Stainless v P. Bronze??

[Geoff]

Hi Everyone,

OK, I feel I should know this, but what are the pro's and cons about using stainless steel BA screws in copper boilers as opposed to phosphor bronze?

My Maid of Kent boiler, although never steamed, was made some years ago, and hasn't got silver soldered bushes for all the fittings, like regulator gland and injector steam gland. Good old LBSC recommended home made PB screws (5 or 6BA), but I see no reason not to use commercially available stainless screws.

Is there a difference between the 'softness' of PB that makes it better for screwing directly into copper? Or is there really no difference? Your views will be much appreciated.

Geoff

[the_viffer]

Some grades of stainless are subject to corrosion in the presence of trace amounts of chloride ions as found in tap water especially some kinds of softened water. The problem may be worse when fitted to a copper boiler.

The advice from one of my club boiler inspectors re my Maid boiler was to use 316 aka A4 stainless and preferably not to let them get in contact with steam.

I'd suggest you check with your boiler tester for definitive advice.

I bought my fasteners from www.a2a4.com (with whom I have no connection) who do metric size ones at very fair prices. I used socket cap head M3 as I recall at a small fraction of the price of BAs. Much more chance of removing them intact than hex head PBs