Fuels and Lubricating oils
Fuel oil properties.
Fuel standards as per ISO.
Lube oil health.
Microbial degradation.
Used oil analysis.
Spot test:- In this test a drop of lube oil is put on the blotter paper and it is then dried for few hours.
Typically, an oil analysis report comes with a written summary section that attempts to put the results and recommendations in layman’s terms. But, since the laboratory has never seen the machine or know its full history, these recommended actions are generic and not tailored to your individual circumstances. Therefore, it is the responsibility of the personnel who receive the lab report to take the proper action based on all known facts about the machine, the environment and recent lubrication tasks performed.
Fuel standards as per ISO.
Lube oil health.
Microbial degradation.
Used oil analysis.
Fuel oil properties.
(A) The calculated carbon Aromaticity index (CCAI) is an index of the ignition quality of residual fuel oil.
Formula for CCAI:
$\displaystyle\mathrm{CCAI=D - 140.7log(log(V + 0.85)) - 80.6 - 483.5log (\frac{t + 273}{332})}$ .
Where:
D= density at 15°C (kg/m3)
V= viscosity (cST)
t = temperature (°C)
D= density at 15°C (kg/m3)
V= viscosity (cST)
t = temperature (°C)
- This will normally give a value somewhere between 800 and 880.
- The lower the value is the better the ignition quality.
- Fuels with a CCAI higher than 880 are often problematic or even unusable in a diesel engine.
- CCAI are often calculated under testing of marine fuel, the values are dependent on density, viscosity and temperature of the fuel. In case of high CCAI, the manufacturers recommendations and guidance limits should be consulted to ensure that the fuel falls within the permissible range for the engine type.
- Attention should be given to the combustion profile, peak pressures and exhaust temperatures on the Engine.
(B) Open flash point and Closed flash point:-The flash point of a volatile material is the lowest temperature at which vapors of the material will ignite, when given an ignition source.
Flash point tests are used to show the lowest temperature that a volatile substance is vaporized into a flammable gas. This is done by introducing a source of ignition, then waiting for the “flash” where the substance is ignited. There are a wide range of methods but most are available in open or closed cup formats.
open flash point:-
- it is conducted in a vessel which is exposed to the air outside.
- a key variable is the height of the ignition source over the cup.
- this test simulates the potential ignition of the liquid spillage in the non-contained condition e.g pool of fuel on floor.
- the results are likely to be interfered by the out side elements.
- fire point, combustibility and sustained burning test use open cup instruments.
- it is quoted in fire fighting techniques for oil spill conditions.
close flash point:-
- it is conducted in a closed vessel which is not opened to the outside atmosphere. the lid is sealed and the ignition source is introduced into vessel itself.
- accumulation of vapour is well contained.
- aim to simulate a fuel inside tank and ignition source is introduced.
- the results are not interfered by outside elements.
- test is highly significant for knowing flash point of a fuel.
- quoted for carriage, transport and bunkering.
(C) The importance of Sodium to Vanadium Ratio:-
- Running with a non - recommended sodium to vanadium ratio extended periods causes Vanadium, Sodium and Ash fouling in the Turbocharger.
- A sodium (Na) to vanadium (V) ratio of 1:3 causes the formation of low melting point vanadium and sodium oxide salts i.e vanadium pentoxide and sodium sulphate.
- A ratio of 3:1 is less likely to cause deposition.
- Most residual fuels have vanadium levels of less than 150 mg/kg. Some fuels however, have a vanadium level greater than 400 mg/kg
- In general, fuel when delivered contains a small amount of sodium, typically below 50 mg/kg. The presence of seawater increases this value by approximately 100 mg/kg for each percent of seawater. If not removed in the fuel treatment process, a high level of sodium will give rise to post-combustion deposits in the turbocharger. Although potentially harmful, these can normally be removed by water washing.
- High temperature corrosion and fouling can be attributed to vanadium and sodium in the fuel. During combustion, these elements oxidise and form semi-liquid and low melting salts that adhere to exhaust valves and turbochargers. In practice, the extent of hot corrosion and fouling are generally maintained at an acceptable level by employing the correct design and operation of the diesel engine. Temperature control and material selection are the principal means of minimizing hot corrosion. It is essential to ensure exhaust valve temperatures are maintained below the temperatures at which liquid sodium and vanadium complexes are formed and for this reason valve face and seat temperatures are usually limited to below 450°C.
