What concerned me was that the main part of the 'plug' consisted of a malleable iron socket. As a material, malleable iron is definitely not recommended for use with steam at 275psi!
The Heritage Railway Association (HRA) has produced a report on boiler washout plugs and go to great length to ensure that the correct tapered threads are used on the plug to match that of the tapered hole. Here, Sentinel have not used a tapered thread at all; it is a parallel thread (1/2" BSPP)!
After much searching, I found a source of suitable parallel plugs made from 316 stainless steel. Peter Hawkins, our boiler inspector, is happy with this as a strong enough material for the plug although he pointed out that it may be difficult to remove in future. Stainless steel tends to snag against stainless steel; however, the boiler itself is not stainless and so I have decided to take the risk. (I hope I'm right as this is a useful hole for putting water into the boiler!).
The plug is now tightened to 50Nm torque on to an annealed copper washer with Steamseal in all the right places to prevent any leaks.
The new and the old:
|And the new one doesn't rip your clothes as you squeeze past!|
|One of the six|
(with lashings of graphite grease!)
|Have Pipe will Travel!|