Sometimes insulation does more than insulating

Got a call at 6 am this morning from a fishfactory nearby, they had an ammonia leak from a pipe on a tunnel/blast freezer that is not in use at the moment.

The engineer has been running the plant in manual to keep the suction pressure down all night, but whenever a defrost kicks in on a another part of the system and the suction pressure rises, the ammonia smell would get worse.

he knew there was a leak on the hotgas return line, because he had had the maintenance crew strip the insulation to paint the pipes, to check them after having "ammonia smell" around that area for 6 months

turned out the hotgas return valves were leaking back into the evaporator (old type danfoss)

This is the pipe where they had had the "ammonia smell" from time to time

Attachment 13745

The hole was big enough for me to stick my finger through it, only thing keeping it somewhat closed was the insulation :)

Yes.. I have seen some old pipes that have this same issue. A vapor barrier on the pipe would have been in e since the pipe gets cold, sweats then warms back up then dries. Mechanical integrity checks in the play t would pay off. Ever see fiberglass insulation on those pipes? It's like a freaking Sponge some times. Good call Tycho!

Poor insulation worksmanship and procedure that caused the condensation around the pipe and inevitably corrosion.

Corrosion under insulation. There are gel-like products on the market that some folks use to smear on the pipes before putting insulation on them. Similar to a coating of oil on a piece of metal - the gel-like substance keeps air from hitting the pipe and rusting it.

I have seen a fad at one time to use polystyrene packers to hold cladding while pouring the polyurethane. The polystyrene holds water so produces a point where corrosion occurs.