ISO 4406:1999 cleanliness codes

ISO 4406:99 ...

ISO 4406:1999 establishes the relationship between particle counts and cleanliness in hydraulic fluids (common practice has extended the application of this standard to lubricants as well). This international standard uses a code system to quantify contaminant levels by particle size in micrometers (µm). Using ISO 4406:1999, a machine owner/operator can set simple limits for excessive contamination levels, based on quantifiable cleanliness measurements.

The table below illustrates the ISO 4406:1999 cleanliness codes.(The ISO standard calls the codes "scale numbers." You may also find them referred to as "range numbers" and represented as R 4 /R 6 /R 14 .)

This standard allows you to quantify current particulate cleanliness levels and set targets for cleanup. The standard provides a 3-part code to represent the number of particles per milliliter (mL) of fluid greater than or equal to 4 µm, 6 µm, and 14 µm, respectively.

For example, referring to Table 1, an ISO code of 17/15/13 would indicate 640 to 1300 particles/mL greater than or equal to 4 µm, 160 to 320 particles/mL greater than or equal to 6 µm, and 40 to 80 particles/mL greater than or equal to 14 µm are present in the lubricant. Notice each step in the ISO code represents either double or half the particle count relative to an adjacent code.

It is important to note that the '/' character in the written form of the code is merely a separator, and does not signify a ratio of the scale numbers.