Special Issue Article
Numerical simulation of gas dispersion
during cold venting of natural gas
pipelines
Advances in Mechanical Engineering
2018, Vol. 10(2) 1–14
Ó The Author(s) 2018
DOI: 10.1177/1687814018755244
journals.sagepub.com/home/ade
Ning Liao1, Kun Huang1, Liqiong Chen1, Zhifang Wang2,
Jin Wu3 and Fang Zhang2
Abstract
This article analyzes the effects of various factors on gas dispersion during cold venting based on the actual cold venting
operations of long-distance natural gas pipelines in China. Under the circumstance that no obstacles existed, unified dispersion model and PHAST software were used to simulate the gas dispersion process of cold venting in order to study
the changes of gas concentration along vertical and horizontal directions over time. FLUENT was used to make numerical simulations to analyze the effect of the existence of high obstacles on gas dispersion. The results indicated that (1)
with an increase in wind speed, the concentration range in which the gas might explode (5%–15%) decreased along the
vertical direction but slightly increased along the horizontal direction; (2) when the initial venting pressure gradually
decreased with the proceeding of cold venting, the downwind distance that might trigger danger reduced significantly;
and (3) with an increase in atmospheric stability, the dispersion height of vented gas first increased and then decreased
continuously. High atmospheric stability could inhibit the gas dispersion height to a larger degree than the wind speed
and aerostatic buoyancy could facilitate it.
Keywords
Natural gas, cold venting, PHAST software, dispersion law, numerical simulation
Date received: 17 January 2017; accepted: 1 December 2017
Handling Editor: Oronzio Manca
Introduction
During the operation management of long-distance
natural gas pipelines, in case of a fault or maintenance
of auxiliary facilities, the pipe section in question will
be cut off by a valve chamber to reduce its pressure
and be vented. Such a venting operation is generally
achieved using a venting flare or a venting riser. It can
be divided into hot venting and cold venting, depending
on whether ignition is required. Cold venting is used to
directly discharge the high-pressure natural gas into the
atmosphere through a venting riser. Along with an
increase in the number of natural gas pipelines, the
safety hazard associated with cold venting has attracted
wide concern. Scholars at home and abroad have conducted a lot of research regarding this issue.
H Wei1 derived a formula that could calculate the
venting time required by the long-distance, natural gas
1
School of Petroleum Engineering, Southwest Petroleum University,
Chengdu, China
2
PetroChina West-East Gas Pipeline Company, Shanghai, China
3
Electromechanical Construction Co., Ltd., China Gezhouba Group,
Chengdu, China
Corresponding author:
Ning Liao, School of Petroleum Engineering, Southwest Petroleum
University, 8 Xindu Avenue, Chengdu 610500, Sichuan, China.
Email: 995761416@qq.com
Creative Commons CC BY: This article is distributed under the terms of the Creative Commons Attribution 4.0 License
(http://www.creativecommons.org/licenses/by/4.0/) which permits any use, reproduction and distribution of the work without
further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/
open-access-at-sage).
2
pipeline. Q Qin et al.2 studied the distance of thermal
radiation due to venting of natural gas pipelines and
compared it with the calculation result of PHAST software. Kong3 derived a calculation formula that used
parameters of an actual pipeline, which could solve the
venting time and venting volume of the pipe section. J
Qi et al.4 simulated the dispersion process of inflammable gas at the outlet of the venting riser using PHAST
software and presented the heat intensity and range in
case of accidental burning of the gas. Y Wang and L
Wang5 identified the safety distance related to the venting system. J Liang6 identified the dangerous zone subject to burning during small-ignition venting of natural
gas and calculated natural gas dispersion law under two
working conditions by taking an actual long-distance
natural gas pipeline as an example. YD Jo and BJ Ahn7
analyzed the effect of various factors on the scope of
danger caused by cracks of high-pressure natural gas
pipeline and proposed a simplified correlative equation
on that basis. H Montiel et al.8 developed a gas release
model applicable to medium and low-pressure relief systems to calculate the venting flow and venting time in
case of emergency venting.
Although scholars at home and abroad have conducted lots of research on this issue, the research is rare
regarding the natural gas dispersion law along the horizontal and vertical directions during cold venting. In
this article, first, different factors that may affect gas
dispersion during cold venting were analyzed, such as
wind speed, atmospheric stability, initial pressure, and
outlet diameter of the riser. An analog calculation for
gas dispersion during cold venting was performed later
using PHAST software, from which the corresponding
concentration-distribution cloud charts were obtained.
