Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


cross-validation calibrations with SD’s of 0.17 and 0.26 mg KOH/g for AN and BN, respectively, recognizing that the FTIRAN/BN methods are limited by the reproducibility of the corresponding ASTM reference methods used as well as how rigorously they are executed.


Operational Performance


Prior to application of this new technology to customer samples, the FTIRAN/BN


methods were extensively validated. Precision,


specificity, linearity/range and accuracy (with respect to the ASTM methods) were all determined. The method detection limit was calculated and QC limits established for all QC sample types (blanks, duplicates, high and low). After set-up and shake out runs to train operators and optimize sample handling and flow, the COAT® system was placed in the production mode and its performance assessed over a period of 6 months by randomly analyzing selected operational samples by both FTIR and ASTM methods. For AN, and BN, 177 and 284 new and used oil samples were analyzed, respectively, the former including oil from hydraulic systems, gear boxes, transmissions, engines, turbines and compressors while for the later diesel and natural gas-fueled samples predominated. Figures 2 and 3 are histograms of the differences between the individual ASTM and FTIR results for AN and BN.


What is noteworthy is that the analytical differences between the ASTM and FTIR methods are normally distributed in both cases, each having an overall mean difference close to zero with a variability reflecting that of the ASTM reference methods. These production sample results clearly indicate that the FTIRAN/BN methods produce ASTM-identical results on average, reflecting the type of data one would normally obtain had one only used the ASTM procedure.


28 LUBE MAGAZINE NO.127 JUNE 2015


Ultimately, sample preparation itself simply consists of adding well-mixed oil to a vial using a calibrated syringe, dispensing the reagent by re-pipette, capping, vortexing, de-capping and loading the vials into the autosampler. COAT UMPIRE software controls the autosampler, pump and spectrometer, makes the spectral measurements, converts the spectral data to mg KOH/g oil which is transferred to the Laboratory Information and Management System (LIMS); typically at a rate of ~1 min/sample. A wide range of mineral oils were assessed with calibrations devised to determine if oil sub-classifications were required, e.g., based on oil type (i.e., hydraulic vs compressor) or fuel type (i.e., diesel vs natural gas). For BN, the bulk of the samples were in-service engine oils representing a wide range of equipment applications (mining, transport, generators, marine etc.) with ~70% using diesel fuel and the balance natural gas. The majority of these oils were SAE Grade 40 and 15W40 oils, but extended to most other common grades with almost all major lubricant suppliers represented. In the case of AN, a mix of new and in-service oils covering a wide range of suppliers and grades were considered, including oils from engines, compressors, hydraulic systems, turbines transmissions and gear boxes. From the calibration development studies, it was determined that one well devised general calibration was adequate for each of AN or BN for all mineral oils, regardless of their quality or soot levels. Figure 1 is illustrative of a typical leave-one-out cross-validation FTIR BN calibration obtained for ASTM D664 (HCl). Highly linear relationships were obtained for the FTIRAN/ BN


No.98 page 3


Figures 3 and 4. Comparative analytical test result distributions of differences between ASTM and FTIR results obtained for random operational samples for AN and BN, respectively.


Advantages and Benefits Based on our comprehensive in-house assessment, the COAT system has proved itself of being able to produce ASTM-identical data. From an operational standpoint, one FTIR is roughly equivalent to ~9-10 titrators, assuming strict ASTM protocols are followed. Table 1 summarizes and compares the key operational variables of the two analytical methods, the advantage clearly being in favor of the FTIR system. As currently configured at Fluid Life, one analyst can analyze ~500 samples per 8 hour shift, a substantial throughput advantage.


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