“Rust Never Sleeps”
An Investigation of Corrosion in Grease Lubrication Joseph P. Kaperick, Gaston Aguilar, Michael Lennon Afton Chemical Corporation • Richmond, VA Abstract
Corrosion of steel or iron doesn’t just happen “out of the blue”. Rust causes damage to untold numbers of machine components not only through direct electrochemical erosion of the metal but through incidental increase in pitting and wear caused by the iron oxide particles. This can be of special significance in mining operations where the potential for exposure to wet or humid environments is extremely high. While grease itself can inhibit some corrosion by reducing ingress of moisture, the addition of rust or corrosion inhibitors is often needed to give additional protection. There is a wide variety of additive solutions as well as a number of different corrosion tests to screen their effectiveness. An overview of some common corrosion tests along with studies comparing the severity of the tests with various aqueous solutions and under different test conditions will be presented.
Introduction
A study on the cost of corrosion in the United States was conducted between 1999 and 2001 with support from the Federal Highway Administration (FHWA) and National Association of Corrosion Engineers (NACE). Their definition of corrosion was that it is a natural phenomenon which results in deterioration of a substance (usually metal) or its properties because of a reaction with its environment. This phenomenon affects everything from cars and appliances, to drinking water systems, to pipeline, bridges and public buildings. According to their statistics, over the past 22 years the U.S. has incurred total normalized losses of more than $380 billion (averaging $17 billion annually) from natural disasters such as tornadoes, hurricanes and earthquakes. In comparison, the direct cost of metallic corrosion is $276 billion on an annual basis which
represents 3.1% of U.S. Gross Domestic Product (GDP). [1] Mining uses a huge amount of water in its daily operations. According to the United States Geological Survey (USGS), roughly 4 billion gallons a day are used in the United States alone. “Mining water use is water used for the extraction of minerals that may be in the form of solids, such as coal, iron, sand, and gravel; liquids, such as crude petroleum; and gases, such as natural gas. The category includes quarrying, milling (crushing, screening, washing, and flotation of mined materials), re-injecting extracted water for secondary oil recovery, and other operations associated with mining activities.”[2] According to its 2005 study, 43% of the water used is saline. The use of saltwater or seawater is increasing in some areas as mines look to take advantage of convenient water sources for their needs. Just one example is BHP Billiton, an Australian-British mining company, whose chemical process needs large amounts of water pumped via pipeline from the nearby Indian Ocean. “Some of the seawater is used in its raw state to cool the bearings in all 152 pumps around the plant, while some is desalinated on site for the metallurgical process. Steam and acid are used to prepare the ore for the refining process.“[3] The focus for the grease formulator, with respect to corrosion, is obviously on providing protection from the rust which often occurs in the presence of water and several studies have been documented by NLGI over the last couple of decades. Hunter and Baker [4, 5] evaluated different rust inhibitors and greases using the two versions of the traditional static rust test (ASTM D1743 and D5969) and the dynamic EMCOR corrosion test
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