Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/136253
OIL ANALYSIS By Michael L indner, Oelcheck , Germany Condition Monitoring Using Electrical Conductivity Oil TABLE 1. API BASE OIL GROUPS Group I – Lightly Refined Base Oils (Solvent Neutral or SN) These are oils with an increased proportion of aromatics and less than 90 percent saturates. The viscosity index (VI) is between 80 and 120. Additives dissolve relatively easily. Base for: Conductivity: Simple gear and hydraulic oils High polarity, values less than 10 pS/m, very low conductivity Group II – Hydrocracked Oils Additional treatment with hydrogen reduces unsaturated compounds. More than 90 percent saturates. VI is between 80 and 120. Improved oxidation resistance and evaporation behavior. Base for: Conductivity: Simple engine oils Less polar, values less than 10 pS/m, very low conductivity Group III – Highly Refined Hydrocracked Oils These oils are labeled as partly synthetic and even as synthetic lubricants in some countries. However, they contain no chemically produced components. They have much more than 90 percent saturates. VI is more than 120. They contain very few aromatics and thus have poor additive solubility. Base for: Conductivity: Engine oils and modern industry lubricants As a base oil with no additives, virtually nonpolar; values less than 10 pS/m; very low conductivity Group IV – Synthetically Manufactured Hydrocarbons (SHC) Polyalphaolefins (PAO) are characteristic examples. Unverifiable proportion of unsaturated components. VI over 130. Base for: Conductivity: Fully synthetic modern engine oils and some industry lubricants (wind turbine gear oils) Values less than 10 pS/m, very low conductivity Group V – Synthetically Manufactured Fluids, Esters or Polyolesters Base for: Conductivity: 38 Flux oils or blend components for the production of additives. Usually not suitable as a base oil. They contain high proportions of polar components. Conductivity is usually more than 2,000 pS/m. May - June 2013 | www.machinerylubrication.com pure distilled water is only slightly conductive. However, if the water contains impurities such as salts, acids or bases, then its conductivity increases. Lubricants are normally only slightly conductive and therefore can work as insulators in transformers or switches. However, oils can also conduct electric current. Their conductivity is dependent on several different factors, including the base oil, additives and polarity. Oil Conductivity The more polar a lubricant is, the less refined and more conductive it is. Based on the manufacturing method and level of refining, the American Petroleum Institute (API) has classified base oils into five groups (see Table 1). The lightly refined, mineral-oil-based base oils of Group I represent the simplest option and previously accounted for the largest proportion of lubricant production. Over the last few years, that proportion has been in steady decline, as the more refined base oils of Groups II, III and IV are increasingly being 200 180 Conductivity in pS/m E Electric conductivity is a measure of a fluid's electrostatic chargeability. It usually is expressed in picosiemens per meter (pS/m). In addition to the type of fluid, conductivity also depends on the concentration of movable charge carriers. For example, 160 140 120 100 GG 80 60 G 40 20 0 20 25 G G GG G G 30 35 G G 40 Temperature in °C Figure 1. The relationship between lubricant conductivity and temperature