Through hulls resistance

Roberto

Roberto

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I just replaced seacocks and through-hulls on my boat, which were 25 year old.

I was surprised by two things:
1. The old ones were brass (don't know which variety, dzr or not) and being pinker than the pink panther showed important signs of dezincification. However, once I had taken them off I tried to break them beating with a hammer over the concrete, just to satisfy myself at how weak they had become but no matter how I tried there was no way of breaking them. Even the smaller one (a 3/8" that is barely 1.5cm diameter) was impossible to break: the threads were ruined, eventually the pipe was bent but it did not break, and anyway it took a lot of pounding before that. /forums/images/graemlins/confused.gif

2. Instead, as I fitted two of the new through-hulls (these were DZR) and tightened and locked the counter nut on the inside of the boat, I noticed the sealant creeping "inside" the through-hull pipe: they had both very tiny cracks but indeed they were both broken; I had to replace the replacement /forums/images/graemlins/frown.gif .
Maybe a bad casting ? but I doubt it might happen in *two* cases..
At the yard they said I might have tightened the nut too much, but in those cramped spaces with a short wrench I'd find it difficult for anyone to provide enough force to split a fitting...

any ideas of the possible reasons ?

Now I fear all the other new through-hulls (which after mounting appear ok) might split open in the darkest night or when I am half a thousand miles away from the boat /forums/images/graemlins/mad.gif
 
[ QUOTE ]
Chinese say, you buy cheap Chinese stuff, your boat go to bottom.

[/ QUOTE ]


Chinese transitive property: Chinese sell cheap things to UK; myself buy same (but suddenly become expensive) things from UK -> I payed a lot of money to buy cheap things /forums/images/graemlins/ooo.gif

/forums/images/graemlins/smirk.gif
 
Isn't DZR dezincification resistant BRASS.
Viv Cox will be here in a moment to tell you if they are a good choice for thro-hull fittings.
Just looking in the TCS Chandelry catalogue I interested that they describe their ball valves as DZR and some of their skin fittings as Brass!!!
It's all a bit worrying!!/forums/images/graemlins/confused.gif
Whatever happened to Marine Bronze???
 
[ QUOTE ]
Isn't DZR dezincification resistant BRASS.
Viv Cox will be here in a moment to tell you if they are a good choice for thro-hull fittings.
Just looking in the TCS Chandelry catalogue I interested that they describe their ball valves as DZR and some of their skin fittings as Brass!!!
It's all a bit worrying!!/forums/images/graemlins/confused.gif
Whatever happened to Marine Bronze???

[/ QUOTE ]

yes AFAIK it's DZR Brass, I guess it should be a bit better than common brass, of course worse than marine bronze but then the cost would go up 5x or more (plus other possible problems like NPT thread instead of BSP, the valve being stuck and having to be replaced anyway, etc), anyway, my personal compromise choice is "change them all now to DZR brass, replace them again in a few years no matter what"; the whole process is a lot quicker than I thought: I managed to unscrew 5 out of 7 seacocks AND through-hulls in less than a couple of hours, I had to use the angle grinder only for the remaining two big ones, they were 1-1/2" and could not possibly be removed by hand, the nut was plain frozen.
 
<<< Isn't DZR dezincification resistant BRASS. >>>

You're right, here I am /forums/images/graemlins/cool.gif

DZR is brass but its zinc content is very carefully controlled and it contains a few trace elements that make it pretty resistant to dezincification. Blakes seacocks have been made of DZR for quite a few years now.

Next step down are the various brasses with a couple of percent of other elements such as tin, manganese, etc. They have names that make you feel that your selection is worthwhile, like Naval Brass, Admiralty Bronze, Manganese Bronze, but they are only improved brasses.

At the bottom come the brasses. I am amazed that so many chandleries proudly announce that their skin fittings are made of Tonval, as if this is something special. It isn't, it's just 60/40 brass with 2.5% lead and almost nothing else. It is very definitely not resistant to dezincification and should be used with caution.

'Proper' bronze is expensive due to the fact that it contains 10% or more of tin. It has superb corrosion resistance but fittings made from it would probably be about twice the price. No doubt this is why Blakes changed from gunmetal to DZR.
 
<<< I had to use the angle grinder only for the remaining two big ones, they were 1-1/2" and could not possibly be removed by hand, the nut was plain frozen. >>

Angle grinder will do it but makes a lot of mess and plenty of opportunity for grinding the hull as well. I picked this up last year, if I remember correctly it was from Skipper Stu. Excellent method, which I see that PBO omitted in their recent article on the subject.

Bang a piece of scrap wood into the skin fitting from the outside. This is simply to act as a support for the pilot drill. Get a hole cutter that is just about the size of the OD of the threaded part of the skin fitting. Drill through from outside the hull. The hole cutter will remove the flange of the fitting and the threaded part can be tapped through into the boat. The whole job takes about 10 minutes, with no risk of unwanted damage.

Perfect!
 
Quite a lot of possible reasons. contaminants such as lead, bismuth and others can cause brittleness, as can heating in a critical temperature range during manufacture. Plating can also be a cause, stress corrosion cracking being the result.

It seems to be quite common, probably due to the general decline in manufacturing standards that has resulted from exporting our business overseas (rant!). I recently bought two central heating radiators. Two of the four brass nipples supplied with them leaked, after I had completely filled the system. On examination they both had cracks, in that case perhaps due to plating.
 
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