A company is carrying out mains work in the street where I live. They turned off the gas in our house while they did their work. When they came to switch the gas on, there was a 2Millibar drop on their manometer, so they cut off the gas supply. A corgi engineer has been round and he told us that in an existing situation, a drop of up to 4 Millibars is acceptable in an existing installation. However, as the company (or rather, one person) has issued a certificate, there is nothing we can do about it, and we have to go hunting for a leak (apparently an expensive process) or have a new main put in. Is there a way to challenge the action of what appears to have been an over-zealous company operative? Any advice gratefully received.
The rule is that a 4mbar drop is permitted provided a) The is no new work. b) The appliances are conencted c) There is no smell of gas.
Let's be clear about this the limit for leakage on pipework whether young or old is zero. "Zero" is defined as less than 0.25mbar in two minutes in this context
A simple way to get the gas back on is to isolate the appliances and then test if you get a pass then try with the appliances on and you get a qualified pass then no further work will be needed.
Thanks Ed. I think I follow, but I'd just like to get a couple of things clear (this is all a new area for me). Yes - the conditions you say that are necessary are all present for the 4Mb limit. Though when I was asked about a smell of gas, I said that as the cupboard where the meter is installed is often left closed for weeks on end (it's a general dumping ground for unwanted things), I sometimes get a bit of a whiff when I open the door - is that what messed things up as far as the definition of a leak is concerned? That would seem a bit harsh as I'm sure this has been true in many of the different houses and flats that I have lived in.
The corgi engineer that we called in isolated the appliances and tested the results. There was still a small drop - is this the point at which you say that the permissible limit is only 0.25Mb? (Of course, this wouldn't be an issue at all if the certificate hadn't been issued in the first place.)
Our biggest problem with this situation is that we are being told that now that there is paperwork in place (i.e. a certificate), there's no going back, even though our house was safe to begin with. That is, we are being advised that even if we can show that there was no problem, the process has to take its course. - It seems a lot of power to be in the hands of one person without recourse to an appeal or reassessment.
If the smell is in the meter cupboard it suggests the leak will be in that vicinity. It shouldn't be that hard to find with a tin of rocoll leak spray. Bear in mind it could be something as simple as a meter union needing a nip although I would have expected the utility technician or your corgi man to have tried that. Also the gas shut off c*ck may need regreasing if its a taper plug type. If you occasionally had a whiff of gas you "should" have acted upon it at the time.
Any smell of gas is unacceptable (even though almost every installation smelt of gas when we were kids...). The leak which is small will be found in the cupboard so won't need tracking down.
The usual way the gas is cut off is to put a blanking disc in the meter outlet and then test for gas tightness. This means the meter and other stuff upstream should be in the clear.
I would expect any fitter with a sniffer to be able to track the leak down in a few minutes.
Clearly this is your own home otherwise the annual gas safety inspection would have picked up the leak earlier.
Whilst the leak was so small that your house was in no real danger (but the leak might have been in an enclosed space where it could build up), the gas installation was not certifiably safe and the "cat is now out of the bag". That's too bad.
If you had reported that you never smelt gas then the original fitter might have turned the gas back on.
A small drop is clearly more than no drop (maximum 0.25 mb which is just about the minimum you can measure). It seems the fitter has followed the correct procedures: you do not have a sound gas installation and the supply cannot be restored.
Most professions give powers to people over a limited range of activites, gas fitting is no exception. If the fitter failed to restore the gas after a satisfactory test then you might have a case. Like many professions there are some ultimate check and balances on individuals power. If you were to appeal to CORGI, then they will, in this case, simply back up the fitter for doing his job correctly.
The problem is not that there is no course for appeal or reassessment but that you do not have a sound gas installation (this fact has now come to light and will not go away until it is fixed). The fact that you were unaware of the small leak before and that was a happy state of affairs for you does not give any excuse for the fitter to break the law, namely to connect a gas supply to an installation which is not gas tight.
So then. What will a registered gas fitter do?