- When a fuel is bunkered with a vanadium level greater than that recommended by the engine designer, fuel additive, and numerous ash-modifying compounds can be used. They should be used with care as situations can arise where the effect of the ash-modifier, by incorrect application, can cause further problems in the downstream post-combustion phase.
(D) Octane Number.
- it is a figure indicating the anti-knock properties of a fuel, based on a comparison with a mixture of iso-octane and heptane
- The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high-performance gasoline engine that require higher compression ratio.
- octanes are a family of hydrocarbons that are typical components of gasoline. They are colorless liquids that boil around 125 °C (260 °F). One member of the octane family, iso-octane, is used as a reference standard to benchmark the tendency of gasoline fuels to resist self-ignition.
- The octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of iso-octane and heptane that would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of iso octane (2,2,4-trimethylpentane, an organic compound with the formula (CH3)3CCH2CH(CH3)2 or C8H18) in that mixture is the octane number of the fuel.
- Heptane is the straight-chain alkane (also called paraffin) H3C(CH2)5CH3or C7H16.
Fuel standards as per ISO.
Amendments to the Scope and General Requirements and the addition of DF grades containing biodiesel (FAME),plus the reporting of cold properties of Cloud Point (CP)and Cold Filter Plugging Point (CFPP)are of principal interest
Changes to the distillate fuels include the following:
— additional grades, DFA, DFZ and DFB have been added with a maximum fatty acid methyl ester(s) (FAME) content of 7.0 volume %;
— the sulfur content of DMA and DMZ has been reduced to a maximum of 1.00 mass %;
— the sulfur content of DMB has been reduced to a maximum of 1.50 mass %;
— requirements for the following characteristics have been added to winter grades of DMA and DMZ: cloud point and cold filter plugging point.
(a) No limit been put on Cloud Point (CP) and Cold Filter Plugging Point (CFPP)
The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. It is defined as the minimum temperature in which the oil has the ability to pour down from a beaker.
Cloud point refers to the temperature below which wax in diesel or biowax in biodiesels forms a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines
Cold filter plugging point (CFPP) is the lowest temperature, expressed in degrees Celsius (°C), at which a given volume of diesel type of fuel still passes through a standardized filtration device in a specified time when cooled under certain conditions.
Increasingly we have seen that new ULSFO fuels can be more paraffinic in certain geographical areas, which may lead to cold flow operability issues when the ship is operating in a colder environment and does not have suitable fuel heating arrangements to compensate; more specifically this has been an issue for distillate fuel oils. While CFPP is part of the European auto diesel fuel specifications standard EN 590, climate related requirements within EN 590 are set at a national level taking into account the specific climate of the country.
Defining a suitable fuel characteristic and a limit to guarantee the cold operability of marine distillate fuels for all ships in all climate regions without significantly impacting other segments of the fuels market, requires more in depth study to ensure that there are no unintended adverse consequences. Therefore, the requirement to report CP and CFPP will provide additional information on the cold flow properties of the fuel that will help ship’s to mitigate cold operability issues ahead of any potential problems being experienced and supply important data to the next revision of the Standard.
(b) No changes to the maximum limits on cat fines (Al+Si)
Every edition of ISO 8217 is based on extensive statistical evaluation of the market at the time and this edition was not different. The Standard specifies the requirements prior to on-board settling, centrifuging and filtering of the fuel. With the centrifuge(s) at the correct operating settings, the cat fines content, as measured by the Al+Si level,can be reduced to an acceptable limit at the engine inlet. In order to provide an increased safety margin, the cat fines limit was reduced to 60 mg/kg in ISO8217:2010. A further reduction of the Al+Si limit would likely have a negative impact on fuel oil availability and cost of the product, therefore, lacking significant overriding evidence of a need, no change in the specification was deemed necessary
(c) FAME (fatty acid methyl ester)
With the increasing demand for maximum 0.10% sulphur fuel oils, some ports may offer automotive diesel fuel containing biodiesel (FAME) as the only fuel available. The maximum 7.0% (v/v) has been chosen as this aligns, at the time of writing this guideline,with the concentrations allowed in those countries applying environmental regulations.
