AS NZS 2022:2003 – Anhydrous ammonia-Storage and handling.
2.7.1 General
Any valve, fitting or accessory used for anhydrous ammonia service shall comply with AS 1271, or an appropriate application Standard.
The pressure rating of any valve or fitting shall be not less than the design pressure of the container, the maximum total discharge pressure of a pump or compressor, or 1 .73 MPa, whichever is the greatest.
2.7.2 Hydrostatic relief valves
A hydrostatic relief valve shall he installed between each pair of shut off valves on anhydrous ammonia liquid piping, so as to relieve hydrostatic pressure. The start-to- discharge pressure of such valves shall be less than or equal to the design pressure.
NOTE: Where piping may be subject to high ambient temperatures, it may be necessary to increase the margin between the operating pressure and the design pressure (see Clause 2.2.2).
A hydrostatic relief valve is not required between isolation valves in small bore piping of
20 mm or smaller, providing the distance between the valves is less than 0.5 m and the
valves are either drain valves in series or a bleed valve is located between them.
The discharge from hydrostatic relief valves shall be directed to a safe location and away from the operators.
NOTE: Where ball valves are used for liquid anhydrous ammonia service, the potential exists for anhydrous ammonia to be trapped within the valves.
2.7.3 Pipeline shut off valve
Where a liquid transfer line, loading arm or hose is not drained of liquid on the completion of the transfer operation, such line or hose shall be fitted with a shut off valve at the discharge end.
2.7.4 Bleed valves
A bleed valve shall be provided at the end of each flexible transfer hose to permit depressurizing and the draining of residual liquid. The orifice of the bleed valve shall be not greater than 6 mm.
NOTE: Where discharge to atmosphere should he avoided, the use of a low pressure drain collection system is recommended.
2.8.1 General
Anhydrous ammonia tanks shall be fitted with excess flow protection as specified in Clause 3.4.
Excess flow protection may be required in pipelines downstream or upstream of storage containers to reduce the risk levels to acceptable limits in the event of a pipeline rupture.
2.8.2 Capacity of excess flow valves
The rate-of-flow capacity of an excess flow valve shall be not greater than 1 .5 times the design flow rate of the system.
Each excess flow valve shall incorporate a bypass that has an opening not greater than 1 mm in diameter to allow equalization of pressure. Where an excess flow valve forms an integral part of an internal quick-closing valve, a permanent bypass is not required, provided that the valve has a manual means for equalization of pressure.
Where the piping volume downstream of an excess flow valve is greater than 200 L, a 15 mm bore bypass line fitted with a globe valve and a restriction orifice with a diameter not greater than 6 mm, may be used to enable quicker equalization of pressure across the excess flow valve. The globe valve shall he locked closed when the bypass line is not in use.
2.8.4 Installation of excess flow valves
Any’ excess flow valve installation shall comply with the following requirements:
(a) Excess flow valves shall close automatically at the rated flows of vapour or liquid as specified by the manufacturer. The connections and line, including valves and fittings protected by excess flow valve, shall have a greater capacity than the rated flow of the excess flow valve.
(b) Shut off valves with an integral excess flow valve shall be designed for proper installation in a container opening so that the excess flow valve shall close in the event that the valve body, extending above the coupling, is sheared or broken off.
(c) Each liquid filling connection shall have a positive shut off valve in conjunction with either an internal backpressure check valve or an internal excess flow valve. Vapour connections shall have a positive shut off valve together with an internal excess flow valve.
(d) Where the capacity of any individual connection of a multiple connection system downstream of an excess flow valve is less than that of the excess flow valve, an additional excess flow valve shall be fitted in the connection.
(e) Where a pipe run is unusually long or restricted due to the number of fittings and valves and it is possible that the flow resulting from a rupture at the downstream end is not sufficient to activate the excess flow valve at the upstream end, one or more additional excess flow valves shall be fitted in the line.