EN 764-7-2002 pdf download.Pressure equipment-Part 7 : Safety systems for unfired pressure equipment.
8.1.1 Pressure relieving devices shall be so installed as to preclude injury to personnel by the relieving process. Pressure shall be vented to a sate location. The effects of the discharge on the environment shall be considered.
8.1.2 Whenever possible, the pressure relief shall follow a short, straight path. The reaction force which occurs as a result of the pressure relief shall be taken into consideration.
8.1.3 Common discharge pipes shall have a sufficient capacity, such that when one or more devices are discharging, there shall be no unacceptable super-imposed back pressure on the remaining devices which may be required to discharge during the failure scenario.
8.1.4 Wherever possible, pressure relieving devices shall be installed such that the discharge line is free draining to the disposal system. Where this is not possible and there is the possibility of liquid collecting in a discharge line, a drain shall be provided to a safe location and consideration given to the prevention of freezing of any liquid buildup. In a liquid system, the impact of static discharge head on the set pressure of a relief valve shall be taken into account.
8.1.5 If pressure discharge pipes are fitted with components to prevent ingress of rainwater or foreign bodies, these components shall not obstruct the free and full discharge of the safety devices.
8.1.6 If the pressure relieving device can discharge a flammable fluid, the danger of ignition in the discharge pipe shall be considered and appropriate measures taken to minimise the hazard.
8.2 Safety valves or the main valve of a CSPRS
8.2.1 General
8.2.1.1 Flange bolting and gaskets
Bolts and gaskets shall be of the correct type, material and dimensions. Gaskets shall not obstruct any part of the
bore of the safety device or its inlet or discharge piping.Stress considerations
Requirements a) to C) shall be met for all operating modes of the plant including start up, shutdown and discharge:
a) External loads
The inlet and outlet piping shall be supported to ensure that no unacceptable external mechanical loads are transmitted to the safety valve or the main valve providing the safety function. In addition, the inlet and outlet piping shall be sufficient to withstand the effects of the reaction forces when the valve discharges:
b) Thermal stresses
Provision shall be made to accommodate any thermal stresses induced in the inlet and outlet piping:
If equipment contains both liquid and gas, and gas is to be relieved, a safety valve for use with gases shall be connected to the equipment in the gas space or piping connected to this space and located in a position chosen to minimise the entrainment of liquid when the valve discharges. Alternatively, if liquid to be relieved, a safety valve for use with liquid shall be connected to the equipment below the liquid level at a point chosen to prevent ingress of gas.
NOTE If two phase flow is possible. the design of relief systems will require special consideration.
8.2.1.4 ProximIty to pressure source
The connection between the safety valve and the equipment shall be as short as possible and have a bore area at least equal to the valve inlet. With all installations, the pressure drop in the inlet piping system to the safety valve shall be In accordance with 8.2.2.
NOTE I In installations where there are pressure pulsations, the valve or the connection should be located in a region where the effects of the pulsations are minimised. consistent with maintaining correct operation of the safety valve.
NOTE 2 Particular care should be taken in selecting a connecting pipe in the NPS (Nominal Pipe Size) system since the bore can be smaller than the nominal size.
8.2.1.5 Sensing line
The line shall incorporate a siphon, where applicable, and stop valves with a test connection to enable the pressure settings and the correct functioning of the instrumentation to be checked.
NOTE The sensing line is the line between the pressure sensor and control module (for CSPRS) or the line between the pressure equipment and the pilot (for Pilot Operated Safety Valves).
For assisted opening and supplementary loaded safety valves, the connection for the sensing line at the pressure source shall be located as remotely as possible from the safety valve mounting to minimise the effect of localised pulsations and system vibrations in the sensing line when the valves are operating.
The length of the pressure sensing line should be as short as practicable in order to avoid dynamic problems.
8.2.1.6 Mounting position
If a valve is required to be installed in other than the vertical position its ability to operate correctly in the required
position shall be checked.
8.2.1.7 AccessibilIty
Easy access and sufficient workspace and height shall be provided for the servicing and removal of safety valves.EN 764-7-2002 pdf download.