De-zincification?

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JimC

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My sink outlet skin fitting had developed a coating of green verdigris. On cleaning this off I found the underlying metal to be be of a much pinker colour than the attached sea cock and started to worry that it might be suffering from de-zincification. It doesn't look like the de-zincification I have seen on other components which has been a localised pink staining. This colour is uniform all over the fitting. The same colour is revealed when scratching the inside bore of the fitting with a file from outside the boat, also the other skin fittings which don't have verdigris on them show the same colour when scratched. The thread form of the fitting is crisp and it rings when struck smartly with a hammer so perhaps it's OK and has always been like this? Any advice appreciated.
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The trouble is, once the thought that it might not be sound is in your mind, you can't escape it. I have replace the skin fittings/ball cocks on the second hand boats we have purchased for just that reason. It's not difficult unless you start to want backing plates and such, but if you just go with like-for-like but in bronze or similar then you can do several in a day. Just use a grinder to grind off the fittings gently outside the boat. Of course when you have removed them they are nearly always OK, but there again an engine seacock came off in my hand once, the fitting so de-zinced that it crumbled like cheese.
 
The valve itself is DZR - the CR marking is clearly visible in your photo. There is no way of knowing whether the skin fitting is or not but taking a file to the threaded part, which should not affect the removal of the nut in future, should reveal bright brass. The best guide as to their strength, which is what you really need to know, is to heave strongly on the hose, levering the skin fitting from side to side.
 
vyv_cox said:
... taking a file to the threaded part, which should not affect the removal of the nut in future, should reveal bright brass....
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It reveals something more like bright copper i.e. pink/brown rather than the yellow of brass, as in the photo, the threads have been wire brushed and the metal is that colour right through.
 
JimC said:
It reveals something more like bright copper i.e. pink/brown rather than the yellow of brass, as in the photo, the threads have been wire brushed and the metal is that colour right through.
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the most critical part to examine is probably the inside where it is in contact with the water. If the pink colour penetrates to any significant depth it would be very wise to change it without delay.
 
I suspect there is a good chance it's bronze. Unfortunately there is no way of telling without it costing more than buying a new one. As I said above, the problem is not the dezincification per se, it's the loss of strength. If it resists your strongest efforts to break it off it will be fine.
 
JimC said:
It's the same uniform pink/brown colour on the inside and the outside. Like on the photo.
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But how deep into the metal does the pink coloration penetrate?

If its only a surface coloration it's not likely to be a problem but if you have to grind into it significantly to find brass or bronze coloured metal then it is .

If its pink all the way through ... dont breathe too hard on it.
 
vyv_cox said:
The valve itself is DZR - the CR marking is clearly visible in your photo. There is no way of knowing whether the skin fitting is or not but taking a file to the threaded part, which should not affect the removal of the nut in future, should reveal bright brass. The best guide as to their strength, which is what you really need to know, is to heave strongly on the hose, levering the skin fitting from side to side.
Click to expand...

The latter best done when the boat is on dry land (one should sometimes state the obvious).
 
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