Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

"That looks like a classic case of de-zinc caused by exposing BRASS bushes and fittings to hot steam and water.

The bushes and all fittings, or at least the threaded portions of fittings, should be made from BRONZE."

I have many 50-70 yr. old Jensen's with all Brass boilers and threads as well , with no signs of erosion and very little wear , am I missing something ?

Hi Guys,

De-Zinc is caused by an electrolytic reaction between the Zinc in Brass acting as an anode and the very much larger area of the Boiler body being made from Copper (a more noble metal)acting as the Cathode in conjunction with hot, often acidic water such as rainwater, or tap water which contains Chlorine etc, acting as the electrolyte.
It can be more pronounced in boilers that are left partially filled and not drained down and dried fully after use.

St Paul,

If the boiler and bushes are both made from Brass then the problem is largely eliminated as there is very little electrolytic action, although there is still some, since Brass is largely Copper with some Zinc added, and can often appear as small brownish spots on the surface, this is especially so if the boiler is not drained and dried properly after use.
Boilers, bushes and fittings made from DZR Brass (De-Zinc Resistant) are generally immune to this problem.

MadeForThat,

Your metallurgical buddy is quite correct, and YES Pure distilled water (PH Neutral) is the best type of water, with DI as a second option, although this too can cause some issues with ion exchange problems.

That is a nice looking boiler and I am sure it could be restored by fitting new bushes and fittings, however, it would need to be done by someone with the correct equipment and skills.

I wish you good fortune whichever way you choose to proceed.

SandyC (retired boiler maker).