Showing 4 results for Gas Pipeline
Aziz Azimi, Fazel Khaliji, Mohsen Shabani,
Volume 13, Issue 4 (7-2013)
Abstract
In this paper, mass flow rate and location of leakage in natural gas pipeline has been estimated simultaneously using inverse analysis. For doing so, at first natural gas transient flow in pipeline has been simulated numerically; this simulation is named direct problem. In the direct problem, it is assumed that the mass flow rate and location of leakage is definite and the governing equations are inhomogeneous well-known Euler equations. In these equations, the leakage effect has been considered as a source term. Steger–Warming flux splitting method has been used for numerical analysis of these equations. Then the location and mass flow rate of gas leakage of pipeline have been estimated simultaneously using Levenberg-Marquardt method for parameter estimation. This method is an iterative algorithm and based on minimizing the sum of the squares of the errors which are difference between pressures computed by the direct problem and pressures measured by pressure gauges. The results of the direct problem have good agreement with Mac–Cormack method and characteristics method of specified time intervals. The results of the inverse analysis demonstrate that Levenberg-Marquardt algorithm is stable and efficient enough to estimate simultaneously the mass flow rate and location of leakage in natural gas pipeline.
, Aziz Azimi, ,
Volume 13, Issue 8 (11-2013)
Abstract
Numerical simulation of non-isothermal transient gas flow is performed using implicit Steger-Warming finite difference method. Because of nonlinearity of the governing equations, they are linearized at each time step. The linearization either reduces computational effort or analyzes the flowfield more conveniently. In order to validate and evaluate the accuracy of current numerical method, Fanno and shock tube flows are investigated first. Then, transient flow in a gas pipeline that its inlet pressure changes with time is simulated. The results of present study show that Steger-Warming finite difference scheme can well captured the sudden changes in the flowfield. Moreover, the present method is able to analyze transient gas flows as nearly accurate as the nonlinear one with less computational effort.
M. Sabokrouh , M.r. Farahani ,
Volume 19, Issue 1 (1-2019)
Abstract
The weld residual stresses decrease the design stress in gas transportation pipelines. In this paper, two X70 steel pipes of 56 inch outside diameter were firstly girth welded. Experimental hole drilling test was conducted to evaluate the residual stress distribution in this joint. Then, the finite element simulation of the welding process was performed to evaluate the residual stress distribution precisely. The numerical results were verified by comparison with the obtained experimental measurements. The qualitative results achieved match properly with the experimental results. Simulation results (with a difference about 15% compared to experimental results) evaluated the maximum residual stress in hoop direction of pipe’s external weld metal. The experimental data showed that the maximum tensile residual stress was located on the center line of the weld gap on the pipe outer surface alongside with the pipe hoop direction. Moreover, the maximum compressive (hoop and axial) residual stresses occurred on the pipe inner surface in heat affected zone. The variations of the hoop residual stresses on the inner and outer surfaces of the pipe had similar trend with tensile distribution at the center line of the weld gap. However, these stresses showed different trends (tensile stress on the outer surface, and compressive stress on the inner surface) with distancing from the weld center line.
Mohammad Tavid, Sayyed Hashemi,
Volume 24, Issue 5 (4-2024)
Abstract
Thermomechanical steels are widely used in oil and gas pipelines due to their high toughness and high resitance against crak growth. A large part of the steel pipelines used in the oil and gas industry in Iran is made of API X65 steel. The fluctuations of internal gas pressure in steel pipes can cause fatigue failure and lead to gas leakage and explosion. So, the control of damage initiation and structural integrity of gas pipelines is of great importance. In this study, the S-N curve and the fatigue strength of the base metal of the API X65 steel were estimated by performing fatigue tests. For this purpose, 24 and 25 test specimens along the seam weld in the coil transverse direction, and perpendicular to the seam weld along the coil rolling direction were prepared according to ISO 1143 standard, respectively. All test samples were cut from an spirally welded pipe with 1219mm outside diameter and 14.3mm wall thickness and were tested on a completely reverse rotating-bending fatigue machine. Statistical analysis of the results was performed by considering the normal logarithmic distribution. The mean curve, characteristic curve, and confidence interval of the results were obtained both in the finite fatigue life range and in the fatigue resistance. The mean endurance limit of the base metal perpendicular to and parallel to the seam seam were 305 and 291 MPa, respectively which were in the range of 0.4 to 0.6 of material tensile strength and above the seam weld endurance limit (258 MPa).
