What Is The Corrosive Sulfur Test?

Andy Shkolnik, Technical Support Scientist at SDMyers, explains the corrosive sulfur test.
Corrosive sulfur is a chemical property of the oil, and the test for it is either pass or fail. While sulfur content relates to the composition of the oil, the presence or absence of corrosive sulfur in new oil is more appropriately considered to be a test for purity - properly refined new transformer oil should pass the corrosive sulfur test.
Transcription:
We're going to discuss a little bit about the actual corrosive sulfur test. If a customer has concern that their oil could possibly be suffering from the corrosive sulfur problem which actually was a problem from roughly the year 2000 to 2006. So if a customer has a transformer with oil from that time frame or they've done any topping off of their transformer fluid with new oil from that time period, they may want to conduct this test. The test itself in the laboratory takes a piece of copper of a certain purity and thickness and we cut it into strips an inch long and a quarter inch wide. Then they're polished to remove any tarnish because you have to have a fresh copper surface to potentially react with any corrosive sulfur in the oil. That copper strip is then bent into a 60 degree V shape and it's put on its edge at the bottom of a flask. The oil sample fills most of the rest of the flask. It is then purged with nitrogen because if there's any oxygen dissolved in the oil or in the head space in the flask, the oxygen can react with the surface of the copper tarnishing it and actually protecting it from the corrosive sulfur compounds.
So we have to drive off the oxygen. So we get a proper test to see whether the corrosive sulfur compounds have reacted with the copper. It then gets sealed and put in the oven for 48 hours at 150 C. So that's stringent enough that if there's any potentially corrosive sulfur compounds, they will break down into their corrosive form and attack the surface of the copper. At the end of the test, we take that copper strip out, we wash the oil off of it, we flatten it out back to a flat shape, and we look at the color of the tarnish of the surface of the copper.
So this is basically a pass/fail test. If we see any tarnish that is gray, black or dark brown - that unfortunately is a fail, that means there are corrosive sulfur compounds in the oil that corroded the surface of the copper. On the other hand, if we see anything other than that, then the result of the test is non-corrosive. So examples would be orange or gold or magenta, or sometimes a little navy even, or a peacock green, as they call it. But any of that is just ordinary tarnish and not from corrosive sulfur. So that's how the corrosive sulfur test works.
For information on this test and to see a list of the other test packages we offer, visit: www.sdmyers.com or call us: 3306307000
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