Abrasive media

Particles in the sealing gap

Particle-contaminated media or abrasion, such as crude oil (refineries), sand contamination (dredgers) or remnants of wear parts can damage the mechanical seal. These damaging events caused by particles were also investigated in the BestSens AG test laboratory on the pump test bench.

In order to clearly detect later deviations, the pump was operated without particles in the first phase of the measurements and the seal was in “good condition” during this phase (Figure 1). After about three days, boron nitride[1] was added in the next phase of the test as an abrasive medium to intentionally damage the sliding surfaces.

During operation, the suspension of water and boron nitride gets between the sliding surfaces after a short time and thus causes artificially induced damage due to drastically increased wear of the mechanical seal. The BestSens system recognizes the change in the lubricating film immediately, which is reflected in the increased ‘Reciprocal Variation’ characteristic value. The ‘Reciprocal Variation’ is a specially calculated parameter of the SAW[2] (Surface Acoustic Waves) and roughly summarizes the shift in the running time of individual shaft packages depending on the condition of the lubricating film.

Leakage at the damaged seal reduced the amount of water, which after a short time led to insufficient lubrication and subsequent dry running of the mechanical seal. The boron nitride was then removed again by cleaning twice. The worn seal was operated over the next few days with insufficient lubrication until it ran dry.

Figure: Acoustic characteristic value shows the start of abrasion on the sensorized mechanical seal

Recognize sealing problems during operation

Damaging events and wear can be detected in the measurement data using these acoustic measurement variables. The tests on the test bench show a simplified picture of the processes in the field, but already underline that the measurement can be used to identify sealing problems in the running application.

BestSens AG specializes in ultrasound-based monitoring of mechanical seals and other rotating components in order to detect and indicate wear and anomalies early on in the process. This reduces unplanned downtimes, optimizes maintenance costs and increases plant safety. By integrating a multi-sensor into the mechanical seal and using the BeMoS measuring system, online condition monitoring is possible at any time.

[1] Boron nitride powder; used for lapping sealing surfaces
[2] SAW: Surface Acoustic Waves