Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
This Specification was prepared after repeated discussion and research by the preparing group according to the requirements of Notice on the Plan for the development and revision of the third batch of professional standards in 2017 (GONGXINTINGKE [2017] No.106) issued by the Ministry of Industry and Information Technology of the People's Republic of China, through extensive investigation, careful summarization of practical experience, reference to relevant domestic and international standards and extensive solicitation of opinions.
This Specification comprises 8 Clauses and 3 Annexes.
The main technical contents of this Specification are: basic requirements of pressure relieving devices, setting principles and requirements, requirements of set pressure and overpressure, analysis of overpressure operating conditions, calculation and selection of relief flowrate and relief area, etc.
China Petrochemical Corporation (SINOPEC) is in charge of the administration of this Specification, SINOPEC Technology Center Station of Technologic System Design is responsible for the daily management, and SINOPEC Engineering Incorporation is responsible for the explanation of the specific technical contents. In case of any opinion and suggestion in the process of implementing this standard, please send it to the daily management organization and the chief development organization.
This Specification was issued in 2020 for the first time.
Process design specification for pressure relieving devices in petrochemical industry
1 Scope
This Specification specifies the process design requirements for pressure relieving devices in petrochemical industry.
This Specification is applicable to the process design of pressure relieving devices in petrochemical industry, but not to the process design of pressure relieving devices in compressor chambers which are self-contained or as components in power boilers heated directly by flames, transportable pressure vessels and rotating or reciprocating-motion mechanical equipment.
2 Normative References
The following referenced documents are indispensable for the application of this Specification. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 150.1 Pressure vessels — Part 1: General requirements
GB/T 567.1 Bursting disc safety devices — Part 1: Basic requirement
GB/T 12241 Safety valves — General requirements
GB/T 12242 Performance test code — Pressure relief devices
3 Terms and Definitions
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 12241, GB/T 12242, GB/T 567.1 and the following apply.
3.1.1
pressure relieving device
device designed to prevent the internal medium pressure from rising above a specified security value when the pressure system is in an emergency or abnormal condition
Note: The pressure relieving devices in this Specification are limited to safety valves and rupture disk devices. Other pressure relieving devices, such as breathing valve, buckling pin valve, breaking pin, fusible plug are not within the applicable range of this Specification.
3.1.2
safety valve
valve that uses the force of the medium itself to discharge a rated amount of fluid to prevent the pressure from exceeding a specified safety value When the pressure is reduced to a certain value, the valve closes automatically and prevents the medium from continuing to flow out. It is also known as pressure relief valve.
3.1.3
rupture disk device
non-reclosing pressure relieving device actuated by the static pressure difference between the inlet and outlet of the medium and designed to realize the pressure relieving function by the rupture of a pressure containing disk
3.1.4
set pressure
set opening pressure of pressure relieving device under use conditions, also known as level pressure
Note: The pressures not specified in this Specification are all gauge pressures.
3.1.5
back pressure
pressure at the outlet of pressure relieving device and is the sum of the built-up back pressure and the superimposed back pressure, also known as backpressure
3.1.6
built-up back pressure
pressure formed at the outlet of the pressure relieving device due to the medium flowing through the discharge system when the pressure relieving device is discharged
3.1.7
superimposed back pressure
static pressure that exists at the outlet of the pressure relieving device before it is about to operate, caused by other pressure sources in the discharge system
3.1.8
overpressure
pressure increment in excess of the set pressure of the pressure relieving device, usually expressed as a percentage of the set pressure
3.1.9
relieving pressure
set pressure plus overpressure, also known as relieving pressure
3.2 Main symbols
For the purposes of this specification, the following major symbols apply.