1) Test the meter for gas soundness. It should pass.
2) Remove the disc from the outlet and test again, it will fail.
3) Ask you if you have noticed anywhere in then house which smells of gas however faintly. The cupboard.
4) Trace around in the cupboard with a sniffer and/or leak fluid.
5) Find and fix the culprit.
6) Test for gas tightness. Hopefully all is well now.
7) Turn gas back on.
8) Get paid and leave.
I'm afraid, Ed, that this falls down at step 5. The corgi man has been around with a sniffer and could find nothing. (He was even so perturbed that he tested the gadget by turning on a cooker ring - and fortunately it did scream, so it was working OK). - The 'leak' is apparently so small that it is only going to be traceable by a specialised company who (I am told) pump something through the system under high pressure to find the leak. I have been told that this is so expensive a new main would be cheaper.
So, as you can see, the leak appears to be so small that it is elusive, and would presumably disperse in the air before becoming a danger. (I am only guessing, but I assume that small amounts of gas must do this, otherwise it would not be sensible to have any permissible quantity as is the case with the 4Mb limit.) I'm not so sure that the lack of provision for appeal or reassessment is not an issue. The lack of such a provision means that there is an assumption within the system that no mistakes can ever be made - and gas fitters are human too!
'round here, there is an option to isolate all the appliances (important!), then pressurize the pipework far beyond normal operating pressure, and then look for the leak -- not with a sniffer, but with a foaming agent. Pressurization is usually done with air from bicycle pump attached with an expanding rubber bung.
Pressure goes to 1.5 bar if memory serves, with regular gas pressure at 50 mbar. Might help find a small, slow leak...
With that level of leak I wouldn't be surprised if a sniffer didn't pick it up but leak detection fluid on the various joints should do so (did your fitter try this?) - unless the leak is out of reach. Is there bare copper pipe going into concrete? That could be corroding and leaking and the gas permeating back up into the cupboard.
If this is the way that the 'experts' find obscure gas leaks, then I have to say that it is not the right way to go about it.
Pipes have joints that are expected to work under specific pressures. By increasing that pressure, one assumes that any leak will be enhanced due to the higher pressure. It doesn't work that way. A higher pressure will / can alter the geometry of a joint and seal any leak there. Increasing the pressure from 50 mbar to say 60 or 70 mbar might show up a leak, but if it didn't, I would go back to the normal operating tolerance for the system and look at it with a much closer eye.
I speak with over 25 years experience of looking for leaks with far more dangerous gasses than mere North Sea gas. Oxygen, LOX, Hydrazine (rocket fuel)
I guess not all sniffers are as good as each other.
I have managed quite easily to pick up a 1mb/minute leak with my sniffer. It's a £120 Anton unit, claimed sensitivity 10 pmm (That's 5000x less than the LEL) There are better and worse units in the market. A leak of this size should just about be noticable by nose as an occasional brief whiff when entering the leak area.
The meter is removed. Usually the union nut on the supply side is just loosened, to preserve the seal, and the consumer side nut is taken completely off, and the meter is swung to the side, and a rubber cone-shaped bung put in.
I was gofer on one job where the pressure couldn't be pumped up to 1.5 bar because there so many large leaks. Some would hardly show with foaming spray because the bubbles would pop almost instantly!
AFAIK, the regulations here call for a test under increased pressure for new pipework. As far as I know and recall, for LPG installations at 50 mbar: Just the pipework, with isolated appliances, are tested at one bar for ten minutes. Then pipework and appliances are tested at 150 mbar, for ten minutes after five minutes for thermal equilibrium.
I can't find the actual regs online, because they must be (dearly) paid for -- the same way it is in the UK, AIUI.
LPG pipework would be compression fittings on 12 mm (or so) steel pipe, or copper pipe and brazed fittings. Natural gas would be 1/2" or more steel pipe, taper thread and hemp, alternatively welded, or stainless steel pipe with special fittings (O-ring fittings and a hydraulic press to connect).
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