AIRCRAFT FUEL

My experience is mainly operational and not installation, but I think I understand what you are trying to find out.

You are correct, flanged fittings are not used underground unless in a pit. If you are questioning the gap in your lining where the two pieces weld together, as I understand it commonly that is left un-lined.

My company had a pipeline that went from our main cross country pipeline tank farm to a smaller tank farm that was not far from the airport. The 25 mile section between the main tank farm and the one by the airport was underground and had gaps in the epoxy lining. This was not considered a problem because we filtered the fuel again through micronic and coalescers before sending the fuel to the air port itself.

If you are describing a pipeline going to and from a hydrant system at an airport, you may have to either find a method of lining the joints after welding or use a hydrant system that includes filter separators between the hydrant and the aircraft.

One Air Force base I was stationed at solved this problem by using stainless steel pipes underground so the fuel could be filtered at the pump-house and only clean dry fuel was ever in the stainless hydrant loop.

I hope this helps. If not, please outline your situation better and we will do what we can.

Drew