Lubricating oils metal additives/contaminants

Lubricating oil analysis, as the name implies, is an analysis technique that determines the condition of lubricating oils used in mechanical and electrical equipment. It is not a tool for determining the operating condition of machinery. Some forms of lubricating oil analysis will provide an accurate quantitative breakdown of individual chemical elements, both oil additive and contaminates, contained in the oil. A comparison of the amount of trace metals in successive oil samples can indicate wear patterns of oil wetted parts in plant equipment and will provide an indication of impending machine failure. 

Spectrographic analysis allows accurate, rapid measurements of many of the elements present in lubricating oil. These elements are generally classified as wear metals, contaminates, or additives. Some elements can be listed in more than one of these classifications. Standard lubricating oil analysis does not attempt to determine the specific failure modes of developing machine-train problems. Therefore, additional techniques must be used as part of a comprehensive predictive maintenance program. 

Scope of the Problem. Petroleum hydrocarbons are the principal components in a wide variety of commercial products (e.g., gasoline, fuel oils, lubricating oils, solvents, mineral spirits, mineral oils, and crude oil). Because of widespread use, disposal, and spills, environmental contamination is relatively common. It is important to understand that petroleum products are complex mixtures, typically containing hundreds of compounds. These include various amounts of aliphatic compounds (straight-chain, branched-chain, and cyclic alkanes and alkenes) and aromatic compounds (benzene and alkyl benzenes, naphthalenes, and PAHs). In addition, many petroleum products contain nonhydrocarbon additives such as alcohols, ethers, metals, and other chemicals that may affect the toxicity of the mixture. 

Finally, deactivation of the catalyst by poisoning elements should be mentioned. Precious metal based catalysts are poisoned by sulfur oxides which mainly originate from the combustion of sulfur-containing fuel constituents, by phosphorus and zinc which mainly originate from some additives in the engine lubricating oil, and by silicium which was sometimes present in some engine seals (Table 21). Also, traces of lead, present in the fuel because of contamination of the fuel supply chain, made an important contribution to the deactivation of the catalyst in the past. 

Not unexpectedly, marine crankcase oils are sometimes contaminated with water, which is normally removed by the lubricating oil centrifuge. To assist further in protecting against rusting, inhibitors such as alkyl sulphonates, phosphonates, amines and alkyl succinic acids/esters can be added. They work by forming a hydrophobic film on the metal surface but must be selected with due regard to the other additives present. 

Commercially available lubricating oils caused relatively little deactivation in comparison with lead and phosphorus contamination from fuel. However, Acres and Cooper (4) demonstrated that when the normal dialkylzinc dithiophosphate additive was replaced by similar compounds without the heavy metal—such as in some forms of ashless oil—catalyst deactivation was rapid. Again the nontoxicity of phosphorus compounds in the presence of heavy metal was associated with formation of inorganic phosphates. 

ASTM Standard D 5185-02, Standard Test Method for Determination of Additive Elements, Wear Metals and Contaminants in Used Lubricating Oils and Determination of Selected Elements in Base Oils by ICP-AES, ASTM International, West Conshohocken, PA. 

Any additive or contaminant that is part of a fiber is likely to be liberated to the environment during subsequent processing. Therefore, it is worthwhile to examine the nonflber content of raw textile fibers. These contaminants, even if present in trace concentrations, can contribute significantly due to the massive amount of fibers that are typically used by manufacturers. The environmental aspects of these contaminants are discussed under fabric preparation, where they are typically liberated into the air or wastewater. Contaminants include natural waxes and oils, metals, agricultural residues, added lubricants, tints, unreacted monomer, catalyst residues, colorants, tines, brighteners, delusterants, fiber finishes, and antistatic additives. Ultimately the fibers themselves also become waste when the textile end-use products are discarded. 

This test method covers the determination of additive elements, wear metals, and contaminants in used lubricating oils by inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific elements are listed in Table 1. 

When the predominant source of additive elements in used lubricating oils is the additive package, significant differences between the concentrations of the additive elements and their respective specifications can indicate that the incorrect oil is being used. The concentrations of wear metals can be indicative of abnormal wear if there are baseline concentration data for comparison. A marked increase in boron, sodium, or potassium levels can be indicative of contamination as a result of coolant leakage in the equipment. This test method can be used to monitor equipment condition and define when corrective actions are needed. 

In addition to releases from the various components or activities that make up the production and distribution system for petroleum products (the oil system), many older waste sites show TPH-related site contamination. Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) site descriptions often mention petroleum, oil and grease, or petroleum, oil, and lubricants (POL) as present at a former waste disposal site. An example is given below for a waste oil recycling site, where TPH-type chemicals were obviously a common site contaminant. The CERCLA clean-up actions, however, focus on a range of specific hazardous or toxic chemicals. Some of the specific chemicals (e.g., toluene) would show up in a TPH test, but the chlorinated solvents and metals do not. Since a site cannot be prioritized for CERCLA attention if the only problem involves TPH site... 

The following is a typical case history [8] from a Northeastern power company. The item being sampled is a condensate vacuum pump. In this case, the commercial laboratory provided oil analysis services for lubricant physical properties and metals including RFS for larger particles. Although the laboratory provides data for 20 wear metals, contaminants, and additives, a trend was observed only for iron and silicon (Fig. 6). 

Waste oil generated from lubricants and hydraulic fluids is one of the more commonly recycled materials. A significant fraction of the approximately 4 billion liters of waste oil produced annually in the United States is burned as fuel, much is recycled, and lesser quantities are disposed of as waste. The collection, recycling, treatment, and disposal of waste oil are all complicated by the fact that it comes from diverse, widely dispersed sources and contains several classes of potentially hazardous contaminants. These are divided between organic constituents (polycyclic aromatic hydrocarbons, chlorinated hydrocarbons) and inorganic constituents (aluminum, chromium, and iron from wear of metal parts barium and zinc from oil additives and formerly lead from leaded gasoline). 

Sometimes the analyst is asked about protocols for taking additional samples from the failed component (or even the reference). Whenever possible samples should be cut by methods in which neither heat nor fluids contaminate the surface to be analyzed. Cutting methods of choice therefore include hacksaws and heavy-duty metal shears. Where use of these is impractical, torch cuts should be as far as possible from the failed area and water, not oil,. should be used as a lubricant with cutting saws. Samples from failures can normally be stored under air in closed containers. 

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