Finally, the effect of different factors on gas dispersion
was identified through comparison and analysis.
Basic theory
Introduction to PHAST software
PHAST software is a piece of software independently
developed by DNV to perform risk analysis and safety
calculation exclusively for petroleum, petrochemical,
and natural gas fields. This software has a wide calculation scope and can quickly output various data related
to the simulated accident. The calculation result fits
well with the experimental data.9 The software could
perform analog computations for the consequences of
many types of accidents. By checking the result reports
and relevant curves, the effect of the pertinent accident
on the surrounding environment and personnel can be
identified. It could be useful to perform analog computation for leakage and dispersion of pipelines and storage tanks, as well as the severity of corresponding
consequences (burning, toxicity, and explosion).10,11
Advances in Mechanical Engineering
Mathematical model
PHAST software uses the unified dispersion model
(UDM) to simulate dispersion of gas when the gas is
continuously being released. Dispersion of a gas cloud
is affected by various factors and may change significantly during the process. UDM is a complex model
that integrates various models to simulate dispersion of
gas, such as Gaussian model, BM model, and P-G
model.12 It could use the concentration-distribution
points of gas being dispersed at a certain moment to
portray an isoconcentration line and describe the width
of the gas cloud, downwind area, as well as other parameters.13–17 The UDM has the following assumptions:
1.
2.
3.
4.
5.
The value of the variable would not change with
time.
When the gas spreads to the ground, complete
reflection occurs, and the ground will not
entrain the gas.
No chemical reaction will take place during the
dispersion.
The average wind speed is not less than 1 m/s.
The ground is flat without any obstacles.
Under stable dispersion, the similar distribution c (x,
y, z) of concentration c was obtained from equation (1)
ð1Þ
cðx, y, zÞ = c0 ð xÞFn ðzÞFh ð yÞ
z n
y m
, Fh ð yÞ = exp Fn ðzÞ = exp Rz
Ry
where x is the horizontal distance along downwind
direction; y is the distance along across-wind direction;
c0 is the concentration at the center line; Fv(z) is the distribution of concentration along the vertical direction;
Fh(y) is the distribution of concentration along the horizontal direction; z is the distance from horizontal plane
to the center line of gas cloud; Rz and Ry are the vertical dispersion factor and lateral wind dispersion factor,
respectively; the constants m and n are to be obtained
through tests.
Operating conditions
1.
2.
Composition. The constituent is taken as pure
methane during the simulation analysis, as
methane takes up over 95% in domestic pipeline
natural gas.
Initial venting pressure. The design pressure of
long-distance natural gas pipelines in our
country is normally between 10 and 12 MPa.
Considering the depressurization measures
taken prior to cold venting and flow regulating
as well as the pressure reducing measures taken
Liao et al.
3
Figure 1. The obstacle height is significantly less than the height of venting riser.
3.
4.
prior to the entrance of gas into the venting
riser, the initial pressure of venting is designed
as 3–9 MPa.
Climate conditions and type of ground surface.
The atmospheric temperature is 15°C with a
relative humidity of 0.85. Some short crops are
growing on the ground surface. There are a few
large obstacles with a length–height ratio larger
than 20. The surface roughness is taken as 0.1.
In order to simulate the effect of different wind
speeds on cold venting, the atmospheric stability
was set as D. In order to simulate the effect of
different atmospheric stabilities on cold venting,
the wind speed was set as 5 m/s. In order to
simulate the effect of venting pressure and outlet diameter of the riser on cold venting, the
atmospheric stability was set as D and the wind
speed as 5 m/s.
The terrain conditions were assessed by whether
or not obstacles exist around the venting area. In
the simulation made by the PHAST software,
there were no obstacles, or the heights of obstacles were far less than the height of the riser, as
shown in Figure 1.
Case study
Venting of long-distance natural gas pipelines can be
categorized into hot venting and cold venting based on
whether or not ignition is required. During hot venting,
it is necessary to consider the effect of heat radiation
and combustion products on the surrounding environment and personnel, as well as the effect of temperature
rise on the performance of related venting equipment.
