Onsite quantitative FTIR analysis of water in turbine oil

Significance of the Topic

The presence of water in turbine oil critically influences equipment performance and lifespan. Excess water alters oil viscosity specific gravity and surface tension thus hindering lubrication and protection of mechanical clearances. It also accelerates additive depletion oxidation nitration and varnish formation posing risks to turbine reliability. Real time on site water monitoring enables timely maintenance decisions and prevents premature failures.

Objectives and Study Overview

This study evaluates a compact portable FTIR spectrometer for quantitative on site analysis of water in turbine oil. Two calibration approaches are developed using Beer s Law peak absorbance and partial least squares chemometric modeling. Both methods are benchmarked against standard Karl Fischer titration across water concentrations from low trace levels to over 1000 ppm.

Applied Methodology and Instrumentation

A homogenized used turbine oil matrix was spiked with known water levels and aged before dilution. Water content of calibration standards and unknown samples was determined by Metrohm 756 Karl Fischer coulometric titration. Infrared spectra were acquired on the Agilent 5500t FTIR spectrometer using a liquid cell. Two quantitative models were built

• Beer s Law peak area of the O H stretching region
• Partial least squares model using multiple spectral regions

Main Results and Discussion

Beer s Law calibration for 22–1460 ppm water achieved an R2 of 0.977 in the low ppm range and improved to 0.996 with high level standards with a standard error of ~40 ppm. The PLS model covering 7–1460 ppm yielded R2 of 0.983 and reduced interference from spectral noise and baseline shifts. Validation on 15 unknowns showed both methods agreed closely with Karl Fischer results. The PLS approach provided better accuracy over the full 100–1500 ppm range while the Beer s Law method excelled below 100 ppm. Measurement replicates varied by 30–60 ppm similar to the titration method.

Benefits and Practical Applications

FTIR analysis delivers water content in under two minutes without reagents or extensive sample preparation enabling true on site testing. Results are more reproducible since they avoid sample transport delays and evaporation bias. Rapid alerts at warning thresholds (100 ppm) and critical levels (200 ppm) support proactive maintenance. The method also integrates additive depletion and oxidation nitration analysis in a single portable instrument.

Future Trends and Opportunities

A novel water stabilizer technique implemented in Agilent 4500 and 5500 instruments further enhances measurement accuracy robustness and applicability across diverse oil formulations. Future developments may include real time field sensors data integration into condition monitoring platforms and expanded chemometric models for comprehensive oil quality profiling.

Conclusion

The Agilent 5500t FTIR spectrometer provides a reliable rapid and reagent free alternative to Karl Fischer titration for on site water analysis in turbine oil. It enables precise monitoring of critical moisture levels that impact turbine efficiency and maintenance scheduling.

Reference

• Frank Higgins Agilent Technologies Application Note 5990 7806EN published June 2013