US State Boiler Code

[Steamchick]

K A Olson (I guess that is your name?), thanks for that. The ASME regulation I refer to is the design regulation. The ASME limit of 100psi for silver soldered copper boilers is based on material properties which do not change by nation or state, so maybe it is good for us all to follow that limit (e.g. In the UK or anywhere else outside of USA).
The hydraulic test I found from ASME, based again on permissable stresses in annealed copper at elevated temperature.
To quote: UG-99: "The hydrostatic test pressure shall be at least 1.3 times the Maximum allowable working pressure multiplied by the lowest ratio of the stress value St for the test temperature for the design temperature." - In the case of a boiler for Max. 100psi (Max limit as required by ASME for Copper boilers) the ratio of St/Sd = 6700/3142 = 2.132: So the test pressure (Hydraulic at 70degrees F.: designed for 100psi = 338degrees F.) shall be 1.3 x 100 x 2.132 = 277psi.
My information source is a design document written by Kozo Hiraoka published in 2006, so I may be out-of-date by now?
The logic I expressed is based on sound engineering principles, of stress calculations and compensation for copper at elevated temperature, but if there is a Service test for in-service annual tests (as the UK test at 1.5 times the NWP) then that is accepted for that certification. But for new boilers there is usually a design hydraulic test - at least done by the designer or agent to prove the strength of the design is good for the simulated stress for 8 x NWP and factored for the material strength at the temperature of the NWP.
My recommendation to Wazrus was that if he had a boiler deform due to pressure, then that pressure should have been at least 8 times the NWP. So there was something wrong with the original design.
If you think being able to withstand 8 times the NWP is excessive for your boiler, then you misunderstand the purpose of the Regulations, in my opinion. It is the regulating authorities' decision that this is the level of safety required to prevent injury to people. So I have re-rated some of my boilers that were "inadequate" when I applied the ASME principles to the designs of those boilers. But I am just an engineer (following Kozo Hiraoki's explanation paper on ASME Boiler and Pressure vessel code and general engineering calculations for stress), with my opinion expressed on this site, so please check with your local test authority if you need your calculations or testing to be confirmed/ratified.
My prime interest is the safe operation of steam boilers by safe design.
Happy ( and safe!) steaming!
K2

 

[Steamchick]

Hi Wazrus,

1. I am fascinated by the boiler design: Do you have any general arrangement drawings you can show so I can better understand the firebox and fire tubes planned? I have had a notion that "conventional flat-sided and stayed" fireboxes are appropriate only because they copy full size Locos. Cylindrical fireboxes are much easier to manufacture and "naturally stronger" than flat plate constructed fireboxes. (I have a "scrap" super Simplex boiler with possibilities of repair - but the stayed flat sides limit the pressure it can take - and leak madly!).
2. I am curious about your idea of the fire-tube burner. Have you lit it yet? What does it do in a fire-tube? Where does the "venturi" fit?

I have attached a copy of a USA Government design of venturi. The jet goes at the left-hand end. The air inlet (between jet and venturi - needs to have a cross-sectional area of 120% of the area of the opening into the venturi. The area of the opening into the venturi is critical: this needs to be at least 250 x the jet cross-sectional area. - then all other dimensions are scaled from that dimension. The drawing attached is suitable for a propane jet about 0.55mm. dia., mounted about 11mm. or 7/16" from the end of the hole, by my reckoning.... but the US government paper suggests "0.5 x D" which would be 0.7" or about 18mm from the end of the venturi. So some degree of adjustment should be made so you can tune the gap between the jet and the venturi to get the optimum flame in your fire tubes.
Scale up or down as appropriate for your planned jets?
Of course, it is intended that the venturi blows the gas-air mixture into a burner - such as the burner that Susan Parker has = a lot of slots in a long tube! But I reckon you will do better with a blow-lamp type burner anyway.
Have you estimated how much heat you need for the boiler to generate the steam you want for the Pea to run happily? - That is the key so you can decide how much gas you need to burn - and then that dictates the jet sizes, etc.

