Building a Three Drum Watertube Boiler

[Johnlanark]

I made a start today on building a boiler for my new 20 ft boat “Corra Linn”. Boiler making is unknown territory for me, so perhaps if I do a build series, forum members might pitch in with help?

The design is basically from SBA Services Boiler Design Library http://www.steamboat.org.uk/sbas_boiler_designs.htm ref WTB 3b, a three drum watertube weldless type, with 32 sq ft heating surface. Tubes are 12mm Cunifer alloy – that’s Cu for copper, Ni for nickel and Fer for iron. However, the designer John King has further developed some of the detailing since the library version, and my variation also has the splayed out angle of the tubes reduced to fit my skinny boat. John has been extremely helpful in sorting me out.

The heart of the boiler is a 6” diameter steam drum and two 4” mud drums, to a detailed specification of course. I sourced them from Ashworth, which has nationwide (UK) branches. They cost £56. They came well overlength.

So the first move was to trim most of the surplus on my long suffering bandsaw. It took an hour per cut.

While the saw worked, I turned up a slightly tapered hardwood plug with a central hole. With this driven into one end, a 4” tube was set up on the lathe using the fixed steady and also with the tailstock providing end support and lengthwise location, and the tube end faced. Taking small cuts, this set-up worked surprisingly well.


Click for video


I suppose most builders will outsource this heavier work to real engineers such as Steamboat Jack. I enjoyed using last year’s new acquisition, an old Colchester Triumph 7½” lathe, that I bought when I realised that the house we moved to recently has three phase power. Glad I went for the long bed version too!

One end done, five more to go….
John

[froya66]

Hi John

Here in DK we have struggled a lot finding a possible way to home make the PED 200 bar x l boilers.

It would be most interesting to follow your paper work, material certification and boiler inspectors involvement along with the pure technical fabrication description.

Best regards
Jørgen Hansen

[Johnlanark]

Hi Jorgen I am a novice at this, and would welcome input from others on your query. My aim is to have this boiler certified by an inspector from SBA Services, and I understand that for this (a) the boiler design must be demonstrated to be safe, by showing strength calculations of materials and so on, and (b) I must keep all receipts/ certificates to show that I have used the correct materials specified.

For my boiler, the design is sold commercially by naval architect Eur. Ing. John King who has various size three drum and Babcock designs available and is working on a two drum design. He admits he is obsessive about boilers! For my boiler, he advised yesterday that he has moved on from the WTB-3 series of drawings in the SBA Library - MK II drawings are available from him and I can pass on genuine enquiries if any forum members send me a personal message. I know that at least two others are in progress. John also provides details of casings, ashpan etc, together with builder’s notes on sources of suitable valves, pipework and fittings.

So I am confident that the design will be acceptable to the inspector. I do not believe that the inspector will want to see the boiler at least until it is ready for the hydraulic test. In practice it will take a long time after this stage till it is ready for the steam test, and I think I will finish it before requesting the tests. It can be readily part dismantled for internal inspection of the workmanship.

If I have this wrong, someone please put me right!

A little more progress, making a tube bending jig. I copied the end elevation of the three drums and the line of the generating tubes on to MDF board.

Then cut out an 18mm plywood disc for the steam drum notched out to feed the Cunifer tube into and to form a stop for length; also two 100mm diameter discs to form the curves around. Still to do is a guide for the mud drum, probably just to let me start a hacksaw cut and then take the pipe to the bench vice to finish off. The idea being that this setup can be moved to the other tube locations.

Thanks to Gordon Boyd for this idea which he used on his new two drum boiler. Again any comments and suggestions are welcome.
I’ll aim to post some progress every week or two. John.

[steamboatjack]

