Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/359954
24 July - August 2014 | www.machinerylubrication.com oIl ANAlYsIs A Different Perspective Looking for existing limit sets for specific applications can reveal different results. While limit information may not always be available, there are industrial fields where detailed guidelines exist. Among the groups that set limit values include component manufacturers, original equipment manufacturers (OEMs), oil companies, laboratories, and technical groups and associations. Component manufacturers often define limits for single parameters that have a direct impact on the component's life- time or performance. Examples would include manufacturers of hydraulic components offering recommendations for oil cleanli- ness or a roller bearing manufacturer stating that a bearing reaches the calculated fatigue lifetime only if the contamination level is within a certain range. This information is valuable, but it is often too general and limited to certain aspects of an oil sample. Nevertheless, component limits are a good reference point if OEM limits are not provided. If OEM limits are available, they should be considered, espe- cially if they are related to warranty issues. For some types of equipment, detailed OEM limits exist, including information about wear values, oil condition and contamination. Their main purpose is to clearly define the conditions for safe equipment operation. Limit values and evaluation guidelines can also be standard- ized. Standards may be independent and official, such as those from ASTM, or based on the work of other specialized associa- tions or organizations. Often these limits are available for equipment with strict safety and reliability requirements. In these cases, the limit values should be considered very closely. Limit values from oil companies are generally focused on oil condition. The main intention is to provide guidelines for detecting when the oil is no longer fit for further use. Some laboratories use sophisticated computer software to support the creation and administration of equipment- and oil-type-related limit sets based on statistical and trend-based methodologies. Actual samples are connected using a matrix code with corresponding limit sets. This allows a computerized flagging of every parameter. The automated system can increase the speed and quality of the evaluation. Absolute vs. Trend Limits The limit information described previously is mainly abso- lute and does not reflect historic trend development. However, sometimes limit values relating to operating hours or distances are available, especially from engine manufacturers. This means the permissible change of a parameter over time is defined, such as iron per 100 hours of operation. Still, in most cases, absolute limits are valid for a typical overhaul or oil drain interval. If no limit is exceeded, no maintenance actions are necessary and the interval may be extended. The evaluation of analysis results based on absolute limits has numerous benefits. For instance, it provides simple handling, quick orientation and can be statistically proven. However, there are also limitations, such as often being valid only for defined intervals. Nevertheless, absolute limits can be effective in some cases. Generally, this is when the failure modes and root causes are known, or the oil property requirements are closely defined and a change in these properties can be directly connected to problems during operation. The surrounding conditions and the goal of the oil analysis are also important. If the samples are always taken during the oil change and the aim of the analysis is to identify repair actions or upcoming problems, statistically based absolute limit values will be sufficient for the evaluation. ANALYTiCAL LiMiT VALUES FOR USED ENGiNE OiLS SAE 40 TEST METHOD LiMiT VALUES Viscosity at 100°C (mm 2 /s) ASTM D445 DIN 51562 Max. 17.5 Min. 11.5 Base number (mg KOH/g) ASTM D2896 ISO 3771 Min. 3 and BN >AN Acid number (mg KOH/g) ASTM D664 New oil value +2.5 ipH value Min. 4.5 Water (% by volume) ASTM D6304 EN 12937 ISO 6296 Max. 0.2 Glycol (mg/kg) ASTM D2982 Max. 100 Oxidation (A/cm) DIN 51453 Max. 20 Nitration (A/cm) IR method Max. 20 Wear elements (mg/kg) RFA, ICP Iron Max. 30 Lead Max. 20 Aluminum Max. 10 Copper Max. 20 Tin Max. 5 Silicon Max. 15 FiGURE 1. An example of an official limit table ppm Operating Hours Absolute Upper Wear Limit Failure ppm Operating Hours Iron Dust (Silicon) Copper FiGURE 2. The function of trend over time FiGURE 3. Absolute vs. trend limits