Oil Condition Monitoring

Transcription

1 Risk Bulletin Oil Condition Monitoring Number 31 January 2011 Report published by Allianz Risk Consulting In Jared Diamond s Collapse: How Societies Choose to Fail or Survive [Viking Books, 2005] we can see how and why a civilization declines through the analysis of its refuse. Similarly, the periodical analysis of the oil in use in a ship s equipment shows the evolution of its condition. When oil analysis results show contamination and/or when wear elements accumulate or increase, immediate and proper action should be taken. Failing this, the equipment concerned will deteriorate and eventually collapse. Reasons for analysis - A reminder Basically, five types of lubrication oils are used on board ships for different equipment: Engine oil for: Trunk piston diesel engines Crosshead engine systems Crosshead engine cylinders Hydraulic oil for: Steering gear Controllable pitch propeller Deck machinery (winch and windlass) Cargo valve control Cargo cranes Compressor oil for: Air compressors Refrigerating compressors All these oils lubricate machines with rotating and translating metallic parts. Even in ideal lubrication conditions, metal to metal contact may occur at times generating wear elements that will contaminate the oil. For the most part, although larger particles are eliminated by filtration and/or purification, the smaller ones remain in circulation in the oil and will accumulate with the running hours. As long as the amount of wear elements is kept under a certain limit, the oil will not lose its lubrication properties. Contamination of the oil may also be caused by external elements entering the oil system such as water from coolers, air, fuel, dust, paint chips etc. Some of these elements can be removed by purification or filtration, but some others, like liquid fuels, require partial or total replacement of the oil. Above a certain limit of contamination, the oil starts to deteriorate causing excessive wear. This in turn increases the insoluble elements in the oil, thus again increasing the wear rate and so on, until eventual component failure. Regular analysis of the oil will give early warning of problems and therefore reduce the risk of breakdowns. Jean-Pierre Ryckaert jean-pierre.ryckaert@ allianz.com Gear oil for: Main engine reducing gear Purifier gear Deck machinery gear Turbine oil for: Steam or gas turbine and turbochargers A destroyed bottom end bearing shell

2 Analysis criteria Some oils are consumable (crosshead engine cylinder oil) and do not require analysis. Some other oils are used in equipment under low load, with little or controllable external contamination (air or refrigerating compressors). In theory, there is no need for periodical analysis of these oils, but sampling before an oil change is advisable. Criteria for identifying equipment where oil condition should be subject to regular monitoring are: Exposure to external pollution: trunk piston engines, gas turbines, stern tube Friction of components under high pressure: diesel engines High load on bearings or gears: diesel engines, reducing gears for diesel or steam main engines, turbo alternators or deck machinery Incidence of small particles in systems mounted with small clearances: hydraulic systems for deck machinery, cranes, and controllable pitch propellers. Good practice is to analyze the oil used in equipment deemed critical for safety of navigation / operation: Propulsion: Main engine system Main engine reducing gear (when fitted) Stern tube Controllable pitch propeller Power generation: Diesel engine or turbine system Reducing gear (for turbo alternators) Steering: Steering gear system Deck machinery Hydraulic system The above should be considered as the minimum standard analysis. The oil or grease analysis of some other equipment should also be considered. Ideally, the cylinder oil scrapedown should be analyzed to detect change in cylinder condition (liner and ring). Inspection through scavenging ports may not be sufficient to optimize the oil feed rate. The following systems are essential to the safety of cargo operations, and should therefore be included in the oil monitoring program: Cargo gear hydraulic (cranes, ramps covers) Cargo valve control (tankers) Steam cargo pumps Cargo crane bearings The above photo shows the broken lower ring of a crane pedestal slewing bearing. Detailed oil analysis including wear particles would have helped to prevent such a dramatic failure. Analysis frequency Three main factors influence the frequency at which samples should be drawn for analysis: The rotation/translation speed The load exerted on the moving parts The physical environment in which the machine operates The analysis frequency should be fixed according to the original manufacturer (OEM) guidelines, if available. The sampling frequency may be adjusted based on the vessel operating conditions with regard to meteorological environment and commercial trading (vessels carrying pulverulent abrasive cargoes in bulk, for example). The analysis interval should preferably be based on running hours whenever possible (some ancillary equipment may not be fitted with a time recorder). Some older OEM maintenance manuals specify intervals in months, in which case it is reasonable to count 6,000 hours per year for all propulsion and associated auxiliary equipment, with the exception of fuel oil purifiers that run 8,000 a year (a full year equals to 8,760 or 8,784 hours). For example, an interval of three months for a two stroke crosshead engine can be considered equivalent to 1,500 running hours. In case of frequent oil changes (500 hours or less), for small engines or compressors, bear in mind that the oil is a record of the condition of the equipment. Therefore, samples should be drawn for analysis before an oil change. When taking delivery of a second hand vessel, the oil of all the equipment fitted on board should be analyzed, if possible before sailing, but in any case as soon as possible.

