Aidan wrote:

I recall BG spraying the insides of the gas main in the street where I
lived, about 15 years ago, to reduce leaks. I believe (i.e., I don't
know the details) that this involved pushing a small plastic pipe,
similar to a drain jetter into the mains to spray it. I didn't hear of
any subsequent problems.

It seems it wasn't very effective, since they dug up the street and
replaced the steel/CI mains with MDPE a year or two later. I don't know
if they still use this technique.

It sounds like blarney to me.

There's a core of historical truth if you go back far enough. Because
coal (town) gas was made by a process involving steam, it contained
significant water vapour. Natural gas did not, so it had to be
deliberately humidified to prevent the packed pipe joints from drying
out and leaking.

That problem is obviously disappearing as the distribution network moves
towards plastic. No doubt plastic brings problems of its own, but there
are limits to the things that can be added to the supply, given that it
mustn't affect the calorific value, and any additive must be safe to be
burnt in an open kitchen.

Come to think, a likely reason for the sudden presence of dust or powder
is that new pipe-laying has required some temporary re-routeing of the
supply, which has disturbed some old deposits.


--
Ian White
Abingdon, England