Cheers!
K2

 

[wazrus]

G'day, Steamchick
Fascinated by the boiler design? As far as I'm aware, the design is almost public domain and I certainly agree with your remarks about the circular firebox. What I have altered, though, is the placement of the boiler 'cylinders' relative to each other. That doesn't sound clear, does it? The boiler, for coal firing, had the barrels of the firebox and the main barrel almost in line at the top, to accommodate the firegrate, below which was, of course, the ashpan. The ash space was, in my opinion, far too small and certainly too small for the high ash coal I had on hand. The steam space above the firebox was reduced. My version has pretty much 'inverted' the boiler, so the firebox 'outer' (such as it now is) centreline is considerably above the barrel centre line. So all I've done is simply 'roll the boiler over' and dispensed with the firebox altogether. Other than the staying, the increased material thicknesses and the gas firing arrangements (flues), nothing else has changed. It's still pretty much a Sweet Pea ((Bagnall) style boiler, with dome and my larger flue tubes running from front to backhead, through what was the coal-type firebox area. So the thing is just two cylinders, silver brazed at the circular throat joint and the 38mmx3mm flues go straight through. Why not make it a simple cylinder? Good point, but I had the barrel(s) and some flanged plates, so why change at this stage? I've also gained much needed steam space and, with the addition of a dome on the larger diameter part, a drier steam collection point. Priming was a problem with the original boiler.
I like your inverted commas used with my 'venturi'. Venturis had sort of been confined, in my private pantheon, to a mysterious black art, as had burners, and no I haven't had the burner 'stick' in a flue, so I'm still in the black art area. I had very little room for a venturi of any sort and looking at the pipe reducer types, it seemed that they might be made shorter, say along the lines of a carburettor intake, with the bell shape. The outlet is probably woefully undersized. You could say that it's all not much more than guesswork and you'd be right!
But I do really appreciate your input which has thrown a little light into the black places.
Note also that my larger flue tubes in the small Pea boiler, have been reduced to two tubes. I plan to use three in the larger boiler.

 

[Steamchick]

Thanks Wazrus. I'll do a bit go digging and find the tube sizes of a regular pea boiler. Are your tubes bigger? And what wall thickness? I'll do a few sums on your fire tubes. I really think a blowlamp burner for each tube is probably best. You get very good control of each burner with screw-down taps, so you can "idle" the boiler by turning down the fires, then "Whack 'em open" when you want to pull away with a load. Blow-lamp makers spend a lot of time and money making their burners "the best" so why try and re-invent the technology? You can buy nozzles for the cost of the brass! (I made a steel burner, but much easier to buy a scrap blowlamp for the burner!).
Cheers!
K2

 

[wazrus]

Steamchick/K2
I must apologise for a bit of a bollocks in the 'explanation'. What isn't clear is that there are none of the usual firetubes at all in my 'revised' boiler. As in Kozo Hiraoka's Pennsy switcher, there will be just two or perhaps three larger (38mmx3mm copper tube) flues, in which I plan to place the 'burners'(!). The tubes (flues) themselves, seem to be OK as regards crushing. By the 'tubes' for a 'regular' Pea boiler do you mean the small fire tubes? If so, in the original, 20 are called up, 1/2" ODx20SWG. These have been eliminated. If you mean the outer barrel/tube, it is 5" ID. The firebox outer diameter isn't shown on the drawings (pages 102 and 103 of Jack Buckler's book)) , but mine is about 7" diameter
Note that I have not used tube, but have rolled the barrels myself and they have
been jointed using Alec Farmer's version of a castellated joint. This joint was debunked by some pundits here in Oz, so I doubled up and strapped it, to be sure. All platework/barrel etc is out of 4mm copper. During dismantling, the joint let go: not the castellated, but the strap, so a friend TIG welded all the legs of the castellations and I plan to strap over that, too. I used Jack Buckler's book 'Build Your Own Steam Locomotive', which is a blow-by-blow construction manual for a 5" Sweet Pea.
I plan to install some radial staying where possible. The large flue tubes will probably get in the way, so that's a work in progress. Longitudinal staying as per the words and music, referring to the AMBSC guidelines. I hope I've made my ideas a little clearer. The burners, as you say, shouldn't be a case of re-inventing the wheel, but I have reservations about whether a blowtorch flame will be long enough to reach the 'end' of my flues and what the characteristics of that flame might be. I know it's hot: I've been experimenting and have made a long lance-type burner, with air intake holes at the 'handle' end and a large head on the other, The result is a large, bushy roaring flame, which I use on household weeds! But the flame isn't very stable and I suspect there's not enough inducted air. For the head I copied a Bulgin burner, but located the air holes remotely. maybe the holes are simply too far away from the head for stability. it tends to be 'touchy' and inclined to self extinguish. I suppose the long 'wand' might be replicated in the boiler flues.....hmmmm.....
Again, many thanks for your input.
Wazrus

