[BITList] Hot Tap

[HUGH]

Mike,

All is now clear. They may have reinvented the wheel. Many years ago I came 
across an item in an old marine engineering book. I never had cause to use 
it, and I never met anyone else who had heard of it, and it was filed away 
in a dungeon of my mind.

The version I read concerned removing a blockage from a connection on a 
steaming boiler - below the water level, but it could have worked above, and 
a variant would be a doddle on a tank.

Given, say, a blocked blowdown cock, close the cock, remove pipe from cock 
and replace it with a blank flange having a long boss attached with a fine 
thread hole through it. Through the tapped hole insert a length of screwed 
rod with the end cut at an angle with sharp edges.  Open cock, and turn 
screwed rod through plug and (hopefully) blockage.

I understand these "hot taps" involve attaching (welding) a pad to the side 
of a tank to take a gadget similar in principle to the above. Reduced to 
basics, a cylindrical cutter is inserted through the flange and cuts the 
required hole.  The oil industry used something similar, I now recall.

Hugh.