Construction of 3' Gauge Blyth for Southwold Railway Trust by NBR Engineering, Darlington

Thank you for that. Sensible move to build the boiler first isn't it. Sounds like 120 for the boiler and 130 for the rest then. That's doable. If only there was a derelict 3' gauge line within 40 miles of me :-(

 

In parts I think. Loco Talyllyn backhead clearly has welded square corners. But, I think the throat plate (the firebox front with its transition to the firebox sides and the boiler barrel bottom) is a pressing with curved/flanged corners - or so it appears. Mike

 

Saw this recently, well done to the team at NBR Engineering.
Looking forward to the next phase ...

 

I think that is right, Mike. Nevertheless, somewhat avant garde for its time. ISTR that the pressure is only 140 psi, but that I believe was due to retention of the original copper box, which meant keeping the original stay spacing.

 

Modern ultrasonics will be able to detect cracks in the plates adjacent to the welds

 

Hello All,

When any boiler is made it goes through a number of checks before any metal is cut.

The design process has to be sound, calculations made and then submitted to an independent Authorising Body, in our case British Engineering Services. They confirm they are happy with the design, including flat ends. Indeed flat end boilers have been around since Victorian times - Lancashire Boilers. All modern plant boilers for hospitals, schools, power stations and alike are welded construction with flat ends. Formed rounded plates are required if the boiler is being manufactured with rivet joints to effectively transfer the joint through 90 degrees down the length of the firebox or boiler. We have manufactured boilers with rounded ends because that is what the client ordered.

After receipt of the BES approval, the certified boiler plates are ordered and when received all edges are prepared at an angle for the potential welding. All stay holes are also prepared at an angle too. Once completed, the BES inspector visits to confirm the plates marry with the steel certificates and the weld preps are to the correct angle for a full pentration weld.

Using TIG method, the certified Welder approved by BES then undertakes the knitting together of the plates using TIG with various fills to bring the joined plate back to level. It is the TIG route and hot pass that is the seal for the boiler and the fill on top collectively makes sure that the plates are not going to split apart. The firebox is assembled, again with appropriate joints and the foundation ring is prepared to weld in. When completed, the firebox is heated to relieve stress with appropriate paperwork re the temperatures and all long seam welds are X rayed, to prove there are no issues, voids and cracks. As with the heat treatment, this is undertaken by a third party specialist who issues their own certificate of conformity.
The BES Inspector makes a final visit to make sure he is happy and all paperwork and the foundation ring prep and front tube plate preps are as designed before installation of the firebox and foundation ring, all the stays and the front tube plate.

When finished all external welded joins and stays are then MPI'd (Magnetic Partical Inspection) to again prove there are no voids or cracks in the welds.

The certified boiler tubes are then prepared and installed.

All inspection and wash out holes are stopped up, the regulator hole and safety valve holes are stopped too for a pressure test to the desired maximum pressure. This is left for some time, often overnight to prove no major loss in pressure.

The BES Inspector makes a final visit, proves the pressure test again, checks all certified paperwork is in place for the plates and tubes, along with the heat treatment and weld MPI checks and then can issue his certificate of conformity and stamp the plaque which is attached to the boiler in his presence.

 

Thank you for your very complete explanation.

 

At this point, how long can a boiler sit on the shelf without further testing being required? I believe that once the fire/steam test is done there is a ten year ticket, but could a boiler sit in the stores, unsteamed, for ten years without being regarded as not new?

 

The boiler has been manufactured to specifications agreed by BES.

The Boiler Inspector is the one that will issue the steam ticket and start the 10 year rolling as and when. It is up to them to decide what, if any additional testing is required. As a matter of course, before the in steam test, it has a further hydraulic to prove the fittings like valves and gauges. The steam test also proves fittings arr all ok and that there are no problems. A full visual inspection is also completed, safety valves tested to make sure there is no accumulation of steam with a roaring fire and it at blowing off level. Finally, all methods of introducing water into the boiler work - pumps and injectors.

If it was sitting around in the wrong type of environment, I am sure that they would be adding additional stipulations before a steam test is undertaken.

 

This is one of the main reasons I come on these forums. To read informative posts from the experts in the know.

 

Thank you - illuminating explanation. Do you have an estimated date for completion that you are able to share?

 

Unfortunately I do not have a completion timescale. This is up to the owners but any financial hrlp for them will be appreciated.

 

According to their website, the Contract is for £300,000 and they would like to get it completed by the end of 2020.........
https://www.southwoldrailway.co.uk/trust-projects/2-4-0t-no-3-blyth/
If they don't get the money coming in on a regular basis, then that date will obviously slip.
Like all "new build" projects, they will only get the job done if people contribute to them!

 

It's a costs vs lifespan issue.

Square cornered boilers are inferior for a number of reasons, mostly related to stress cracking. They therefore tend (and I know that is not a definitive statement - there are exceptions for various reasons) to have shorter working lives that boilers with flanged endplates. They are however also much cheaper to build, to the point that one can probably build two all welded square cornered quarry hunslet boilers for the cost of one traditional one.
The issues are more or less proportional to the boiler's size - a corner welded boiler on a small loco like this should have a reasonable lifespan - put one on a black five and I'd be surprised if it managed 10 years.
Most of the cracking in boilers is due to the expansions and contraction as the boiler goes through steaming cycles - the slower it's brought into and out of steam, the better the life span is likely to be.

 

The problems with stress cracking is very much related to size. Big boilers should definitely not have square corners, but small narrow gauge boilers are usually OK.
But one thing related to stress cracking that could not be emphasised enough is the heating up process. Rapid firing up will always lead to cracking. Most critical is getting the whole boiler (including foundation ring) over 50 C when the steel becomes less brittle. And it is only when the water starts to boil at 100 C that the water starts to circulate and evens out the temperature differences between the upper and lower parts.
For our medium size locos of 12 ton total weight we state at least 90 minutes to get up to boiling temperature.

 

It's not just the bringing into steam - it's also the putting to bed. An engine brought on shed with the glass nearly empty and blowing off, which then has the injector stuffed on in one long burst to take it from 180lbs to 50lbs whilst the crew empty the ashpan and shovel the fire out will have a much shorter boiler life than one fetched on shed with 100lbs, and nearly full glass, when then gets injected down to 50lbs to top the boiler up, and is left with a grate covered glowing embers and a ashpan full of hot ash. It's much kinder to an engine to empty the firebox and ashpan the following day once it's gone cold.

 

True, but the dominating problem in that case is the introduction of water with dissolved oxygen (air) in it.
When the injected water is warmed up the air forms small gas bubbles that stick to any irregularities on any surface, and lead to local corrosion.
Next time the irregularity is slightly bigger and the gas bubble will stick to the exact same spot again, and again, and again.
This leads to pitting corrosion that soon will go through the metal plate or tube.

Don't top up the boiler if the fire is to be dropped. We have the rule that after the loco enters the terminal station at its last run for the day the injectors should not be touched. The shunting at the end of the day gives enough steaming to make the oxygen bubbles go away. Our relative small boilers are almost pressure-less the next morning. We have water hose connections on all boilers and can top up with some extra water if needed before lighting up.
For big boilers you keep the pressure up with some fire on the grate, and then the pitting problem is not as grave.

 

Are they also cheaper/easier to make?

 

Much!
Ray.

 

It's probably me but those frames look incredibly thin?
John