SURGE PRESSURES IN PEXGOL PIPES
The expression for a = the velocity of pressure wave is a function of the short term Modulus E and the dimension ratio
d/e, which is the same for each pipe class:
d/e = (D-2xe)/e = (D/e) – 2 = SDR-2
It is possible to calculate the values for a for each pipe class.
In the following table, the values of the pressure velocity a were calculated for the following design temperatures:
- 20°C – for buried pipes
- 30°C – for above ground pipes at ambient temperature of 20°C
- 40°C – for above ground pipes at ambient temperature of 40°C
The values of P were calculated for line velocity of 1.0 m/sec.
Low surge pressures expected in Pexgol pipes
| SDR | E = 67,425 psi | E = 50,750 psi | E = 33,060 psi | |||
|---|---|---|---|---|---|---|
| 20ºC | 30ºC | 40ºC | ||||
| a [m/sec] | Surge pressure [Psi] | a [m/sec] | Surge pressure [Psi] | a [m/sec] | Surge pressure [Psi] | |
| 17 | 172 | 25 | 150 | 22 | 121 | 18 |
| 13.5 | 196 | 29 | 170 | 25 | 138 | 20 |
| 11 | 221 | 33 | 192 | 28 | 156 | 23 |
| 9 | 250 | 37 | 218 | 32 | 176 | 26 |
| 7.3 | 286 | 42 | 249 | 37 | 202 | 30 |
| 6 | 327 | 48 | 285 | 42 | 232 | 34 |
The value of a = Velocity of pressure wave was calculated using the instantaneous Modulus of Elasticity. Please note the surge pressure P is in direct linear relation to the value of the line velocity V.
Therefore, values for different surge pressures for the same pipe class can be calculated by changing the values of the Line velocity V.
Example: calculating the surge pressure in paragraph 4. Pexgol 10” SDR 9.
- Above ground installation ambient temperature is 40°C.
- Design temperature is 40°C.
- Design pressure of the pipe is 214 PSI at 40°C.
- Maximum allowable total transient pressure is 535 PSI.
OD 10.75”, w.t. 1.19”, d = 8.36”, V = 2.7m/sec.
From the table n°24: “Low surge pressures in Pexgol pipes”, the surge pressure for SDR 9, velocity of 1 m/sec and design temperature of 40°C is 26 Psi. For the Pexgol 10” SDR 9 which has a velocity of 2.7 m/sec, the surge pressure will be: 26 x 2.7/1 = 70 Psi
For water density higher than 1.0, divide the value of the Velocity of the pressure wave a (taken from the table n°24: “Low surge pressures in Pexgol pipes”) by the square root of the actual water density.