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GB/T 20801 consists of the following 6 parts under the general title of Pressure piping code - Industrial piping:
——Part 1: General;
——Part 2: Materials;
——Part 3: Design and calculation;
——Part 4: Fabrication and assembly;
——Part 5: Inspection and testing;
——Part 6: Safeguarding.
This is Part 6 of GB/T 20801.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20801.6-2006 Pressure piping code - Industrial piping - Part 6: Safeguarding. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 20801.6-2006:
——The definition of safety protection device is added (see 3.1);
——The limit on set pressure and maximum relieving pressure of the safety relief device is modified (see 4.1.5; 4.1.6 of Edition 2006);
——The influence of back pressure on performance and relief capacity of safety relief device is added (see 4.1.6);
——The criteria for determining the required relief capacity is added (see Table 2);
——The measures for preventing "water hammer" and "steam hammer" and those for lightning protection are added (see Table 2, 7.4.3 and C.1.6);
——The selection method of safety relief device is added (see 4.4 and Annex C);
——The classification of MESG is modified (see Table 3; Table 1 of Edition 2006);
——The fire emergency block valve and mechanical interlocking device are added (see clause 6);
——The calculation method of gas-liquid two-phase minimum relief area is added (see B.3.4 of Annex B);
——The category and selection of flame arresters are added (see Annex D);
——The MESG test values of typical combustible gases and vapors are added (see Table E.1).
This part was proposed by and is under the jurisdiction of SAC/TC 262 National Technical Committee on Boilers and Pressure Vessels of Standardization Administration of China.
The previous edition of this part is as follows:
——GB/T 20801.6-2006.
Pressure piping code - Industrial piping -
Part 6: Safeguarding
1 Scope
This part of GB/T 20801 specifies the basic requirements for safety protection devices and safety protection for safety relief device, flame arrester, fire emergency block valve and mechanical interlocking device of pressure piping system.
For other safety protection requirements not specified in this part see other parts of GB/T 20801 as well as the current regulations, standards and specifications of the nation.
This part is applicable to the safety protection of pressure piping systems defined in GB/T 20801.1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB 12158 General guideline for preventing electrostatic accidents
GB/T 12242 Performance test code - Pressure relief devices
CB/T 15605 Guide for pressure venting of dust explosions
GB/T 15706 Safety of machinery - General principles for design - Risk assessment and risk reduction
GB/T 20801.1-2020 Pressure piping code - Industrial piping - Part 1: General
CB/T 20801.2-2020 Pressure piping code - Industrial piping - Part 2: Materials
GB/T 20801.3-2020 Pressure piping code - Industrial piping - Part 3: Design and calculation
GB/T 20801.4-2020 Pressure piping code - Industrial piping - Part 4: Fabrication and assembly
CB/T 20801.5-2020 Pressure piping code - Industrial piping - Part 5: Inspection and testing
GB 31571 Emission standard of pollutants for petroleum chemistry industry
GB 50016 Code for fire protection design of buildings
GB 50057 Design code for protection of structures against lightning
GB 50160 Fire prevention code of petrochemical enterprise design
GB 50984 Code for design of petrochemical plant layout
TSG ZF001 Safety technical supervision regulations for safety valves
TSG ZF003 Safety technical supervision regulations for bursting disc devices
ISO 16852 Flame arresters - Performance requirements, test methods and limits for use
ISO 23251 Petroleum, petrochemical and natural gas industries - Pressure-relieving and depressuring systems
NFPA 68 Standard on explosion protection by deflagration venting
PD CEN/TR 16793 Guide for the selection, application and use of flame arresters
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T 20801.1-2020, GB/T 20801.2-2020, GB/T 20801.3-2020, GB/T 20801.4-2020 and GB/T 20801.5-2020 as well as the following apply.
3.1
safety protection device
mechanical (physical) protection device that works in case of failure of automatic control instrument and manual intervention when analyzing according to the safety protection layer (refer to Annex A)
Note: Safety protection devices are the last barrier to prevent accidents or reduce accident losses, including safety relief devices, flame arresters, fire emergency block valve and mechanical interlocking devices.
3.2
safety relief device
device opened by the inlet static pressure or the inlet and outlet static pressure difference to release fluid so as to prevent the pressure in the system from exceeding the preset safety value in case of non-fire or fire accident
Note: It includes safety valve, rupture disk device and buckling pin relief valve.
3.3
safety valve
valve acted by a spring or controlled by pilot valve, which opens when the static pressure at the inlet (for ordinary valves, the static pressure difference between the inlet and outlet) exceeds the set pressure to release the fluid so as to prevent the pressure in the system from exceeding the preset safety value, and automatically closes when the pressure drops to the re-seating pressure
Note: The types of safety valves are ordinary, balanced and pilot.
3.4
rupture disk device
non-reclosing safety relief device composed of rupture disk and holder, of which the rupture disk ruptures or falls off when the pressure difference between the two sides of the rupture disk reaches a predetermined value at a predetermined temperature
Note: The categories of bursting disks are conventional domed type, reverse domed type, slab type and graphite type. The bursting disks are of common type, slotted type, knife (groove) type, alligator teeth type and shedding type.
3.5
buckling pin relief valve
non-reclosing safety relief device consisting of a valve and a box with a bursting pin outside the valve body, of which the bursting pin bears the load on the valve disc through the mechanical transmission mechanism, and becomes unstable and bent when the static pressure at the valve inlet reaches the bending pressure, resulting in valve disc full open and fluid release
Note: Buckling pin relief valves are of angular type or linear type.
