Pressure rating of flexible hose??

[MadDog88]

Hello all,

In our refrigeration area of our ammonia plant, we have numerous double block and bleeds for isolations. As these isolations are carried out infrequently there is no hard piping on the bleed/drain line to vent. So, once the two block valves are closed, a flexible hose is connected to the 1 inch bleed and the ammonia vapour is vented to a safe location away from the operator opening the valve.

There have recently been questions asked as to why the flexible hose is not rated to the full system pressure (can be up to 10 000kPa). The hose they have been using is rated to only 1800kPa. Does the hose (or pipe if necessary) need to be rated to full line pressure or is a lower rating acceptable due to the downstream end of the hose being open to atmosphere and also the pressure drop across the drain valve? Do we need to install a pressure gauge between the globe valve and the flexible hose to ensure that the pressure is let down to the rated pressure of the hose?

Thanks in advance for your help.

 

[Montemayor]

Maddog:

If you are talking about an NH3 mechanical refrigeration system (and I assume you are), how can the system achieve 1,450 psig (10,000 Kpa)? The highest rating on NH3 refrigeration that I've employed is 300 -350 psig, and that's plenty.

I vented my NH3 with a Low Pressure hose to a drum filled with water and made ammoniated water, a fertilizer which we used in our plant's gardens and green area. The hose will not reach a pressure any higher than the hydrostatic head of the water - which is negligible. I don't understand your explanation of why the venting hose has to have a pressure rating - especially one on a par with your HP process. You can install a pressure gauge on the venting hose, but you're not going to see any pressure registering on it - not if you're venting to atmospheric pressure.

As long as you do not install any valves on the hose, downstream of where you are connecting it to your vent nozzle, there will be essentially no pressure generated in the hose. You haven't identified the state of the NH3 you're venting, and I assume it's essentially vapor - not liquid. You can vent liquid NH3, but you have to take precautions due to the low temperature flashing that results. But it can be done - with care, and depending on the quantity handled. I assume you're taking all the safety precautions recommended for handling NH3 - liquid or vapor.

I hope this explanation helps you out and have a safe vent.

 

[svanels]

I rather be concerned if the flexible hose is compatible with the amonia. Another thing, I assume that there are proper lock-out, tag-out procedures and people do not open valves on "life" systems.

10.000 kPa = 1450 psi and for draining purpose it would be overkill, using a stronger hose, it just 20% of the system pressure.
I am against installing appendages on a hose, somebody easily could make a dead end system.

Steven van Els
SAvanEls@cq-link.sr

 

[MikeHalloran]

I figure Maddog may have to install the pressure gage anyway, at least long enough for a demonstration. The question sounds like something posed by a union Safety Committee during an inspection tour.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[MadDog88]

Thankyou all for your help, it has answered all of my questions.

Montemayor, I may have not explained myself well but for your information, it is a plant that makes ammonia (at approx 10 000kPa and 420 deg C) and the same ammonia is also used as a refrigerant to cool it to –33 deg C for storage.

Thanks again.

Cheers