May 2021

Valves, Pumps and Turbomachinery

Use infrared thermal imaging for pump system condition monitoring and early failure detection

Thermal imaging technology has evolved over the years, and investment costs have decreased significantly.

Thermal imaging technology has evolved over the years, and investment costs have decreased significantly. Early deployment of thermal imaging technology in industrial applications was primarily geared towards electrical inspections. In recent years, these thermal imaging cameras have been successfully implemented for mechanical inspections, including rotating equipment. Typical applications for thermal imaging fall under three main categories outlined here:

  • Electrical
  • Process/mechanical equipment
  • Building inspections.

Mechanical equipment inspections, specifically for centrifugal pumps, will be the main focus of this article. Typical thermal imaging applications for pumps will be presented, including a specific case example showing an interesting case study that resulted in the identification of severe throttling/leakage across a multi-stage pump center-stage bushing.

TYPICAL INSPECTION METHODOLOGIES

Three main methodologies should be considered when implementing thermal imaging inspections as outlined here. The method applied depends on the equipment being inspected and the type of data required:

  • Baseline
  • Comparative
  • Thermal trending.

Baseline method

Baseline inspection establishes a reference point of equipment operating under normal conditions and in good working order. The field of view (FOV) of the thermal camera may dictate taking several images to capture all components. For pump applications, it is advisable to take an image of the entire pump, including the entire casing, bearing housing(s) and mechanical seal support systems, including flush lines, heat exchangers, cyclone separators, etc.

Comparative method

Comparative inspection compares similar components operating under similar conditions to analyze the condition of the equipment being tested. When this method is applied correctly, the comparative difference will be indicative of the condition. For pump applications, an example could be several pumps operating in parallel with individual minimum flow recycle valves. A comparative analysis of all recycle valves can identify a possible passing condition of one or more of the recycle valves.

Thermal trending method

This method is used to compare temperature distributions of the same component over a period of time. This method works well for inspecting mechanical equipment when normal thermal signatures are complex. In these cases, thermal signatures indicate failure slowly, such as electrical components, valve leakage, seal flush line blockage or fouling, etc.

PUMPING SYSTEM PRACTICAL APPLICATIONS

The following outlines typical thermal imaging applications related to pumping systems:

  • Pump and driver bearing housings to baseline, and detecting early bearing failure or oil and cooling system inadequacies
  • Pump recycle and discharge check valve passing conditions
  • Mechanical seal support systems, including flush lines, heat exchangers, cyclone separators and seal glands
  • Pump casings to detect center-stage throttle bushing distress.

Mechanical seal support system

A thermal signature of a mechanical seal API Plan 21 seal flush system, including the heat exchangers, is shown in FIG. 1. Thermal imaging identified high skin temperatures on the heat exchanger shells resulting from fouling of the water side of the cooler.

FIG. 1. An API Plan 21 seal support system with fouled exchanger.
FIG. 1. An API Plan 21 seal support system with fouled exchanger.

FIG. 2 shows a thermal signature of an API Plan 11 seal flush line, which showed significant temperature difference (~26°F) between the take-off point and the downstream seal flush line. Periodic thermal scanning can quickly identify plugged seal flush lines, which can result in early mechanical seal failure.

FIG. 2. A plugged API Plan 11 flush connection.
FIG. 2. A plugged API Plan 11 flush connection.

Pump recycle valve passing condition

FIG. 3 shows a thermal signature of a boiler feedwater pump recycle valve, where the temperature profile across the valve clearly indicates a passing condition. As shown, the recycle line downstream of the recycle valve is similar to the process fluid temperature.

FIG. 3. Thermal signature of recycle valve passing condition.
FIG. 3. Thermal signature of recycle valve passing condition.

Multi-stage pump center-stage bushing failure

A typical axially split, multi-stage, opposed impeller design pump is shown in FIG. 4. The opposed impeller design is used by pump designers to balance axial thrust forces, and requires a center-stage bushing to isolate the higher pressure from the crossover stages.

