ISO 12669:2017

ISO 12669 specifies a method of determining the required cleanliness level of a hydraulic system, that is, the most appropriate fluid cleanliness level for an operating hydraulic system based upon the individual requirements of that system.
It is applicable to systems where the level of fluid cleanliness is expressed in accordance with ISO 4406, although conversion to other contamination coding systems is possible.
It is applicable to both high and low pressure fluid power systems and also lubrication systems.
It does not include the effects of soft deformable particles that can be generated by thermal decomposition of the hydraulic fluid.