method is usually in the form of static data. Thermocouples or resistance temperature devices (RTDs) are often inserted either into a fluid stream or on or below metal surfaces to measure temperature. Portable infrared temperature guns can also be used to monitor machine surface temperatures. In some applications, thermography is employed to visualize temperature distributions across a machine in order to identify component issues such as failing bearings. Thermography has been successfully used to spot electrical problems in the field on motors and control panels.
•Oil analysis—Oil analysis requires that oil samples be sent off-site for lab testing. This step can lead to a delay in prompt information. Although most oil properties are usually determined by lab testing, some oil properties can be monitored in real time.
•Analysis of piping, duct work, and structural components—Equipment attached to the machine—such as piping, vents, duct work, and supporting structures—can be sources of information; they can path sources for vibrations, flow issues, and loadings.
•Electrical measurements—These measurements are usually in the form of dynamic data because electric power is sinusoidal. Voltage and current waveforms must be analyzed in real time so that they can be converted to real power, root mean square voltage, average current, power factor, etc.
•Performance analysis—The required data for this type of study are static in nature. They are usually taken with temporary or field mounted sensors.
Because there is such diversity in machine designs and applications, we will now provide more specific monitoring recommendations. Below is a listing of the most common process machinery along with recommendations as to what should be monitored and when. Keep in mind these are general recommendations; they should be compared with manufacturer’s guidelines and company best practices.
Monitoring Guidelines for Centrifugal Pumps
Figure 3.1 Typical Centrifugal Pump
Vibration Collection and Analysis: Most centrifugal pump vibration levels are monitored on a periodic basis using “walk around” data collection programs. Assessments are made by placing a vibration sensor, usually an accelerometer, with a magnetic base on the bearing housings. Overall vibration amplitudes are trended to see if any changes are occurring. If a significant change in overall amplitude is observed, a frequency analysis is performed in an attempt to identify the nature of the malady.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Temperature Monitoring: Bearing temperatures can be taken at the same time vibration data is collected. Assessments may be made by using either absolute or relative criteria. For example, you may decide that if a bearing temperature exceeds 200°F (93.3°C), you will shut down (an example of absolute criterion). Or if you see a 20°F (6.7°C) increase in bearing temperature from one inspection to the next, you will investigate (an example of relative analysis criterion).
Inspection frequency: At the same time the vibration data is taken.
Oil Analysis: Oil analyses are typically reserved for critical machines with large oil reservoirs. Therefore, oil analyses are not usually warranted for most small spare pumps with small bearing sumps.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Pressure Pulsation Analysis: This type of analysis is usually performed only when an internal pump issue is suspected or an unwanted pump/piping interaction is occurring. Clues as to when a pressure pulsation analysis is required are excessive piping vibration, broken bolts, high pulsations observed on a pressure gauge, high blade vane pass vibration in the vibration spectra, etc.
Inspection frequency: Only required when issues arise
Piping Vibration: This type of analysis is normally conducted only if piping failures have occurred or if the piping is deemed to be moving excessively. Piping analysis methods are similar to a vibration analysis performed on rotating machinery, except the assessment criteria are quite different.
Inspection frequency: Only required when issues arise
Performance Monitoring: To ensure that all your pumps are performing as advertised, it is important to assess their performance on a periodic basis. A performance analysis involves collecting pump pressures, flow, and horsepower data in order to determine overall efficiency and whether the pump delivers the performance required by the process.
Inspection frequency: Annual performance evaluations are common.
Monitoring Guidelines for Centrifugal Compressors
Figure 3.2 Centrifugal Compressor Rotor
Vibration Collection and Analysis: Due to their criticality, most centrifugal compressors have dedicated vibration monitoring systems consisting of either case-mounted accelerometers or non-contacting proximity probes at each bearing. If a significant change in overall vibration amplitude is reported by the monitoring system, a detailed frequency analysis is performed in an attempt to identify the nature of the malady. Critical monitoring systems usually have capabilities of generating trend plots, spectral comparisons, orbits, and other forms of data trending and presentation.
Inspection frequency: Additional monthly and quarterly inspections are often conducted by a technician to determine if any changes from the baseline have occurred.
Temperature Monitoring: Due to their criticality, centrifugal compressors typically have thermocouples or RTDs embedded in the bearing Babbitt near the location of where the maximum expected bearing temperature would occur. The proper placement of thermocouples and RTDs in the bearing allows accurate and repeatable bearing metal temperature measurements that can better track changing load and lubrication conditions.
Inspection frequency: At the same time the vibration data is taken.
Oil Analysis: Periodic oil analyses are typically performed on centrifugal compressors. These analyses can help detect oil contamination or bearing deterioration issues.
Inspection frequency: Monthly and quarterly inspection intervals are common.
Pressure Pulsation Analysis: These types of analyses are usually not conducted on a centrifugal compressor.
Inspection frequency: Only required when issues arise
Piping Vibration: These types of analyses are usually not conducted on a centrifugal compressor.
Inspection frequency: Only required when issues arise
Performance Monitoring: To insure that a compressor is performing as advertised, it is important to assess its performance on a periodic basis. A performance analysis involves collecting compressor pressures, flow, and horsepower data in order to determine overall efficiency and whether the compressor is delivering the performance required by the process.
Inspection frequency: Annual performance