3.6
first safety relief device
safety relief device with the lowest set pressure and opened first in multiple safety relief devices set in parallel and graded
3.7
additional safety relief device
one or several safety relief devices other than the basic safety relief device for non-fire conditions when multiple safety relief devices are set in parallel and graded
3.8
supplemental safety relief device
one or several safety relief devices other than basic safety relief device and additional safety relief device for fire conditions when multiple safety relief devices are set in parallel and graded
3.9
independent pressure system
pressure system which is connected by one or more equipments through piping and has no valve in the middle or will not produce blockage, on whose both ends valves capable of being cut off from other systems are provided
3.10
design pressure of system
design pressure of the protected independent pressure system which is not greater than the design pressure of all equipment, piping and instruments in the system
3.11
set pressure of the safety relief device
pressure that causes the safety relief device to start releasing
Note: It includes the opening pressure of safety valve, maximum marked bursting pressure of rupture disk device and bending pressure of bursting pin device.
3.12
maximum relieving pressure
maximum system pressure borne by the independent pressure system during the pressure relief process of the safety relief device
3.13
back pressure
pressure at the outlet of the safety relief device which is caused by the pressure in the discharge system
Notes:
1 It is the sum of additional back pressure and accumulated back pressure.
2 After the safety relief device is opened, the pressure at the outlet is increased due to the flow of medium, which is called accumulated back pressure and is variable.
3 Before the safety relief device is opened, the static pressure at the outlet caused by other pressure sources in the discharge system is called additional back pressure which may be constant or variable.
3.14
required relief capacity
flow capacity discharged by the safety relief device to prevent system overpressure
3.15
minimum relief area
net flow area when safety relief device is fully opened
3.16
block valve or stop valve
valve used to block or connect the fluid in a pipe
Note: It includes gate valve, ball valve, plug valve, butterfly valve and diaphragm valve.
3.17
flame arrester
safety protection device that allows medium to flow and can prevent flame and explosion from spreading
3.18
deflagration
explosion that travels at subsonic speed
3.19
detonation
explosion that travels at supersonic speed, which is characterized by shock wave
3.20
maximum experimental safe gap
MESG
maximum gap between the two components of the inner cavity preventing the flame from igniting the external gas mixture through a 25 mm long channel when the mixture of test gas or vapor and air in the inner cavity (at various concentrations) is ignited under the specified test conditions [(1.013±0.02) kPa and (20±2)℃]
3.21
explosion group
explosion hazard level of combustible gas and vapor classified according to the MESG
3.22
fire emergency block valve
FEBV
block valve which is able to be automatically shut off without manual intervention and external power (electricity, gas and liquid) supply under fire conditions, which has the properties of fire resistance, anti-static, high sealing and impact resistance
4 Safety relief device
4.1 General requirements
4.1.1 The safety relief device shall prevent overpressure accidents in any part of the independent pressure system. Designers should adopt various process hazard assessment (PHA) methods to study all possible overpressure conditions of specific process. When identifying various overpressure conditions, the following criteria shall be followed:
a) Any single event shall be credible;
b) The related events occurred in sequence shall be credible;
c) Two or more unrelated independent events occurring at the same time shall not be credible.
4.1.2 Automatic control instruments and alarm interlocking devices shall not replace safety relief devices as overpressure protection facilities of the system. If the discharge is not allowed or the safety relief device cannot be installed, all overpressure conditions may be evaluated and analyzed through the process hazard, and the systematic design method, i.e. intrinsically safety design or HIPS, shall be adopted to eliminate the cause of overpressure of the system or carry out overpressure protection of the system.
4.1.3 Equipment or piping systems that meet the following conditions shall be provided with safety relief devices:
a) Equipment and piping systems whose design pressure is less than that of external pressure source and whose outlets may be shut off or blocked;
b) Outlet piping system of displacement pump and displacement compressor whose outlet may be shut off;
c) Gas phase piping system at the top of distillation column brought to overpressure due to cooling water or reflux interruption, and excessive heat input from re-boiler;
d) Equipment and piping systems where non-condensible gas accumulates and generates overpressure;
e) The upstream piping system of the block valve or the regulating valve, in the outlet piping of heating boiler;
f) Piping systems thermally expanded or vaporized due to the influence of ambient temperature, sunlight or heat after the block valves at both ends are closed ;
g) Piping systems upstream of the block valve at the outlet of reactor where exothermic reaction runs out of control due to failure in cooling or stirring, ingress of catalytic impurities, and interruption of reaction inhibitors;
h) Steam outlet piping system of condensing steam turbine;
i) Outlet piping systems of steam generators and other steam production equipment;
j) Outlet piping systems of low boiling point liquid (liquefied gas, etc.) containers;
k) Outlet piping systems on low-pressure side of a heat exchanger, which may lead to overpressure if tube side rupture or leakage occurs;
l) Outlet piping system of air cooler tube side with cooling load decreased due to fan failure;
m) Outlet piping system of equipment and containers that may be exposed to external fire.
4.1.4 Independent pressure system shall be provided with one or more parallel installed safety relief devices at appropriate positions.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Safety relief device
5 Flame arrester
6 Other safety protection devices
7 Safeguarding
Annex A (Informative) Analysis of safety protection layer
Annex B (Informative) Calculation for safety relief device
Annex C (Informative) Selection of safety relief device
Annex D (Informative) Types and selection of flame arresters
Annex E (Informative) MESG and explosion group of combustible gas and vapor
Bibliography
