Optimizing Shaft Alignment: Addressing Thermal Growth for Enhanced Machinery Performance

Introduction

Precision shaft alignment is a cornerstone of effective rotating equipment maintenance, directly impacting machinery efficiency, reliability, and longevity. A frequently overlooked yet crucial factor in alignment is thermal growth—the expansion of machine components due to operational heat. Failure to consider thermal growth can result in excessive vibration, premature bearing failures, and even catastrophic equipment breakdowns.

This article explores the fundamentals of thermal growth in shaft alignment, its impact on machinery, and best practices for compensation in industrial applications.

Understanding Thermal Growth

Thermal growth refers to the expansion of machine components as temperatures rise during operation. This occurs because materials, particularly metals, expand when heated. The extent of expansion depends on the material’s coefficient of thermal expansion (CTE) and the temperature increase experienced during operation.

For rotating equipment such as pumps, turbines, compressors, and motors, thermal growth is a critical consideration. As these machines heat up, their shafts, housings, and other components expand at different rates, leading to misalignment—even if initial alignment was perfect at ambient temperature. This makes "cold alignment" insufficient unless thermal growth is properly accounted for.

The Impact of Temperature on Machinery Alignment

During startup and continuous operation, temperature changes cause expansion in key machine components, including shafts, bearings, and casings. For example, in a pump-motor system, the pump casing and motor may heat at different rates, and the shaft itself may elongate depending on the material and temperature rise.

Industrial equipment typically operates within a temperature range of 30°C (86°F) to over 150°C (302°F), depending on load and operating conditions. Even small differences in CTE between materials can cause significant misalignment if not properly addressed.

Calculating Thermal Growth

The expansion of a material can be determined using the formula:

where:

• L = Original length of the component [mm]
• CTE = Coefficient of thermal expansion [/°C]
• ΔT = Temperature change [C]

For example, a 500 mm steel shaft (CTE = 12 × 10?? mm/mm/°C) experiencing a 40°C rise expands by:

While this may seem minor, in precision machinery, even sub-millimeter misalignment can cause severe operational issues.

Types of Misalignment Due to Thermal Growth

Thermal growth results in three primary misalignment types:

• Angular Misalignment: Shafts become misaligned at an angle due to unequal expansion across machine components.
• Parallel Misalignment: Both shafts expand linearly but at different rates, leading to horizontal or vertical displacement.
• Combination Misalignment: Most real-world cases involve a mix of both angular and parallel misalignment.

Industries such as power generation, refineries, and petrochemical plants often deal with high temperatures, where ignoring thermal growth can lead to:

• Increased vibration and operational instability
• Accelerated bearing wear
• Seal failures and fluid contamination
• Coupling damage and efficiency losses

Strategies for Compensating Thermal Growth

To ensure proper alignment under operational conditions, the following strategies are recommended:

1. Cold Alignment with Offset

One of the most effective methods involves intentional misalignment during the cold state, allowing for expected expansion. For example, if a pump is predicted to rise by 0.5 mm due to thermal growth, it is aligned 0.5 mm below the motor at ambient temperature.

2. Utilizing Thermal Growth Data

Modern laser alignment tools can predict thermal growth by analyzing machine parameters, material properties, and temperature changes, recommending precise alignment offsets.

3. Precision Shimming

For vertical expansion, shims can be placed under machine feet to counteract expected growth. The correct shim thickness is calculated based on anticipated expansion values.

4. Real-Time Monitoring

In critical applications, LIVE TREND Feature from Pruftechnik Rotalign is a great tool to measure in real time

Case Study: Pump-Motor Alignment in a Refinery

A high-pressure feed pump in a refinery experienced excessive vibration and premature bearing wear post-startup, despite precise cold alignment. Investigation revealed significant vertical thermal growth due to heat transfer from process fluids. The steam turbine driving the pump expanded at a different rate, creating misalignment.

By calculating the expected thermal growth (1.2 mm vertical expansion) and adjusting the cold alignment accordingly, vibration levels dropped significantly, and bearing lifespan improved, leading to reduced downtime and maintenance costs.

Note In EX enviroment a EX certified device is mandatory!

Conclusion

Thermal growth is an unavoidable factor in rotating machinery, but proactive alignment strategies can mitigate its negative effects. By understanding material expansion, using advanced alignment techniques, and leveraging modern monitoring tools, maintenance professionals can enhance equipment reliability and efficiency.

For industries operating in high-temperature environments, addressing thermal growth in routine maintenance can prevent costly failures and extend equipment lifespan, ensuring optimal performance under demanding conditions.