Gas Flow In Pipe Research Articles

Three-Dimensional Visualization Of The Behavior Of Solid Particles Traveling In A Horizontal Gas Pipe Flow By Color PTV Using Discontinuously Changing Hue Illumination

In a gas pipe, a lot of solid particles remained during its construction. They are called dust and gas supply companies have tried to remove them using filters because they cause various problems. To optimize the maintenance period of dust removal filters, it is required to understand the behaviors of particles in the pipe. However, we do not fully understand yet because of their very complex behaviors caused by dune accumulated in the pipe. Furthermore, it is hard to investigate their behaviors with a traditional volumetric PTV using multiple cameras. Normally, its calibration is difficult because of the curvature of the pipe and the plural number of cameras. Therefore, we developed a new volumetric color PTV algorithm with discontinuously changing color illumination in the camera shooting direction, i.e. the depth direction. Color PTV can determine particle positions in three dimensions using a single camera but has low depth accuracy. Our new PTV measures particle positions and velocity vectors in the plane of picture using the same algorithm used in the normal planar PTV. On the other hand, particle positions and velocity vectors in the camera shooting direction are measured by a pattern of color changing on particle scattering light, which is our original method. To adopt the new volumetric PTV in the pipe flow, a volumetric light changing color discontinuously in the flow direction was irradiated and the particles were visualized using a camera installed at the outlet of the pipe. When a dune exists, the particles are thrown to the top of the pipe and their advection velocity is increased by the wakes generated by the dune. As a result, the dune makes more particles to be advected to a longer distance.

Computation of flow rates in rarefied gas flow through circular tubes via machine learning techniques

Kinetic theory and modeling have been proven extremely suitable in computing the flow rates in rarefied gas pipe flows, but they are computationally expensive and more importantly not practical in design and optimization of micro- and vacuum systems. In an effort to reduce the computational cost and improve accessibility when dealing with such systems, two efficient methods are employed by leveraging machine learning (ML). More specifically, random forest regression (RFR) and symbolic regression (SR) have been adopted, suggesting a framework capable of extracting numerical predictions and analytical equations, respectively, exclusively derived from data. The database of the reduced flow rates W used in the current ML framework has been obtained using kinetic modeling and it refers to nonlinear flows through circular tubes (tube length over radius l∈[0,5]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$l \\in [0,5]$$\\end{document} and downstream over upstream pressure p∈[0,0.9]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p \\in [0,0.9]$$\\end{document}) in a very wide range of the gas rarefaction parameter δ∈[0,103]\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta \\in [0,10^3]$$\\end{document}. The accuracy of both RFR and SR models is assessed using statistical metrics, as well as the relative error between the ML predictions and the kinetic database. The predictions obtained by RFR show very good fit on the simulation data, having a maximum absolute relative error of less than 12.5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$12.5\\%$$\\end{document}. Various expressions of the form of W=W(p,l,δ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W=W(p,l,\\delta )$$\\end{document} with different accuracy and complexity are acquired from SR. The proposed equation, valid in the whole range of the relevant parameters, exhibits a maximum absolute relative error less than 17%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$17\\%$$\\end{document}. To further improve the accuracy, the dataset is divided into three subsets in terms of δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta$$\\end{document} and one SR-based closed-form expression of each subset is proposed, achieving a maximum absolute relative error smaller than 9%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$9\\%$$\\end{document}. Very good performance of all proposed equations is observed, as indicated by the obtained accuracy measures. Overall, the present ML-predicted data may be very useful in gaseous microfluidics and vacuum technology for engineering purposes.

