Maximum allowed gas PPM from joints?

[Seri]

I have a new boiler (finally) and am considering doing some of the gas pipe re-routing myself (a possible topic for another time), before I even consider this I thought it was a great excuse to purchase an 'okay' little flammable gas detector and add another toy to the toolbox.

I'm a paranoid type of person when it comes to things that can kill me, so as soon as the thing arrived today I carried it over to the existing cooker a opened a hob the minimum amount to measure the amount (over 1000ppm but less than 10000ppm). Next I recalibrated it and tested the existing gas piping put in some years ago by the previous owner, one of the joins in the existing pipework manages to just get the detector to tick over to the first level (above 100ppm but less an 1000ppm), this made me realise, I don't actually know if this is an allowed amount, I had (possibly stupidly) assumed that no gas would be allowed.

To cut this simpler, what is the allowed maximum PPM of flammable gas from a join?

Thanks for any answers.

Seri

[Jim Ingram]

even

existing cooker

1000ppm but

pipework manages

100ppm but

I am not a gasfiitter however I can tell you that the Lower explosive limit of methane in air is ~5%(v/v) (the minimum concentration of gas required to sustain flame propagation) which equates to 50,000 ppm so not much chance of an explosion in your case. I suspect that the regs quote an allowable amount of leakage in terms of volume of gas. I think what gasmen actually do is to turn off the gas supply and connect a manometer (pressure gauge) to the gas pipe work for a period of time and calculate the amount leaked from the pipework volume and the pressure drop.

Jim

[Ed Sirett]

Have a look in the Gas Fitting FAQ below. Whilst a Flammable Gas Detector is a useful (but not absolutely essential) gadget for tracing leaks it is NOT the tool used to certify that gas pipe work is gas tight. The limit for Domestic Natural gas pipework is NO drop of pressure in

2minutes when measured with a U-gauge and less than 0.25mBar when measured electronically.

The method is fully explained in the FAQ.

Even tiny leaks can have gas concentrations by the pipe that are approaching the 'LEL'. This means that were you to be so foolish as to trace them with a naked flame they would be big enough to ignite and support a flame.

[Set Square]

I don't know what the official answer is - but I wouldn't be happy with

*any* detectable leakage from a joint. Rather than using fancy kit, buy a can of leak detection fluid (such As Screwfix 12266) and spray it onto each joint. If you can see *any* bubbles coming out - even one per 10 seconds - remake the joint.

[Seri]

I read through the FAQ in its entirity, and whilst the sections on testing I can mostly adhere to, the fact that there's already a boiler and cooker fitted to the gas piping I can't easily perform a 'pipes only test'. Today I purchased a 12"/30mBar Manometer and tested at the gas meter test point, I followed the instructions in the FAQ, brought the pressure slowly to 20mBar, timed two minutes and noted the difference. I know the FAQ says up to 4mBar drop over 2 minutes is allowed, but I wanted to triple check. I have 1mBar drop (1.2 if being pedantic) testing at the meter test point over the space of 2 minutes, this is with the cooker and boiler connected to the pipework but in an 'off' state, is this a natural and allowable drop?

Thanks again for any responses

Seri

[Ed Sirett]

It would be best at this point to turn the cooker and boiler off at their respective isolators or remove the bayonet hose. The boiler will likely have some sort of 1/4 turn cut off. If you then get a 0 drop (you did allow a 1 min settling time before beggining the test?) AND there is no smell of gas then that is adequate.

If you still get a non zero drop then the leak MUST be found. It could be anywhere from the MCV, meter, govenor or pipe work.

Likely placed where it is good to start looking:

1) any place where the pipe comes out of a concrete floor. 2) anywhere the pipe goes unprotected through a wall. 3) around the meter especially if it has been changed recently. 4) New pipe work. 5) The anaconda (flexible corrugated stainless pipe) especially if it had flux on it and/or got wet.

A pro will probably

1) test the U guage for leaks (to eliminate the wild goose chase). 2) Put a disc in the meter outlet to split the problem between the meter and your pipes.

