Dealing with boiler expansion?

[Lawrence]

Knowing nothing about steam locos, a discussion at work left some unanswered questions namely; in general, how was the bolier mounted on the chassis and how did the engineers deal with expansion of a hot and under pressure boiler?

We chucked many theories about between us but would be grateful if someone could provide the real answer, thanks all

[greenglade]

The boiler expanded by a considerable amount around the firebox area, on live steam models which I'm sure follow full size practise the firebox section is held on a sliding plate while the smokebox is fixed solidly which in turn is bolted to the frames. This allows the boiler to expand and contract on it's rear mounting point safely, I believe the full size A3's would have something like 2-3 inches of movement which can clearly be seen in some photo's.

 

Pete

[IWCR]

As stated boilers are fixed at the smoke box end and the firebox end is supported on sliding plates.

The figure of 2-3" given is however excessive; for a small loco I would not expect it to exceed 1/2", probably

around 1" for a big express engine. Road locomotives (Traction Engines) use the boiler as a structural member

hence actually get slightly longer when in steam.

 

Pete

[Lawrence]

Thanks for your reples gents, that clears that up then

[Katier]

On a related note, were the tubes of the same material as the boiler itself... Reason I ask is that you'd want the whole thing to expand at a uniform rate, and different materials expand at different rates.

[New Haven Neil]

Sensible supposition really, but not always is the answer. Older locos in the Victorian era sometimes had brass tubes with iron boiler barrels, but the norm more recently is all steel as you would expect.

 

Dolgoch is mentioned as having brass tubes and a Lowmoor Iron boiler barrel, presumably a copper inner firebox too.

 

NHN

[JeffP]

Weren't the tubes in mnay steam locos made from copper? I thought that was why they were always the first thing removed? Most valuable?

[RANGERS]

My father worked in the steel industry all his life, tubemaking for most of it. He always reckoned one of the most fascinating processes was the production of seamless tubes for boilers, basically forged lengthways from a solid billet using a mandrel to punch through to produce the hollow centre. The quality control for these was intensive, clearly to avoid failures under pressure. In many cases, the plant was subject to production checks by engineers representing the insurance companies of customers buying the tubes, only when they were satisfied would the insurers give cover to the customers for the boilers they were being installed into. Presumably, they followed the installation with the same intense interest.

[Castle]

As stated boilers are fixed at the smoke box end and the firebox end is supported on sliding plates.

The figure of 2-3" given is however excessive; for a small loco I would not expect it to exceed 1/2", probably

around 1" for a big express engine. Road locomotives (Traction Engines) use the boiler as a structural member

hence actually get slightly longer when in steam.

 

Pete

 

Hi All,

 

The solution as stated above is correct. There is a boiler lift going on at Didcot at the weekend so I will take a few pictures and post it on Little Didcot for you to enjoy too. There are a series of bolts that fix a GWR boiler to the saddle which is usually part of the cylinder arrangements at the front end of the locomotive. The slides are mounted on the sides of the firebox and have what Western Engineers call holding down brackets to - errr - hold them down. The slides are not always well lubricated and can sometimes stick. If this happens then you get a situation a bit like an earthquake building up and eventually the boiler will win and the pressure is released with a sudden bang! This is perfectly ok in terms of the machinery but it doesn't make it any the less scary though! What is known as a 'brown trouser moment'... It is true about the controls getting an inch further into the cab as it the engine warms up!

 

Hi Jeff: as Neil says, it was only in earlier locomotives were boiler tubes made of copper. The first prize as far as the scrap man was concerned was the non ferrous fittings but these paled into insignificance when compared to the tons of copper in a large locomotives inner firebox. As an odd little adjunct, the deal with the scrap men was that the whitemetal from the bearings (still in use on BR after the end of steam) still belonged to the railway and was returned after the locomotive was dismembered! There were a lot of copper pipes on a steam engine though. All the lubrication pipe work where you have oil pots remotely mounted from the site of the bearing for example and pipes in the cab are mainly (although not exclusively) copper on a western engine. Superheated GWR locomotives have two approximately 3" copper pipes between the regulator and the superheater header. Lots of copper pipes - just not the ones you were thinking of!