Convergence study for composite gas flow in pipes

AbstractUtilizing hydrogen in energy sources plays a crucial step towards a complete transition to renewable energies since production at‐scale is possible. The study works towards developing monitoring and control strategies of proportionally induced hydrogen in existing pipeline infrastructure. With this aim, a scalable model is utilized to compute the flow of composite gas along a pipe. The transient model is solved using finite element discretization and error convergence is studied for a test case. Coupling of species transport to track mixture composition along the pipe is also studied for a test case and error behaviors are investigated. Finally, simulations performed for a practical testcase are compared with a recently available open‐source tool for studying flow dynamics. The study highlights the deployment and usage of state‐of‐the‐art simulation tools against existing industrial necessities while providing invaluable insights into dynamics of gas mixtures.

Experimental test and theoretical calculation of the fracture height limit of gas pipe flow to Darcy flow

Low-speed flow experiments in which ultra-fine copper tubes are used to simulate micro-fractures in carbonate strata are conducted to analyze the variations of gas flow state in fractures of different fracture heights, determine flow state transition limit and transition interval, and establish the calculation method of flow state transition limit. The results show that the ideal Hagen-Poiseuille flow is the main form of gas flow in large fractures. Due to the decrease of fracture height, the gas flow in the fracture changes from Hagen-Poiseuille flow with ideal smooth seam surface to non-Hagen-Poiseuille flow, and the critical point of the transition is the boundary of flow state transition. After the fracture height continues to decrease to a certain extent below the boundary of the flow state transition fracture height, the form of gas flow gradually changes to the ideal Darcy flow, thus the transition interval of the gas flow state in the closing process of fracture can be determined. Based on the three-dimensional microconvex body scanning of the fracture surface, the material properties of fracture and properties of fluid in the fracture, a method for calculating the boundary of flow state transition is established. The experimental test and theoretical calculation show that the limit of the fracture height for the transition from pipe flow to Darcy flow is about twice the sum of the maximum height of the microconvex bodies on the upper and lower sides of the fracture.

Application of EOR Using Water Injection in Carbonate Condensate Reservoirs in the Tarim Basin

The largest carbonate condensate field has been found in the Tarim Basin, NW China. Different from sandstone condensate gas reservoirs, however, the conventional gas injection for pressure maintenance development is not favorable for Ordovician fracture-cave reservoirs. Based on this, in this paper, 21 sets of displacement experiments in full-diameter cores and a pilot test in 11 boreholes were carried out to study enhanced oil recovery (EOR) in complicated carbonate reservoirs. The experimental results show that the seepage channels of the gas condensate reservoirs are fractures, which are quite different from sandstone pore-throat structures. Condensate oil recovery using water injection was up to 57–88% in unfilled fractured caves and at ca. 52–80% in sand-filled fractured caves. These values are much higher than the 14–46% and 17–58% values obtained from the depletion and gas injection experiments, respectively. The water injection in 11 wells showed that the condensate oil recovery increased by 0–17.7% (avg. 3.1%). The effective EOR for residual oil replacement using water injection may be attributed to fractures, as the gas channel leads to an ineffective gas circulation and pipe flow in fracture-cave reservoirs, which is favorable for waterflood development. The complicated fracture network in the deep subsurface may be the key element in the varied and lower oil recovery rates obtained from the wells than from the experiments. This case study provides new insights for the exploitation of similar condensate gas reservoirs.

