BR Standard class 6 No. 72010 'Hengist' and Clan Discussion Thread

My pleasure. I could add the welded seam and the presence of washout plug holes so close to the bottom . It could, however be built to BS2790 with only a relatively thin plate (c30mm) welded to inner and outer box instead of a foundation ring except for the fact that it is obviously curved when looking at the rear trough.

 

The big unresolved question regarding a steel firebox is probably who will design it... ?
In light of what is happening with Tornado i am kind of surprised that it got its CE stamp despite significant departure from the recommendations/ normal practice of its builders, however in Germany a firebox is seen as a consumable and has more than likely already exceeded its best before date...

 

It is a poor quality image but I think what you are referring to are studs to support something like the grate rocking mechanism.

 

Those wash out plugs in the rear corner are a real give away.

 

A place on web for general arrangement drawings of steam locomotives should have been included in UN human rigths.
It can maybe also be some parts for securing boiler to frame?

 

They are bosses welded to the backhead for the studs and nuts for the support plate and bracket.

 

Really agree on this, trying to work through something I find myself crying for detailed drawings which you can make sure of things from e.g. inner and outer firebox dimensions, staying, indication of any patches of drop grate & the tube bundle .........

NB Notwithstanding the above it is surprising how useful a simple locomotive diagram can be: outline drawing, length over outer buffers, details of both the wheel spacing and the the weights on their axles, basic dimensions and also - not always but worth keeping an eye out for & quite often - what I take to be the length over the outer firebox.

 

Sorry to ask a question about wheel slip. Watching a dvd sometime ago on Brit’s. The dvd talked about a brit wheel slipping at speed with the regular close and they put it down to the atomiser. Why would the atomiser cause the loco to wheel slip at speed with the regular closed .

thanks

 

Slipping with steam off was a phenomenon not unique to Britannias. The L&YR 'Highflyer' Atlantics had quite a reputation for it, and no-one ever came up with a plausible explanation.

To answer your question, sort of, the cylinder mechanical lubricator used steam from the boiler to atomise the oil on its way to the valve chest because of the high temperatures there. I assume the theory to be that some of this atomiser steam entered the steam circuit and so powered to pistons leading to the slipping. I can't see it myself, so await other explanations with interest.

 

thanks for the reply.

 

Of course and thank You

 

I’m aware of the phenomenon with the Brits but don’t know the reasons why. The obvious one would be a passing regulator but that would be too obvious for anyone involved. Atomiser steam is obviously present and has been known to move a loco not properly stabled which is why the standards had the atomisers controlled by the drain cock operating valve.

 

Initially the Standards had regulator controlled atomisers, with all the associated operational problems unless you were an ex-GWR driver. Excessive carbonization occurred in the cylinders and valves so the steam supply to the atomisers was changed to the drain cock operating valve. Indeed, it is recorded that the conversion was not completed on all of the Britannia Class until 1955!

 

Which was what the LMS used, GWR practice having influenced the Standards as built (which is a bit weird as the GWR generally used hydrostatic lubricators). Cox' paper to the ILocoE on experience with the Standards refers to the change. Opening of the drains closed a valve on the atomiser circuit to stop the steam flow to prevent a build up of pressure when stationary and avoided the need to get drivers to crack the regulator while drifting. I would have thought it unlikely that there was enough steam from this source to cause the loco to slip while it was in motion.

The attached image is from a booklet on advice to other regions on the Fairburn and Ivatt locos.

 

What I would very strongly suggest to the Clan team is to spend the money and do a full FEA of the firebox, with different staying and wrapper (inner and outer) spacing, and on top of this asses the threaded v welded staying. You don’t need to do the barrel, its much simpler.

Having given this some thought, if it were my call, I would be more relaxed about a fully welded boiler barrel, and outer wrapper, with threaded stays for the inner, primarily because that design limits the heat input to the firebox assy due to welding.

Welded barrels are a good call actually because the lapping joints on rivetted ones are a faff, and the numbers demonstrate its not really required.

What would make me a bit more nervous is a fully welded staying regime, because without a heat treatment process to remove residual stress, its going to be utterly riddled with residual stresses which could become problematic at overhaul. This is potentially part of the story with tornado, but im yet to hear a good counter argument that discounts the effect of residual stress.

Also, are we using inconel stays and welding them to mild steel plate? Because, without a heat treat, that is asking for trouble without very carefully controlling the weld input, pre-heat, post weld cool down and potential post weld heat treatment.

And yes, finally, as others have noted, careful calculation and consideration to the water jacket thickness will make a significant difference to the overall life of the boiler. The clan team could run back to back studies in their FEA thermal model and find which one delivers the lowest peak stressses.

We have clearly defined envelope on this.

We know the frame thickness, and firebox space and we know what kind of inner firebox dimensions we have to play with in terms of suitable grate areas.

Its a perfect MEng/MSc study for a university student. "Minimise staying stress on a fully welded firebox using FEA."

You are moving 3 basic variables.
1. Staying regime. How many and in what pattern.
2. Water jacket thickness.
3. Mechanical fastening. Does moving to a threaded stay reduce peak stresses in the firebox.

It would be tempting to start with a 2D assessment to find which staying regime is optimal, what the layout and pattern is, and go from there.

We know mechanical fastening with threaded stays has zero residuals, but does the effect of the large nuts on the end of threaded stays actually provide so much more support to the plates that peak stresses are reduced solely by this feature. If so, do you make the welded stays have a similar geometric feature, a sort of unthreaded bolt is used as a stay and a fictional nut is used at the other side and fillet welded in where the threads would be on a traditional stay? I guess that’s a 4th variable, but its worth considering.

There are papers out there already on how to model in the residual stress due to welding which can be baked in to the FEA model.
Finite Element Modelling of Residual Stress - A Powerful Tool in the Aid of Structural Integrity Assessment of Welded Structures

There is time to get this right. Id highly encourage the group to consider it and approach some academics who might only be too happy to take on the work and deliver an outcome for very little capital outlay.

 

An FEA would be a sensible approach. A welded barrel can be fine but seam peaking has got to be avoided otherwise it is a recipe for trouble. Who is going to be the certifying authority? One thing that they like is a standard to work to and that gets harder if you are not going to use the original design with grandfather rights. The only thing that we really have is BS2790 and, whilst not technically applicable to loco boilers that seems to be the fall back for most insurance companies. I've not got a copy to hand so I can't look at what it says about staying.

 

Glad you agree on the FEA. If the tools exist, why not use them...?

I suppose you could weld in a backing/doubler plate to guard against this, but im not sure how much of a worry it is....or, another option, could you get someone to roll a seamless tube of the correct dia.... Need some big rollers, could be expensive tho...


BS-2790-1992.pdf Page 19 is where staying appears to begin.

Notable on the wet backed wrapper consideration....

 

The Stanier Class 5s and 8Fs have the same set up as shown in the diagram.

 

I think it was standard on the LMS. I assembled that same type of atomiser and connected up the pipework and taps linkage on 2968 during its overhaul.

 

Whilst a very interesting read, the BS Standard that the pdf refers to is, I quote "This standard does not apply to water-tube boilers (see BS 1113) nor to boilers of the locomotive type."