In cold venting, it is necessary to consider the dispersion process of natural gas in the air and the possibility
of flash burn and other hazards during dispersion of
natural gas. Compared to hot venting, cold venting has
fewer hazards but is still risky due to flammable and
combustible characteristics of high-pressure natural
gas. To learn the effects of different influence factors
on gas dispersion during cold venting, an analog calculation was performed using PHAST software to
understand the dispersion results of the vented gas. For
comparison and analysis purposes, corresponding
concentration-distribution cloud charts were derived.
Input parameters for simulation
To study the effects of wind speed and atmospheric stability on cold venting, the venting volume was set as
800,000 m3, the initial venting pressure as 5 MPa, the
temperature as 15°C, and the outlet diameter of the
venting riser as 300 mm. Different methane concentrations were taken as the minimum monitoring concentrations depending on different situations. The natural
gas was made of pure methane. The initial venting pressure was set as 5 MPa and the riser as 20 m high with
an outlet diameter of 300 mm. The atmospheric stability was set as D and the wind speed as 5 m/s. Table 1
displays part of the initial data used in the software
simulation.
Analysis of results
Different initial parameters corresponding to different
influence factors were inputted into the PHAST software. In the dispersion cloud charts obtained, different
colors represent different concentration ranges of natural gas. In the cloud charts made of brown, blue, yellow, and red, brown indicates a concentration of less
than 0.5%, blue between 0.5% and 2.5%, yellow
between 2.5% and 5% (flash burn range), and red
between 5% and 15%. In the cloud charts made of
blue, green, yellow, and red, blue indicates a concentration of less than 1%, green between 1% and 2.5%, yellow between 2.5% and 5% (flash burn range), and red
between 5% and 15%.
Effect of wind speed on gas dispersion. An analysis was
made regarding the environmental conditions at the
place where the long-distance, natural gas pipeline stations are located. A strake was often mounted on the
top of the riser to mitigate the effect of high wind speed
on the venting riser itself. In this study, different wind
speeds of 2, 4, 6, 8, 10, and 12 m/s were selected for
simulation purpose. Part of the dispersion cloud charts
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Advances in Mechanical Engineering
Table 1. Part of the initial data in cold venting simulation.
Condition
Entry
Input data
Basic date
Composition
Venting amount
Gas temperature
Spraying direction
Height of the riser
Atmospheric temperature
Relative humidity
Surface temperature
The surface roughness
The sun radiation
The initial blow-down pressure
Outlet diameter
Atmospheric stability
The initial blow-down pressure
Outlet diameter
Wind speed
Outlet diameter
Wind speed
Atmospheric stability
The initial blow-down pressure
Wind speed
Atmospheric stability
Composition
Venting amount
Gas temperature
Spraying direction
Height of the riser
Atmospheric temperature
Relative humidity
Surface temperature
The surface roughness
The sun radiation
The initial blow-down pressure
Outlet diameter
Atmospheric stability
The initial blow-down pressure
Outlet diameter
Wind speed
Outlet diameter
Wind speed
Atmospheric stability
The initial blow-down pressure
Wind speed
Atmospheric stability
Methane
80 3 104m3
15°C
Vertical upward
20 m
16°C
0.85
10°C
10 cm
0.5
50 bar
300 mm
D
50 bar
300 mm
5 m/s
300 mm
5 m/s
D
50 bar
5 m/s
D
Methane
80 3 104 m3
15°C
Vertical upward
20 m
16°C
0.85
10°C
10 cm
0.5
5 MPa
300 mm
D
5 MPa
300 mm
5 m/s
300 mm
5 m/s
D
5 MPa
5 m/s
D
Different wind speeds
Different atmospheric stabilities
Different outlet pressures
Different standpipe outlet diameters
Basic data
Different wind speeds
Different atmospheric stabilities
Different outlet pressures
Different standpipe outlet diameters
obtained is shown in Figure 2. The dispersion cloud
charts indicated the dispersion conditions within 50 m
along the downwind direction.
The concentration distribution of the vented gas
under different wind speeds is obtained, in which the
minus symbol indicates upwind direction. Using these
data, the relation curve of wind speed versus dispersion
height of methane of 5% concentration and the relation curve of wind speed versus downwind distance
were portrayed, which are shown in Figures 3 and 4.
The simulation results show that the dispersion height
decreases insignificantly with the increasing wind speed,
but it has an instability influence on the downwind
distance when the wind speed increases. What is more,
the scope of the dispersion has narrowed obviously
with the increasing wind speed, which is more safe.