A——the heated surface area of the container;
Cp——the liquid specific heat capacity at constant pressure;
Cv—— the average specific heat at constant volume of gas at the relieving and operating temperatures;
D——the diameter of the container;
d——the inner diameter of feed pipe of gas storage tank;
F——the relieving reduction coefficient;
G——the relative density of liquid;
GL—— the liquid relief flowrate;
h——the wetting height of the container, which refers to the distance from the lower tangent line of the tank to the highest liquid level;
L——the total length of the container;
M——the molecular weight of the fluid;
Pd——the relieving pressure (absolute pressure);
Pn——the operating pressure (absolute pressure);
Ps——the set pressure;
Q——the maximum heat capacity of the system;
r——the latent heat of vaporization of the liquid under the relieving pressure;
T1——the relieving temperature;
Tn——the operating temperature;
TW——the wall temperature of equipment under fire condition;
t——the saturated temperature of relieving liquid under the pressure relief condition;
W——the relief flowrate of pressure relieving device;
WG——the relief flowrate of gas storage tanks of pressure relieving device;
ΔT——the temperature difference between the relieving temperature and operating temperature;
δ——the insulation thickness;
λ——the heat conductivity coefficient of thermal insulation material at room temperature;
ρ——the density;
ρG——the gas density under relieving pressure Pd;
v——the flow rate in the feed pipe of gas storage tank;
ω——the volume expansion coefficient, which refers to the volume expansion of liquid for every 1°C increase.
4 Basic rules
4.1 The pressure relieving devices shall be set up in accordance with the requirements of the pressure system under abnormal conditions to determine the overpressure analysis:
4.2 The independent pressure system of the pressure relieving devices shall be able to meet the system's relief requirements.
Note: Independent pressure system refers to the system separated from other systems with isolating devices. When a pressure system consisting of multiple containers is provided with shut-off devices (such as shut-off valves and control valves, or although there is a pipeline connection, the pipeline is not enough to relieve pressure), it is necessary to divide the pressure system into several independent pressure systems according to the position of the shut-off devices, and each independent pressure system is provided with pressure relieving devices.
4.3 When the system design pressure of the independent pressure system is greater than or equal to the highest possible pressure under the working conditions, the independent pressure system may not set up pressure relieving devices.
4.4 In addition to the reliability of protective instrument system reaches the reliability of pressure relieving device or the pressure relieving device cannot be used, the automatic interlock system, automatic shutdown system and other conventional instrument systems with anti-overpressure function shall not replace the protective effect of pressure relieving device on pressure system.
4.5 The setting of pressure relieving devices shall meet the requirements of its inspection cycle.
4.6 If the medium is viscous, strong corrosive or the toxicity degree is highly harmful or above, the auxiliary safety valve should be set up, and the auxiliary safety valve shall be of the same specification as the safety valve in use.
4.7 The inlet and outlet shut-off valves of safety valves in use shall remain opened then locked or car seal open; the inlet shut-off valve of auxiliary safety valves shall be closed then locked or sealed, and the outlet shut-off valve should be opened then locked or car seal open.
5 Principles and requirements of safety relief device setting
5.1 Setting principles
5.1.1 The safety valves shall be provided in the following situations:
a) The design pressure of the system is less than the pressure at the pressure source;
b) Except that the equipment itself has a safety valve and its set pressure and relieving capacity meet the relieving requirements of the system, the outlet of each section of reciprocating compressor or the outlet of positive displacement pump such as electric reciprocating pump, gear pump and screw pump shall be equipped with safety valves;
c) The system is connected with the outlet of blower, centrifugal compressor, centrifugal pump or steam reciprocating pump, and the design pressure of the system is less than its maximum outlet pressure;
d) The medium of the system expands or vaporizes when heated, and the system pressure may exceed the system design pressure.
5.1.2 The rupture disk device should be set separately in the following situations:
a) The system pressure increases rapidly, and the opening of the safety valve cannot meet the requirements of fast response time;
b) The safety relief flowrate required by the system is large, and the selection of safety valves is difficult;
c) The operating pressure of the system is very low or high, and the safety valve is difficult to manufacture;
d) The temperature during the safety relief of the system is low, and the operating characteristics of the safety valve may be affected when the process medium is relieved;
e) For the disposable pipeline system, the rupture of rupture disk device will not affect the operation and production.
5.1.3 The combination of safety valves and rupture disk devices should be set up in the following situations:
a) Under vacuum condition, no gas or air outside the system is allowed to enter the system through pressure relieving devices;
b) The system does not allow the process medium to leak through the safety valve during normal operation;
c) Long-term contact between the relief medium and the safety valve may lead to failure of the safety valve in the system;
d) The process medium is corrosive, so it is necessary to use corrosion-resistant materials or lined with anti-corrosion materials, and the safety valve has a high manufacturing cost;
e) The system has multiple and complicated overpressure conditions.
5.1.4 The setting of rupture disk devices shall meet the following principles:
a) Rupture disk devices should not be set for systems with frequent overpressure;
b) Rupture disk devices are not suitable for systems with large temperature fluctuations;
c) Apart from having a follow-up treatment system and meeting the requirements of safety and environmental protection, rupture disk devices shall not be used alone in places where the discharged medium is liquefied petroleum gas or explosive, or of extreme toxicity or high hazard.