 

Hi Katier: The thing to remember here is that there were always different materials in a boiler. British locomotives almost always had a copper inner firebox but steel outer firebox and boiler barrel. Stays can be made from metals such as steel or copper dependant upon diameter. The other thing is that the metal is in different thicknesses too. The foundation ring of the firebox is far thicker for example than the plate work of the firebox sides it is riveted to. This is why it is always good practice to allow a locomotive to warm up and indeed cool down slowly. Especially on a big GWR engine like a King or a Castle, the boiler is always better served by a nice warming fire the day before the main event! One of the biggest problems that we in full size preservation face is the fact that in steam days boilers were, as far as possible, kept at least warm if not hot and therefore it went through fewer complete thermal cycles. The number of thermal cycles that a boiler in preservation goes through is far higher due to the far more intermittent use. Hence the careful and cautious heating and cooling procedures to lessen the stresses on the pressure vessel.

 

I hope this helps!

 

All the best,

 

Castle

[New Haven Neil]

Nice post, Castle. Brass tubes though, not copper, although maybe copper was used in earlier days, I think it's a bit soft for higher pressures in a more modern full size boiler? All copper boilers are of course common in the model engineering scales.

 

I think the scrappies removing tubes first would have been to get to the copper firebox.

 

Just ask the Tornado boys about thermal cycles!

 

Is monel metal still used for firebox stays? That would be valuable, lots of nickel in it IIRC.

[Castle]

Hi Neil,

 

Copper or brass - the answer is still no!* I think that Wantage Tramway No. 5 Shannon at Didcot has non ferrous tubes but I could be wrong there though.

 

There has been some use of Monel stays in preservation. One of (I think) the Halls in the GWS collection has Monel stays. Our boilersmiths and I had a chat about the use of this material as stays a little while back and the outcome of it was quite interesting. The Monel stays are great and will last for a very long time. So long in fact that the economies of this has to be balanced against the life expectancy of steel plate work of the firebox they are screwed and caulked into. You can get into a situation where the stays are good but the plate work isn't. Then you are faced with the prospect of getting rid of the perfectly good and very hard stays which were much more expensive than the equivalent steel and copper ones when the old metal is cut out and the new welded in. In essence you could have stays that last, for example, 40 years but if the ageing plate work will only do another 10 or 20 before it needs replacing then what is the point? Product lifespan Vs cost. The challenges facing modern steam preservation are not always as clear cut as you might think!

 

All the best,

 

Castle

 

*Just kidding!

[Ohmisterporter]

Not all the holes in boiler tubeplates were for tubes. Longitudinal stays were fitted that bolted the smokebox and firebox tubeplates together. I think the idea was to prevent the tubeplates from bowing outwards under pressure, thereby reducing the risk of the tubes in the middle of the plates becoming loose or shearing. Obviously they were subject to expansion and contraction along with the tubes and boiler barrel. A lot of these things were found by trial and error in the early boilers and some unfortunates paid with their lives to gain us that knowledge.

[jamie92208]

The copper fireboxes were also retained by BR in some cases. there are pictures of rows of Black 5 fireboxes still mounted on the rear drivin g wheels waiting to be reclaimed. it is suggested tin Steam for Scrap that the copper was reused to make the Overhead line on the WCML electrification so ther might still be parts of the Duchesses hanging above the main line. It could make a good start for a ghost story.

 

Jamie

[Castle]

Hi Geoff,

 

That is quite correct. There are areas where there are no tubes and these areas are reinforced with some of the longest 'bolts' you ever did see! The longitudinal stays are screwed then caulked into the steel tube plate at one end and the copper one at the other. The GWR superheater or 'flue' tubes have what is called a 'bottle end' welded on the rear end which is shaped exactly as it sounds and there is a thread on the end that screws into the copper tube plate. The front end is expanded and beaded in place in the normal manner. Nos. 4144 and 2999 are currently having new front tube plates fitted. The Saint had longitudinal stays that were good and the old tube plate was cut out around them and the scrap section 'gently persuaded' to give up its hold! The 41XX has needed the front sections of stays replacing and therefore were cut off back to good metal. The cut ends were dressed and then threaded with a die. A large section of hexagonal bar was machined and threaded to provide a joining method between the old and new sections.

