Equipment Alignment Check

Read about START-PROF pipe stress analysis software


Equipment flange must perfectly match the piping flange otherwise the problems will occur during bolting procedure. If alignment between pipe and pump, compressor, turbine or other equipment is not perfect, then several problems may happen during installation like problems with bolting, and during operation like too high loads transferred on equipment nozzle, vibration etc. The alignment check should be performed for both inlet and outlet lines.

API RP 686 code provides the piping to equipment alignment requirements:

Also, the equipment manufacturers may offer their own guidelines regarding the allowable misalignment values.

Alignment Check Procedure in START-PROF

Create the piping model. Check that all weights are correct (pipe, insulation, product, bends, valves, tees, reducers, flanges etc.).

The goal is to reduce the force-controlled loads on equipment nozzle (weight, pressure thrust forces) to zero. This can be achieved by two steps.

First step. Specify the zero thermal expansion. To do this, create the separate operation mode in operation mode editor "Alignment check" and set the operation temperature equal to ambient temperature. Remove all support movements and cold spring. After that tune the piping system to achieve the almost zero loads on the equipment nozzle. In this case you can't check the flange misalignment at the installation stage. But you can modify your piping system and always check the nozzle loads in this special operation mode "Alignment check" after each model design change.

You can use the option "Remove Restraints for Hanger Selection", select it to remove the vertical restraint during hanger selection. In this case START-PROF will select the springs that generate very low weight loads on the equipment nozzle. After that you can tune the supporting force of the variable spring hanger to reduce the vertical load on the nozzle to zero.

Second step. Create separate project file with the same model. Convert the springs into the custom restraints. Delete the equipment nozzle, and replace it by the cap. Set the operation temperature equal to ambient temperature. Remove all support movements and cold spring. It will be the installation mode, just before flange bolts installation procedure. Run analysis and check the equipment node displacements. The displacements should not be greater than allowable limits:

It is recommended to use adjustable support types near the equipment nozzle like variable spring hangers or supports. It is needed to have an ability to tune the piping system to satisfy the above requirements.


  1. API RP 686 Recommended Practice for Machinery Installation and Installation Design
  2. WRC 499 Guidelines for the Design and Installation of Pump Piping Systems