In the dark old days when I went to work:- it was drummed into us the importance of knowing that the material you used was of the correct grade and quality, so you had to keep a detailed build records the material Certificates of Conformity for every part that you made so that things could be traced back if anything went wrong, particularly with a safety critical part.
Wind forward to a happily retired Stew beavering away in is shed making the regulator for his loco, the drawing states that the cone and rod should be made from stainless steel, the material for the rod was ordered and stainless steel material was delivered as ordered, for the cone I found a piece of what I thought was stainless steel salvaged from a printer, it looked and tasted like stainless so certain was I that I didn't bother to test it with a magnet, the cone was made and silver soldered to the Rod and the whole lot fitted to the loco, when it came to running the loco last year all worked fine.
Last week after the winter lay off and after a bit of maintenance work on it I took the loco out for a pre season steam up just to test everything out. With a good pressure showing on the gauge I put it in gear and she started to move off with the regulator still closed:- panic panic, quickly put her back mid gear and she stopped phew
checked every thing out regulator closed put her in gear and off she set again, obviously there was something wrong with the regulator, nothing for it but to drop the fire and take her home for an investigation.
Stripped the regulator down and it was immediately obvious what was wrong the cone was heavily corroded it was made from mild steel:- it must have been a piece of ground mild steel that I salvaged from the printer making it look like stainless
I was lucky it could have resulted in a nasty accident but I got away with it this time.
I've now made a new cone and recut the seat and its now fitted:- I'm absolutely certain that it is made from stainless steel this time.