Oil analysis stands as a cornerstone in the arsenal of tools for monitoring and ensuring the reliability of rotary screw air compressors. This practice not only saves costs but also optimizes oil change intervals, detects potential issues early on, and allows for corrective actions before they escalate into expensive repairs and downtimes.
However, it’s crucial to recognize that not all oil analysis test packages are created equal. Standard industrial oil analysis packages, often provided by oil suppliers at no cost, may fall short in addressing the unique design and challenges of rotary screw air compressors. To truly harness the benefits of oil analysis for compressors, a tailored approach is necessary. Following are seven essential variables that must be considered for effective oil analysis in rotary screw air compressors.
Viscosity:
Viscosity, a measure of oil’s resistance to flow, holds paramount importance in compressor oil analysis. Deviations in viscosity can signify potential issues such as reduced flow, heightened friction, and elevated operating temperatures. Monitoring viscosity allows for early detection of varnish formation, particularly in oils prone to varnish due to their composition. By identifying abnormal viscosity changes—either a significant increase (>20%) or decrease—prompt investigations and interventions can prevent costly complications.
Acid Number (AN):
The acid number (AN) or total acid number (TAN) serves as a key indicator of oil’s oxidative state and remaining useful life. Employing the ASTM D664 “potentiometric” test method ensures accuracy and repeatability compared to the ASTM D974 “colorimetric” test, which is less reliable. While AN offers insights into oxidation levels, it’s vital to supplement it with additional acid tests like pH or Strong Acid Number (SAN). This comprehensive approach guards against corrosive threats posed by ingested acid-gas contaminants, ensuring a more accurate assessment of oil condition and safety for compressor operation.
pH and SAN:
Distinct from AN, pH and SAN tests are tailored to detect strong acids in compressor oils, originating from acid-gas contaminants in the air. Monitoring pH and SAN values provides early warnings of corrosive conditions, especially in environments with elevated levels of acid-gas contaminants. In such settings, these indicators reach critical changepoints—pH of 4.5 and SAN of 1.0—before AN, highlighting the need for a multifaceted approach to oil analysis.
Water Content:
Water contamination, omnipresent in compressor oils, poses significant risks ranging from reduced lubrication to accelerated additive depletion. Routine testing, employing methods like the “Crackle” or Karl Fisher (KF) tests, enables timely detection of excessive water levels. Addressing underlying causes such as inadequate cooling or faulty condensate drains mitigates water-related issues, emphasizing the importance of targeted interventions over premature oil changes.
Spectrochemical or Elemental Analysis:
Spectrochemical analysis delves into metallic element concentrations in oil, providing insights into wear, contaminants, and additives. While wear metals like iron, chromium, and molybdenum warrant scrutiny, correlations with other oil properties enhance diagnostic capabilities. For instance, spikes in contaminant metal boron may signify external contamination from sources like weedkillers, underscoring the interconnected nature of oil analysis parameters.
ISO Particle Count:
ISO particle count serves as a gauge of oil cleanliness, vital for prolonging component longevity. The choice between Laser Light Scattering and Pore Blockage methods hinges on factors such as oil color and entrained air or water. In environments prone to solid contaminant ingress, prioritizing ISO particle count testing aids in identifying contamination sources and optimizing maintenance strategies.
Direct Reading (DR) Ferrography:
For users suspecting bearing wear or corrosion, DR Ferrography offers a comprehensive assessment of ferromagnetic debris. By quantifying particle sizes and ratios, this test provides insights into wear severity and corrosion activity, guiding targeted maintenance interventions.
In summary, oil analysis emerges as an indispensable cost-cutting tool for rotary screw air compressors. Tailoring test packages to compressor-specific needs ensures accurate assessments and informed decision-making. Embracing a holistic approach to oil analysis, encompassing key parameters and supplementary tests, empowers reliability engineers to maximize equipment uptime and mitigate maintenance costs effectively.