PYRTE Traction engine nearing comletion, but back to te beginning

[JCSteam]

would a vacuum leakdown test with an automotive vacuum tester be suitable for a small boiler?

paulr

Although I can kinda see where your going with this in that if there is holes in the boiler yould not see vacuum.
1. Yould have no way of determining where the boiler would need work.
2. Boilers are designed to with hold pressure, subjecting the boiler to vacuum means that atmospheric pressure will try to crush the boiler barrel.
So therefore not testing what the boiler is designed to do. And not identifying where the boiler may need additional work.
Jon

 

[Peter Twissell]

A vacuum is only 1 Bar, or just under 15 psi.
It will find leaks, but it won't be any kind of safety test.
Also, depending on the boiler design, it could cause deformation, as boilers are designed for positive pressure.

 

[Steamchick]

Depending on your country - re local regulations (I.E. The LAW!) - testing of boilers must be an Hydraulic test at 2 to 2 1/2 times normal working pressure, to prove it is strong enough to be safe.
Then it needs testing under FULL FIRE to prove the safety valve can prevent the pressure rising 5 or 10% above the Normal Working Pressure.
Actually the NEW quoted is a maximum pressure you should use to control the fire.
It is BAD PRACTICE to always run with the safety valve lifting, as it is NOT intended by the regulators to be a "pressure control" for your convenience, but a SAFETY DEVICE. I. E. WHEN the safety device operates you should take immediate action to bring the situation back to normal.
But many model loco drivers have innadequate training (not being engineers, just amateur machine drivers perhaps?) and therefore you see people steaming locos and traction engines with the safety valves lifting. It simply demonstrates their lack of control of the fire and water....
Industry is held to account for safety, so would have a lot of paperwork if their safety valves were blowing off regularly. So they managed their fires and use of steam much better.
How professional are you?
A vacuum test cannot test the mechanical strength and integrity under internal pressure.
Please note the reference above to "a Bomb," and think again about the object between your thighs. (YOUR LOCO BOILER!). Even a tiny leak can issue steam that will cook flesh in seconds! Cooked flesh does not grow back, and is possibly up with the most painful things you can experience.
So get a copy of the regulations from your local club (become a member) and seek advice from their professionals.
Please take care. STEAM AND BOILER CAN KILL.
Sorry to be an aud werrit!
K

 

[Steamchick]

When first made, it is good practice to apply a few psi of air to a boiler - under water - to determine where it leaks. Only when you cannot find any more leaks under water should you consider an hydraulic test. I.E. filled to the top with water (not "under water!), then pressure raised slowly to the test pressure. The UK specifies a minimum of twice the Designed pressure, which may be higher than the NWP, but ANSI specifies this differently. And Australia Finland, etc. all have different regulations.
K

 

[Cogsy]

Even a tiny leak can issue steam that will cook flesh in seconds! Cooked flesh does not grow back, and is possibly up with the most painful things you can experience.

Minor to moderate steam (or anything) burns are incredibly painful but in my experience, when you get a truly bad burn the pain disappears in seconds. That's when you know the nerves have been cooked/killed and it's going to be a bad one with a long recovery. Thankfully I've only ever had such burns a couple of times.

 

[reichpaul630]

wow, drew a lot of comments. i thought a quick "go/no-go" vacuum test might useful. looks like there's a a bit more to it that. good learning experience. thanks!

paulr

 

[Ken Ratcliffe]

Hi All,
Thanks for all the comments. It dawned on me that car pump was just push-on, so I went ahead put water in the boiler and gave it a few pumps......as I suspected might be the case, several leaks detected immediately, so no high pressure testing needed yet. Some remedial work needed before moving ahead...….crankup the torch !
Ken

 

[Steamchick]

Good!
You are learning, without using any dangerous pressures (yet). Be sure to pickle the boiler well after brazing/soldering, as fluxes can be "seemingly pressure tight!" until dissolved when they leak like a pensioner's whatsit. I currently have a boiler that after 3 picklings has developed a leak where a dot of flux has finally dissolved, and a wee pin-hole wept when I put more than 1 bar of water pressure on it. Didn't show when I was chasing a couple of other leaks after air-under-water tests and the soapy water tests - which look for fine bubbles, when 5 ~ 10 psi is applied and the air supply locked-off for 5 ~15 minutes to check for any pressure decay.
My process.