Numerical Simulation of Choke Size Optimization in a Shale Gas Well

To optimize the flowback system of shale gas horizontal wells after fracturing and to maximize the production capacity of gas wells, pipe flow and flowback models of shale gas multistage fractured horizontal wells were established based on the actual geological engineering conditions and the fracture parameters inverted from automatic history matching by combining experimental and numerical simulation methods. Optimization of the maximum choke size, reasonable opening choke size, replacement stages, and choke replacement frequency were studied. The research results show that the larger the production pressure difference in the early period, the higher the initial gas production rate but the easier the migration of proppant and the higher its stress sensitivity, which increases the permeability damage and weakens the reservoir recovery ability. Thus, the fracture conductivity gets worse and the later gas production rate and liquid production rate get lower. Specifically, the research results mainly include the following: (1) The laboratory experiment results show that the effective stress exceeding 19 MPa caused a proppant breakage and embedding phenomenon, leading to difficult recovery from reservoir permeability damage. Therefore, the maximum production pressure difference corresponding to the single-well maximum choke size shall not exceed 19 MPa. (2) A small opening choke size of a shale gas well is superior to the large one, and according to the numerical simulation, the choke size of 3 mm is recommended to be the reasonable opening choke size. (3) Under the drainage and production systems of replacing the choke size from small to large, the simulation results indicate that the production effect under the drainage and production systems of increasing the choke size incrementally stage by stage with an increase in amplitude of 1 mm is much better than that under the drainage and production systems of increasing the choke size by skipping the stage. (4) When the choke size is increased stage by stage, the research results indicate that the optimal duration of each grade of choke size is 3 days, beyond which, the increase of EUR will not be remarkable. The application of the proposed fine choke system research method in Well-CN001 indicates that the influence amplitude of the reasonable choke system on the daily gas production of Well-CN001 is in the range of 65.96%–121.67% and that on single-well EUR increase amplitude in 20 years is in the range of 5.2%–22.27%. The research results provide technical support for understanding the influence of different choke systems on the productivity of shale gas wells and optimizing the reasonable drainage and production systems of shale gas wells after fracturing.

Computational and experimental estimation of the heat transfer intensity of stationary gas flows in pipes with different cross sections, taking into account flow turbulence

Computational and experimental estimation of the heat transfer intensity of stationary gas flows in pipes with different cross sections, taking into account flow turbulence

Fuzzy Regulator for Two-Phase Gas–Liquid Pipe Flows Control

The paper presents an intelligent module to control dynamic two-phase gas–liquid mixtures pipelines flow processes. The module is intelligent because it uses the algorithm based on AI methods, namely, fuzzy logic inference, to build the fuzzy regulator concept. The developed modification has allowed to design and implement the black-box type regulator. Therefore, it is not required to determine any of the complicated computer models of the flow rig, which is unfortunately necessary when using the classic regulators. The inputs of the regulator are four linguistic variables that are decomposed into two classes and two methods of fuzzification. The first input class describes the current values of gas and liquid pipe flows, which at the same time are the controlled values manipulated to generate desired flow type. The second class of the input signals contains a current flow state, namely, its name and the name preferred by the operator flow type. This approach improves the control accuracy since the given flow type can be generated with different gas and liquid volume fractions. Those values can be optimized by knowing the current flow type. Moreover, the fuzzification algorithm used for the input signals included in the first-class covers the current crisp signal value and its trend making the inference more accurate and resistant to slight measurement system inaccuracy. This approach of defined input signals in such environments is used for the first time. Considering all mentioned methods, it is possible to generate the desired flow type by manipulating the system input signals by minimum required values. Furthermore, a flow type can be changed by adjusting only one of the input signals. As an output of the inference process, two linguistic values are received, which are fuzzified adjustment values of the liquid pump and gas flow meter. The regulator looks to be universal, and it can be adopted by multiple test and production rigs. Moreover, once configured with a dedicated rig, it can be easily operated by the non (domain) technical staff. The usage of fuzzy terms makes understanding both the control strategy working principles and the obtained results easy.

Closed loop control of gas flow in a pipe: stability for a transient model

Abstract This contribution focuses on the analysis and control of friction-dominated flow of gas in pipes. The pressure in the gas flow is governed by a partial differential equation that is a doubly nonlinear parabolic equation of p-Laplace type, where p = 3 2 p=\frac{3}{2} . Such equations exhibit positive solutions, finite speed of propagation and satisfy a maximum principle. The pressure is fixed on one end (upstream), and the flow is specified on the other end (downstream). These boundary conditions determine a unique steady equilibrium flow. We present a boundary feedback flow control scheme, that ensures local exponential stability of the equilibrium in an L 2 {L^{2}} -sense. The analysis is done both for the PDE system and an ODE system that is obtained by a suitable spatial semi-discretization. The proofs are based upon suitably chosen Lyapunov functions.

