GB/T 42368-2023 PDF English
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Determination of explosion limits of combustible vapors and gases at elevated temperature and pressure
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GB/T 42368-2023: PDF in English (GBT 42368-2023) GB/T 42368-2023
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 13.300
CCS A 80
Determination of explosion limits of combustible vapors and
gases at elevated temperature and pressure
ISSUED ON: MARCH 17, 2023
IMPLEMENTED ON: OCTOBER 01, 2023
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of China.
Table of Contents
Foreword ... 3
Introduction ... 4
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Test principle ... 7
5 Test device ... 7
6 Test steps ... 8
7 Test data processing ... 11
8 Safety measures ... 12
9 Calibration of the test device ... 13
10 Test report ... 13
Appendix A (Informative) Test device ... 15
References ... 21
Determination of explosion limits of combustible vapors and
gases at elevated temperature and pressure
Warning – After igniting the mixture of combustible gas (vapor) and air according
to the method specified in this document, even if no propagation of flames is
formed, it cannot be completely considered that the mixture will not explode.
Warning – The personnel who uses this document shall have hands-on experience
in formal laboratory work. This document does not address all possible safety
issues. It is the responsibility of the user to take appropriate safety and health
measures and to ensure compliance with the conditions which are set by the
relevant national regulations.
1 Scope
This document describes a method for the determination of explosion limits of the
combustible mixture of combustible gases (vapors) and air at a given initial temperature
and initial pressure.
This document applies to the determination of explosion limits of combustible gases
(vapors) under the conditions of initial temperature below 200 °C, initial pressure below
1.0 MPa (absolute pressure), and maximum explosion pressure not greater than 15.0
MPa (absolute pressure).
This document does not apply to the determination of explosion limits of chemically
unstable gases or mixed gases in which components may react with each other.
2 Normative references
The following documents are referred to in the text in such a way that some or all of
their content constitutes requirements of this document. For dated references, only the
version corresponding to that date is applicable to this document; for undated references,
the latest version (including all amendments) is applicable to this document.
GB/T 12474, Method of test for explosion limits of combustible gases in air
GB/T 16425, Determination for minimum explosive concentration of dust clouds
GB/T 21844, Standard test method for concentration limits of flammability of
chemicals (vapors and gases)
4 Test principle
Under the given initial temperature and initial pressure conditions, pre-mix a certain
volume fraction of combustible gas (vapor) and air in the explosion reaction vessel; use
electric spark or electric heating wire to ignite; judge whether an explosion occurs by
the rising value of the explosion pressure (not less than 5% of the given initial pressure);
systematically change the concentration of the combustible gas (vapor) until the
minimum or maximum concentration where the explosion occurs is measured.
5 Test device
5.1 General
The test device for explosion limits is mainly composed of an explosion reaction vessel,
an ignition device, a pressure measurement unit, a gas distribution unit, a temperature
control unit, etc. See Appendix A for a schematic diagram of the test device.
5.2 Explosion reaction vessel
5.2.1 The explosion reaction vessel shall be a spheroidal shape or a cylindrical test
vessel with an aspect ratio of 1, which is resistant to high temperature and high pressure.
The volume shall not be less than 1 L and should be 20 L, 12 L or 5 L; the shape
specifications shall be in accordance with the relevant provisions for test device in GB/T
16425 and GB/T 21844 respectively.
5.2.2 The expected operating temperature of the explosion reaction vessel under initial
pressure conditions shall not be less than 200 °C, and the explosion-resistant pressure
shall be able to withstand a maximum explosion pressure of not less than 15.0 MPa
(absolute pressure) without permanent deformation.
5.2.3 The maximum explosion pressure of combustible gases (vapors) at elevated
temperature and pressure shall not be higher than the maximum working pressure of
the explosion reaction vessel.
5.2.4 For the determination of explosion limits of low-flammable substances such as
ammonia, halogenated substances and certain amines, a 20 L spherical stainless steel
explosion tank or an explosion reaction vessel with a larger diameter should be used.
