Semi-Empirical Correlation to Quantify the Effects of Pipe Diameter and Internal Surface Roughness on the Decompression Wave Speed in Natural Gas Mixtures

2012 ◽  
Author(s):  
K. K. Botros ◽  
Lorne Carlson ◽  
Brian Rothwell ◽  
Philip Venton
Keyword(s):  
Surface Roughness ◽  
Natural Gas ◽  
Pressure Gradient ◽  
Shock Tube ◽  
Wave Speed ◽  
Correction Term ◽  
Gas Mixture ◽  
Decompression Wave ◽  
Semi Empirical ◽  
The Ideal

GASDECOM is typically used in the design of gas pipelines for calculating decompression speed in connection with the Battelle two-curve method used throughout the pipeline industry for the control of propagating ductile fracture. GASDECOM idealizes the decompression process as isentropic and one-dimensional, taking no account of pipe wall frictional effects. Previous shock tube tests showed that decompression wave speeds in smaller diameter and rough pipes are consistently slower than those predicted by GASDECOM for the same conditions of mixture composition and initial pressure and temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation showed a correction term to be subtracted from the ‘ideal’ value of the decompression speed. One parameter in this correction term involves a dynamic spatial pressure gradient of the outflow at the rupture location. While this is difficult to obtain without a shock tube or actual rupture test, data from 14 shock tube tests, as well as from 14 full scale burst tests involving a variety of gas mixture compositions, were analyzed to quantify the variation of this pressure gradient with gas conditions and outflow Mach number. A semi-empirical relationship was found to correlate this pressure gradient parameter with two basic parameters representing the natural gas mixture, namely the molecular weight of the mixture and its higher heating value (HHV). For lean gas mixes, the semi-empirically obtained correlation was found to fit very well the experimentally determined decompression wave speed curve. For rich gas mixes, the correlation fits both branches of the curve; above and below the plateau pressure. This paper provides the basis for the derived semi-empirical correlation, and suggests a procedure (with examples) to correct the ‘ideal’ (frictionless) GASDECOM prediction to account for both the effects of pipe diameter and pipe internal wall surface roughness.

Measurements of Decompression Wave Speed in Natural Gas Containing 2-8% (Mole) Hydrogen by a Specialized Shock Tube

2016 ◽  
Author(s):  
K. K. Botros ◽  
S. Igi ◽  
J. Kondo
Keyword(s):  
Natural Gas ◽  
Shock Tube ◽  
Hydrogen Concentration ◽  
Wave Speed ◽  
Accurate Determination ◽  
Initial Pressure ◽  
Propagation Speed ◽  
Wave Speeds ◽  
Decompression Wave ◽  
Curve Method

The Battelle two-curve method is widely used throughout the industry to determine the required material toughness to arrest ductile (or tearing) pipe fracture. The method relies on accurate determination of the propagation speed of the decompression wave into the pipeline once the pipe ruptures. GASDECOM is typically used for calculating this speed, and idealizes the decompression process as isentropic and one-dimensional. While GASDECOM was initially validated against quite a range of gas compositions and initial pressure and temperature, it was not developed for mixtures containing hydrogen. Two shock tube tests were conducted to experimentally determine the decompression wave speed in lean natural gas mixtures containing hydrogen. The first test had hydrogen concentration of 2.88% (mole) while the second had hydrogen concentration of 8.28% (mole). The experimentally determined decompression wave speeds from the two tests were found to be very close to each other despite the relatively vast difference in the hydrogen concentrations for the two tests. It was also shown that the predictions of the decompression wave speed using the GERG-2008 equation of state agreed very well with that obtained from the shock tube measurements. It was concluded that there is no effects of the hydrogen concentration (between 0–10% mole) on the decompression wave speed, particularly at the lower part (towards the choked pressure) of the decompression wave speed curve.