A leakage particle–wall impingement based vibro-acoustic characterization of the leaked sand–gas pipe flow

Solid particle leakage detection in double-wall pipes is industrially important, especially in chemical and petroleum engineering. Here, we developed vibration and acoustic sensor approaches for the characterization and comparative study of the applicability of leakage sand particle detection from the flow of gas pipes. A specific wideband vibration sensor and pressure-field microphone were selected to identify the vibro-acoustic characteristics within 50kHz of the particle leakage. The vibro-acoustic time-behaviours and characteristic frequencies of particle leakage were observed by the time-frequency method. The leakage gas flow noise was verified by coherence analysis and minimized by a digital bandpass and band-elimination filter. Corresponding experiments were performed, and good agreement was found between the release pressures (0.1–0.3MPa) with different leak sizes (0–8mm) under different sand masses (120μm) and vibro-acoustic Root-Mean-Square (RMS) levels. In the comparison of the two methods, the vibration method has a better frequency response for the leakage flow and is good for identifying whether there are particle leaks. The acoustic method has a time behaviour response and is good for establishing the relationship between the particle mass and signals. In addition, the acoustic method has frequency shift features with a better signal to noise ratio. The acoustic method lays the foundation for future work of more complex leakage detection combining the advantages of vibration and the acoustic method.

Multi-frequency sequential and simultaneous parametric shape optimization of reactive silencers

Silencers are widely used to attenuate unwanted noise emitted by engines, exhaust, and ventilation systems or from intermittent gas flow in pipes. In recent years, the study of noise control using optimization techniques applied to silencers has been growing. The main objective of the present work is to parametrically optimize the shape of a compact reactive silencer with a single expansion chamber, modifying its construction dimensions. Sequential and simultaneous optimizations are applied to the shapes of three reactive filter types so that their sound transmission losses are maximized over pre-established frequency ranges. The optimized reactive filters are the expansion chamber with modified surface profile, extended ducts and the bi-partition of the chamber. The optimization process is carried out with the aid of the finite element method using a formulation for axisymmetric problems and with the models being discretized with linear quadrilateral elements. The optimizations were evaluated in 16 frequency range combinations totaling 98 possible results. The results showed that both optimization techniques are efficient in improving the efficiency of silencers above the first TL drop frequency of the base model, which is composed of a single expansion chamber. However, the sequential strategy presented optimized models with more regular final shapes. In addition, the methodologies are validated using the traditional three-dimensional Finite Element Method and with the experimental verification of two optimized models.

In-Service Welding Simulation of 28” Pipeline Using Finite Element Method

To maintain the integrity of the gas pipeline, the repairing of pipeline system with common method such as cut and replaces method by conducting hot tap and bypass or clamp method is conducted. Both methods require in-service welding in the process. During in-service welding, the process affects the structure strength. The structure then needs to be analysed during the welding process. There are two common problems associated with in-service welding. Firstly, the high gas flow in pipe causes the weld rapidly to cool due to the convective transfer of heat. The other problem is burn-through during in-service welding. Pressurized natural gas imposes a significant stress on the pipe wall, and since the pipe strength is decreased during welding, this cause failure in pipe wall. Burn-through occurs when the region around the weld pool has insufficient strength to withstand the internal gas pressure. This paper shows the finite element analysis procedure of In-Service Welding Analysis to avoid burn-through failure. A thermal-mechanical based Finite Element model had been conducted to assess the risk. The model is simulated using three-dimension (3D) mechanical, thermos-elastic-plastic-metallurgical finite element computational procedure. The temperature, stress and strain parameters of inner surface were used to assess the model. The temperature and strain check are below the allowable value while the stress check with some applicable method which are based on either stress or strain based.