It can be derived from the simulation results that
1.
2.
The duration required for the gas cloud to disperse to a certain distance (to 50 m along downwind direction of the riser) shortened with an
increase in wind speed.
Under low wind speed, the natural gas mainly
disperses upward; with an increase in wind
speed, the gas cloud significantly shifts to the
horizontal direction.
Liao et al.
5
Figure 2. Gas dispersion cloud charts of different wind speeds (2, 6, 10 m/s).
3.
4.
With an increase in wind speed, the concentration range in which the gas might explode (5%–
15%) decreased along the vertical direction, but
it slightly increased along the horizontal
direction.
Within the wind speed range used for simulation
purposes, the concentration range in which the
gas might explode decreased with an increase in
5.
wind speed along the vertical direction, which
was varied to a relatively large degree.
Under the assumption that there is no obstacle
under certain conditions (5 MPa and atmospheric stability of D), if there are no combustion sources within 30 m during cold venting,
then the probability of combustion or explosion
was extremely small.
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Advances in Mechanical Engineering
as shown in Figures 7 and 8. The simulation results
show that the dispersion height increases first when the
atmospheric stability is between A and D and then
decreases. Despite the fact that the downwind distance
has a growing tendency as the increase in atmospheric
stability, the influence on it is unstable. What is more,
the scope of the dispersion has narrowed obviously
with the increasing atmospheric stability.
It can be derived from the simulation results that
1.
2.
Figure 3. The effect of wind speed on the dispersion height
(methane concentration is 5%).
3.
Figure 4. The effect of wind speed on the downwind
dispersion distance (methane concentration is 5%).
Effect of atmospheric stability on gas dispersion. Atmospheric
stability refers to an air mass in the air rising or falling
due to the buoyancy caused by the intensity of the density, temperature, and velocity of the surrounding air,
which can be divided into strong unstable, unstable,
weakly unstable, neutral, more stable, and stable six
atmospheric stabilities, and they are expressed as A, B,
C, D, E, and F. Using PHAST software, gas dispersion
cloud charts corresponding to atmospheric stabilities A–
G were obtained. Part of the cloud charts is presented in
Figures 5 and 6, which show the dispersion conditions
within 40 m along the downwind direction.
The concentration distribution of the vented gas
under different atmospheric stabilities is obtained, in
which the minus symbol indicates upwind direction.
Using these data, some relation curves were portrayed,
The duration required for the gas cloud to disperse to a certain distance (to 40 m along the
downwind direction of the riser) shortened with
an increase in atmospheric stability;
With an increase in atmospheric stability, the
vented gas dispersed more easily along the horizontal direction. Along the vertical direction,
the dispersion height of natural gas first
increased, followed by a continuous decrease.
Similar to the effect of wind speed, increase in
atmospheric stability was also conductive to the
gas to disperse along the horizontal direction.
Along the vertical direction, the atmospheric
stability could inhibit the gas dispersion height
to a larger degree than the wind speed could
facilitate it.
Effect of initial venting pressure on gas dispersion. A survey
was performed regarding the operation pressure of
long-distance natural gas pipelines during cold venting
operations. The initial venting pressure of 3–9 MPa was
taken to make the simulation considering the depressurization measures taken prior to cold venting and the
pressure reducing effect of the air-release valve. Part of
the cloud charts obtained is presented in Figure 9,
which shows the dispersion conditions within 50 m
along the downwind direction.
The concentration distribution of the vented gas
under different initial venting pressures is obtained
from the simulation results, in which the minus symbol
indicates upwind direction. Using these data, some
relation curves were portrayed, as shown in Figures 10
and 11. The simulation results show that the dispersion
height and downwind distance increase with the
increasing initial venting pressure, and the downwind
distance has a fluctuant growing tendency. What’s
more, the scope of the dispersion does not change obviously with the increasing venting pressure.
It can be derived from the simulation results that
1.
The duration required for the gas cloud to disperse to a certain distance (to 50 m along the
downwind direction of the riser) lengthened with
a decrease in initial venting pressure.
Liao et al.
7
Figure 5. Gas dispersion cloud charts under different atmospheric stabilities (A and C).
2.
3.
4.
Under the conditions that wind speed and other
external conditions remained unchanged, with a
decrease in the outlet pressure, the gas cloud
shifted more toward the horizontal direction.