 

All the best,

 

Castle

[Lawrence]

Knowing nothing of the construction of a steam loco this has turned out to be quite a fascinating read following my initial query. Thanks for all your input and I look forward to seeing the pictures.

[Castle]

Hi All,

 

The previously mentioned photos are now on Little Didcot. Click the link below and go to page 10 to have a look!

 

All the best,

 

Castle

[New Haven Neil]

I have also seen 'stay tubes', tubes of much heavier section than the majority, but to be fair this was on very olde worlde lowish pressure stationary boilers, not locomotives. 'Super Lancashires' should curiosity get the better of you. Most of the boilers I have intimate knowledge of had the water inside the tubes though, at pressures that would make Mr Churchward blanche!

 

Very interesting about the monel stays Castle, although I had heard or read about their use I had no practical knowledge. I wonder if they would prove economical in an all new boiler, or whether the need to repair the inner 'box would come along too early as you say.

 

I am a little surprised the 'powers that be' aka insurers allowed the repair to the longitudinal stays as described, in this day and age. I have no issue personally, but I know what they can be like!

 

Great informative thread.

[Castle]

Hi Neil,

 

It is a technique that has been use successfully in the past. When No. 4079 had a new tube plate in 1977 she was repaired this way and that repair is still in her boiler. As long as you can put a sound and solid engineering case to the insurance company, they are fine with it.

 

All the best,

 

Castle

[roythebus]

ISTR being told that a Terrier boiler would expand by 1.5 inches, quite a lot for a small loco.

[New Haven Neil]

Hi Neil,

 

It is a technique that has been use successfully in the past. When No. 4079 had a new tube plate in 1977 she was repaired this way and that repair is still in her boiler. As long as you can put a sound and solid engineering case to the insurance company, they are fine with it.

 

All the best,

 

Castle

 

Good, the clue of course is having a boiler inspector who understands your particular boilers, sometimes an issue. Quite the opposite, we had one come on a ship when I was at sea who was, er, a little overawed by the huge high pressure watertube boilers of a 30,000 shp turbine installation, (this was NOT in the UK I hasten to add!) we could have got anything past him to be honest, quite worrying. Lloyds wouldn't have been impressed..... Equally later saw another in the far east somewhat confused by a Cochrane vertical auxilliary boiler! He was thorough though, used it as a learning experience.

[unclebobkt]

Good, the clue of course is having a boiler inspector who understands your particular boilers, sometimes an issue. Quite the opposite, we had one come on a ship when I was at sea who was, er, a little overawed by the huge high pressure watertube boilers of a 30,000 shp turbine installation, (this was NOT in the UK I hasten to add!) we could have got anything past him to be honest, quite worrying. Lloyds wouldn't have been impressed..... Equally later saw another in the far east somewhat confused by a Cochrane vertical auxilliary boiler! He was thorough though, used it as a learning experience.

 

      I note that only LONGITUDINAL expansion of boilers has been considered;  how about any INCREASE to the circumferance?

[Beatty 139]

The effect on diameter is limited by the fact of it's correlation to cirrcumfrence so the linner expansion of the boiler plate will only increase the diameter by around a 1/3.

 

Don't forget boilers move a lot that's one reason why welded boilers tend to suffer from cracking far more than rivited ones, and the reason why major examinations take place only 10 yearly on riveted boilers but every 5 on welded ones.

[jamie92208]

Having re read the whole thread today I presume that the reason that boilers tend to be fixed at the front is because that is where they need most steam tight joints with the high pressure flows to the cylinders. Thus logically that is the end to fix.

 

The other question that emerges is whether the cabs are fixed to the boilers or not. I seem to remember reading that Riddles fixed the cab structures to the fireboxes of the BR standards.

 

Jamie

[John_Miles]

Until about 1850, the practice was to fix boilers rigidly at each end. I think this was due to ignorance but the result was some spectacular explosions and sadly quite a few deaths.

[Ohmisterporter]

IIRC it was an engineer on the Sheffield and Rotherham Railway who came up with the idea of fixing the front end and having the rear end supported on slides. Not all the best ideas came from the big companies.