Thrust block and surge

[Camell]

I am busy with the design of a pumped main. Regarding the design of thrust blocks: What is the accepted practice with respect to the pressure considered. I see three alternatives:
1) Normal duty point and flow
2) Pump maximum pressure (potentially zero flow, but not nessarily)
3) Surge pressure.....what flow?

I am sure no 3 will govern, but may be excessive!

Also the restriant factors involved in the resistance will be different: if soil resistance, the surge pressures will invoke passive resistance which will be significantly larger, whereas under normal operation a bearing capacity calculations is more appropriate.

My specific situation is the flanged steel bends leading upto the approach of a steel pipe bridge ( VJ expansion joints on steel pipe on bridge and PVC leading upto it, so non continuous piping.) I am not able to make much use of soil resistance and must provide a mass of concrete on these bends. The question of surge pressure now becomes much more important

Any comments?

 

[RWF7437]

You probably want to design for the test pressure. If this is a municipal water main, in my part of the country, that is about 150 psig. That's typically twice the normal duty pressure.

good luck

 

[stanier]

WSA Codes in Austrralia require that the surge pressure be taken into account when designing thrust blocks.

If this results in excessive size of thrust blocks do something about the surge.

Check out

http://www.pipingdesign.com

for paper on risks associated with surge.