5.2.5 An oil-free stirring device shall be equipped in the explosion reaction vessel.
5.2.6 The connecting pipe fittings between the explosion reaction vessel and the high-
pressure gas cylinder shall be made of 316 stainless steel pipes with a pressure not lower
than 4.0 MPa (absolute pressure). All pipelines and joints connected to the explosion
reaction vessel shall be able to withstand a pressure not lower than 15.0 MPa (absolute
pressure).
5.3 Ignition device
5.3.1 The mixture of combustible gas (vapor) and air can be ignited by electric spark,
or by electric fuse or high-temperature hot wire.
5.3.2 The ignition energy of the ignition device shall be sufficient to ignite the
combustible gas mixture to be tested, and the pressure increase of the ignition source to
the mixed gas shall not be greater than 0.5% of the initial pressure.
5.4 Pressure measurement unit
5.4.1 Pressure sensors with low-pressure range and high-pressure range, which are
installed in the explosion reaction vessel, shall be able to withstand the continuous high
temperature of 200 °C during the test. The response frequency of the pressure sensor
with high-pressure range shall not be lower than 10 kHz; it should be installed flush.
The distance between the top of the sensor probe and the inner wall of the container for
non-flush installation shall not exceed 10 cm.
5.4.2 The pressure sensor with low-pressure range is used to measure the partial
pressure of different component gases in the gas distribution process. The lower limit
of the range of the pressure sensor with low-pressure range shall reach 0.07 kPa
(absolute pressure), and the reading error shall not exceed 1%, and shall be able to meet
the gas distribution accuracy requirements. The range of the pressure sensor with high-
pressure range shall be able to meet the requirements for measuring the maximum
explosion pressure, and shall be able to detect and determine whether an explosion has
occurred.
5.5 Gas distribution unit
5.5.1 The gas distribution unit shall adopt an oil-free vacuum pump, and shall realize
vacuuming the explosion reaction vessel to below 0.002 MPa (absolute pressure).
5.5.2 The gas distribution accuracy shall not be lower than 0.1% volume fraction.
5.6 Temperature control unit
The ambient temperature in the explosion reaction vessel shall be measured by a k-type
thermocouple. The controllable temperature range is from room temperature to 200 °C,
and the temperature control accuracy is ±2 °C.
6 Test steps
Warning – It is strictly forbidden to disassemble the explosion reaction vessel
under pressure.
6.1 Test preparation
±2 °C of the initial temperature set for the test. Turn on the oil-free stirring device and
stir for 5 minutes to mix the combustible gas and air in the explosion reaction vessel
evenly. When measuring a variety of combustible gas mixtures with different
concentrations, fill them into the explosion reaction vessel in sequence from low to high
concentrations of combustible gases to be measured to the set partial pressure value.
6.2.5 Close the protective valve on the pipeline connecting the pressure sensor with
low-pressure range and the explosion reaction vessel.
6.2.6 Turn on the pressure sensor with high-pressure range to record the pressure inside
the explosion reaction vessel.
6.2.7 After mixing and stirring, let stand for 2 minutes before igniting. Use the pressure
sensor with high-pressure range to measure and record the pressure change with time
in the explosion reaction vessel after ignition. Compare the change of the maximum
explosion pressure before and after ignition, and analyze and judge whether an
explosion occurs according to 7.1.
6.2.8 After the ignition test, open the exhaust valve in the explosion reaction vessel, to
release the test exhaust gas to the outside, and use inert gas to purge the explosion
reaction vessel and corresponding pipelines, for no less than 5 purging times.
6.2.9 Repeat the test steps in 6.2.1 ~ 6.2.8, and use the progressive method to determine
the explosion limit value. When determining the lower (upper) explosion limit, if no
explosion occurs at a certain concentration, increase (decrease) the concentration of
combustible gas (vapor) until the minimum (maximum) concentration that can cause
explosion is measured; if an explosion occurs at a certain concentration, decrease
(increase) the concentration of combustible gas (vapor) until the maximum (minimum)
concentration at which the explosion cannot occur is measured. When the determination
is close to the lower explosion limit, the change amount of the sample to be tested shall
not be greater than 10% of the last injection volume each time; when the determination
is close to the upper explosion limit, the change amount shall not be greater than 2% of
the last injection volume each time. The unstable temperature and large fluctuation of
pressure or temperature after filling a certain gas indicates that a reaction may have
occurred before ignition, where the test shall be stopped immediately. Halogen
reactions can cause a pressure drop, and oxidation reactions can cause a pressure rise.