1. Hot assembly work.
2. Clean, examine, pickle, examine. - back to 1 if required.
3. If "OK", fit plugs, add 1~5psi, submerge in water and locate leaks from the stream - or single bubbles. - Back to 1!
4. If OK, dry it, then apply 5~10 psi, and using soapy water with a dropper or brush, search every joint (including the plugs) to check for micro-bubbles. Watch the gauge and if dropping identify where the air is escaping! Sometimes you can dry a known leak and temporarily seal with blue-tak before searching for any other leaks. - Back to 1 and start again.
5. If OK, you can increase to 15psi and close off the valve, then watch the gauge unchanged for at least 15 minutes to see the boiler is tight. - or back to 1!
6. If OK, Try another pickle, rinse, then 4 again, if OK proceed to hydraulic test in stages, 1 bar, 2 bar, etc. up to 1 1/2 times NWP. At each 1 bar step, STOP PUMPING, lock the valve and watch for 5 mins that no pressure drop occurs. Bide your time by measuring and recording outside and inside diameters that are accessible, lengths over ends, etc, to determine actual deformation of the boiler (mark and number positions with a felt pen, and photograph so you can repeat exactly at a later date). Steps of "ZERO", 1/4, 1/2, 3/4, & 90% NWP, then NWP and 10% intervals from there up to over 2 x NWP are plenty. of measurements. TAKE YOUR TIME. This is the most valuable job you can do. When you get to the Test pressure (may be 2 ~2 1/2 times the NWP - depending on design and the Regulations for your country) - LOCK OFF the pump, and watch the pressure for 15 mins. Examine thoroughly and take final deformation measurements. Slowly and carefully release the pressure, and at say 5 ~ 10 steps while the pressure is dropping, check some of the deformation measurements (I select the largest changing dimensions) and record results of your measurements.
7. When at "ZERO" on the gauge, crack-open a blank plug to relieve any odd residual pressure not showing on the gauge. when you are sure there is no pressure, re-check all the dimensions have returned to their original sizes. ANY PERMANENT DEFORMATION must be strengthened before any further pressure is applied. - Consult an expert (a properly trained pressure vessel/boiler Engineer, not a mechanic. No dis-respect intended, but this is SAFETY we are talking about, and we all surely want the best advice? - I respect Mechanics and consult them on how to Make things, but equally expect in return that they consult me for proper technical decisions). Any rectifications will take you back to where? - Step 1 of course! (There has to be an exam question with any training instructions).
8. If all is OK, proceed to get the boiler tested at your local club/agent.
9. When he passes your boiler as "fit", you can proceed to build it up with water gauges, Safety valves, super-heaters, economiser (water pre-heaters), Insulation/cladding/cleading , smoke-box, water-pumps/supply connections, Firebox equipment, flue draughters, etc...
10. When completed for firing, you will need to do a firing test to prove the Safety Valves, at FULL FIRE, including full blowers, etc, dampers wide open, etc. and, if gas or pressurised fuel, a full (max gas pressure) fuel supply. This test must have the final pressure gauge, etc. fitted, as these gauges belong with each boiler and are a necessary part of the test. (Temporary parts borrowed "from your mate", or another boiler are NOT permissible, and the test may be aborted). With a full (water) boiler, raise heat slowly while the boiler and fittings are checked for leaks, and raise pressure to something below NWP and demonstrate fire management that can hold the pressure without it continuing to rise, or it may even allow it to drop, (Easy with gas, not so easy with coal?). When "OK" continue at full fire to raise steam to NWP - marked gauge on the boiler should be confirmed with the certified gauge pressure. RED LINE for NWP + 10% should also be marked. Raise pressure over NWP with Max fire until the safety valve(s) lift: If more than 1 safety valve is fitted, the first shall be blowing at <105% NWP and the second before 110% NWP is reached, and with full fire continue to confirm that the safety valves prevent any rise OVER 110% NWP. If 110% NWP is exceeded, the test is failed, and equipment must be reset before proceeding.
11. If 110% is not exceeded with full fire maintained, all feedwater pumps must be demonstrated (including all injectors), water-gauge must be demonstrated (may need blowing down to show sensible water-level), and the boiler run for typically 15 minutes to show everything is controlled and continues to work safely. During this period the Safety valves must be demonstrated to both close effectively and blow again, to confirm the first time wasn't a fluke! (Usually, from "full blow", a few pumps of cold water is all that is needed to drop the pressure enough to close the safety valves, without disturbing the fire, so pressure can then rise again to another "blow".).
12. Any other instructions from the Boiler Inspector must be followed, after which he will decide if he will issue the certificate of test.
13. If the certificate is denied, he will advise some remedial work which should be demonstrated before a re-test is conducted.

