# 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.