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Decoding the ISO Cleanliness Code

Fluid cleanliness is critical to establishing equipment reliability and there is a direct correlation between oil cleanliness and component life.

When a wear condition advances, the size and concentration of wear particles in the oil increases. The best method for measuring particle size and concentration is particle count testing. Results are reported in particles per milliliter or particles per 100 milliliters (depending on the lab) at a given size (microns) and ISO Cleanliness Code. The ISO Cleanliness Code was developed for measuring fluid cleanliness and is widely used for determining particle counts in lubricants. It specifies the size of particles measured and the method for coding the level of contamination.

The ISO 4406 standard utilizes a three number system to classify system cleanliness — example: 19/16/13. The first number means there are between 2,500 and 5,000 particles >4 μm, between 320 and 640 particles >6 μm and between 40 and 80 particles >14 μm. The second represents particles greater than 6μm and the third represents those greater than 14μm. Consider the particle count data shown in Table 1 below. Use the ISO range codes in Table 2 to determine the system's ISO Cleanliness Code.

Table 1
Size Particles / mL
4μ 2852
6μ 541
10μ 198
14μ 56
21μ 11
38μ 1
70μ 0
100μ 0

Table 2

ISO/Range Code Min. particles /mL Max particles /mL
1 0 0.02
2 0.02 0.04
3 0.04 0.08
4 0.08 0.15
5 0.15 0.3
6 0.3 0.6
7 0.6 1.3
8 1.3 2.5
9 2.5 5
10 5 10
11 10 20
12 20 40
13 40 80
14 80 160
15 160 320
16 320 640
17 640 1,300
18 1,300 2,500
19 2,500 5,000
20 5,000 10,000
21 10,000 20,000
22 20,000 40,000
23 40,000 80,000
24 80,000 160,000
25 160,000 320,000
26 320,000 640,000
27 640,000 1,300,000
28 1,300,000 2,500,000
29 2,500,000 5,000,000
30 5,000,000 10,000,000

The ISO Cleanliness Code for the test data shown in Table 1 would be 19/16/13. Because the number of 4μm particles is between 2,500 and 5,000, the corresponding ISO code is 19. Because the number of 6μm particles is between 320 and 640, the corresponding ISO code is 16. Because the number of 14μm particles is between 40 and 80, the corresponding ISO code is 13.

Work with the OEM, your lubricant and filter suppliers and your oil analysis laboratory to determine acceptable ISO cleanliness code limits for machinery by application.

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