Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
1. Chemical composition – reformulate any toxic components 2. Biodegradation – 20-60% biodegradation in 28 days 3. Bioaccumulation – Log Pow < 3 or proof that the molecular weight exceeds 900
4. Aquatic toxicity - algae, crustacean, fish LC50 /EC50 >1000 ppm, sediment-dweller >10,000 ppm
Traditionally anti-seize compounds contain heavy metals to inhibit localised welding between similar metals during engagement, additionally anti-corrosion and anti-wear chemistries can be toxic to aquatic life. Many of the conventional additive types: copper, lead, zinc, Molybdenum disulphide, organophosphates and many sulphur compounds are wholly unsuitable to environmental applications. Inorganic alternatives were sort with many solid boundary lubricants were tested in combination with different particle sizes. Calcium fluoride with a hardness comparable to iron and good thermal stability in combination with Jet-Lube’s patented micronised fibre additives (EP0832173 A1) yielded the desired frictional and galling resistance / anti-wear performance. To measures improvement in galling resistance and frictional properties a modification to the “Test Apparatus for Universal Friction Evaluation” outlined by the American Petroleum Institute (API) Recommended Practices 7A1 and 5A3 was utilised.
As with most Industrial lubricants the majority of the performance characteristics are intrinsically related to the base oil. To develop an inherently biodegradable product base oil selection is key, due to sulphur content and undefined chain length conventional mineral oil grades are unstable. Jet-Lube reviewed a range of base oils for suitability:
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Initially Jet-Lube considered a biodegradable grease based on esters and aluminium complex thickeners. Group 5 oils where considered too expensive for this application. Since then extensive environmental studies on other synthetic, natural, petroleum base oils and blends have been completed. Using an optimised blend of vegetable oils and calcium sulfonate grease thickener we were able to deliver environmental performance while constraining costs within industry expectations (EP2876151 A1 Patient Pending). For increased functionality a small amount of naphthenic oil (for enhanced low temperature flow properties) and PAO (added thermal stability) were added to optimise the formulation. Because of the calcite particles’ lubricating properties, performance additives containing sulphur, phosphorous or zinc where not needed to enhance the extreme pressure functionality. The strong polar action of the sulphonate micelle and the calcite calcium carbonate yields superior corrosion resistance proprieties hence improving the formula’s anti corrosion properties. Furthermore as an over-based grease (high total base number (TBN)) it is wholly compatible with high pH drilling muds. Being less soluble to drilling muds allows the thread compound to adhere to threads better than other grease types and less subject to dissociation by the “cleaner” properties of the drilling fluids.
Additionally, the massive molecules formed in the grease making process make bioaccumulation potential nil. Biodegradation by-products in the high molecular weight, near pseudo-polymers, may or may not result in a concern. The high hydrophobicity of calcium salts such as calcium 12-hydroxystearate or calcium sulfonate can make biodegradability much slower (as determined by OECD 306), but as such would also make bioaccumulation in individual organisms that much more unlikely in a marine environment.
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LUBE MAGAZINE NO.137 FEBRUARY 2017
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