The International Organization for Standardization (ISO) has developed a cleanliness code that is the primary piece of data reviewed on most industrial oil analysis reports. The value of this code can help determine the overall cleanliness of the monitored system. Often times, an end user will establish a target value to achieve, thus offering a level of confidence so long as the used oil sample meets this established target.
The trend in the oil analysis world is to give too much credit to the value of the ISO cleanliness code. Some laboratories have even begun to only report the ISO code. There is also a heavy reliance on this value by end-user analysts.
The ISO code is a fantastic tool to use for setting target alarms and establishing a goal to achieve and maintain as it relates to system cleanliness. It is also the perfect value to use for key performance indicator (KPI) tracking, charting and posting. However, the ISO code should play only a secondary role when it comes to evaluating used oil sample data.
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How the ISO Cleanliness Code is Determined
Most oil analysis samples that receive particle counting are getting what is known as automatic particle counting (APC). The current calibration standard for APC is ISO 11171. When sending a sample through an APC, particles are counted either through laser or pore blockage methods. Although different laboratories may report different particle count micron levels, an example of the various reported micron levels includes those greater than 4, 6, 10, 14, 21, 38, 70 and 100 microns.
ISO 4406:99 is the reporting standard for fluid cleanliness. According to this standard, a code number is assigned to particle count values derived at three different micron levels: greater than 4 microns, greater than 6 microns and greater than 14 microns. The ISO code is assigned based upon Table 1. This can be seen in the example on the left.
However, without seeing the raw data, the only thing the ISO code can positively identify is whether a sample has achieved the desired target value. The ISO code does nothing to help determine any type of real trend information unless the value of the raw data at the given micron levels changes enough to raise or lower the ISO code.