3 Process The full oil condition monitoring process should be described in a procedure manual held in the ship and office quality management files. The steps to be followed are: Sampling Procedure The procedure must: List the equipment from which oil has to be analyzed, Specify sampling interval for each unit and the type of analysis which should be carried out (water content test or more comprehensive analysis) Indicate the sampling point(s) which must remain the same at each sampling Describe the sampling method, Stipulate that each sample should be carefully labelled, the label displaying the following: - Equipment - Oil brand name - Date of sampling - Equipment running hours - Oil hours Analysis on Board Analysis covering at least the determination of water content and viscosity should be carried out onboard. Analysis Ashore Analysis carried out ashore should preferably be done in the oil manufacturer s laboratory. These would typically cover contaminants, wear elements and oil condition. Results & Action The result of tests carried onboard should be recorded, at least, in the engine log book. It is good practice to record these tests in the maintenance records. Analysis results received from shore laboratories should be reviewed by the technical superintendent in charge of the vessel before transmission to the vessel. After this review of shore analysis results, the technical department should prescribe adequate corrective measures where there is oil condition degradation or excessive contaminants and/or wear elements. Sampling Conditions and Points The accuracy of the analysis results depends essentially on the sampling method. The main topics are: Sampling conditions: The machinery must be operating at normal running load and normal conditions Sampling point: The sampling point of a designated piece of equipment must always be the same. It must be situated before filters and after the machinery components that are subject to wear down. As the filters catch debris and wear elements, a sample drawn after the oil has passed through the filters will have no significance unless the performance of the filter is being evaluated. On a diesel engine, for example, the sampling point should be located behind the pump and before the filter (see Castrol lube oil sampling instructions below). The oil sampled must not be in still condition and must be drawn from a point where the oil is circulating, preferably in turbulent mode (e.g., in an elbow). When detected by onboard tests, the presence of water in oil systems (diesel engines, stern tubes) or abnormally low viscosity (diesel engines) should be remedied as far as possible by the ship s staff, in conjunction with the technical department. The actions taken should be recorded in the maintenance plan. When sampling valves are located at a right angle on long straight lines, some particles will escape, thus resulting in reduction of the particle concentration The lack of analysis followed by action led to the excessive wear of this CPP sliding shoe. The sampling valve must be flushed prior to sampling. If not, the amount of foreign particles might not be representative of the real oil condition. The sampling interval must be strictly respected.