In some areas, it may be difficult to buy FAME free distillate fuels and this Standard now provides a marine biodiesel specification that suppliers can offer instead of DMA or DMB when those grades are unavailable.
(d) Hydrogen sulfide (H2S),
Maximum limit of dissolved hydrogen sulfide is 2.00 mg/kg as per both 2010 and 2017 standard.
Hydrogen sulphide is commonly created by bacterial decomposition of organic matter such as septic tank debris and faecal material. This process is conducted by sulphate-reducing bacteria (SRBs) in the absence of oxygen. In the presence of water, it is acidic and is known as hydrosulphuric acid. This is the cause of the corrosion in sour gas or sour oil processing equipment. However, it can be neutralized using an (H2S) scavenger.
Hydrogen sulphide is lethal by inhalation at concentrations of 500ppm; it can quickly kill animals and humans at this concentration.
Benefits of using ISO 8217:2017 Standard over the previous editions (ISO 8217:2005 and/or 2010/12):-
While there are only minor changes to existing characteristics already included in the 2010/2012 edition, additional requirements have been included for distillate fuels to protect against cold operability issues. Hence, adopting the latest revision of the ISO 8217 offers improved quality control and better protection against operational issues while the introduction of DF (Distillate FAME) grades will improve fuel oil availability in some ports. Compared to ISO 8217:2005, this revision carries over the more stringent limits on minimum viscosity for distillate grades, lubricity, cat fines, acid number, H2S content and CCAI found in the 2010/2012 edition.
With the impending implementation in 2020 of MARPOL Annex VI’s global max 0.50% sulphur requirement for marine fuels, we anticipate a surge in VLSFO RM and DM type fuels coming to the market. We can therefore expect a broader choice from different geographic areas of fuel formulations which ships will have to manage. Although we expect similar fuels to those we have seen with the 0.10% ULSFO, the ISO Committee will continue to collect and monitor the statistics to strengthen the content of the next ISO 8217 Standard and will keep the industry advised.
Changes to the distillate fuels include the following:
— additional grades, DFA, DFZ and DFB have been added with a maximum fatty acid methyl ester(s) (FAME) content of 7.0 volume %;
— the sulfur content of DMA and DMZ has been reduced to a maximum of 1.00 mass %;
— the sulfur content of DMB has been reduced to a maximum of 1.50 mass %;
— requirements for the following characteristics have been added to winter grades of DMA and DMZ: cloud point and cold filter plugging point.
(a) No limit been put on Cloud Point (CP) and Cold Filter Plugging Point (CFPP)
The pour point of a liquid is the temperature below which the liquid loses its flow characteristics. It is defined as the minimum temperature in which the oil has the ability to pour down from a beaker.
Cloud point refers to the temperature below which wax in diesel or biowax in biodiesels forms a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines
Cold filter plugging point (CFPP) is the lowest temperature, expressed in degrees Celsius (°C), at which a given volume of diesel type of fuel still passes through a standardized filtration device in a specified time when cooled under certain conditions.
Increasingly we have seen that new ULSFO fuels can be more paraffinic in certain geographical areas, which may lead to cold flow operability issues when the ship is operating in a colder environment and does not have suitable fuel heating arrangements to compensate; more specifically this has been an issue for distillate fuel oils. While CFPP is part of the European auto diesel fuel specifications standard EN 590, climate related requirements within EN 590 are set at a national level taking into account the specific climate of the country.
Defining a suitable fuel characteristic and a limit to guarantee the cold operability of marine distillate fuels for all ships in all climate regions without significantly impacting other segments of the fuels market, requires more in depth study to ensure that there are no unintended adverse consequences. Therefore, the requirement to report CP and CFPP will provide additional information on the cold flow properties of the fuel that will help ship’s to mitigate cold operability issues ahead of any potential problems being experienced and supply important data to the next revision of the Standard.