Experimental evaluation of sand particle identification in oil–water–gas multiphase flows based on vibration signal analysis

Sand–oil–water–gas pipe flow is common in the chemical and petroleum industries. In this paper, the identification of the solid phase in sand–oil–water–gas bubbly flow was investigated using a vibration-sensing method. Four identical high-frequency vibration sensors were selected to obtain the multiphase flow signals around the exit of a pipe elbow. Typical frequency-domain, mutual coherence, time-domain statistical, and time-domain joint analysis methods were applied for sand-vibration signal identification and characterization. Verification experiments were performed, and good agreement was found between the sand concentration (0.05–0.25wt.%), particle size (96–180μm) and vibrational energy in water–gas bubbly flow and oil–water–gas bubbly flow. Sand characteristic frequency bands of 14–15.39 and 15.63–16.09kHz for water–gas bubbly flow and of 14–16.45 and 19.31–20kHz for oil–water–gas bubbly flow were found. Sand particles were more easily identified by varying the water velocity than the gas velocity. The validity of the detected sand signals was also verified using an acoustic sensor. It was proven that the vibration-sensing method can be used to characterize solid particles in oil–water–gas bubbly multiphase flows, laying the foundation for solid identification in more complex multiphase flows.

Vibration sensor method for the identification of solid particle leakage from gas pipe flow based on particle-wall interaction

Leakage flow carrying solid particles from a two-layer pipe system is widely encountered in the oil and gas industry. In this paper, the identification of particle-gas leakage flow from an inner pipe was developed, and leak point simulation equipment was designed. Typical statistical vibration time-behavior and time-frequency joint analyses were applied to characterize the particle leakage signal. Verification experiments were performed, and a sand particle identification frequency band from 10.2–10.95 kHz was discovered. Additionally, good agreement was found for sand particle (150 μm) identification from the leakage gas flow at different leak points (diameters from 2 to 8 mm) under different release pressures (from 0.4 to 0.8 MPa). The sand vibration energy from one leak point increased with released pressure and leak size, while for two leak points, the sand vibration energy is more sensitive to the first point and decreases with the diameter of the second point.

Triboelectric freestanding flapping film generator for energy harvesting from gas flow in pipes

We are reporting on the conversion of gas/air flow energy in pipes to electrical signals using the triboelectric effect. A flapping triboelectric generator design with all freestanding flexible films is introduced in this regard. The generator can be integrated within a regular pipe infrastructure, as it is independent of the pipe material, for implementing the triboelectric effect. All flexible materials are used to develop the triboelectric generator, utilizing a simple fabrication process that is easily scalable. The performance of the triboelectric device was influenced by several physical parameters, as well as by the gas flow speed, which has been optimized here for a pipe diameter of 5 cm. The triboelectric generator implementing a flexible silver material in combination with polytetrafluoroethylene (PTFE) exhibits 100% higher optimum average power output compared to a generator made of PTFE and polyurethane. A harvester unit with two pairs of triboelectric films with an active film area of 5 × 3.3 cm2 with 6 mm gaps was demonstrated. The device produced total average power of 1.64 mW across an optimum load resistance of 16.7 MΩ under the air flow speed of 9.8 ± 0.2 m s−1.

An investigation of the detection of acoustic sand signals from the flow of solid particles in pipelines

The development of a simple, reliable and low-cost on-line particle detection method for liquid flows has been recognized as a global challenge in the chemical engineering industry. To overcome the existing limitations in the detection of sand particles in water–gas pipe flows, a non-invasive acoustic method with two special acoustic devices (installed separately on a straight pipe and a bend pipe) for the detection of miniscule sand particles was evaluated. A series of detection methods, namely, time-frequency analysis, mutual-coherence analysis, and multi-band elimination filter methods, were developed to extract weak sand features submerged in the background noise of strong flows. Verification experiments were conducted to record acoustic signals from sand-carrying flows, thereby revealing five sand characteristic frequency bands in a water–gas bubbly flow: 20.59–21.31 kHz, 24.10–24.82 kHz, 27.64–28.36 kHz, 31.10–31.84 kHz, and 34.61–35.33 kHz. Additionally, good agreement was found between the sand concentration (0.06–0.24 wt.%) with a particle size of 150 μm and the acoustic sand root mean square (RMS) level within the discovered sand frequency multi-bands, verifying the use of the proposed acoustic detection devices and the corresponding weak sand identification method. This study provides the foundation for the future detection of solids in more complex multiphase flows.