6.2.10 Test to obtain the minimum concentration L1 of combustible gas (vapor) for
explosion and the maximum concentration L2 for non-explosion near the lower
explosion limit, where L2 is lower than L1, and the difference between L2 and L1 is not
more than 0.2% of the volume fraction. Repeat the test 3 times at the L2 concentration
to ensure that no explosion will occur at this concentration.
6.2.11 Test to obtain the maximum concentration U1 of combustible gas (vapor) for
explosion and the minimum concentration U2 for non-explosion near the upper
explosion limit, where U2 is higher than U1, and the difference between U2 and U1 is
not more than 10% of U1. Repeat the test under the concentration of U2 3 times to ensure
that no explosion occurs at this concentration.
6.2.12 After the test is over, clean up the carbon deposits or other residues in the
explosion reaction vessel in time.
6.3 Determination of explosion limits at elevated temperature and pressure
6.3.1 According to the determination method specified in GB/T 21844, gradually
increase the temperature to determine the explosion limits of the combustible gas (vapor)
under normal pressure and high temperature, where the temperature increase range shall
not be higher than 50 °C. When the maximum explosion pressure of the mixed gas is
close to the maximum working pressure of the explosion reaction vessel during the test,
the determination test shall be terminated immediately.
6.3.2 Preheat the explosion reaction vessel and related components to the initial
temperature set for the test and keep the temperature constant. If the sample to be tested
is liquid vapor, the liquid container shall be preheated to the initial temperature set for
the test, and the connecting pipeline shall be heated and protected; also, remote control
of sample injection shall be realized.
6.3.3 After preheating the test device and related components to the set initial
temperature, carry out the test and measurement according to the steps in 6.2.1 ~ 6.2.11.
7 Test data processing
7.1 When the explosion pressure increment after the combustible gas (vapor) is ignited
is not less than 5% of the given initial pressure, it is determined that the mixed gas has
propagation of flames, that is, an explosion has occurred. The calculation method is
shown in Formula (1).
Where:
P1 – the value of the initial absolute pressure, in megapascals (MPa);
P2 – the value of the maximum absolute pressure of explosion after ignition, in
megapascals (MPa).
Note: A pressure increment of 5% is equivalent to an increase of 0.005 MPa per unit
atmospheric pressure.
7.2 The lower explosion limit of combustible gas (vapor) is calculated according to
Formula (2), and the upper explosion limit is calculated according to Formula (3).
and causes a sudden change in pressure, the test shall be stopped immediately and
corresponding protective measures shall be taken.
8.5 An explosion-proof barrier shall be set up between the test device and the operator
to prevent casualties caused by the rupture of the explosion reaction vessel.
8.6 The ignition device shall be provided with functions such as interlock and remote
control, and it shall be ensured that the operator can only start the ignition when he is
in the safe area outside the explosion-proof barrier.
8.7 Where the test device is equipped with a constant temperature box, the box shall be
installed with an explosion-proof pressure relief sheet that opens outwards, and filled
with inert gas to prevent explosion caused by accidental leakage of the mixed gas to be
measured.
8.8 After the test, the exhaust gas shall be discharged outdoors in time and treated
according to safety and environmental protection requirements.
8.9 The test operator shall carry out the test in strict accordance with the operating
procedures, and shall use the necessary protective equipment to avoid harm to the
human body caused by the mixed gas to be tested or explosive products.
8.10 The laboratory shall prepare necessary safety emergency materials.
9 Calibration of the test device
9.1 The pressure sensor and temperature sensor of the test device shall be regularly
verified according to the requirements of the instructions, and the verification period
shall not exceed 3 months.