FIG. 4. Multi-stage, axially-split, opposed impeller pump.
FIG. 4. Multi-stage, axially-split, opposed impeller pump.

FIG. 5 shows a 12th-stage, opposed impeller design with the center-stage bushing to isolate the 12th stage from the 6th stage. This center-stage bushing arrangement is designed for controlled throttling of this high differential pressure across the bushing, as well as for hydrodynamic support of the rotor.

FIG. 5. A 12-stage, opposed impeller with center-stage bushing.
FIG. 5. A 12-stage, opposed impeller with center-stage bushing.

The subject-produced water injection pumps were critical to plant operations and, therefore, were tested annually to monitor and trend performance. Part of this testing included thermal imaging checks compared to baseline thermal signatures to identify any anomalies for early detection of failures.

A baseline thermal signature under normal conditions (FIG. 6) shows a uniform casing temperature across the pump with no more than 1°F (0.8°F) difference.

FIG. 6. Baseline signature with uniform casing temperature.
FIG. 6. Baseline signature with uniform casing temperature.

During subsequent tests, operations began to complain about a decrease in injection flowrate for this particular pump. This was confirmed during the performance testing, which indicated a significant amount of total dynamic head (TDH) deterioration (~6%). When the thermal imaging was conducted on the pump casing and compared to the baseline image, a significant temperature gradient was noticed across the center-stage bushing. The pump casing was now showing a temperature difference of ~4°F across the center-stage bushing (FIG. 7).

FIG. 7. Thermal signature with casing temperature anomaly.
FIG. 7. Thermal signature with casing temperature anomaly.

FIG. 8 shows the same casing thermal image with a high-resolution temperature palette applied, which clearly shows the temperature difference on both sides of the center-stage bushing.

FIG. 8. Casing anomaly with high-resolution palette.
FIG. 8. Casing anomaly with high-resolution palette.

FIG. 9 shows the results of the inspection of center-stage bushing, showing the significant erosion damage. This was confirmation of the identified anomaly detected with the thermal imaging.

Fig. 9. Center-stage bushing and case split-line damage.
Fig. 9. Center-stage bushing and case split-line damage.

Takeaway

Based on the casing thermal signature anomaly and the measured head deterioration, it was suspected that the center-stage bushing running clearance may have increased, resulting in excessive leakage across the bushing. With this condition, a temperature rise will occur due to the Joule-Thomson Effect. The temperature increase of the fluid leaking from 12th-stage discharge back to 6th-stage crossover resulted in the observed casing temperature profile. Based on these findings, it was recommended to inspect and overhaul this pump at the next opportunity.

Upon internal inspection, the center-stage distress was confirmed. The loss of center-stage bushing clearance, and subsequent excessive leakage rate, resulted in significant casing split-line damage from high-velocity cutting. Internal inspection also confirmed the presence of an abnormal amount of abrasive material, which was determined to be the root cause of the loss of running clearances.

The cost of thermal imaging equipment has become more economically attractive for maintenance and reliability professionals. Using thermal imaging for condition monitoring of pumps and other rotating equipment can identify thermal anomalies and provide early detection of pending failures.

The aforementioned case studies are good examples of how these techniques can be applied to pump condition monitoring. The case studies resulted in not only early detection of failures, but also can be used to identify energy savings potential, as with the case of passing pump recycle valves.

Many of the common pitfalls of using infrared devices, such as emissivity and other issues, were not addressed here. A slight learning curve exists for effective measurement and analysis.

Training and certification courses are readily available to maximize any return on investment of this technology. As with all field related activities, safety should come first. Thermal imaging in the field can inhibit the ability to keep “eyes on path,” which can result in potential slips, trips and falls. HP

The Authors

Related Articles

From the Archive

Comments

Comments

{{ error }}
{{ comment.comment.Name }} • {{ comment.timeAgo }}
{{ comment.comment.Text }}