Why do I get a white powder round my skin fittings? should I worry about it?
The presence of a white crystalline powder on skin fittings and valves should always be investigated in case it is evidence of dezincification. White powder is often assumed to be salts from evaporated seawater and therefore harmless, but it could be something different and much more serious. This can be tested by trying to dissolve the powder in water which, if successful will identify it as ordinary salts. If it does not dissolve in water but will dissolve in vinegar then it is almost certainly not salt but a metal hydroxide.
The hydroxide, usually caused by a leaking skinfitting can have several causes. Some are harmless such as nickel hydroxide or zinc hydroxide formed by the surface plating or galvanising oxidising. This usually happens because a hose tail is leaking seawater over the surface of a fitting. More potentially damaging is zinc hydroxide on non-plated or non-galvanised brass fittings. Zinc hydroxide is white and can be distinguished from copper hydroxide which is green. Where the zinc content of a brass fitting oxidises out it will leave a weakened porous copper rich alloy which will appear carrot red in colour and sound dull when hammer tested.
Most damaging and potentially dangerous is where there is no evidence of an obvious external leak or water source and the powder appears on or around the fitting. This can be evidence that the metal has become sufficiently porous for water to pass through the fitting itself. This fitting will soon fail completely with potentially disastrous results. All powder deposits should be scraped back to bare metal and the metal examined for colour and soundness, and if doubtful must be replaced as soon as possible.