Under the same concentration, the dispersion
height upward became smaller.
Proceeding with the venting operation, the outlet pressure decreased, and the concentration
range in which the gas might explode decreased
along both the vertical and horizontal
directions.
In the areas where obstacles were not considered, during cold venting under certain conditions (wind speed of 5 m/s), if there was no
combustion source within 50 m, the probability
of explosion was extremely small.
Effect of outlet diameter of the riser on gas dispersion. There
was an analysis of the statistical data of specifications
of venting risers used in the natural gas industry. The
outlet diameters of 150, 200, 250, 300, 350, and 400 mm
were selected for simulation purposes. Part of the cloud
charts obtained is presented in Figure 12, which shows
the dispersion conditions within 50 m along the downwind direction.
The concentration distribution of the vented gas
under different outlet diameters is obtained, in which
the minus symbol indicates upwind direction. As shown
in Figures 13 and 14, using these data, some relation
curves were portrayed. The simulation results show that
the dispersion height and downwind distance increase
with the increasing riser outlet diameter, and the downwind distance has a fluctuant growing tendency. What
is more, the scope of the dispersion becomes larger
obviously with the increasing atmospheric stability,
which increases the risk of venting process.
It can be derived from the simulation results that
1.
2.
The duration required for the gas cloud to disperse to a certain distance (to 50 m beyond the
outlet of the venting riser) shortened with an
increase in the outlet diameter of the riser.
Under the conditions that wind speed and other
external conditions remained unchanged, along
with an increase in the outlet diameter, both the
height and horizontal distance of the gas cloud
increased, as well as the dispersion range.
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Advances in Mechanical Engineering
Figure 6. Gas dispersion cloud charts under different atmospheric stabilities (E and G).
Figure 7. The effect of atmospheric stability on the dispersion
height (methane concentration is 5%).
3.
When other conditions remained unchanged,
with an increase in the venting diameter, the area
in which the gas concentration was at the edge
of explosion (5%–15%) significantly increased.
Figure 8. The effect of atmospheric stability on the downwind
dispersion distance (methane concentration is 5%).
Changes of various factors. During cold venting, more
than one factor may be changed. For a planned cold
venting operation, the size and the outlet pressure of
the venting riser could be controlled by the initial
Liao et al.
9
Figure 9. Gas dispersion cloud charts of different venting pressures (9, 7, and 5 MPa).
pipeline pressure and the opening of the air-release
valve. However, the external environmental factors,
such as wind speed and atmospheric stability, are not
controllable. Wind speed, however, could be measured
10
Advances in Mechanical Engineering
2.
could trigger danger also significantly decreased.
This means that it is necessary to depressurize
the pipeline prior to venting.
It can be seen from Figure 16 that under the
same initial venting pressure, the higher the
wind speed, the lower the dispersion height.
This trend became more obvious when the initial venting pressure became smaller.
Discussion
Figure 10. The effect of initial venting pressure on the
dispersion height (methane concentration is 5%).
Figure 11. The effect of initial venting pressure on the
downwind dispersion distance (methane concentration is 5%).
simply. The statistical data of concentration distribution under different wind speeds and different initial
venting pressures are obtained. The venting volume was
800,000 m3, and the riser is 20 m high with a diameter of
300 mm. The atmospheric stability is D, and the atmospheric temperature is 15°C.
The effect of wind speed and initial venting pressure
on the dispersion height and downwind distance of
methane was derived, as shown in Figures 15 and 16.
According to the relationship curves, the following
conclusions were derived:
1.
Figure 15 demonstrates that when the initial
venting pressure decreased gradually during the
venting operation, the downwind distance that
PHAST software could produce different curves and
concentration cloud charts for different heights but
could not reflect the effects of obstacles on gas dispersion. For this end, FLUENT was used to perform
numerical simulation to analyze the effect of obstacles
on gas dispersion. Figures 17 and 18 displayed the case
of venting in a mountainous area and a forest area.
And Figures 19 and 20 display the dispersion cloud
charts that the obstruction exists or not.
The dispersion cloud charts at different time points
from FLUENT software indicated that during the initial period of venting, the velocity at the outlet of the
riser was relatively fast. As a result, the gas cloud soon
reached the windward side of the obstacle and formed a
concentration accumulation area. Proceeding with cold
venting, the velocity at the outlet of the riser decreased.
