SAE AS4059 is a standard for classification of particle contamination in oils and fluids. It was developed by SAE, which stands for Society of Automotive Engineers. Originally, it was developed for use in the aerospace industry in the US and Canada. AS stands for Aerospace Standard.

AS4059 has over time replaced the NAS1638 as the most commonly used cleanliness standard in the oil-, offshore and subsea industry of Norway.

It has had multiple revisions since the standard’s initial release. Each revision is labeled with an uppercase letter after the standard denomination. The last revision came in 2022, i.e. SAE AS4059 rev. G.

In the same way as for NAS1638, a cleanliness code is given based on the number of particles within a particle size range pr. 100 ml in an oil sample, with code 12 being the dirtiest and code 00 being the cleanest.

The results are given on the basis of 2 different tables.

Table 1 indicates the cleanliness codes based on the number of particles in 5 different particle size ranges :

•   6-14 μm(c)     ( 5-15 μm )
• 14-21 μm(c)     ( 15-25 μm )
• 21-38 μm(c)     ( 25-50 μm )
• 38-70 μm(c)     (50-100 μm )
•     >70 μm(c)    ( > 100 μm )

This is also how NAS1638 is indicated.

Table 2 indicates a code based on the cumulative number ( the total number of particles larger than the specified particle size ) for 6 different particle sizes :

• 4  μm(c)   ( 1 μm )      = A
• 6  μm(c)   ( 5 μm )      = B
• 14 μm(c)  ( 15 μm )     = C
• 21 μm(c)  ( 25 μm )    = D
• 38 μm(c)  ( 50 μm )   = E
• 70 μm(c)  ( 100 μm ) = F

• The sizes in paranthesis are according to the old particle size standard.
• The different sizes are usually specified by a capital letter.

The cleanliness standard SAE AS4059 was originally developed 14th of June 1988. After that the standard has had several revisions. The latest revision ( Rev. G ) was released in 2022. Below is an overview of all the revisions.

• Rev. A = 30.03 1990
• Rev. B = 01.03 1995
• Rev. C = 01.08 2000
• Rev. D = 01.04.2001
• Rev. E = 18.03 2011
• Rev. F = 05.05 2020
• Rev. G = 22.11 2022