P2 Locomotive Company and related matters

Why would a stay on the RHS of the firehole be easier/harder to replace than the same stay on the other side? The reason for the asymmetry is probably much simpler - for whatever reason, they didn't have sufficient flexibles and placed the five stays required away from the corners.

 

Er..... I hope that no inner firebox ever gets near 600C, even for a short time. If it does, its time for serious panic. The plates are kept relatively cool by the boiler water. Even allowing for a temperature gradient between the flame side and the water side I wouldn't expect it to exceed 250deg.
I do wonder whether the number of flexible stays being installed on this boiler is overkill. I can understand the need for them where copper fireboxes are in use but the differential expansion between steel inner and outer fireboxes is going to be a lot less. I doubt that there has been any FEA carried out (although happy to be told that's not the case) and I suspect it is a jerk reaction to the problems casued by the effectively short stays of the original boiler.

 

I really hope boiler makers are not making design changes on the fly like this because they haven't ordered the right parts. If they are, a great deal else comes into question.

 

We are talking about five stays difference!

 

I'm talking about the underlying engineering practices - if changes are being made on the fly like that, it makes me ask what else I should worry about.

 

Flexible (socketed) stays with a copper firebox? The nearest you get to that is a copper stay. Most likely, the copper firebox is the flexible part.

 

That's something I've never thought about and, when I do, the only flexible stays I've had any involvement with have been on steel fireboxes. Is there a reason why they wouldn't be used on a copper box?

 

I would be utterly gobsmacked to hear that an ISO9001 registered boilermaker had changed the specification unilaterally because they were a piece short.

 

A copper firebox is much more malleable than a steel one. HBSS make their copper firebox sections with a former and a (large) hide hammer!

 

I think on your first point, the evolution of Tornado's boiler fits with Bulleid's aphorism (expressed in the Q&A session to his paper on the Merchant Navy class to the IMechE in 1945) that using flexible stays throws the stress onto the adjacent row of rigid stays (which then get replaced by flexible stays at the next overhaul / re-design and so on).

Adrian Tester (The Physiology of the Locomotive Boiler Part 1, p.245) shows some results of tests undertaken by Flannery of movement of the inner end of stays relative to the other end for three stay positions - front, centre and rear in the top row, one boiler using all rigid stays and one using flexible stays, studying a cycle from lighting up to dropping the fire. Stay holes on the inner sheet initially mainly move upwards, but there is also a forward and backward component (the last most pronounced on the rearmost stay), there being a temperature difference of course between the two sheets, exacerbated in steam days by deposits of scale, which hinders the heat flux. Raising of steam pressure causes a downward movement, but the plates are in constant motion. The maximum displacement was 0.044 inches, the flexible stays generally moved further but not always.

 

In A.F. Cook's "Raising steam on the LMS" he has a long section discussing staying of LMS boilers, and the variations over time between copper, steel and Monel stays, along with the concept of "breaking zones" where the stays were particularly susceptible to fracture.

With regard flexible stays, he writes (page 192):

The above discussion has dealt with rigid stays, that is, stays which were screwed into both firebox plates. In other countries, especially North America, extensive use was made of so-called "flexible" stays, in which the inner end was screwed into the inner firebox plate, but the outer end had a spherical bulb formed on it, which was housed in a spherical cap welded to the outside of the firebox. This reduced the rigidity of the stay considerably, and these stays were considered essential in the very long fireboxes and combustion chambers of latter-day American boilers. The only engines for a British railway built with flexible stays were the Bulleid Pacifics, which had one annulus of them in the throatplate around the neck of each thermic syphon, but a more conventional application of these stays was made in the WD 2-10-0. These had flexible stays around the combustion chamber and the front breaking zones at the sides.

A spare boiler for the 2-10-0s was made at Crewe in February 1952 under order BS9/156; the boiler class was BR11 and the boiler number BR11/960. This was the only boiler with flexible stays to be built at Crewe. These stays gave satisfaction in the 2-10-0s, and it is therefore interesting to note that R.A.Riddles, who had overall responsibility for the WD designs, and must therefore have been party to the fitting of these flexible stays, did not specify them for the wide firebox BR boilers. There was, however, the difference that the WD 2-10-0s, like the Bulleid Pacifics, had steel fireboxes, whereas the BR standards had the usual British copper fireboxes.
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So that suggests that in British usage, and presumably as well in North American, flexible stays were only used on locos that had steel inner fireboxes.

Tom

 

That book by Adrian has passed me by and it’s a bit late to ask Santa for it now but I’ll have to save my pennies and get it. It will be interesting to read what he has to say about things.

 

I think that copper boxes was largely a UK practice although not exclusively so. The British loco builders who exported to other countries had much more experience of steel boxes as they had to provide what the buyers wanted. I believe that Riddles consulted with the private builders before building the Austerities and they probably recommended flexible stays as that what they would have supplied on the larger boilers.
My experience of flexible stays has been confined to the Austerity 2-10-0’s and the S160 and, even then, confined to preparing the outer wrapper to fit them. I’ve no experience of maintaining them.

 

In France there is no current legislation covering copper fireboxes so they can't be steamed. There aren't that many anyway, the last being produced in the early 20th century. The 230D that used to be at the NVR and once owned by the NRM, is one such loco. Before it returned to France it was at the former Resco in Woolwich for lap repairs but Resco couldn't source any copper that matched the existing copper (arsenic content probably).