Sediment in insulating oil may deposit on transformer parts and interfere with heat transfer and may choke oil ducts; thus hindering oil circulation and heat dissipation. Inorganic sediment usually indicates contamination of some type and organic sediment indicates either deterioration of the oil or contamination.

Soluble sludge indicates deterioration of the oil, presence of contaminants, or both. It serves as a warning that formation of sediment may be imminent.

The determination of sediment and soluble sludge in a used insulating oil assists in deciding whether the oil may continue to be used in its existing condition or should be replaced, reclaimed, or reconditioned.

1.1 This test method covers the determination of sediment and soluble sludge in service-aged insulating oils of petroleum origin. Also, provision is made for determining organic and inorganic content of the sediment. The method is intended primarily for oils of comparatively low viscosity; for example 5.7 to 13.0 cSt (mm²/s) at 40°C (104°F). Suitability for high viscosity oils have not been determined.

1.2 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.