4 Sampling cans Always use clean sampling cans supplied by the oil manufacturer or independent laboratory for shorebased analysis. For onboard tests, where the analysis can is also used for sampling, clean the sample bottle with cleaning agents specified by the maker prior to sampling. Sampling labeling The label must be stuck on to the sample can; avoid tie-on labels. Oil Condition Monitoring Process: Sampling > Analysis > Result > Review > Action The description of the process and the sampling method were outlined above. The Oil Analysis Is Used To Detect External contaminants Oil properties degradation Internal wear External contaminants: The principal contaminants and their means of identification are as follows: Water: the presence of water is expressed in percentage of volume or weight: - Sea water: Sodium (Na), Magnesium (Mg) - Fresh water: the additives present in the closed cooling water system inhibitor such as Boron (B), sodium nitrite, sodium borate and sodium molybdate. Fuel Oil: a change in kinematic viscosity and/or the presence of the following elements: - Nickel (Ni), present in heavy fuel oil (HFO), can also be found in intermediate fuel oil (IFO). - Vanadium (V), present in HFO, can also be found in IFO. - Aluminium (Al), present in HFO. - Silicon (Si), present in HFO. - Sodium (Na) present in HFO, associated with presence of water (it may also indicate sea water). Incomplete or inaccurate labelling may induce errors in the analysis result interpretation. Mentioning of the equipment and oil running hours is particularly important. When sampling cylinder oil of a two stroke diesel engine, the running hours since overhaul, the cylinder oil feed rate and the cylinder liner maximum wear must always be reported for each piston. Oil manufacturers supply complete sampling kits, as below, including a sampling instruction leaflet, a set of bottles and their labels. Remark: the association Al + Si may indicate the presence of cat fines (hard, extremely abrasive particles of aluminium and silicon oxides, a byproduct of the cracking process used in fuel distillation) in oil. Thus, if cat fines are detected in HFO it is prudent to analyze also the lube oil for presence of Al + Si. Soot: identified by the index of contamination (IC) expressed in percentage of weight. Make-up with wrong lubricant: Can be identified mainly by a change in alkalinity (base number - BN) or/and viscosity. Oil properties degradation is indicated by a change in the following measures: Base number (BN) expressed in milligrams of potassium hydroxide per gram of oil (mg KOH/g), represents the alkaline reserve of the oil formulated to neutralize the acidic products of combustion. The higher the sulphur content of the fuel, the higher the BN should be. A too low BN will require an oil change.

5 Acid Number (AN) or Total Acid Number (TAN) is a measure of the total acids present in lubricating oil (strong acids from fuel combustion and weak acids from oil oxidation). It is the quantity of potassium hydroxide in mg necessary to neutralize the acids present in one gram of oil (mg KOH/g). It is usually used for non-engine oils. Kinematic Viscosity (V) change is the result of oil degradation, contamination, or both. Oxidation will cause an increase of viscosity. Mixing with fuel oil may cause increase or decrease of viscosity. The decrease of viscosity is most dangerous, as it may lead to the rupture of the lubricating film and/or crankcase explosion if the lower viscosity is due to the presence of MDO or MGO in oil. The result of a crankcase explosion Oil additives. These include mainly: - Detergent additives to reduce deposits and avoid their formation. - Dispersant additives to maintain deposits in suspension. These are organic additives. - Anti-oxidant additives to prevent and delay oxidation. - Anti-corrosive additives to prevent non-ferrous metals from external corrosive attack. - Ant-rust additives to prevent metallic parts from corrosion due to the presence of water. - Anti-wear additives to strengthen the film of oil (or replace it) in extreme pressure and speed conditions. - Antifoaming additives to prevent the formation of foam due to the mixing of oil and air. Most oil analysis reports include the following additives: - Phosphorous (P) and Zinc (Zn) are extreme pressure (EP) and anti-wear additives. - Calcium (Ca) and Magnesium (Mg) are BN additives, they have alkaline, detergent and anti-oxidation properties. - Silicon is an antifoaming additive. - Barium is a demulsifying agent. Remark: Magnesium also can be present due to ingress of sea water in oil. In this case, there is also Sodium present and the ratio Mg/Na may be 1/3 for an engine oil, and up to 1/6 for non-engine oil. Internal wear: The wear of internal components of machinery or systems, is illustrated by the measure of the wear metal quantities expressed in parts per million (ppm). These include mainly: Iron (Fe): typically indicates the piston and cylinder liner wear on engines. Chromium (Cr) indicates mainly the piston ring wear on engines. Aluminium (Al) present in piston alloys for four stroke engines. Molybdenum (Mo) may be present in components of the upper part of the engine. Lead (Pb) and Tin (Sn) used in engine bearings. Copper (Cu) used in an engine s big end or main bearing, but may also come from pump bearings, rocker arms etc. Nickel (Ni) found in some machinery components Another index: The Particle Quantifier (PQ) Index illustrates the amount of ferrous particles, also called ferrous density. The PQ index does not necessarily give an indication of the size of the particles, but might; it also can provide information about the type of wear, when compared to the ppm of iron. Analysis on Board A full analysis cannot be carried out onboard ships, in particular the spectrographic analysis used to determine the elements in the oil. However, most oil makers supply at least water content and viscosity test kits. Water test: the water test should be carried out at least once a week on: - Stern tube - Main engine (diesel or steam) system - Auxiliary engines (diesel or steam) And once a month on other systems sensitive to the presence of water like hydraulic systems for deck machinery and cargo valve control. The viscosity test kit should be carried out at least once a week on four stroke engines crankcase oil and once a day in case of decrease in viscosity.