 

[Steamchick]

Thanks Wazrus, I have a better understanding of what you are doing. Using my ready-reckoner (spreadsheet for calculations) I deduce that the 38mm OD x 3 mm wall copper tubes can withstand 100psi external pressure with a factor of safety of 11. - Good in my opinion!
This means you have a 32mm hole to put a blow-lamp into. Looking at manufacturer's data, a Bullfinch blow-lamp - dia 32mm (ref 1240) generates about 8.5kW of heat. As these burners are designed to draw-in maximum air - balanced to the max. gas through the jet - they are much more stable than my home-made equivalents, and this is as big as you'll get a burner in that hole. This is a good as it gets in a flue tube. The flame will progress 2/3rds of the way down the tube if not all the way, so you should get 75% of the heat before the hot flame/exhaust goes up the lum! If you can put a simple triangular tube of Stainless wire mesh inside the tube you'll increase this by at least another 10% so you'll get 85~90% of the heat into the boiler - by my reckoning.
3 tubes like this at 85% efficiency will be ~21kW... which should pull the skin off a rice pudding... - But only if 2 tubes with burners you will keep the safety blowing-off when in the station, but run out of puff when you reach an incline! - Can you fit 4 or 5 fire-tubes and burners in the 5" boiler tube? - You'll need 19mm of metal between each tube and from tube to outer edge of the tube plate.
The biggest problem is lighting burners. This needs a clever and reliable arrangement of spark ignition, or a means of withdrawing burners for ignition.
Have fun!
K2

 

[wazrus]

Steamchick/K2
Many thanks for your efforts and I do like the idea of not making burners or jets, especially, as you suggest, the flame should blow about 2/3 of the way down the flues. That sounds pretty well OK by me! As you say, too, your efforts (and mine) building burners etc weren't too auspicious. I have ordered a couple of 'sets' of weed burners, which comprise handle and other bits and the only items of real interest are the burner heads themselves. The only issue is that the burner 'sets' come in 30mm, 40mm and 50 mm diameters. the 30mm is the one of most appeal, of course. Not quite the 32mm, but the set is priced at $A30, so I won't quibble too much: there shouldn't be too many issues adapting the 30mm job to the 32mm flue. like you, I think, I'd rather not mess around making the things, if it can be avoided!
Medical things have intervened yet again and it may be a while until I get sufficient time in the shed, especially now that the Southern hemisphere is entering summer and the stinking heat is on the way. I do hope, too that my Australian sense of humour hasn't been mistaken for insult, in calling Cds4byu a 'cheeky bugger'. That's Australian for a sort of endearment.
Wazrus

 

[Steamchick]

Hi Wazrus,
I have no problem making jets down to 0.25mm drill. But without the boiler for tuning against back pressure, and cooling (which all changes the combustion pressures and air fuel ratio) the burner is cheaper and easier if a proprietary item. I have bought a few second-hand blowlamps for burners, gas- taps & gas connections. Then fitted them in my own applications. But I have made my own blowlamp style burners, with the trials and tribulations of the various boiler influences on the combustion. From experience, I have even re-worked old early attempts and made better burners. So it isn't quite as easy as one hopes!
Maybe your 30mm burner in a 32mm ID tube will leave 2mm for a wire to the spark for an igniter.? Extracted from an old cigarette lighter? For the wire, I would use flame-proof wire from a scrap electric cooker. But then making the sparky end is a problem I have not yet tackled. There may be room inside the 30mm burner - where there is more space? - to insert a piece of ceramic tube, such as from a domestic fuse, with steel or copper wire up the middle to where a spark will light the burner? This wire takes the spark from the wire off the piezzo igniter. Bit of design thought needed.... Over too you?
K2

 

[Steamchick]

I could use some of your Stinking Heat. 22 deg. C in summer - MAX. now 5 deg. C but feeling sub-zero. We may even get down to -2deg.C this winter if it is very cold... We have had snow for 2 days already this winter, but the roses and chrysanthemums are till in flower. The cold killed the dahlias though... Some spring plants are starting through... - they will die if we do get a week of freezing weather.. No wonder we Brits complain about the weather all the time!
K2