Machinery Alignment

A report published by Senseye shed light on the consequences of improper equipment maintenance. Large industrial and manufacturing facilities lose an average of 323 production hours annually due to unplanned downtime (Automation.com, 2021). This downtime may lead to millions of dollars of lost revenue depending on cost.

One of the main contributors to unplanned downtime is improper machinery alignment. There are multiple consequences of misaligned equipment (Luedeking, 2008):

• Premature bearing and seal failure
• Increased power consumption
• Increased vibration

Machinery alignment is an essential practice in industrial facilities. When misaligned, rotating equipment (pumps, turbines, compressors) will not operate efficiently. Increased wear will require corrective maintenance. Instead of performing preventive maintenance as scheduled, premature outages will occur to correct issues.

What is Alignment?

Two coupled shafts are considered to be perfectly aligned when their centerlines are on the same straight line (coaxial) at operating conditions.

Perfect alignment is not realistically obtainable as many forces are occurring during operation that will cause slight misalignment. It is important, however, to align equipment within the tolerances specified by the equipment manufacturer.

Operating conditions can cause properly aligned equipment to become out of tolerance during operation. The following is a list of factors that can affect the alignment of a piece of equipment:

• Movement of equipment relative to each other due to thermal expansion
• Settlement of foundations
• Foundation cracking
• Excessive force placed on equipment by piping stresses
• Expanding grout, rusting of shims, etc.
• Loose anchor bolts

Performing regular equipment inspections and checking for these conditions will minimize the resulting wear.

Types of Misalignment

Misalignment falls into two categories, angular and parallel. Typically, equipment will experience a combination of both angular and parallel misalignment. Both types of misalignments can occur in the horizontal plane, vertical plane, or both. Angular misalignment occurs when the equipment centerlines cross.

Parallel misalignment exists when the centerlines of the two shafts are parallel but not concentric; that is the centerlines do not lie in the same line (plane).

Pre-Alignment Steps

The techniques and methods of checking alignment vary for each piece of equipment depending on installation and the type of coupling used. However, there are standard checks performed that minimize the chance of misalignment during operation. In general, perform the following checks before aligning and coupling equipment:

• Soft Foot: The first step performed before aligning equipment is to check for soft foot. Soft foot is a condition where alignment changes when tightening the base bolt. A typical cause is a poor foundation with cracked cement, cracked grout, or poor structural iron.
• Shaft and Coupling Runout: The second step in alignment is to check for shaft or coupling runout. Runout appears as a misalignment since the centerlines of the shafts or faces of the couplings will move in different planes. A bent shaft or coupling bored off-center will cause runout. Correct these conditions by either straightening the shaft or replacing the coupling with a new one bored correctly.
• Bearing Clearances: Another check should be made for shaft movement in the radial direction. This can be done by placing a block of wood under the shaft and prying up on the shaft with a pry bar to see if there is any movement. Barring the shaft from side to side will also show any movement in that direction. Depending on the type of bearings installed, some movement may be acceptable if it is within tolerance.
• Coupling End Gap: Verify the space between the two shafts is within equipment manufacturers’ and coupling manufacturers’ specifications. This requires that the gap between the coupling halves be within the coupling manufacturer specifications so that the coupling will have the proper engagement between the hub and shroud and sufficient room to allow for thermal expansion and end movement.

What Can You Do?

Understanding the importance of machinery alignment is not enough to ensure all the equipment at your facility runs smoothly. Maintenance procedures and qualification and training programs must be in place. Defining the skills and knowledge for each plant job creates a pathway to success. Providing employees with training and qualification milestones creates a highly proficient workforce. Expert craftsmen armed with detailed and accurate procedures are the surest way to keep equipment running.

References

Automation.com. (June 30, 2021). World’s largest manufacturers lose almost $1 trillion a year to machine failures. ISA. https://www.automation.com/en-us/articles/june-2021/world-largest-manufacturers-lose-almost-1-trillion

Luedeking, A. (July 1, 2008). Why alignment? Power Engineering. https://www.power-eng.com/news/why-alignment/