Significance and Use
5.1 This practice is intended for the application of online, full-flow, or slip-stream sampling of wear debris via inductive sensors for gearbox and drivetrain applications.
5.2 Periodic sampling and analysis of lubricants have long been used as a means to determine overall machinery health. The implementation of smaller oil filter pore sizes for machinery has reduced the effectiveness of sampled oil analysis for determining abnormal wear prior to severe damage. In addition, sampled oil analysis for equipment that is remote or otherwise difficult to monitor or access is not always sufficient or practical. For these machinery systems, in-line wear debris sensors can be very useful to provide real-time and near-real-time condition monitoring data.
5.3 Online inductive debris sensors have demonstrated the capability to detect and quantify both ferromagnetic and non-ferromagnetic metallic wear debris (1, 2). These sensors record metallic wear debris according to size, count, and type (ferromagnetic or non-ferromagnetic). Sensors can be fitted to virtually any lubricating system. The sensors are particularly effective for the protection of rolling element bearings and gears in critical machine applications. Bearings are key elements in machines since their failure often leads to significant secondary damage that can adversely affect safety, operational availability, operational/maintenance costs, or combinations thereof.
5.4 The key advantage of online metallic debris sensors is the ability to detect early bearing and gear damage and to quantify the severity of damage and rate of progression toward failure. Sensor capabilities are summarized as follows:
5.4.1 Can detect both ferromagnetic and non-ferromagnetic metallic wear debris.
5.4.2 Can detect 95 % or more of metallic wear debris above some minimum particle size threshold.
5.4.3 Can count and size wear debris detected.
5.4.4 Can provide total mass loss.
Note 1: Mass is an inferred value which assumes the debris is spherical and made of a specific grade of steel.
5.4.5 Can provide algorithms for RUL warnings and limits.
5.5 Fig. 1 (5) presents a widely used diagram to describe the progress of metallic wear debris release from normal to catastrophic failure. This figure summarizes metallic wear debris observations from all the different wear modes that can range from polishing, rubbing, abrasion, adhesion, grinding, scoring, pitting, spalling, and so forth. As mentioned in numerous references (6-12), the predominant failure mode of rolling element bearings is spalling or macro pitting. When a bearing spalls, the contact stresses increase and cause more fatigue cracks to form within the bearing subsurface material. The propagation of existing subsurface cracks and creation of new subsurface cracks causes ongoing deterioration of the material that causes it to become a roughened contact surface as illustrated in Fig. 2. This deterioration process produces large numbers of metallic wear debris with a typical size range from 40 μm to 1000 μm or greater. Thus, rotating machines, such as wind turbine gearboxes, which contain rolling element bearings and gears made from hard steel, tend to produce this kind of large metallic wear debris that eventually leads to failure of the machines.
5.6 Online wear debris monitoring provides a more reliable and timely indication of bearing distress for a number of reasons.
5.6.1 Firstly, bearing failures on rotating machines tend to occur as events often without sufficient warning and could be missed by means of only periodic inspections or data sampling observations.
5.6.2 Secondly, because larger wear metallic debris particles are being detected, there is a lower probability of false indication from the normal rubbing wear that will be associated with smaller particles. And because wear metal debris particles are larger than the filter media, detections are time correlated to wear events and not obscured by unfiltered small particles.
5.6.3 Thirdly, build or residual debris, from manufacturing or maintenance actions, can be differentiated from actual damage debris because the cumulative debris counts recorded due to the former tend to decrease, while those due to the latter tend to increase.
5.6.4 Fourthly, bearing failure tests have shown that wear debris size distribution is independent of bearing size (2, 3, 6, 12, 13).
Scope
1.1 This practice covers the minimum requirements for an online inductive sensor system to monitor ferromagnetic and non-ferromagnetic metallic wear debris present in in-service lubricating fluids residing in gearboxes and drivetrains.
1.2 Metallic wear debris considered in this practice can range in size from 40 μm to greater than 1000 μm of equivalent spherical diameter (ESD).
1.3 This practice is suitable for use with the following lubricants: industrial gear oils, petroleum crankcase oils, polyalkylene glycol, polyol esters, and phosphate esters.
1.4 This practice is for metallic wear debris detection, not oil cleanliness.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5.1 Exception—Subsection 7.7 uses “G’s”.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
