An industry study a few years ago found that about 38% of the overhead cost of operating construction equipment was attributable to component failures. One of the most important deterrents to parts failure is planned preventive maintenance. Preventive (and now predictive) maintenance can be characterised by a wide variety of interrelated processes, including the control of contamination in lubricant supplies and the monitoring of lubricant and equipment condition by used oil analysis.
Using a high quality lubrication product from a quality supplier does not guarantee that you will get long life from your equipment. Maintaining quality products to prevent contamination is essential. This is true if the products are in bulk tanks or smaller containers, and in all dispensing equipment.
Bulk tanks have breathing devices on them to allow air to enter and prevent tank wall collapse. If these tanks are located in a dusty environment, or the tank may be subjected to heavy rain or high humidity, filtration devices may be required to minimise dirt and/or moisture contamination.
Small containers such as drums must also be properly stored. Drums should be kept horizontally or on a slant with the caps in place and tight. This will minimise the entry of moisture into the containers as they “breathe”. Very small containers should have the lids replaced as soon as product is removed and the containers stored in an environment that is not dusty or can be rained upon.
Dispensing equipment such as hoses, nozzles, funnels, small containers such as cans, must be kept clean and thoroughly wiped clean before moving lubricants from their storage to the equipment compartment. This is true of grease dispensing equipment as well as liquid lubricant dispensing equipment.
Finally, before the compartment cap and/or fill plug is removed, the area should be wiped to prevent induction of dirt as the cap or plug is removed and while the product is put into the compartment.
Another type of contamination is the presence of either the wrong product or some of the wrong product; i.e., hydraulic oil in a gear case requiring an EP gear oil. Sometimes, product mixing or the use of the wrong product will have little impact on compartment operation or component life. In other instances catastrophic failure may occur.
To help prevent compartment contamination by the wrong lubricant, it is essential to maintain the proper labels on all containers; bulk tanks, service truck tanks, drums and small containers. In instances where either language barriers or lack of reading skills may result in technicians putting the wrong product in a compartment, colour coding of tanks, nozzles and the marking of compartment fill plugs can help minimize cross contamination occurrences.
In instances where products are carried on service trucks where tanks are separated by a single bulkhead, it is a good idea to sample all compartments annually to assure individual tank integrity. These samples, if cross-contamination is indicated, may require additional sample analysis to indicate if the cause is lack of tank integrity or mistakes.
If dirt, moisture, and the wrong lubricant products are present in a compartment, how can they be detected? Occasionally, it may be obvious. Engine oil and gear oil mixed will result in severe foaming. Water and/or antifreeze, and fuel dilution may cause sludge formation. An over-oxidised lubricant may cause thickening of the product and may be accompanied by a pungent odour. However, to tell the presence of these aforementioned contaminants or oil breakdown, used oil analysis must be used.
Just as proper care of lubricant storage and dispensing is essential to keep the lubricant uncontaminated before entry into a compartment, obtaining a sample, which is indicative of the compartment’s condition, is essential. Without such a sample it will be impossible for a meaningful follow-up to occur.
The first step to obtaining a “good” sample is to insure that the equipment used to obtain the sample is clean: clean suction pump, clean sample valve, clean hose, clean bottle, and clean drain pan if required.
Secondly, the sample port cover, dipstick or plug must be wiped clean prior to removal.
Thirdly, it is best to follow the same method of obtaining the sample each time, i.e., suction gun, sample port or catch method. Next, the compartment should be at or nearly at operating temperature. This helps ensure that the sample is representative of the lubricant in the compartment.
Lastly, the sample should have the lid replaced as soon as possible, be properly labeled, and shipped to the lab in a timely manner.
If you suspect product contamination, be certain that you communicate this to the lab so that tests other than those which are “normal” may be included to either substantiate whether or not the contaminant is present.
Since its development by the Navy and the railroads at the end of World War II, used oil analysis has evolved from a tool used mainly for failure analysis, into a fully computerised array of specialised predictive maintenance programs. The data provided by used oil analysis can be very beneficial to crane fleet owners when planning preventive and predictive maintenance. The data can include information about oil condition, contaminants, and wear particles.
Although used oil analysis is useful for maintaining all types of lubricated compartments, the hydraulic system is probably of most concern to crane operations. It is the highest capacity system, and the most critical to keep free of contaminants and wear metals.
