76077

Although built with Monel (or steel for that matter) as stays are changed they get bigger and there comes a point where it is necessary to change to copper for flexibility.

 

The change from steel to copper occurs at about 3/4" dia. Above this, the poor conductivity of steel means that they just erode away. For Monel, copper is probably cheaper at these sizes.

In the late 1980s, the cost of material for replacing all small 1/2" steel stays (about 700) in 6106 with Monel was about £2,000.

 

Thanks. That sort of suggests that the monel stays (or perhaps the copper plate around the holes) wears fairly quickly and there was a general approval to switch from one stay material and diameter to another. From the video, the stays seems to be uniform within areas with the larger copper stays in the lower part of the sides and smaller diameter stays higher up - perhaps still monel?

Nickel is the largest component of monel and is currently around 50% more expensive than copper on the LME. Presumably one needs more copper than nickel as the stay diameter is larger but monel seems to be a multiple of the nickel price. I suspect staying a firebox with monel would be an eye-watering cost but I don't think I have seen mention of monel being used in boiler mfr/overhaul bulletins on NP.

 

6106 certainly has Monel stays but the GWS haven't used Monel stays since, to my knowledge. It's tough stuff to machine! The Bluebell Railway's Q is currently having Monel stays installed by Leaky Finders. Many BR Standards had Monel stays from new.

 

Thanks, that is interesting, I wonder how much that is costing? (There is an update at https://www.bluebell-railway.co.uk/bluebell/loco_news/oh_541_2023.html). I think model engineers find monel stays difficult both because of machining and taking flux for the silver soldering.

 

There’s a photo here which shows the boiler before the previous overhaul. You can see a mixture of stay sizes for Monel and copper stays.

This is I think essentially the state of the boiler as it left BR service, including the patches to wartime bomb damage. Those were replaced last time round. This time round there is more extensive platework replacement.

https://www.bluebell-railway.co.uk/bluebell/loco_news/12/boiler_robf4348h.jpg

Tom

 

Thanks, very interesting. There are also some other very interesting images in the reports albeit somewhat small, such as the image of the replacement steel outer plate in the June 2024 bulletin which is being drilled for the stays. I wonder how they can confidently determine the locations and the angle of the holes as the inner plate seems to be remaining as is with the original stay holes. (I have taken the liberty of enlarging and tweaking the image).

 

At this stage, they would probably be smaller pilot holes which would be enlarged later for tapping.

 

Crown stays have to be steel because of the length. The crown stays nearest to the seams have to be riveted rather than nutted to allow access to the seams. Of course, on 6106, the heads had burnt away so had to be replaced. At the time, Didcot didn't have the means to put the boiler on its side so drilling was not possible. Also the next size up stay tap was not available, so all the crown had to be replaced same size. Removal of the lower end is easy with oxy-acetylene, apart from the risk of getting molten steel in your boots! The top ends had small holes drilled in them at an angle into the water space; this was then carefully enlarged with oxy-acetylene. The remaining shells were collapsed with a small chisel.

 

In response to an earlier question about the copper and the problems of welding in new copper. I’m told that we have no issues with 76077 (relief). There is now the technology to do chemical analysis of materials and we took advantage of a kind offer to do a thorough exam of the boiler.
We are hopeful to have 77 on display in the car park on Saturday 7th June at Toddington after which it will be returning to LMS at Loughborough. Keep any eye on this page as things may change if the weather is horrendous.