How to Reduce the Nozzle Loads in START-PROF

Read about START-PROF pipe stress analysis software

When equipment loads exceed allowable values, first identify the cause. High loads may result from:

• Force-controlled loads: Weight loads, pressure thrust forces. Analyze with operating temperature equal to ambient temperature and weight multiplier = 1.0
• Displacement-controlled loads: Thermal expansion, support displacement. Analyze with weight multiplier = 0 in operation mode editor

For high force-controlled loads:

• For weight loads: Add vertical supports, variable spring hangers, or constant spring supports
• For expansion joint thrust forces: Redesign piping to remove non-pressure balanced expansion joints or add anchors to resist thrust forces

For high thermal expansion loads, apply these methods:

• Increase piping system flexibility

• Add bends - bends provide more flexibility than straight pipe
• Reduce pipe and bend wall thickness where possible - thinner walls increase flexibility
• Reduce diameter where possible - smaller diameters increase system flexibility
• Add nozzle flexibility using WRC 297/PD 5500, API 650, or Nozzle FEM
• Add support structure flexibility using custom restraints with defined flexibilities

Example: Straight pipe between two anchors

Without anchor flexibility, axial force calculates as:

With right nozzle flexibility λ:

Example: Pipe 219x6 mm, L=6m, ΔT=100°C, α=0.000012, E=2,000,000 kg/cm², A=40.1 cm²

kgf

With nozzle flexibility λ=0.14 mm/tf (stiff nozzle), load reduces 3x:

kgf

Complete equations for support loads, internal forces, and stresses:

• Add gimbal, lateral, or pressure-balanced axial expansion joints

Use unbalanced expansion joints carefully - thrust forces may transfer significant axial loads to equipment

Correct and incorrect pump piping with unbalanced expansion joints:

• Reduce temperature difference - lower operating temperature or raise ambient temperature
• Direct thermal expansion away from equipment using U-shaped loops with proper restraints (guides or directional anchors). Consider friction forces in anchors

• For high friction loads: Use Teflon, graphite, or polished stainless steel plates to reduce friction
• Use hot modulus of elasticity for equipment nozzle loads ("Use Eh for support loads" in Project Settings)
• Apply cold spring as last resort (does not reduce expansion stress range)
• Offset equipment by half the thermal expansion value from installation to operating position

If loads remain above allowable limits after optimization, submit actual loads (increased by 20% if piping data is not final) to equipment vendor for FEA analysis and acceptance.