Why should shaft alignment be verified at operating temperature and load?

• A. Room temperature checks are sufficient.
• B. Only visual inspection is needed.
• C. Runout is not affected by temperature.
• D. Thermal expansion during operation can introduce misalignment that must be verified under operating conditions.

Answer: (D)

The main idea is that shaft alignment must reflect the conditions the equipment operates under. When the system is running, parts heat up and expand, and the shafts, couplings, bearings, and housings don’t stay in the same positions as they do at room temperature. This thermal growth, along with deflections caused by the load and dynamic forces during operation, can shift the centers and angles of the shafts. If you set alignment at room temperature, you’re optimizing for a state that won’t exist once the machine is hot and loaded, which can lead to vibrations, uneven bearing wear, and seal problems.

That’s why verifying alignment under operating temperature and load is the best approach. It captures the real geometry the shafts adopt in service, so you can make an adjustment that remains correct when the machine runs hot and under normal operating stresses.

Room-temperature checks won’t account for thermal expansion or the deflection that happens with load. Visual inspection alone can miss subtle misalignments or shifts that don’t show up as obvious gaps or contact. And runout measurements taken in a cold state don’t guarantee the alignment will stay correct when the machine is hot, since temperature, bearing condition, and loading can all change the relationship between the coupled shafts.