Problem of conjugate heat transfer between main gas pipeline and frozen ground

Mathematical model of non-isothermal gas flow within the framework of tube hydraulics including change of tube cross-section due to hydrate formation and the dependence of coefficient of heat transfer between gas and hydrate layer on varying flow area is proposed. The corresponding conjugate problem of heat exchange between imperfect gas in the pipeline and the environment is reduced to the solution of differential equations describing non-isothermal flow of gas in pipes and heat transfer equations in ground with the corresponding conjugation conditions. In the quasi-stationary mathematical model of hydrate formation (dissociation), the dependence of gas-hydrate transition temperature on gas pressure is taken into account. Some decisions taken in the design of the first section of the main gas pipeline «Power of Siberia» have been analyzed. It has been shown that if gas is not sufficiently dried, outlet pressure may drop below the technological limit in about 6-7 hours. At the same time, for completely dry gas ,it is possible to reduce the cost of thermal insulation of the pipeline at least two fold.

Diffusive heat and mass transfer in oscillatory pipe flow

The enhancement of axial heat and mass transfer by laminar flow oscillation in pipes with axial gradients in temperature and concentration has been studied analytically for the cases of insulated and conducting walls. The axial diffusivity can exceed its molecular counterpart by many orders of magnitude, with a quadratic scaling on the pressure-gradient amplitude and the Prandtl or Schmidt number, and is a bimodal function of oscillatory frequency: quasi-steady behavior at low frequencies and a power-law decay at high frequencies. When the pipe wall is conductive and of sufficient thickness, and the flow oscillation is quasi-steady, the axial diffusivity may be enhanced by a further factor of about ten as a result of increased radial diffusion, for liquid and gas flows in pipes with walls with a wide range of thermal conductivities. Criteria for the wall thickness required to achieve this additional enhancement and for the limits placed on the validity of these solutions by viscous dissipation are also deduced. When the heat transfer per unit flow work achieved by oscillatory pipe flow is contrasted with that of a conventional parallel-flow heat exchanger, it is found to be of comparable size and the ratio of the two is shown to be a function only of the pipe geometry, heat-exchanger mean velocity, and fluid viscosity.

The flows structure in unsteady gas flow in pipes with different cross-sections

The results of numerical simulation and experimental study of the structure of unsteady flows in pipes with different cross sections are presented in the article. It is shown that the unsteady gas flow in a circular pipe is axisymmetric without secondary currents. Steady vortex structures (secondary flows) are observed in pipes with cross sections in the form of a square and an equilateral triangle. It was found that these secondary flows have a significant impact on gas flows in pipes of complex configuration. On the basis of experimental researches it is established that the strong oscillatory phenomena exist in the inlet pipe of the piston engine arising after the closing of the intake valve. The placement of the profiled plots (with a cross section of a square or an equilateral triangle) in the intake pipe leads to the damping of the oscillatory phenomena and a more rapid stabilization of pulsating flow. This is due to the stabilizing effect of the vortex structures formed in the corners of this configuration.

Modelling of Natural Gas Pipe Flow with Rapid Transients-case Study of Effect of Ambient Model

The paper presents a study of gas pipeline to soil heat transfer. The effect of simplifications of the heat transfer model is investigated. Studied are steady, one dimensional unsteady and two dimensional unsteady models of the pipe wall and soil. Flow conditions at the pipeline inlet are varied. The effects of rapid changes in gas mass flow rate and temperature at the pipeline inlet are studied. The case presented is representative for export natural gas pipelines, containing offshore and buried sections along the route. Results are compared to experimental data from an existing export natural gas pipeline.