Hope this is useful? - Any other comments from the experts out there? - Surely I have missed the obvious point? (According to my missus I usually do!).
K

 

[chrsbrbnk]

HYDRO A BOILER AT 1.5 TIMES WORKING PRESSURE! not more ! the thought is that stress out things messing about with 2 or 3 times boiler pressure. ask any boiler inspector .

 

[Steamchick]

OK. I hear you. But I'll check with Regulations. I'm sure ( having been doing this for 20 years or more myself) that all the books and the Southern Model Engineering pamphlet on the Regulations gives the Design Hydraulic test at 2 x NWP, later repeat tests (annual tests, etc.) are are 1.5 x NWP for the UK. But ASME states (according to Model Engineering mag of December 2006 Volume 40 number 6) the test shall be in accordance with a table, that accounts for the temperature weakening at the temperature of the steam pressure, so (E.g.) the test pressure for an 80psi NWP would be about 205psi. Actually, these regs seem more stringent than the UK regs, as for an "80 psi NWP" boiler I would test upon first manufacture, or after repair, or if the certificate has expired, I would first test at 160psi - which is only 80% of the ASME regs. As I have a Simplex boiler drawing stating NWP = 80 psi, Initial Hydraulic test at 160psi, (Designed max.) then to take this for examination in the USA it would only qualify under ASME as a 67psi NWP boiler and need the safety valves resetting accordingly.
Therefore I advised CHECKING THE LOCAL REGULATIONS, as many people are on the thread from different countries.
I am probably out-of-date if the regs have changed in the past 20 years. (But I use ASME for my designs and testing - my local tester uses UK regs. for the certification.).
I'll study further.
An extract from the UK Southern Federation paper of the test codes 2018: For boilers of less than 3Bar-litres: "The boiler shall be subjected to an initial hydraulic shell pressure test of twice Working Pressure (2xPW) and the certificate is valid for the life of the boiler. The test procedure is as described in section 10 of this code. 6.6 A repeat hydraulic test shall be conducted after the working components have been attached to the boiler shell to prove the structural integrity of the boiler fittings and their attachment to the boiler. This includes the pressure gauge where feasible. The applied pressure shall be one and a half times Working Pressure (1.5xPW). The test procedure is as described in section 10 of this co ".
For anything larger: "3.7 Initial hydraulic shell pressure test: The hydraulic pressure test carried out on the boiler shell on the initial completion of manufacture. The boiler shell shall be fitted with blanking plugs as appropriate. The test pressure shall be twice the Working Pressure (2x PW). 3.8 System hydraulic pressure test: The hydraulic pressure test carried out on the boiler once all the boiler fittings except the safety valves have been attached to the boiler shell. The system hydraulic pressure test shall be carried out at intervals prescribed in paragraph 12.5b. The test pressure shall be one and one-half times the Working Pressure (1.5x PW). "
Does this clarify the situation FOR THE UK?
But this is for boilers that are "in service" - I.E. covered by an insurance policy for 3rd party injury or somesuch, such as you will have for driving your traction engine on the road, or your model at a show, or otherwise where the public have access. What you do in the privacy of your own home is your business, providing any other persons are advised and are responsible for any situation that an operating boiler puts them in...
just be VERY careful, as Boilers are Bombs, and can explode! - Or simply blast steam jets that cause scalding!
Be safe, be certified.
K
Thanks.
K

 

[Steamchick]

UK Regs FYI.
https://www.sfmes.co.uk/ydrRoot/committees/boilerSC/Forms/testCode2018_volume1.pdfFor the US of A... ASME Boiler and pressure vessel code: Search the web...
K