Oil condition problems include oxidation, additive depletion, and viscosity changes. Oxidation occurs when oxygen molecules combine with base oil molecules. It is usually a result of either overheating or overextending the lubricant change interval, or a combination of the two. Oil thickening and increased acidity usually occur, contributing to increased wear. Clues to this include an acrid odour, dark brown colour, an increase in viscosity, and it can be detected by infrared instrumentation, where it is reported as an absorbance value.
Additive depletion begins as soon as the oil is placed in service. Detergent/dispersant additives in engine oils combine with contaminant molecules to reduce deposits and to keep them suspended in the oil so they can be filtered or drained out. Anti-wear and extreme pressure additives in engine oils and other types of lubricants chemically combine with metal surfaces to help prevent scuffing and other forms of wear. Additive depletion is detected by spectrographic testing and by other evidence such as excessive oxidation and/or increased wear rates.
Excessive fuel dilution or accumulation of combustion by-products such as soot can result in viscosity changes in engine oils. Reduced viscosity from fuel dilution results in loss of base oil film strength, which provides cushioning protection for journals and bearings, gear teeth, and ball or roller bearings and races. It also reduces the natural lubricating ability of the base oil. Viscosity increases from soot in engines (or from oxidation in all compartments) can also cause reduced lubrication and increased wear.
Viscosity changes are determined by using a viscometer, which reports the viscosity as a numeric value and also as an SAE grade. Most viscosity changes are not critical unless the SAE grade has gone up or down by two grades.
Oil condition problems and contamination can be closely related, and both are directly related to wear. Fuel is a common contaminant in all engines, and soot is common in virtually all diesel engines. These contaminants result from fuel-to-air ratio problems, problems with fuel delivery to the combustion chamber, and other operational problems. Problems such as plugged air filters, blocked fuel lines, weak injector springs, and dirty injector tips contribute to fuel and soot problems, as do operational problems like lugging and over-speeding. Excessive fuel dilution and soot are detected by infrared analysis and may be reported as an absorbance value or as a percentage.
Moisture contamination can be a major problem in crane hydraulic systems (and gearboxes). Moisture can enter the system by way of contaminated lubricant supplies, condensation of damp air in the reservoir, missing fill cap, or cooling system leak. Excessive moisture contamination can result in oil thickening, additive drop-out, sludge formation, filter failure, and excessive wear. Because draining, flushing, and refilling of contaminated systems can be time consuming and lubricant intensive, especially in high capacity systems, regular monitoring of moisture levels is essential for maintaining optimum hydraulic system function in crane operations. Used oil analysis can provide that monitoring, reporting moisture by infrared analysis as a percentage.
In the event of a cooling system leak (in engines, powershift transmissions, and some hydraulic systems) the problem of the fluid contamination can be compounded by the presence of elements such as iron, copper and silicon that invalidate spectrographic analysis for wear metals and dirt.
The most common contaminant in lubricated systems is dirt. It can enter in contaminated lubricant, through a hole in an air filter element, leaks in seals and gaskets, missing fill cap, cooling system leak, poor cleaning during a rebuild, and many other ways. Dirt contamination results in abrasive wear, shortened component life, and even loss of oil control on cylinder walls and journal bearing surfaces. The damage it does is immediate and usually irreversible. Proper attention to prevention of dirt entry, particularly in hydraulic systems, is critical in every crane operator’s preventive maintenance programme, as is monitoring of dirt levels in used oil by spectrographic analysis.
The reason for so much attention to maintenance, both preventive and predictive – for putting so much time, energy, and money into trying to control oil condition and contaminants – is to prolong component life and to get as much value for the equipment dollar as possible. The most important way to see how you’re doing is by monitoring of wear particles and trends. There are several methods commonly used, including spectrographic analysis, particle count, and ferrography. Spectrographic analysis, usually by either arc-spark analysis or ICP, determines the composition and levels of “normal” sized wear particles, those that are smaller than about 10 microns. This analysis is also used to establish wear trends, which is the real key to monitoring wear – tracking wear per hour of operation for consistent oil drain intervals. Particle counting is used for tracking larger wear particles.
Current methods look at particles up to the 70 micron size, about the size of a human hair. Some earlier methods detected particles as large as 150 microns. Particle count is used to determine the ISO Cleanliness Code, which is being depended on by many equipment manufacturers to track wear, particularly in hydraulic systems and powershift transmissions. Ferrography determines particle size in a wide range of sizes, well into the visible range, and can also identify particle composition. It is used frequently for particle studies in gear lubricants.
