Corrosive Sulfur

“This test is used to determine the presence of corrosive sulfur in mineral oil. The mineral oil is heated under established conditions with a polished copper coupon (and in one test with additional paper). The copper coupon (and paper) is inspected for the characteristic appearances of corrosive sulfur. One of the sources of sulfur which can lead to corrosive sulfur present in mineral oil can be the crude oil from which it was refined if it was not severely hydro-treated. The sulfur may also come from other sources, such as rubber hoses used for oil processing or from replacement gasket material. In addition, one other important source has been identified: Dibenzyldisulfide (DBDS), which was used for a period as an oxidation inhibitor enhancer, has been found to produce corrosive sulfur in operating transformers.”

(Quote from IEEE C57.106-2015)

What method is used to analyze the sample?

ASTM D1275

IEC 62535

How do you interpret the results?

IEEE C57.106-2015

What do the results indicate?

“In most of their uses, insulating liquids are continually in contact with metals that are subject to corrosion. The presence of elemental sulfur or corrosive sulfur compounds will result in deterioration of these metals and cause conductive or high resistive films to form. The extent of deterioration is dependent upon the quantity and type of corrosive agent and time and temperature factors. Detection of these undesirable impurities, even though not in terms of quantitative values, is a means for recognizing the hazard involved.” (Quote from ASTM D1275)

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