9.2 Before the formal test of the test device, use ethylene with a purity of not less than
99.9% to calibrate. Under the initial conditions of 50 °C and 0.3 MPa (absolute
pressure), the lower explosion limit is 2.6%, and the upper explosion limit is 40.0%. If
the test results meet the following requirements, the device is considered to be operating
normally:
a) For repeated test results measured in the same laboratory, the error shall not be
greater than 5%;
b) For repeated test results measured in different laboratories, the error shall not
exceed 10%.
10 Test report
The test report shall include the following contents:
6 – pressure relief door;
7 – explosion reaction vessel;
8 – stirring blade;
9 – magnetic stirrer;
10 – explosion pressure sensor;
11 – ignition electrode;
12 – observation window.
Figure A.1 – Schematic diagram of 5 L/12 L long neck high temperature and
high pressure explosion limit test device
A.1.2 Heating chamber
The heating chamber uses hot air circulation to maintain a constant temperature. The
temperature ranges from room temperature to 200 °C.
A.1.3 5 L explosion reaction vessel
Place the 5 L explosion reaction vessel in the heating chamber, and test the high
temperature and high pressure explosion limit of combustible gas or vapor in the
explosion reaction vessel. For the size and specification of the vessel, see GB/T 21844.
A.1.4 Pressure sensor
The test device (inside) is equipped with a pressure sensor 1 and a pressure sensor 2 for
gas distribution, and a pressure sensor 3 for testing the explosion pressure rise value,
wherein the test range of the pressure sensor 1 is 0 MPa ~ 0.1 MPa (absolute pressure),
the test range of pressure sensor 2 is 0 MPa ~ 1.0 MPa (absolute pressure), and the test
range of pressure sensor 3 is 0 MPa ~ 15.0 MPa (absolute pressure).
A.1.5 Temperature sensor
The test device is provided with two temperature sensors, which are the temperature
sensor of the sample to be tested and the temperature sensor of the heating chamber.
The temperature sensor of the sample to be tested is used to test the temperature of the
gas or vapor introduced into the explosion reaction vessel and the temperature
measurement range is from room temperature to 800 °C. The temperature sensor of the
heating chamber is used to test the temperature in the heating chamber, and the
temperature measurement range is from room temperature to 300 °C.
A.1.6 Magnetic stirrer
The magnetic stirrer is set in the 5 L explosion reaction vessel, to mix the combustible
gas or vapor to be tested with air in the vessel evenly.
The temperature control jacket is arranged outside the explosion reaction vessel, the
explosion reaction vessel is heated by heat conduction oil, and the temperature control
range is from room temperature to 200 °C.
A.2.4 Ignition electrode
The ignition electrode is set in the explosion reaction container, and is used to ignite the
sample gas or vapor to be tested in the vessel.
A.2.5 Pressure sensor
The test device is provided with two pressure sensors, which are respectively the gas
distribution pressure sensor and the explosion pressure sensor, wherein the test range
of the gas distribution pressure sensor is 0 MPa ~ 1.0 MPa (absolute pressure), and the
test range of the explosion pressure sensor is 0 MPa ~ 15.0 MPa (absolute pressure).
A.2.6 Temperature sensor
The test device is provided with two temperature sensors, which are the temperature
sensor of the sample to be tested and the jacket temperature sensor. The temperature
sensor of the sample to be tested is used to test the temperature of the gas or vapor
introduced into the explosion reaction vessel, and the temperature range is from room
temperature to 800 °C. The jacket temperature sensor is used to test the temperature
inside the jacket, and the temperature measurement range is from room temperature to
300 °C.
A.2.7 Magnetic stirrer
The magnetic stirrer is set in the 12 L explosion reaction vessel, to mix the sample gas
or vapor to be tested with air in the vessel evenly.
A.3 20 L spherical high temperature and high pressure explosion limit test device
Figure A.3 is a schematic diagram of the 20 L high temperature and high pressure
explosion limit test device. The device is composed of a 20 L spherical explosion
reaction vessel, an ignition electrode, a temperature control jacket, a pressure sensor, a
temperature sensor, a magnetic stirrer and other parts. The size and specifications of the
device shall be in accordance with the device requirements of GB/T 16425.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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