The Steamboating Forum

Air tanks and steam vessels are different animals. Orders of magnitude different energy levels and temperature regimes and hot cold cycles. The state change when super heated water flashes to vapor when the pressure is released is incredible! We want you to be around a long time!

As to your other questions:

Theoretically the gauge could be anywhere but putting it above the water level reduces the chance of high temperature liquid getting past the loop in the gauge line and overheating the guts of the gauge. Most of us have our gauge fitting near the top of the boiler.

Very few fittings are in the tube sheets as they are not easy to get to there. Important.

Sight glass fittings can be as close together as right at each end of the glass. More importantly (ask Bart!) there must NOT be any loops that will trap water in the bottom of the glass when the level goes below the bottom of the glass. I wouldn't put the bottom fitting too low lest crud obstruct the free flow.

Blowdowns should be as low as possible. The idea is to get mung out of there. It's called the mud ring for a reason.

Inspection ports are nice but add expense and need to be designed correctly to be safe. Many, if not the majority, of our small boilers have none. We mostly are running closed condensing systems where there is little scale buildup. Removing such hard stuff is the main reason for having large openings of this sort.

For my small welded all steel boilers, if I see scale in there after a few years I go and buy a few gallons of Muriatic Acid (Concrete cleaner-Hydrochloric acid). It's dirt cheap. Fill the boiler up with as strong a solution as I can stand to be around (gives off Chlorine gas. Do this outside in a breeze!) and when it stops foaming, the scale is gone. Then drain and wash it out several times. A solution of baking soda as a last wash will make sure there is no residual acid in there. Usually I don't get much action. And then only in my shop steam source boiler which runs off of my wretched tap water!

Thanks Mike for answering my questions.
I apologize if i came off as rude, this was not my intention. My comment about air compressors was just an example of how materials have changed. I think I'll include just one hand hole to pressure wash down the inside as I don't plan on running a condensing system. All the places I plan on taking her out are spring fed lakes, but being in WI most springs are coming through limestone making some pretty hard water...

Diverting yet again I want some opinions on my testing procedure, as I want to stick around a good long while I know old traditions die hard but bear with me. Instead of the formal hydro test, I'm going to use a air compressor to bring it up to the safety valve release pressure. I'll keep an eye on the pressure gauge and spray soapy water on all welded joints, pretty much how you'd fix a leaky tire. My reasoning is that an air leak is a lot easier to repair than a water leak... having to drain the boiler and dry the affected area thoroughly... thoughts?

I know things are different each side of the pond, but I cant see our boiler inspectors passing a joint designed like that.

With the water gauge it is essential to make sure that the 'bottom nut' is above the tubeplate/crown, so that when the water is just visible there is a good safety margin of water covering the plate. The pressure gauge should be fed from the driest available direct connection point in the shell (usually the highest).

The point of a hydro (water) test is that if there should be any sort of failure during test, there is no explosive force as there would be with air.

Sorry let me rephrase that. I'd be slowly bringing it up to pressure, any creaking or groaning of the metal and you just hit the blowdown valve and vent the air.

The problem with your test proceedure is that the time from hearing the "creaking - groaning" and the rupture of the tank will often be about 0.001 seconds or less. You need a very fast valve to save yourself.

Hydro testing should always be done with a liquid filled pressure vessel. After you do a liquid pressure test at 150% (or 300% depending on what type of boiler you have designed) of maximum allowable working pressure (MAWP), you know the vessel can take the pressure. Only after this you can use compressed air to find and fix leaks. The compressed air should never exceed the MAWP, and after the leaks are resolved, then the liquid hydro test can be repeated.

Ok... if a regular air compressor tank is rated at 300 psi with 1/16" walls a vessel with 4x the thickness 1/4" walls would hold 250 psi 150% operating pressure of my system of 125-150 psi. I've shot many a spray paint can with a .22 the most they've ever done is twirl around making a nice petty circle of paint... I can understand not pressurizing it to the point it will explosively decompress but at these relatively low pressures it's not going to be a problem.

I know I've ruffled some feathers and old traditions die really hard but c'mon lets put aside the bias and look at this objectively.

Josh

Filling the boiler completely full with water and testing it to 1-1/2 times working pressure in that manner equally stresses all parts therein as the water does not compress (or very little). Just using air will not suffice.

There is good reason for all testing and construction methods.

ASME boiler code has been updated since its inception to accommodate advances in materials and construction methods (i.e. welding). One must remember that the ASME code outlines the MINIMUM for boiler construction, meaning that anything less is not considered acceptable by a board of engineers. The ASME code was thought out by a group of engineers with more collective experience and knowledge than probably all of the members on this forum combined.

The tubes will only act as stays if they're constructed and installed as such.

Knowingly cutting corners in building a steam pressure vessel is a wanton disregard for the safety of yourself and the general public.

I am sorry if I am coming off as harsh, but one must remember that, especially in the case of a firetube boiler, you are making something that has the potential to explode causing serious injury or (most likely) death if not cared for or constructed correctly.

Look up "Boiler explosion" on YouTube and watch the videos. Most are stationary units with very few people around at the time of the failures. There is also a post mortem report on a regularly inspected code boiler that had no equipment failures (water level, etc) that unexpectedly failed.



I read somewhere that 1 gallon of water at 10lbs steam pressure has the explosive capacity of a half stick of dynamite.

Some may frown on my harping on the dangers of our hobby, but it will only take one good accident to bring the world down upon us like the 2001 Medina Ohio accident did in some states.

Crack from corrosion in a regularly inspected code boiler. The operating conditions would actually be quite similar to our hobby boilers, with many heat cycles and oxygen in feedwater.

Spanky wrote:Ok... if a regular air compressor tank is rated at 300 psi with 1/16" walls a vessel with 4x the thickness 1/4" walls would hold 250 psi 150% operating pressure of my system of 125-150 psi. I've shot many a spray paint can with a .22 the most they've ever done is twirl around making a nice petty circle of paint... I can understand not pressurizing it to the point it will explosively decompress but at these relatively low pressures it's not going to be a problem.

I know I've ruffled some feathers and old traditions die really hard but c'mon lets put aside the bias and look at this objectively.

Josh

Ah for the good ole days of simplicity. Cut down the tree, remove the bark, shape it with an adze, and set it in place. In no time you've got a house. But today you've got to research the design for thermal efficiency, select the materials carefully for resistance to rot and structural strength, fasten and secure them in such a way that they will remain fastened in all weather and movement (earthquake) conditions, etc. Just because it worked well for great, great, granpa in ground stable upstate New York doesn't mean it will stand up in LA, California. Structual strength of oak vs. cottonwood, resistance to rot (corrosion) of teak vs. hemlock, "toe nailing" vs. "strapping", wide head nails vs. staples... New materials/techniques are constantly being developed to improve the quality of the things we use. Density, compression, temperature - particularly when rapidly changed - can dramatically affect strength of materials. Get your local hot water tank people to show you a film of what happens when the temperature/pressure relief valve fails to function on an ordinary home water heater. Talk about rocket science (and you can blow the corner off a two story brick building too).

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