Measurement of Decompression Wave Speed in Rich Gas Mixtures at High Pressures (370 bars) Using a Specialized Rupture Tube

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
K. K. Botros ◽  
J. Geerligs ◽  
R. J. Eiber
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Wave Speed ◽  
High Pressures ◽  
Equations Of State ◽  
Gas Mixtures ◽  
Internal Diameter ◽  
Decompression Wave ◽  
Predicted Values ◽  
Fracture Arrest

Measurements of decompression wave speed in conventional and rich natural gas mixtures following rupture of a high-pressure pipe have been conducted. A high-pressure stainless steel rupture tube (internal diameter=38.1 mm and 42 m long) has been constructed and instrumented with 16 high frequency-response pressure transducers mounted very close to the rupture end and along the length of the tube to capture the pressure-time traces of the decompression wave. Tests were conducted for initial pressures of 33–37 MPa-a and a temperature range of 21–68°C. The experimentally determined decompression wave speeds were compared with both GASDECOM and PIPEDECOM predictions with and without nonequilibrium condensation delays at phase crossing. The interception points of the isentropes representing the decompression process with the corresponding phase envelope of each mixture were correlated with the respective plateaus observed in the decompression wave speed profiles. Additionally, speeds of sound in the undisturbed gas mixtures at the initial pressures and temperatures were compared with predictions by five equations of state, namely, BWRS, AGA-8, Peng–Robinson, Soave–Redlich–Kwong, and Groupe Européen de Recherches Gaziéres. The measured gas decompression curves were used to predict the fracture arrest toughness needed to assure fracture control in natural gas pipelines. The rupture tube test results have shown that the Charpy fracture arrest values predicted using GASEDCOM are within +7% (conservative) and −11% (nonconservative) of the rupture tube predicted values. Similarly, PIPEDECOM with no temperature delay provides fracture arrest values that are within +13% and −20% of the rupture tube predicted values, while PIPEDECOM with a 1°C temperature delay provides fracture arrest values that are within 0% and −20% of the rupture tube predicted values. Ideally, it would be better if the predicted values by the equations of state were above the rupture tube predicted values to make the predictions conservative but that was not always the case.

Effects of Pipe Internal Surface Roughness on Decompression Wave Speed in Natural Gas Mixtures

2010 ◽  
Author(s):  
K. K. Botros ◽  
J. Geerligs ◽  
Leigh Fletcher ◽  
Brian Rothwell ◽  
Philip Venton ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Wave Speed ◽  
Large Diameter ◽  
Initial Pressure ◽  
Internal Surface ◽  
Analytical Framework ◽  
Wall Friction ◽  
Spatial Gradient ◽  
Decompression Wave ◽  
Frictional Effects

The control of propagating ductile (or tearing) fracture is a fundamental requirement in the fracture control design of pipelines. The Battelle two-curve method developed in the early 1970s still forms the basis of the analytical framework used throughout the industry. GASDECOM is typically used for calculating decompression speed, and idealizes the decompression process as isentropic and one-dimensional, taking no account of frictional effects. While this approximation appears not to have been a major issue for large-diameter pipes and for moderate pressures (up to 12 MPa), there have been several recent full-scale burst tests at higher pressures and smaller diameters for which the measured decompression velocity has deviated progressively from the predicted values, in general towards lower velocities. The present research was focused on determining whether pipe diameter was a major factor that could limit the applicability of frictionless models such as GASDECOM. Since potential diameter effects are primarily related to wall friction, which in turn is related to the ratio of surface roughness to diameter, an experimental approach was developed based on keeping the diameter constant, at a sufficiently small value to allow for an economical experimental arrangement, and varying the internal roughness. A series of tests covering a range of nominal initial pressures from 10 to 21 MPa, and involving a very lean gas and three progressively richer compositions, were conducted using two specialized high pressure shock tubes (42 m long, I.D. = 38.1 mm). The first is honed to an extremely smooth surface finish, in order to minimize frictional effects and better simulate the behaviour of larger-diameter pipelines, while the second has a higher internal surface roughness. The results show that decompression wave speeds in the rough tube are consistently slower than those in the smooth tube under the same conditions of mixture composition and initial pressure & temperature. Preliminary analysis based on perturbation theory and the fundamental momentum equation indicates that the primary reason for the slower decompression wave speed in the rough tube is the higher spatial gradient of pressure pertaining to the decompression wave dynamics, particularly at lower pressure ratios and higher gas velocities. The magnitude of the effect of the slower decompression speed on arrest toughness was then evaluated by a comparison involving several hypothetical pipeline designs, and was found to be potentially significant for pipe sizes DN450 and smaller.

