Ammonia piping

[jonesey]

Hi,
we have to modify some existing 2"/3" 316L liquid ammonia piping. Looking at the existing installation, nearly everything is welded, valves included. I'm presuming that this is to reduce the number of potential leakage points in the system, therefore no flanges. Some of our team are requesting that we now put flanges in the system, because it is easier for fabrication/hydrotesting. This to me is not a valid argument to introduce potential leakage points in a toxic system just because it makes the work easier. Anybody have any experince with ammonia piping and industry guidelines ?

 

[unclesyd]

Comeback with a little more information on the process, like temperature and pressure.

What is the NH3 purity?
Why the 316L as NH3 piping is normally CS?

Flanges are used in NH3 systems but are usually kept to a minimum as you state to prevent a potential leak.

 

[ApC2Kp]

jonesey,

Ammonia is one of those fluids where one plant may handle it as a normal common fluid, and another plant considers it to be a ASME B31.3 Category 'M' lethal fluid service. Large amounts of ammonia can be found in refrigeration systems of ice making plants, and the ammonia piping could be old cast iron technology. Newer process plants having concerns about carbon steel's impact toughness (being reduced at low temperatures of liquid ammonia flashing to vapor) will upgrade from carbon steel to stainless steel to ensure adequate material toughness.

The need for flanges to perform maintenance is understood. Keep the number of added flanges to a minimum. Use a high integrity gasket like a spiral wound SS grafoil gasket for blowout resistance - not a plain sheet gasket of rubber or composition fiber. Consider using upgraded flanges CL300 in place of usual CL150 flange to get additional safeguarding and strength.