Appliances are allowed to leak slightly provided they don't smell. Pipes are never allowed to leak, any.

-- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at

Gas fitting FAQ CH FAQ

[Seri]

"Ed Sirett" wrote in message news: [e-mail]... | On Mon, 24 May 2004 14:31:51 +0000, Seri wrote: | | >

| > "Ed Sirett" wrote in message | > news: [e-mail]... | > | > "Seri" wrote | > | >> I have a new boiler I thought it was a great excuse to purchase a | > | >> flammable gas detector I tested the existing gas piping , | > one of the joins in the existing pipework manages | > | >> to just get the detector to tick over to the first level (above | > | >> 100ppm but less an 1000ppm), | > | >> What is the allowed maximum PPM of flammable gas from a join? | > | | > | Have a look in the Gas Fitting FAQ below. | > | The limit for Domestic Natural gas pipework is NO drop of pressure in | > | 2minutes when measured with a U-gauge and less than 0.25mBar when measured | > | electronically. | >

| > I read through the FAQ in its entirity, I can't easily perform a 'pipes only test'.

| > I know the FAQ says up to 4mBar drop over 2 minutes is allowed, but I wanted | > to triple check. | > I have 1mBar drop (1.2 if being pedantic) testing at the meter test point | > over the space of 2 minutes, this is with the cooker and boiler connected to | > the pipework but in an 'off' state, is this a natural and allowable drop? | | It would be best at this point to turn the cooker and boiler off at their | respective isolators or remove the bayonet hose. The boiler will likely | have some sort of 1/4 turn cut off. | If you then get a 0 drop (you did allow a 1 min settling time before | beggining the test?) AND there is no smell of gas then that is adequate. | | If you still get a non zero drop then the leak MUST be found. | It could be anywhere from the MCV, meter, govenor or pipe work. | | | Likely placed where it is good to start looking: | 1) any place where the pipe comes out of a concrete floor. | 2) anywhere the pipe goes unprotected through a wall. | 3) around the meter especially if it has been changed recently. | 4) New pipe work. | 5) The anaconda (flexible corrugated stainless pipe) especially if it had | flux on it and/or got wet. | | A pro will probably | 1) test the U guage for leaks (to eliminate the wild goose chase). | 2) Put a disc in the meter outlet to split the problem between the meter | and your pipes. | | Appliances are allowed to leak slightly provided they don't smell. | Pipes are never allowed to leak, any.

Thanks for the continued help, unfortunately the previous owner of this property (well, his dad) installed everything himself and had 'interesting' ideas about the way things should have been done, this has ranged from the water plumbing to the electrics to the extension to the gas fittings, the entire thing.

I can't locate any easy way of isolating either the hob or the central heating boiler, the upstairs water on demand boiler has a master gas 'off' valve which I turned off before starting any testing but the same doesn't seem to be possible for the other two devices.

I left the gauge to settle for a minute before starting testing, but as said, the hob and the heating boiler were off but not isolated from the gas supply.

I also ensured that the testing screw was tested with gas leak detection fluid and the new electronic gas detector before turning on the gas supply.

Basically, my question now is this, from what's been said so far, the gas here needs some extensive testing. I've been in this property with the current state of affairs for just over two years. All of the 15mm gas pipe will need to be replaced with 22mm pipe to accomodate the new boiler (this would take it almost all the way back to the meter) The hob is fed from an entirely seperate feed from the meter. The replacement pipework and the installation of the boiler will be happening in about 4 weeks.

Q: Should this be okay as it is until the new boiler is installed? Q: With no device other than the hob connected is it normal that I'll notice any drop? (I seem to recall hobs can be a little 'lossy')

thanks again

Seri

[Ed Sirett]

IME appliances rarely leak, leaks are usually the pipework.

Well if you were registered and you found a leaking installation you need to do one of two things: a) Fix it. b) Turn it off and label it as dangerous.

Anything else is not competant gas fitting so you are invited to make you own assessment.