Natural gas rupture includes three (3) models that determine depth, radius and Width of the crater. Gasunie, NEN 3651 Radius of Crater and PRCI/Gasunie/Battelle combined model.
GASUNIE MODEL
This model applies to a guillotine rupture wherein two separate pipe ends exists after the rupture.
Crater Depth:
๐ค โ Soil Parameter
๐ท๐ โ Pipe Outside Diameter(m)
๐๐ โ Pipe Pressure(Pa)
๐ท๐ โ Depth of Cover from ground surface to center of the pipe(m)
๐ท โ Depth of Crater(m)
๐
โ Soil Parameter Function
Soil Parameter Functions:
๐ (๐ค) = 0.28+0.62(5 โ ๐ค) โ 0.07(25 โ ๐ค2)
Allowable limits for R are between 0.28 and 1.3
if ๐ค โค 0.6 ๐ท = 4.3๐ท๐ + ๐ท๐
if 0.6 < ๐ค < 2
if ๐ค โฅ 2 ๐ท = 2.2๐ท๐ + ๐ท๐
The crater angles are determined from empirical equations:
๐ผ1 = tanโ1(๐ค + 1)
Considering crater and dimensions shown in Figure 1. The equation of the ellipse is given by
Differentiating this at the ground level and substituting for x give
Evaluating this on the ground level and half crater depth gives
These can be solved simultaneously
The width of crater W is given by
NEN 3651 MODEL RADIUS OF THE CRATER
Model may be applied for guillotine type rupture, NEN 3651 define radius of the crater as:
PRCI/GASUNIE/BATTELLE COMBINED MODEL
This model may be applied for guillotine type rupture only. Computation of the crater depth in combined PRCI/Gasunie/Battelle model is the same as described above for Gasunie model.
The crater width is calculated as:
Where:
๐
๐ =
๐๐ค = ๐ท๐ + ๐ ๐ โ Distance from the Ground to the Center of the Pipe[m]
๐๐ ๐๐๐ โ Soil Density[kg/m3]
๐พ โ Gas Specific Heat Ratio(1.031 for Natural Gas)
๐ข๐๐ = 2.54[m/s] โ Critical Gas Velocity [m/s]
๐ข๐ฅ โ Velocity of the Explosive Gases[m/s]