Gas Pipes.

Ignition source, basically


If the equipment is correctly earthed, then if the gas main is bonded it won't carry significant currents (comparatively)


Regards


OMS

Have there been any scientific experiments or studies showing the dangers of copper domestic gas pipes with soldered fittings carrying electrical currents OMS? Just what is the explosion risk, and at what currents and durations?


Z.

Just do it!

Regards, UKPN.

UKPN:

Just do it!

Regards, UKPN. 

Just do what?

Just do what?

I suspect UKPN was (jokingly) suggesting Zoomup tries some scientific experiments will gas filled pipes and electric currents...


   - Andy.

The risk is nil while the pipes remain closed. Nasty things happen, as they have to plumbers as well, when a fitting or union is loosened to change a meter or an ECV and current was flowing.

There is at least one case of a plumber being killed while removing a stopcock in a supply pipe outdoors, as he unwittingly also interrupted the neutral return for quite a lot of load at the same time. With gas far smaller currents could still pose an ignition hazard during disconnection if a spark can be drawn.

Insulating joints (IJs)  are supposed to be the fix for that, but are rarely seen.

I was thinking of diverted neutrals causing largish currents to flow in copper gas pipes as an example.


Is there an explosion risk with 20, 30, 40 or 50 Amps flowing. Will the pipe get so hot that fittings start to leak gas due to softened solder at fittings?


Will the gas explode inside the pipe if it gets very hot or is there insufficient heat and lack or air to prevent an explosion?


Will diverted neutral current be limited in magnitude by the new artificial (perhaps high impedance) "Ra" caused by a lost neutral, when load currents try to travel down copper gas pipes or water pipes to earth?

Or is the perceived gas explosion risk just a loose assumption and not a proven risk?


Z.

Current of itself does not cause an ignition risk. The ignition risks are heat (auto-ignition of the gas at a high temperature - for methane this is around 480-490 degrees Celsius) or sparks causing ignition (as used to light a gas hob). As mapj1 says the risks (of explosion) while the pipe is closed is probably nil as there is no gas outside the pipe which is therefore not an explosive atmosphere, and only pure gas inside the pipe and therefore also not an explosive atmosphere. However there are other dangers he points out which need to be considered.

Alasdair

You need hundreds of amps to warm up a 15mm or 22mm dia pipe to any thing like a dangerous temperature, the resistance is so low.


The wall thickness is 0.7mm on  a 15mm pipe, and more like 0.9mm on a 22 .

Pi* diameter* thickness = 47mm*0.7=  32mm2 for the 15mm pipe

= 69* 0.9 = 62mm2 for the 22mm pipe.


If you compare these areas with the rating of similar cross-sections of PVC insulated cable you'd be looking at 170A and 250a for method C , but then the pipe is better cooled than a solid cored wire as it has a far larger exposed surface, and in any case that current rating only gets you up to 70C - solder melts at about 200C, so you'd need to increase the current by a large multiple to get hot enough to unsolder a joint ! Though water pipe is better cooled against hot spots.


Generally, the only problems arise really when screwed joints are being un-done for maintenance, or in very odd cases where perhaps there is tape in a join, or an earth clamp is loose so that all the current is tunnelled into a much smaller area and it sizzles and burns through,and that is not common.

Diverted neutral current is as much a risk as the CPC if not more so, but at least if there is bonding where the pipes come in, we are not passing current via internal piping of gas cookers and boilers and their CPC of unknown cross-section.

543.2.3: gas pipe, oil pipe - they contain fuels; flexible materials, or parts subject to mechanical stress - these may fail.

543.2.6 an ECP, for example a water pipe, may be used under certain circumstances.


So the reason does appear to be the risk of fire, however remote.


I might add that daughter's bonded (private) water supply provides a better earth than the conventional rod.