Vibration Analysis

All electro-mechanical machinery vibrates due to normal system operation, minor defects and manufacturing variations. All machinery will have some vibration considered normal or inherent. As machine components wear, vibration levels increase.

Vibration analysis starts with converting machinery vibration collected during normal operation to an electrical signal using an accelerometer. Using hardware, software or both, these electrical signals are converted to vibration signatures ready for analysis.

Vibration analysis is the cornerstone discipline of most PdM programs because minimal investment pays large returns overall minimal time. Also, vibration analysis identifies the most potential failures modes for the majority of a manufacturing organizations high value, high risk assets. Vibration analysis is often used in conjunction with oil analysis.

Infrared Thermography

While rotating equipment dissipate energy through vibration, not all critical assets rotate. Examples include motor control centers, electrical control systems, substations, and furnaces. In these cases, infrared thermography studies measure variations in energy (heat) emissions to identify potential failure modes. This non-destructive test is very effective for identifying electrical problems and structural issues.

While infrared thermography can also identify some of the problems identifiable using vibration analysis, these studies usually take more time and are less effective at identifying problems that degrade over time. Leading PdM programs focus resources by using vibration analysis for rotating electro-mechanical machinery and infrared thermography for non-rotating electrical or structural systems.

Oil Analysis

Lubrication is critical to all electro-mechanical machinery, and insufficient or excessive lubrication are two of the most common asset failure modes. Analyzing oil and grease lubrication provides information on particle wear and fluid contaminants. Common tests include spectrographics, total solids breakdown, % water, viscosity, pH levels. Some oil analysis programs include specialty tests for problems common to a particular application.

For some types of assets and industries, oil analysis can provide the most ROI over time because of the criticality of lubrication. Oil analysis is often used in conjunction with vibration analysis.

Ultrasonic Testing

Ultrasonic testing is a non-destructive test using high-frequency energy from sound waves. There are two principle applications of ultrasonic testing: (1) material characterization and (2) leak detection.

With material characterization studies, a pulse is introduced to a material and the pulse is received via either reflection or attenuation. With reflection, the pulse is received by the device transmitting the pulse. With attenuation, a separate receiver is used to receive the pulse. Both methods offer significant advantages and disadvantages depending upon the application. Material characterization studies are often used to identify flaws in structures or pressure vessels.

Leak detection testing uses a “listening” device capable of receiving high-frequency sound energy undetectable to the human ear. Small leaks in pressure and vacuum systems potentially represent significant problems. As the leak moves from a high pressure area to a low pressure area, energy is also emitted as a sound and is therefore detectable.

Material characterization studies require highly skilled and certified individuals because of the complexity of the work. These studies are often very expensive to conduct, but may be warranted given potential risks and ROI.

Leak detection testing is a common discipline used within a PdM program. These studies are less expensive to conduct and offer significant potential ROI depending upon the industry and production environment. Ultrasonic leak detection studies are often conducted in conjunction with infrared thermography testing.

Motor Testing

Unlike the previous tests, motor testing is performed offline and by definition, is considered a destructive test. Using a winding tester, current is applied to the windings of an electric motor up to a percentage of the recommended voltage and the voltage loss is measured. Several standards exist for conducting motor testing, but IEEE 95-2002 and IEEE 43-2000 are two commonly used.

If performed correctly on a good motor, the motor is unharmed. Error-proofing techniques make it impossible for technicians to damage good motors during the testing. However, this test may result in additional damage to the motor if the motor is already in a damaged state.

Other PdM Technologies

The disciplines described above are the most common PdM disciplines used across the major industries, but others are also used based on industry and application. Examples include radiographic (X-ray) testing, electromagnetic testing, finite element modeling and analysis and design of experiment (DOE) studies using maintenance data.