Under the action of wind speed and buoyancy, the concentration of methane was reduced in the front of the
obstacle. When the venting operation approached the
end, the velocity at the outlet of the riser decreased
more.
Compared to the case where there is no obstacle, or
the obstacle is lower than the venting riser, the case
with the large obstacle is different. In the initial period
of venting, the gas at the outlet of the riser swelled into
a high-speed stream and was sprayed into the air.
Pushed by the strong initial kinetic energy, the gas
stream moved upward rapidly and turned to the right
direction under the action of wind speed after reaching
a certain distance. Following that, the velocity component along the vertical direction became smaller. The
gas stream reached the windward side of the obstacle,
and its speed along the horizontal direction was offset
by bumping. Part of the gas cloud still climbed alongside the obstacle under the action of buoyancy. The rest
accumulated in the front of the obstacle and formed a
high-concentration area.
Conclusion
PHAST software was used to calculate the effect of
wind speed, atmospheric stability, initial venting pressure, and outlet diameter of the riser on the gas dispersion during cold venting. This was based on the actual
Liao et al.
11
Figure 12. Gas dispersion cloud chart of different standpipe outlet diameters (200, 300, and 400 mm).
conditions of cold venting operation in our country’s
long-distance natural gas pipelines. The following conclusions and control measures were obtained after analysis of the charts and tables:
1.
The higher the wind speed, the shorter the duration
required for the gas to disperse to a certain distance. With higher wind speed, the concentration
range in which the gas might explode (5%–15%)
2.
decreased along the vertical direction but slightly
increased along the horizontal direction. Therefore,
to prevent gas from accumulating, the reduction of
its dispersion concentration, and to minimize possible hazards, cold venting should be performed
under relatively high wind speed in order to accelerate gas dispersion.
With an increase in atmospheric stability, the
dispersion height of vented gas first increased
12
Figure 13. The effect of riser outlet diameter on the
dispersion height (methane concentration is 5%).
Advances in Mechanical Engineering
Figure 16. Maximum dispersion height under different wind
speeds and pressure conditions (methane concentration of 5%).
Figure 17. Sketch map of mountain-type obstacle.
Figure 14. The effect of riser outlet diameter on the
downwind dispersion distance (methane concentration is 5%).
Figure 18. Sketch map of forest-type obstacle.
3.
Figure 15. Maximum downwind dispersion distance under
different wind speeds and pressure conditions (methane
concentration of 5%).
and then decreased continuously. High atmospheric stability could inhibit the gas dispersion
height to a larger degree than the wind speed
and aerostatic buoyancy could facilitate it.
Hence, it is necessary to choose proper atmospheric stability to facilitate the gas to disperse
along the horizontal and vertical directions. The
simulation results indicated that the vented gas
dispersed quite well when the atmospheric stability was around D.
When the initial venting pressure gradually
decreased with the proceeding of cold venting,
the downwind distance which might trigger danger reduced significantly. Therefore, it was necessary to depressurize the pipeline prior to venting.
Liao et al.
13
Figure 19. Gas dispersion cloud chart without obstacles.
Figure 20. Gas dispersion cloud chart with obstacles.
It could be seen from the relevant charts that when
an obstacle existed and reached a certain height, a
high-concentration area would be formed in front of
the obstacle. Any object that required protection on
the windward side of the obstacle would be seriously
damaged by the venting. Moreover, PHAST software alone could not reflect the entire situation of
actual venting. If there are buildings, forests, or hills
with a height higher than the safety height within the
safety distance, FLUENT software should be used to
further simulate the gas dispersion law. The gas concentration within the accumulation area should be
monitored at all times, and all possible fire sources
should be excluded to minimize the hazard of fire
and explosion. Hot venting may be considered if
necessary.
Funding
Acknowledgements
The utilization of facilities and resources of PetroChina
West–East Gas Pipeline Company is very much appreciated.
The guiding idea of Prof. Huang is also acknowledged. The
authors are also very grateful for the support of the national
key projects (2016YFC0802100) ‘‘Pipeline and storage facilities inspection evaluation and safety assurance technology’’ in
‘‘13th Five-Year’’ and the consulting research project of
Chinese Academy of Engineering (2015-XZ-37) ‘‘The research
on the development strategy of oil and gas pipeline network
system safety.’’
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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