surface corrosion on hot/cold ammonia pipe
surface corrosion on hot/cold ammonia pipe
(OP)
After only 2 years a leak occurred on a 3/4" seamless carbon pipe (schedule 40) carrying ammonia liquid and gas.
The pipe is insulated with pre-moulded pu and the cladding are with plastic tape. The pipe wills every 4 hours be cold (-25 dg C/-13 dg F) for approx 3 min, chilled (5 dg C/42 dg F) for 20 min and hot (50 dg C/120 dg F) for 2 min.
The pipe was not surface treaded before it was insulated and no damage of the insulation was found.
The pipe is on the sealing in a food processing plant and the roof space is normally good ventilated.
There is many other refrigeration pipes in same space with same conditions but only with constant temperature ranging from (-25 dg C/-13 dg F) to (5 dg C/42 dg F), those pipes have no corrosion.
I have a feeling that the temperature is the main reason and this is due to the insulation is not moisture tight enough since the leaks occurs where the pre-moulded insulation is joining and the rest of the pipe has a high but constant surface corrosion.
My intention is to change the pipe to a schedule 80 and then use a good insulation.
Any comments or experience will be very welcome.
The pipe is insulated with pre-moulded pu and the cladding are with plastic tape. The pipe wills every 4 hours be cold (-25 dg C/-13 dg F) for approx 3 min, chilled (5 dg C/42 dg F) for 20 min and hot (50 dg C/120 dg F) for 2 min.
The pipe was not surface treaded before it was insulated and no damage of the insulation was found.
The pipe is on the sealing in a food processing plant and the roof space is normally good ventilated.
There is many other refrigeration pipes in same space with same conditions but only with constant temperature ranging from (-25 dg C/-13 dg F) to (5 dg C/42 dg F), those pipes have no corrosion.
I have a feeling that the temperature is the main reason and this is due to the insulation is not moisture tight enough since the leaks occurs where the pre-moulded insulation is joining and the rest of the pipe has a high but constant surface corrosion.
My intention is to change the pipe to a schedule 80 and then use a good insulation.
Any comments or experience will be very welcome.





RE: surface corrosion on hot/cold ammonia pipe
RE: surface corrosion on hot/cold ammonia pipe
You mentioned joint in insulation. Was this at an pipe elbow where erosion could occur? What is flow rate?
Presuming that the pipe rusted from condensation, I prefer coating rather than using Sch. 80.
It's probably cheaper to use PVC-wrapped or epoxy painted pipe rather than aluminized.
Re using Sch.80: your system might then require 1" to get sufficient flow, plus it's heavier to support.
If your plant is going to be around for a long time and your piping has long runs with few fittings, consider 316 Sch. 10S. Weighs less, better flow, won't corrode & has lower heat transfer coefficient (1/3 of steel).