John,

Hi I was going to suggest you talk to Gordon Boyd but It looks like you are doing, he is building a two drum similar to mine but with steel tubes, copper (and I guess copper alloy) tube is now so expensive. I am thinking of renewing the first row of tubes on my boiler as they are suffering from erosion on the outside after twelve years of coal products passing them.
I only need ten metres of copper for the first row but that's an arm and a leg!
I guess its too late but I would recommend using a eight inch tube for the steam drum, six inch does not leave much room for all the bits & bobs. schedule 80 eight inch is quite a bit thicker at 12.7mm Gordon has done this to allow the safety valve etc. to be tapped directly on to the top of the steam drum.
I have a six inch steam drum and so I fitted the feed inlets to the bottom drum due to lack of room, Ideally they would be better in the steam drum not only for circulation but to help if you had the same problem as me last month in Scotland!!!
Having just lit the fire I set up the feed recirc to tank to warm up the engine (never rush these things). Not noticing the dropping water level until it was too late, I had a disaster on my hands. Luckily as there was next to no pressure I have got away with a failed drum end gasket. The cause was the water passing back through the feed check valve, should the feed inlets have been in the steam drum I may have got away with it.
The lesson? even experienced steam nuts can get caught out!
Regarding inspections I would ensure you keep the certificates of material, John King's boilers should already have a design assesment with them as per SBAS regs.
I seal the centre stays with a single o-ring held in place by a collar with a 45 deg chamfer in way of the ring, this seals on two surfaces ( details of chamfer available from Walkers gaskets)
Regards
Jack

[Johnlanark]

Thanks Jack for looking in, and for your advice. I’ll stick rigidly to the drawings for the pressure vessel, which John has specified with a 6” steam drum, no doubt to keep the weight down. These boilers are designed for 250 psi, and so copper tubes are not suitable of course. The drum end caps are sealed with O rings and the stays are sealed with Dowty washers and dome head nuts.

The drawings provide “expanded” views of the tube hole layouts in the drums, converting the angles around the drum to flat measurements, from a datum of zero degrees at the top (mud drums) or bottom (steam drum). Today I drew out both sides of datum for the steam drum, and tack taped it on to the drum with masking tape. Intended just to see how it looks, I had taken care to trim the paper length to the drum length and in fact it aligns itself and looks quite accurate. It looks OK to tape it down properly, then punch the holes through the paper to locate them, then clamp down on the mill to drill and ream them. What do you think?





I also did the hardest bit and hit the VISA to the tune of about £700, to order most of the materials and the expander tool for the pressure vessel, superheater and feedwater heater. These are
-12mm Cunifer Tube from Dorset Tubes. John advises it is best to buy from this manufacturer, as others such as the ebay advertised “Kunifer brake pipe” has poor dimensional tolerances. Unfortunately I bought this stuff already, so will need to resell it.
- Boilerplate discs for the 6 drum end caps, also the 8 discs for the superheater and feed water heater, from Precision Profiles in Bristol.
- 16mm and 20mm EN3B for the stay rods from Metal Supermarket Glasgow Branch. Dome nuts for them.
- An E2 expander from Wicksteed.

John

[steamboatjack]

John,

Hi again, yes the paper layout should work (although I am no Boilermaker) I still think o-rings are better than dowty washers and this detail would not compromise the design, as for the drum end plate seals, I know Gordon has used o-rings here also, I would be grateful if you could e-mail me the groove details? my e-mail in SBA book is good. I have just had a quote for CNC ring gaskets!!!!!
regards
Jack

[Johnlanark]

Jack, I'll ask John King if it's OK to copy these to you.

Roger Eske is building this boiler, and has finished the pressure vessel. Roger has kindly allowed me to post these photos of the planning stages.



Now can anyone advise me on the tooling I need to drill and ream finish all these 12mm holes. I thought the process would be to drill say 11.75mm and then pass through a reamer that is slightly undersize at the end and then parallel 12mm further up the flutes. I phoned Tracy Tools to order these, but they offer either a straight flute reamer or a taper pin reamer that has a distinct taper. So I am confused now. John

[Laurence]

Hi.
A couple of things I thought of after my last email. Someone I have talked to about the holes, I think it may have been Malcolm Richards, said that they found 12mm too tight and had to go to 12.1mm. The only reamer this size i could source was about £57 so I got an adjustable reamer from Chronos for around £10.
You describe your hull as "skinny", what is the beam?

[Laurence]

Hi John,
I've just found the answer to my last question, spotted your boat on the Selway Fisher site.

[steamboatjack]

John,
drill size is ok, Usually a traditional "hand reamer" with a tap wrench square has a slight "lead" with the first 1/2 inch or so undersize. A Machine reamer is parallel without a lead, same goes for "chucking" reamers (short flute reamers for machine use)
I would suggest in this size a hand reamer would be best.
taper pin reamers are for taper pins only. Alternative supplier is www.mscjlindustrial.co.uk although Tracy is ok
regards
Jack