For run-of-the-mill purposes, the material from which these items are made does not matter; however, when the items being fixed are steam fittings supporting 275psi pressure, I (and the boiler inspector) have to get this right.
|Boiler shell fixing studs (EN3B)|
|Outer shell in place with fittings & blanking plates|
(for hydraulic testing)
After some considerable amount of searching, I came to the conclusion that the fixings' material required for steam fittings is more to do with what should be avoided rather than what precisely should be used. The material to be avoided is 'leaded' mild steel such as EN1A. Whilst EN1A is easily machined and welded, it is not for this application. This therefore answers why some suppliers of engineering studs do not specify the precise mild steel their stock is made from; hopefully it is safe to assume that they are fit for purpose and will not be made from EN1A!
|Nut and Bolt Inscriptions|
The '8.8' bolt head and compatible '8' nut pictured above are a medium grade metric type suitable for pulling together steam pipe joints; they are easily available off the shelf.
I think I've got to the bottom of these fixing requirements now and have at last placed an order for 11kg of them. So shortly reconstruction of Sentinel 7109 will be able to commence!