PIPE STRAIN P014
The strain on the pump volute caused by stresses in the piping.
Here are a couple of things to consider:
- Pipe strain will cause excessive mechanical seal movement and possible contact between rotating and stationary pump and seal components.
- Expansion joints do not restrain the axial forces in the piping due to the liquid pressure.
- The axial force caused by 150-PSI pressure in a 6” Schedule 40 pipe is 4,334 pounds.
- The piping trys ti restrain this force, but with an expansion joint having no tie rods, the pipe cannot do this.
- The resulting forces must be carried by the pump if there are no anchor points between the expansion joint and the pump.
- Standard procrdure should be to pipe from the pump to the rack and not the other way.
The maximum allowable individual nozzle load on the discharge flange of an 8X6X13 [A90] ANSI/ASME B73.1M pump is 3,500 pounds according to ANSI/HI 9.6.2-2001
- At 150 PSI internal pressure this allowable limit would be exceeded.
- The use of properly designed and installed tie rods across the expansion joint can significantly reduce the transmission of these axial loads.
In limited applications, you can prevent pipe strain by using a free-floating pump or a spring-mounted baseplate.
- The baseplate must have sufficient stiffness to maintain coupling alignment, without relying on a concrete foundation.
- Close-coupled pump designs can sometimes use this approach.
- Vertical-in-Line (VIL), ANSI/ASME B73.2M pumps are a variation of the close-coupled design and are available for many process applications. VIL pumps can transmit substantial forces through the casing between the discharge and suction pipe.
o prevent pipe strain you should pipe from the pump to the rack and not the other way.