What is thermal growth in shaft alignment?

Thermal growth is the vertical expansion of a machine's centerline height as it heats up from ambient to operating temperature. The formula is ΔH = H × α × ΔT, where H is foot-to-centerline height, α is the coefficient of thermal expansion, and ΔT is the temperature rise.

Why pre-offset cold alignment?

Machines are aligned cold but run hot. If both machines grow by different amounts, perfect cold alignment results in misalignment at operating temperature. Pre-offsetting the cold alignment by the expected differential growth ensures alignment when hot.

How do I determine operating temperature?

Operating temperatures can be measured on running equipment using infrared thermometers or contact probes at the bearing housing or machine feet. Typical values: electric motors 60–90°C, pumps 40–70°C (process dependent), steam turbines 80–200°C.

What are typical temperatures for motors and pumps?

Electric motors typically operate at 60–90°C at the casing. Centrifugal pumps range from 40–70°C for cold water service, but can be much higher for hot process fluids. Steam turbines may reach 150–300°C. Gearboxes typically operate at 50–80°C.

What is a hot alignment check?

A hot alignment check is performed while the machine is at operating temperature (immediately after shutdown). It verifies that the thermal growth predictions were correct and the machines are aligned under actual operating conditions. This is the gold standard for validating alignment.

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.

Driver + Driven ΔH = H × α × ΔT Cold Offset Target

Ambient Temperature (°C)

Enter data for both machines below. The difference determines the cold pre-offset.

Driver (e.g. Motor)

Machine Type

Material

Foot-to-Centerline Height H (mm)

Operating Temperature (°C)

Driven (e.g. Pump)

Machine Type

Material

Foot-to-Centerline Height H (mm)

Operating Temperature (°C)

Quick presets

Results

Cold Pre-Offset Target (Differential Growth)

—

Driver Thermal Growth

—

Driven Thermal Growth

—

Driver ΔT

—

Driven ΔT

—

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)
T_op — operating temperature (°C)
T_amb — 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

Example — Motor + Pump Train

Given: Ambient = 20°C

Motor: H = 200 mm, Steel (α = 12×10⁻⁶), T_op = 80°C

Pump: H = 250 mm, Steel (α = 12×10⁻⁶), T_op = 60°C

ΔH_motor = 200 × 12×10⁻⁶ × (80 − 20) = 0.144 mm

ΔH_pump = 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 Compensation Calculator | Vibromera

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026