Mysterious 'holes' in gas pipes....

[JimClay]

Help....
I woke up recently to notice the tell tale smell of gas. Checking all the usual suspects (hob etc.) we resorted to calling transco who reported a 'major' gas leak in the domestic side of the gas supply (i.e. your problem, but I have to cut you off for now). Upon completing a trace and repair the gas engineer, Corgi registered of course, found not one but multiple 'pitted' holes in the copper gas pipes mid section. Some 5 sections were replaced in the kitchen, dining room and lounge. Some of this pipework was under 15 months old as we had it fitted by the same person.
At the same time a water leak was repaired. This may have been leaking for some weeks as it was under a slate floor! This water leak was within 1mtr of the largest of the gas leaks, under the slate kitchen floor.

My question is what could have caused this pretty concerning failure of the gas pipes? The holes appear to have corroded leaving a greenish tinge to the edges of the holes. the pitting also appears to have occured from outside to inside.
When repairing the problem the engineer reported low level voltage (40-50v) when touching the gas and water pipes. The pipes were under the ground floor joists, not touching the subsoil surface. We have since had the electrics checked and cross-bonding to gas and water mains has been re-instated but during the inspection no 'live' wire was traced. So far no-one has offered a logical explaination for the cause of the pipe failure.
Any ideas?

 

[ollski]

maybe wire wool and flux was left on the outside of the pipe. You say the pipe was buried under a slate floor, was it wrapped?

 

[kevplumb]

im not an electrician but it sounds like elecrolytic corrosion to me ie voltage damp earth

if you have a voltage of 50v to earth get an electreician to test the installation

QUICK

 

[Chris B]

Hi there,

I posted a question of my own earlier - but I think I can help you to answer yours!

As somebody else has pointed out, the problem sounds very much like electrolysis. I'm not a plumber but the symptoms you describe are something I often encounter in my own field of work (marine engineering).

The problem may be caused by disimilar metals being electrically joined by an electrolyte (salt water is a frequent culprit in my job), which results in a voltage being generated and a consequent transfer of molecules from one metal to the other - which is what electrolytic corrosion is all about.

The voltage you mention is, however, unusually high and my first thought is that your boiler is (or was) not properly earthed. You don't mention if your electrician measured the presence of DC or AC voltage leakage - but if it's AC (and it probably is at that voltage) then get your boiler wiring AND the electrical supply to it checked for earth continuity! Damp air and / or traces of conductive chemical contamination on the pipes won't have helped the problem. If you've dealt with the earthing problem properly - in other words, if you can no longer measure a voltage flow between known earth points and any other part of your CH system, then you should be in the clear.

If you have any unions or fittings in your CH pipe circuit that are not electrically conductive, you might do well to bridge across them with cable and earth bonding clips. That'll make sure that all of your system is at earth potential, instead of just some of it.

Unattended ships have been known to quietly sink because of this problem - be grateful that you're on dry land!

Hope this helps,

Chris B.

 

[ChrisR]

All above is true! Spots of soldering flux of the aggressive variety can hole pipes, and there are bad pipes sometimes. A lot of gas fitters use the wrong fluxes. Electrical leaks in things like pumps can lead to alarming corrosion.

 

[PTH]

Chris B has, in my opinion got the culprit. I once measured a potential of 65 V between a valve body on a buried 8" gas main and an earth rod. I investigated after a fitter reported a shock when trying to use the valve. The voltage I measured varied from 0 to 65 to -65 in precise 3 minute cycles, the pipe was steel but denso and coal tar wrapped so was fairly well isolated from the surrounding ground. The cause did not take too long to spot - the pipe ran within 100m of a large rotating microwave (I think) dish and the voltage I was measuring was purely induced energy - It makes you wonder what that level of energy does to the people working on the site!

To get back to the problem, I would think that the voltage in this case is, as previously noted, leakage rather than induced (unless Jim Clay lives next to a very large sub-station or radar installation!).

 

[ChrisR]

"Scruff" on another site advocates using a clamp meter to look for such things, often finding currents in pipes of attacked systems.

I used to work in cable TV electronics development, next to a hospital. Our building was smothered in cables, which picked up all sorts of signals from the kit in the hospital. Learned a lot about conducted and radiated susceptibility and emissions. Don't ask me anything complicated about it now, but I can sell you some books...