Shaft Alignment & Thermal Growth Targets – What to Do When You Don’t Know the Values

By ORBIT LINE – Precision Condition Monitoring & Reliability Services
Updated: 2025

Thermal growth is one of the most overlooked — yet most important — factors in achieving accurate shaft alignment. Many machines expand when they heat up, causing the shaft centerline to shift in the vertical and/or horizontal direction. If thermal expansion is not considered, a machine that looks “perfectly aligned” when cold can drift into severe misalignment once in operation.

This increases the risk of:

  • Bearing failures
  • Coupling wear
  • Shaft fatigue
  • Increased vibration
  • Unexpected shutdowns

For this reason, many rotating machines require thermal growth targets.

What Are Thermal Growth Targets?

Thermal targeting simply means adjusting the alignment while the machine is cold to compensate for how much it will expand or move as it reaches its operating temperature.

A machine might appear misaligned when cold — but once it heats to normal operating temperature, the shafts move into perfect alignment.

This ensures reliability, reduces vibration, and increases the life of bearings and couplings.

Where Do the Targets Come From?

Sometimes the manufacturer provides thermal growth target values. You might find them in:

  • Installation drawings
  • Machine nameplates
  • Technical manuals
  • OEM commissioning documents

However, these values are often estimated based on ideal conditions.
Real-world factors that affect thermal growth include:

  • Ambient temperature in the plant
  • Ventilation and airflow
  • Enclosed or open machine installation
  • Heat from nearby equipment
  • Shaft elevation
  • Expansion of the baseplate or supporting structure

This means OEM values may not match real operating behavior.

When You Don’t Know the Thermal Growth — What Should You Do?

If the manufacturer did not provide thermal growth data (or if the machine behaves differently than expected), Orbit Line recommends calculating the real thermal growth using a method based on measuring actual temperature changes across the machine structure.

This ensures true on-site accuracy.

How to Calculate Thermal Growth (Practical Method)

  1. Measure temperatures at multiple points:
    • At the base
    • At the foot of the machine
    • Near the bearing housing
    • At shaft centerline level
  2. Record temperature rise from cold to normal operating temperature.
    Use:
    • Infrared thermometer
    • Thermal imaging camera
    • Contact temperature probe
  3. Measure the distance between:
    • The base and shaft centerline
    • The shaft and coupling plane
    • The coupling plane to foot locations
  4. Use a thermal growth calculator or software to compute:
    • Vertical rise
    • Horizontal expansion
    • Foot correction targets

At ORBIT LINE, we use professional software and laser alignment systems capable of inputting thermal growth values for:

  • Pumps
  • Motors
  • Compressors
  • ID/FD Fans
  • Gearboxes
  • Tensioners
  • Turbomachinery

Why Thermal Growth Must Be Considered

Ignoring thermal expansion can lead to:

  • Misalignment developing after startup
  • Excessive vibration
  • Premature bearing wear
  • Mechanical looseness
  • Unstable motor load
  • Increased power consumption

In critical industries like oil & gas, petrochemical, power generation, steel, and cement, this can cause serious operational losses.

Orbit Line technicians always verify thermal behavior as part of our Advanced Shaft Alignment Procedure, following ISO standards.

What If Vertical and Horizontal Growth Happen Together?

Many machines do not expand in only one direction.
Example:

  • Vertical thermal growth: +0.08 mm
  • Horizontal thermal movement: 0.21 mm to the right

To handle this:

  • Use a laser alignment system that supports 4-dimensional thermal input
  • Enter vertical AND horizontal target values
  • Adjust shim and move machine accordingly
  • Validate final alignment with a soft-foot check

Orbit Line’s alignment team can calculate these values accurately on-site.

Thermal Growth Is Real — Let Orbit Line Handle It Professionally

Thermal movement is one of the key reasons machines go out of alignment after startup.
With the right measurements, tools, and expertise, you can ensure long-term reliability.

At ORBIT LINE, we offer:

✔ Precision Laser Shaft Alignment

✔ Thermal Growth Calculation & Analysis

✔ Infrared Thermography for Bearings & Motors

✔ Advanced Vibration Diagnostics

✔ Structural Resonance & Soft Foot Correction

✔ Full Mechanical Health Assessment of Rotating Equipment

Need Help with Shaft Alignment or Thermal Growth?

Orbit Line provides complete on-site support for all industries in Saudi Arabia.
🌐 www.orbitlinetechnologies.com
✉️ admin@orbitlinetechnologies.com

 

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