Equipment Alignment Check

Learn more about START-PROF pipe stress analysis software

Requirements

Equipment and piping flanges must align perfectly to prevent bolting issues. Misalignment between pipe and equipment nozzles—such as pumps, compressors, turbines, or other machinery—can cause installation difficulties and operational problems including excessive nozzle loads and vibration. Perform alignment checks on both inlet and outlet lines.

API RP 686 specifies piping-to-equipment alignment requirements:

• Lateral misalignment: Maximum 1.5 mm (1/16 in.) total offset between flange axes. This ensures bolts install without force.
• Axial misalignment: Maximum 1.5 mm (1/16 in.) deviation from gasket spacing. Use only one gasket per connection.
• Angular misalignment: Maximum 0.0573 degrees. Flange faces must be parallel within 0.01 mm per 10 mm of outer diameter, up to 0.75 mm total. For flanges under 25 cm (10 in.), parallelism must be within 0.25 mm (0.010 in.).

Equipment manufacturers may provide additional alignment tolerances.

Alignment Check Procedure in START-PROF

Create your piping model and verify all weights—including pipe, insulation, fluid, bends, valves, tees, reducers, and flanges.

Minimize force-controlled loads (weight, pressure thrust) on equipment nozzles using these steps:

Step 1: Zero Load Analysis
Create an "Alignment check" operation mode in the operation mode editor. Set temperature to ambient and remove all support movements and cold spring. Adjust the model until nozzle loads are near zero. Use this mode to verify alignment after each design change.

Enable "Remove Restraints for Hanger Selection" to exclude vertical restraints during spring sizing. This helps select springs that minimize nozzle loads. Fine-tune variable spring hangers to reduce vertical loads to zero.

Step 2: Installation Alignment Check
Duplicate the model in a new project. Convert springs to custom restraints. Replace the equipment nozzle with a cap. Set temperature to ambient and remove support movements and cold spring. This simulates conditions before bolting. Check that displacements at the equipment node are within limits:

• Lateral: 1.5 mm max
• Axial: 1.5 mm max
• Rotation: 0.0573° max

Use adjustable supports (e.g., variable spring hangers) near equipment nozzles to simplify alignment adjustments.

References

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