bronze, and started to melt in the flame. Quite a lot of fittings are an alloy called Tonval, which is in fact a brass (i.e copper-zinc rather than copper-tin)
 
I know for gas and fuel regs they state that compression joints must be used as vibration over time can break a solder joint.

I would guess this being the case, if it cracked and allowed the oggin in your insurance may not be too pleased.

This is not based on any facts, except the first sentence, just thought it might help your decision. Any reason you do not want to use hose?
 
Thanks folks, I think as the replies suggest It's probably best to find another jointing method to be on the safe side.
thanks again
Paul
 
Silver soldering alloys are available with a range of melting points the one I have is suitable for brass and bronze so it should be possible for you to find something similar.

I ought to be able to comment on the susceptibility of silver solders and tin/lead solders to corrosion but I'm afraid I can't. One day I'm going to set up some little experiments with them to try and find out a bit more.
 
VicS said:
Silver soldering alloys are available with a range of melting points the one I have is suitable for brass and bronze so it should be possible for you to find something similar.

I ought to be able to comment on the susceptibility of silver solders and tin/lead solders to corrosion but I'm afraid I can't. One day I'm going to set up some little experiments with them to try and find out a bit more.
Click to expand...
I am contemplating a silver solder job on the sea water intake. I notice that silver solder does contain zinc. Do you think the joint could de zincify?
Plus what are your thoughts on ordinary lead tin solders, I imagine the new stuff is zinc tin combination?
Stu
 
skipper_stu said:
I am contemplating a silver solder job on the sea water intake. I notice that silver solder does contain zinc. Do you think the joint could de zincify?
Plus what are your thoughts on ordinary lead tin solders, I imagine the new stuff is zinc tin combination?
Stu
Click to expand...

Some info on Johson Matthey's website In particular see page 13 for suggestions re use in contact with seawater. http://www.jm-metaljoining.com/pdfs/Silver Brazing Alloys and Fluxes.pdf
The materials to be joined may be significant.

I think only solders for "difficult to join" metals are tin/zinc. Personally I have enough tin lead solder to see me out.
 
I can't in all conscience advise you to go ahead, but the joint is basically a push fit with solder wicked in by capillary action. Therefore, the width of the joint is substantial compared with the cross section which will be attacked by seawater corrosion. It is quite likely that the copper pipe will be more of a problem than the joint itself. Having said that, I once constructed a manifold for the heat exchanger on a marinised engine entirely from plumbing joints and its still going well ten years on - better than a lot of commercially supplied equivalents! I guess the main thing is that the line should be isolated by a seacock so it can be sut off should it develop a leak.

Rob.
 
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