6 Remark: if there is no water test kit onboard and ingress of water is suspected in some machinery, a simple test can be carried out using a chemical test tube or any similar glass-made receptacle. Pour a sample of oil to be tested and heat up the bottom of the tube. If a sizzling noise is heard, a significant amount of water is contained in the oil that has to be considered at least disturbing (crackle test). Analysis Ashore Some independent specialized companies provide comprehensive test kits. The use of such kits require extensive training of the crew for using these portable laboratories, and more importantly, for interpreting the results given. The most reliable results will be given by shore based laboratories whether they are owned by the maker or not. We have to keep in mind that the standard analysis covers only the oil characteristics, the detection of contaminants and wear metals. If the presence of other than usual elements is suspected, the oil samples should be preferably sent to an independent specialized laboratory. In this case, the circumstances of the suspected or recognized oil degradation should be clearly indicated and acknowledged by the laboratory. Some external circumstances may dictate a non-routine analysis. As an example, if a vessel sailing close to the Mauritanian coast is affected by a sandstorm from the desert, it is prudent to search for silicon in all machinery that may have been impacted by the presence of sand in the air. Results & Action The advantage of onboard analysis in comparison to shore analysis is that one can react immediately. Onboard analysis must be considered as a tool in that respect and not just as a line in the planned maintenance system. Settling, draining and centrifuging are the common solutions. In case of stern tube oil contamination, a replacement afloat of stern tube sealing rings must be considered. Failing to do this may result in failure of stern tube bearings and tail shaft. Viscosity: a lower viscosity, if not associated with water ingress, is the indication of the presence of MGO or MDO in oil. The lower limiting value is normally 25% of the new oil value (at same temperature). If the limit is reached, there is no other option than to drain the oil. However, draining the oil does not preclude searching for and identifying the cause of the problem. Iron content: the abnormal level depends on the system; a higher level is tolerated on engines running on HFO. The comparison with PQ index is indicative of the kind of wear. - If the PQ index is much lower than the iron ppm content, this may indicate only corrosive wear. - If the PQ index and Fe ppm numbers are very close, this means that the particles are most likely small particles, which may be normal in gear systems, for example. - If the PQ index is higher than the Fe ppm content, this is a probable indication of presence of large wear particles. In all cases the filters must be examined for iron debris presence to confirm the diagnosis. Contamination by HFO: the viscosity may increase or not. However, the flash point of the oil will decrease; there is a danger of crankcase explosion. Oil is to be changed. The interpretation of the analysis results, other than basic as water, fuel or iron, must take into account all the system components. A comprehensive review of all components in each system that contains oil is to be analyzed, and their metallic (or plastic) composition should be reviewed. The list of the components material should be integrated in the oil monitoring procedure. The analysis results review should be carried out in accordance with the nature of the system components to avoid misinterpretation of the results. Some contamination indications and remedies are indicated below: Water content: as per oil manufacturers, the following levels require action. - System oil for crosshead engines: 0.5% - Crankcase oil in 4 stroke engines: 0.2% - Steam turbines and gear systems: 0.1% - Hydraulic systems: 0.2% - Stern tubes: - Normal lubricants: 5% - Emulsifying lubricants: 15% ARC-RB-31-en Copyright 2012 Allianz Global Corporate & Specialty AG. All rights reserved. The material contained in this publication is designed to provide general information only. Please be aware that information relating to policy coverage, terms and conditions is provided for guidance purposes only and is not exhaustive and does not form an offer of coverage. Terms and conditions of policies vary between insurers and jurisdictions. Whilst every effort has been made to ensure that the information provided is accurate, this information is provided without any representation or warranty of any kind about its accuracy and Allianz Global Corporate & Specialty cannot be held responsible for any mistakes or omissions.