From napkins to fabrication VFT boiler design

[Spanky]

Thank you all for your insights,

I just want to set a few things straight... I'm still just designing it, I will be changing it back to the tube plates inside the shell, as I honestly hadn't thought about grinding it down to fit... I was looking for a simple way to construct it that would be economical in weight and cost. It has never been my intention to cut corners on safety. It's a lot easier to find flaws in other's ideas than your own. (which is why I joined this forum and posted my ideas)

I looked up videos of boilers exploding on your request. All of them cited some maintenance oversight as the cause.

And Scott, I do hope you mean a ride in my steamboat, I mean we've only just met, You gotta buy me dinner and get to know me before you make that kind of request... Jokes aside, can I get some details on your boat? Did you have any trouble getting it registered? and where in WI are you located?

Thank you all, again

Josh

[artemis]

Josh,

As a fellow Wisconsin steamboater who would like a ride on your boat one day (and would be happy to have your company on mine), I'd like to respectfully urge you to consider the possibility that a lot of the concern you are hearing is not the sound of old habits dying hard, but of folks with a lot more experience (and in many cases, valuable formal training) trying to help keep us all safe in our hobby.

The boiler code may be antiquated in some respects, but it certainly isn't simply a throwback to the days of rivets. If you spend time reading post accident reports on recent boiler explosions (depressing, but instructive), you will see that very few boilers fail for the reasons you are confident in avoiding - i.e. the pressure vessel is just too weak and gives up. What actually happens is that someone accidentally lets the water get too low, or dry fires a vessel (see previous comments about setup of sight glass), or that imperfect management of feedwater causes corrosion to attack a small section of weld, or that an accidental overpressure occurs.... the list goes on. The point is that some details that seem nit-picky to non-experts in the field like me turn out to be there for exceptionally good reasons - and reasons that won't necessarily show up in a hydro test of a new boiler. Issues of corrosion and thermal stress that really do blow up boilers do not show up in a new vessel hydro and are largely dependent on weld quality, material specificaion and little design details that go way beyond calculating basic hoop stresses on the boiler barrel and heads.

Best regards,
Scott

The ASME code (which only governs the materials and assembly techniques) allows hydro testing to a maximum of 1.5 times Maximum Allowable Working Pressure and water temperature not less than 70F for new construction . The NBIC (National Board Inspection Code) which is used for testing "vessels in service" (not new construction or repair) limits pressure to less than 90% of MAWP and temperature to not less than 60F nor more than 120F. The NBIC states: "The Inspector is cautioned that a pressure test will not provide any indication of the amount of remaining service life, or the future reliability of a pressure retaining item. The pressure test in this instance only serves to determine if the pressure-retaining item contains defects which will not allow the item to retain pressure. In certain instances, pressure tests of inservice components may reduce the remaining service life of the component due to causing permanent deformation of the item." So despite all the advances in materials, techniques, etc. testing at above design limits may so weaken the test vessel that its service life is severaly limited.

[Spanky]

Alright all, I'm leaving for about a week. When I get back I might have a boiler with holes in it! Yay progress.

Happy steaming,
Josh

[Lopez Mike]

Ouch! I feel like I'm piling on here but this is probably the most serious issue that the steam boat, tractor and R.R. hobby faces today.

In every other facet of our construction and operation we can make a fool of our selves (me regularly) and/or just get frustrated. But boiler safety is so stinking important that we have and are taking fairly draconian measures to deal with it. If we can avoid an incident, then we can avoid any further regulation that would apply serious restrictions on our operations. It is within the memory of living persons when any steamboat was required to have a licensed engineer aboard. Period. It was one of the lesser reasons that internal combustion engines took over power boating so rapidly. Naptha launches squeaked by on a technicality for a few years before thermodynamic considerations killed them.

Here in Puget Sound we have a rule that every boiler has to pass an annual inspection and hydro test by one of our safety committee members before it can be steamed at an association event. Committee members not excluded. Our regulations do not require code construction specifically.They are more concerned with obvious screwups. My boat, as a horrible example had a shut off valve between the boiler and the safety valve when I found it in a mini storage. But we do have what we refer to as a common sense clause where if the inspector's hair rises noticeably, the boat doesn't steam with us.

It won't cause you that much money or time to play it straight. We don't have so many steam boat enthusiasts that we can afford to loose you to an incident!

[Spanky]

Hello again all!

Been awhile since I've posted anything, but I have a question about valves... I was shopping around on McMaster.com today and came across these bronze body gate valves. http://www.mcmaster.com/#gate-valves/=gx9w0r Would these be appropriate for use as my throttle and safety valves between boiler and fittings. Do you also use these kinds of valves for blowdown?

Also I got a job that pays decent enough that I can start to buy material for the engine. Anyone know where to get a block of cast iron 4.5"x4"x5"?

Josh

[farmerden]

Don't use gate valves! Gate valves work best in open and closed situations.Anything inbetween they will vibrate and wear.I learned this with water and irrigation instalations.I would assume with steam it would be worse! Den
http://www.mcmaster.com/#steam-globe-valves/=gxas4t

[fredrosse]

Valves with a rating, say "125 SWP" means that the valve is rated for "125 PSI Steam Working Pressure". 125 SWP and 150 SWP are fairly common, and other pressures can also be had. The SWP rating is needed, because many valves have seals and packing that cannot take the steam temperatures.

Ebay has valves very often at much lower prices than retail, but buy valves that are a reputable North American brand names.

[Mike Rometer]

I'm sure someone will correct me if I'm wrong, but I always understood that (in the UK at least) SWP stood for "SAFE Working Pressure". ???

[fredrosse]

USA Valve Data

Abbreviation Type of Valve
BB Bolted Bonnet
BC Bolted Cap
BV Ball Valve
BWE Butt Weld End
CV Check Valve
CWP Cold Working Pressure
DD Double Disc
DI Ductile Iron
DWV Drainage, Waste, Vent Fitting
FE Flanged End
FF Flat Face
FLG Flange
FTTG Fitting
FW Flexible Wedge
HF Hard Faced
HW Handwheel
IBBM Iron Body Bronze Mounted
IPS Iron Pipe Size
ISRS Inside Screw RS
GV Gate Valve
MJ Mechanical Joint
NPS Nominal Pipe Size
NPT National Pipe Taper Thread
NRS Non-Rising Stem
OWG Oil, Water, Gas Pressure
PRV Pressure Reducing Valve
RF Raised Face
RJ Ring Type Joint
RS Rising Stem
RWD Resilient Wedge Disc
SB Silver Brazed
SE Solder End
SOV Shut Off Valve
SW Solid Wedge Disc
SWE Socket Weld End
TB Threaded Bonnet
TE Threaded End
TC Threaded Cap
SWP Steam Working Pressure
UB Union Bonnet
UC Union Cap
WOG Water, Oil, Gas Pressure
WWP Water Working Pressure

[87gn@tahoe]

Welcome back.

Gate valves aren't really suited to steam (there are some exceptions, such as locomotive blow down valves).

Most use globe valves with the separate bonnet cap (not the one-piece thread-in bonnet). One will also see ball valves in use on steamboats, but one must take into consideration the seat material used in the ball valve.

I would suggest getting valves rated for twice what your MAWP (maximum allowable working pressure) is, allowing a good margin of safety and when you hydro test, you will not damage your valves.