5.2 Setting requirements
5.2.1 When the safety valve and rupture disk device are used in combination, the combined relief flowrate shall not be less than the safety relief flowrate of the protection system.
5.2.2 Safety valves and rupture disk devices used in series shall meet the following requirements:
a) There shall be measures to detect rupture or leakage of rupture disk devices between rupture disk device and safety valve.
b) When the rupture disk device is connected in series on the inlet side of the safety valve:
1) The marked bursting pressure of rupture disk device should not be greater than the set pressure of safety valve.
2) The nominal diameter of rupture disk device shall not be less than the nominal diameter of the inlet flange of the safety valve.
c) The rupture of rupture disk device shall not affect the normal operation of safety valve.
d) When the rupture disk device is connected in series on the outlet side of the safety valve, it shall ensure that the safety valve can be opened at the set pressure.
5.2.3 When rupture disk devices are used in series, there shall be measures to detect rupture or leakage between the two rupture disk devices.
5.2.4 When the safety valve and rupture disk device are used in parallel, the marked bursting pressure of rupture disk device shall not exceed 1.05 times the design pressure of the system.
5.3 Installation requirements
5.3.1 Safety valves shall meet the following installation requirements:
a) The safety valve shall be set on the part of the protection system which is easy to install, inspect and maintain.
b) The safety valve shall be set near the pressure source. When it is used in gas medium, it shall be set in the gas-phase space (including the gas-phase space above the liquid) or the pipeline connected to this space.
c) The flow sectional area of all pipes, valves and pipe fittings between the safety valve and the pressure source shall be greater than or equal to the inlet sectional area of the safety valve, and the connecting pipe shall be short and straight. When two or more safety valves are installed on one connector, the sectional area of the connector inlet shall be greater than or equal to the sum of the sectional areas of the inlets of these safety valves, excluding the auxiliary safety valves.
d) The nominal diameter of safety valve inlet pipe shall not be smaller than that of safety valve inlet flange, and the nominal diameter of safety valve outlet pipe shall not be smaller than that of safety valve outlet flange.
5.3.2 The rupture disk devices shall meet the following installation requirements:
a) The inlet pipe of rupture disk devices shall be short and straight, and the pipe diameter shall not be less than the nominal diameter of rupture disk devices.
b) Shut-off valves should not be set on the inlet pipeline of rupture disk devices. When the process requires a shut-off valve, the shut-off valve shall be opened then locked or car seal open, and the circulation area of the shut-off valve shall not be smaller than the relief area of rupture disk device.
6 Rules for set pressure and overpressure
6.1 When an independent pressure system is provided with a single safety valve, the set pressure of the safety valve shall not be greater than the design pressure of the protection system.
6.2 The percentage of set pressure and maximum overpressure of safety valve shall not exceed the values in Table 6.2.
Table 6.2 Percentages of set pressure and maximum overpressure of safety valves (in %)
Item Single safety valve Multiple safety valves
Ratio of set pressure of safety valve to design pressure of protection system Maximum overpressure percentagea Ratio of set pressure of safety valve to design pressure of protection system Maximum overpressure percentagea
Non-fire Primary valve 100 10Note 1 100 16Note 2
Other valves — — 105 16Note 2
Fire Primary valve 100 21 100 21
Other valves — — 105 21
Note 1: The greater of 10% of design pressure or 20kPa.
Note 2: The greater of 16% of design pressure or 30kPa.
a Maximum overpressure percentage refers to the ratio of the maximum overpressure to the design pressure of the protection system.
6.3 The maximum marked bursting pressure of rupture disk devices shall not be greater than the design pressure of the protection system.
Foreword I
1 Scope
2 Normative References
3 Terms and Definitions
4 Basic rules
5 Principles and requirements of safety relief device setting
6 Rules for set pressure and overpressure
7 Case of overpressure and calculation of relief device
8 Selection
Annex A (Informative) Volume expansion coefficient of hydrocarbon liquid and water at 15.6°C
Annex B (Informative) Calculation of relieving flowrate and relief area in chemical reaction runaway (temper system)
Annex C (Informative) Calculation of relief area in gas-liquid two-phase relief
Explanation of wording in this Specification
