What are some common oil analysis tests?

Some of the most common oil analysis tests include:

• Viscosity tests
• Particle counting
• Karl Fischer water titration
• Spectroscopy, such as ICP spectroscopy and FTIR

Viscosity tests

A viscosity test determines the kinematic viscosity (or the thickness) of an oil sample at a set temperature.

In a viscosity test, the oil is poured into a tube immersed in a bath at a specific temperature (typically 40°C). The oil is timed as it flows down from one point to the other, and that time is used to measure its kinematic viscosity.

Measuring the oil’s viscosity at different temperatures (40°C and 100°C) gives a viscosity index (VI). The amount by which flow changes may indicate problems, such as dilution or overheating.

Particle count tests

Another test is particle counting, which aims to diagnose excess amounts of particulate matter in the oil. A few methods exist:

• Optical microscopy – Particles are counted manually under a microscope.
• Automatic optical microscopy – Particles are counted using a white light or laser.
• Pore blockage – Sample is poured through a screen, which catches particles and slows the flow.

Karl Fischer water test

A Karl Fischer water titration test is often used after oil tests positive on a visual crackle test.

In this test, an oil sample is placed in a vial with a reagent. The vial is warmed in an oven, causing water to evaporate and collect in a separate container, where it reacts with iodine. The amount of iodine left over is used to calculate moisture content.

Spectroscopy

Spectroscopy tests use electromagnetic radiation to measure the presence of certain elements. The types used in oil analysis include:

• Inductively coupled plasma (ICP)
• Fourier transform infrared (FTIR)
• Rotating disk electrode (RDE)
• X-ray fluorescence (XRF)
• Atomic absorption (AAS)

Each method has its advantages and drawbacks. For instance, ICP spectroscopy is often used to find wear materials, but it can only detect particles up to a certain size.

Choosing the right test

Multiple tests are needed to thoroughly analyze an oil sample as part of condition monitoring and predictive maintenance. Starting with the abovementioned tests will help you get a clear idea of what your equipment’s condition.