I/we've refered to it as a "Live Tap" when the product was non-petroleum. As in a "Hot Tap" on crude oil and refinery production piping, if there is no oxygen (no meaning 0%, "0" ppm of oxygen) then there is no risk of internal combustion. Ignition temperatures of any flammable substance under pressure with oxygen present, is going to be lower than the "normal" / ambient atmospheric environment that flash point charts are based on.
So, depending on the residue, % of 02 and pressure...Hmmm.... What is downstream? If it were to flash internally, could it just flare off the residue with nothing more than a small spike in pressure??? Or could you open a vent/blow down valve as a safety device?
If I were involved with such a project, I'd definately want a proceedure from a competent engineer of applicable discipline and said engineer standing right there during the operation!!! Or, have I just turned chicken in my old age?
Best to think this one through carefully.
It's been one of the biggest rushes of my career making hot taps in a refinery, knowing there is 600 degree F high pressure hydro carbon fluid only a fraction of an inch away and the slightest slip,cough, sneeze could instantly vaporize you, your co-workers and place the facility on "live CNN Breaking NEWS"!Good luck!