Measurements of Decompression Wave Speed in Simulated Anthropogenic Carbon Dioxide Mixtures Containing Hydrogen

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
K. K. Botros ◽  
J. Geerligs ◽  
B. Rothwell ◽  
T. Robinson
Keyword(s):  
Carbon Dioxide ◽  
Shock Tube ◽  
Phase Boundary ◽  
Ductile Fracture ◽  
Critical Point ◽  
Wave Speed ◽  
Plateau Pressure ◽  
Boundary Crossing ◽  
Decompression Wave ◽  
The Impact

In order to determine the material fracture resistance necessary to provide adequate control of ductile fracture propagation in a pipeline, a knowledge of the decompression wave speed following the quasi-instantaneous formation of an unstable, full-bore rupture is necessary. The thermodynamic and fluid dynamics background of such calculations is understood, but predictions based on specific equations of state (EOS) need to be validated against experimental measurements. A program of tests has been conducted using a specially constructed shock tube to determine the impact of impurities on the decompression wave speed in carbon dioxide (CO2), so that the results can be compared to two existing theoretical models. In this paper, data and analysis results are presented for three shock tube tests involving anthropogenic CO2 mixtures containing hydrogen as the primary impurity. The first mixture was intended to represent a typical scenario of precombustion carbon capture and storage (CCS) technology, where typically the concentration of CO2 is around 95–97% (mole). The second mixture represents a worst case scenario of this technology with high level of impurities (with CO2 concentration around 85%). The third test represents a typical chemical-looping combustion process. It was found that the extent of the plateau on the decompression wave speed curves in these tests depends on the location of the phase boundary crossing along the bubble-point curve. The closer the phase boundary crossing to the critical point, the shorter the plateau. This is primarily due to the change in magnitude of the drop in the speed of sound at phase boundary crossing. For the most part, the predictions of the plateau pressure by both of the EOS that were evaluated, GERG-2008 and Peng–Robinson (PR), are in good agreement with measurements by the shock tube. This by no means reflects overall good performance of either EOS, but was rather due to the fact that the isentropes intersected the phase envelope near the critical point, or that the concentration of H2 was relatively low, either in absolute terms or relative to other impurity constituents. Hence, its influence in causing inaccurate prediction of the plateau pressure is lessened. An example of pipeline material toughness required to arrest ductile fracture is presented which shows that predictions by GERG-2008 are more conservative and are therefore recommended.

Decompression Wave Speed in Rich Gas Mixtures at High Pressures (37 MPa) and Implications on Fracture Control Toughness Requirements in Pipeline Design

2010 ◽  
Author(s):  
K. K. Botros ◽  
J. Geerligs ◽  
R. J. Eiber
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Wave Speed ◽  
Equations Of State ◽  
Gas Mixtures ◽  
Internal Diameter ◽  
Decompression Wave ◽  
Fracture Control ◽  
Predicted Values ◽  
Fracture Arrest

Measurements of decompression wave speed in conventional and rich natural gas mixtures following rupture of a high-pressure pipe have been conducted. A high pressure stainless steel rupture tube (internal diameter = 38.1 mm, and 42 m long), has been constructed and instrumented with 16 high frequency-response pressure transducers mounted very close to the rupture end and along the length of the tube to capture the pressure-time traces of the decompression wave. Tests were conducted for initial pressures of 33–37 MPa-a and a temperature range of 21 to 68 °C. The experimentally determined decompression wave speeds were compared to both GASDECOM and PIPEDECOM predictions with and without non-equilibrium condensation delays at phase crossing. The interception points of the isentropes representing the decompression process with the corresponding phase envelope of each mixture were correlated to the respective plateaus observed in the decompression wave speed profiles. Additionally, speeds of sound in the undisturbed gas mixtures at the initial pressures and temperatures were compared to predictions by five equations of state, namely BWRS, AGA-8, Peng-Robinson, Soave-Redlich-Kwong, and GERG. The measured gas decompression curves were used to predict the fracture arrest toughness needed to assure fracture control in natural gas pipelines. The rupture tube test results have shown that the Charpy fracture arrest values predicted using GASEDCOM are within +7 (conservative) and −11% (non-conservative) of the rupture tube predicted values. Similarly, PIPEDECOM with no temperature delay provides fracture arrest values that are within +13 and −20% of the rupture tube predicted values, while PIPEDECOM with a 1 °C temperature delay provides fracture arrest values that are within 0 and −20% of the rupture tube predicted values. Ideally, it would be better if the predicted values by the equations of state were above the rupture tube predicted values to make the predictions conservative but that was not always the case.

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