Free Engineering Tool
Thermal Growth Compensation for Shaft Alignment
Calculate vertical centerline growth due to thermal expansion for driver and driven machines. Determine the cold alignment pre-offset target to achieve alignment at operating temperature.
Results
Thermal Growth Formula
When a machine heats up, its frame expands vertically, raising the shaft centerline:
- H — foot-to-centerline height (mm)
- α — coefficient of thermal expansion (×10⁻⁶ /°C)
- Top — operating temperature (°C)
- Tamb — ambient temperature (°C)
Material CTE Values
| Material | α (×10⁻⁶ /°C) |
|---|---|
| Carbon Steel | 12.0 |
| Cast Iron | 10.5 |
| Stainless Steel (304/316) | 16.0 |
| Aluminum | 23.0 |
Typical Operating Temperatures
| Machine Type | Typical Casing Temp (°C) |
|---|---|
| Electric Motor | 60 – 90 |
| Centrifugal Pump (cold water) | 40 – 70 |
| Steam Turbine | 80 – 200 |
| Gearbox | 50 – 80 |
| Compressor | 60 – 120 |
Practical Example
Given: Ambient = 20°C
Motor: H = 200 mm, Steel (α = 12×10⁻⁶), Top = 80°C
Pump: H = 250 mm, Steel (α = 12×10⁻⁶), Top = 60°C
ΔHmotor = 200 × 12×10⁻⁶ × (80 − 20) = 0.144 mm
ΔHpump = 250 × 12×10⁻⁶ × (60 − 20) = 0.120 mm
Difference = 0.144 − 0.120 = 0.024 mm
The motor grows more → set motor 0.024 mm LOW during cold alignment.
💡 Tip: The machine that grows more should be set LOW at cold alignment. When both heat up, the differential growth brings them into alignment.
⚠️ Note: This calculation assumes uniform thermal expansion of the machine frame. In practice, thermal gradients, piping strain, and foundation effects may cause additional movements. Always verify with a hot alignment check when possible.
Thermal growth is the vertical expansion of a machine's shaft centerline height as the machine heats up from ambient to operating temperature. All materials expand when heated, and for rotating machinery this means the shaft centerline rises.
The growth is calculated as: ΔH = H × α × (Top − Tamb), where H is the foot-to-centerline height, α is the coefficient of thermal expansion, and the temperatures are in °C.
Machines are aligned when cold (not running) but operate when hot. If the driver and driven machines grow by different amounts vertically, perfect cold alignment will result in misalignment at operating temperature.
By intentionally offsetting the cold alignment by the expected differential growth, the machines come into proper alignment when they reach operating temperature. The machine that grows more is set low during cold alignment.
Operating temperatures can be measured on running equipment using:
- Infrared thermometer — quick non-contact measurement at machine feet or bearing housings
- Contact thermocouple probes — more accurate surface temperature
- RTDs/thermocouples — permanently installed sensors
Measure at the machine feet or base, not at the top of the casing, as this best represents the temperature affecting vertical growth. Allow the machine to reach thermal steady state (typically 2–4 hours).
Typical casing/foot temperatures for common machines:
- Electric motors: 60–90°C (depending on frame size and load)
- Centrifugal pumps: 40–70°C (cold water), up to 200°C+ (hot process)
- Steam turbines: 80–200°C
- Gearboxes: 50–80°C
- Compressors: 60–120°C
These are approximate values. Always measure on the actual equipment when possible.
A hot alignment check is performed immediately after shutting down equipment that has been running at normal operating temperature. The alignment is measured before significant cooling occurs (typically within 15–30 minutes of shutdown).
This check verifies whether:
- The calculated thermal growth predictions were accurate
- The cold pre-offset was correct
- Other factors (piping strain, foundation movement) are affecting alignment
A hot check is the gold standard for validating alignment and should be performed whenever practical, especially on critical machinery.
The procedures described on this page were developed and field-tested by the Vibromera team using the Balanset-1A, a portable dual-channel balancer and vibration analyzer for on-site rotor balancing.
Professional laser alignment and vibration analysis instruments. Achieve precision alignment with thermal growth compensation on-site. Used in 50+ countries.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