(b) No changes to the maximum limits on cat fines (Al+Si)
Every edition of ISO 8217 is based on extensive statistical evaluation of the market at the time and this edition was not different. The Standard specifies the requirements prior to on-board settling, centrifuging and filtering of the fuel. With the centrifuge(s) at the correct operating settings, the cat fines content, as measured by the Al+Si level,can be reduced to an acceptable limit at the engine inlet. In order to provide an increased safety margin, the cat fines limit was reduced to 60 mg/kg in ISO8217:2010. A further reduction of the Al+Si limit would likely have a negative impact on fuel oil availability and cost of the product, therefore, lacking significant overriding evidence of a need, no change in the specification was deemed necessary
(c) FAME (fatty acid methyl ester)
With the increasing demand for maximum 0.10% sulphur fuel oils, some ports may offer automotive diesel fuel containing biodiesel (FAME) as the only fuel available. The maximum 7.0% (v/v) has been chosen as this aligns, at the time of writing this guideline,with the concentrations allowed in those countries applying environmental regulations.
In some areas, it may be difficult to buy FAME free distillate fuels and this Standard now provides a marine biodiesel specification that suppliers can offer instead of DMA or DMB when those grades are unavailable.
(d) Hydrogen sulfide (H2S),
Maximum limit of dissolved hydrogen sulfide is 2.00 mg/kg as per both 2010 and 2017 standard.
Hydrogen sulphide is commonly created by bacterial decomposition of organic matter such as septic tank debris and faecal material. This process is conducted by sulphate-reducing bacteria (SRBs) in the absence of oxygen. In the presence of water, it is acidic and is known as hydrosulphuric acid. This is the cause of the corrosion in sour gas or sour oil processing equipment. However, it can be neutralized using an (H2S) scavenger.
Hydrogen sulphide is lethal by inhalation at concentrations of 500ppm; it can quickly kill animals and humans at this concentration.
Benefits of using ISO 8217:2017 Standard over the previous editions (ISO 8217:2005 and/or 2010/12):-
While there are only minor changes to existing characteristics already included in the 2010/2012 edition, additional requirements have been included for distillate fuels to protect against cold operability issues. Hence, adopting the latest revision of the ISO 8217 offers improved quality control and better protection against operational issues while the introduction of DF (Distillate FAME) grades will improve fuel oil availability in some ports. Compared to ISO 8217:2005, this revision carries over the more stringent limits on minimum viscosity for distillate grades, lubricity, cat fines, acid number, H2S content and CCAI found in the 2010/2012 edition.
With the impending implementation in 2020 of MARPOL Annex VI’s global max 0.50% sulphur requirement for marine fuels, we anticipate a surge in VLSFO RM and DM type fuels coming to the market. We can therefore expect a broader choice from different geographic areas of fuel formulations which ships will have to manage. Although we expect similar fuels to those we have seen with the 0.10% ULSFO, the ISO Committee will continue to collect and monitor the statistics to strengthen the content of the next ISO 8217 Standard and will keep the industry advised.
Lube oil health.
Functions of a Lubricant
- The primary function of a lubricant is to prevent friction by creating a boundary layer between two surfaces
- Dissipate heat from surfaces
- Transport contaminants to filters
- Protects from oxidization and corrosion
- Power transmission
The properties of lubricating oil need to be maintained within the specified parameters, in order to the engine to operate smoothly and efficiently. following properties of lubricating oil are desirable:
- Viscosity
- Pour Point
- high Flash point
- high Oxidation stability
- low Carbon residues: To be low
- Total acid number or TAN
- Total basic number or TBN
- Detergency
- Dispersancy
Effects upon failure to maintaining the quality of lube oil
1. If very low quality of system lube oil is maintained in circulation ,function of lubrication will be disturbed.
2. Less amount of lube oil in circulation causes rise in temperature thus reducing the viscosity leading the failure of boundary lubrication due to decrease in oil film thickness.
3. Insufficient time for de-aeration and it accelerates the process of oxidation of oil .Due to oxidation Lubrication oil properties are lost Forms sludge and high temperature sludge adhere to metal surface. Formation of acids/corrosive attack. Increase the viscosity of oil.
5. Additives will deteriorate faster results in loosing properties like detergency and depersency .
(A) Role of Automatic back flushing filters
Continuous back-flushing ensures constant pressure and long intervals between inspections. auto back wash filter offers considerable man-hour savings due to their high level of reliability and the fact that they require virtually no supervision.
A Controller keeps monitoring the differential pressure across the filter. The backwash cycle starts when the differential pressure reaches at a pre-selected level. Once the backwash process gets completed, the controller resets automatically, and the whole process starts again when differential pressure rise again.
(B) Role of lube oil saparator:-
Lub oil separators which work as purifiers are very essential in maintaining the crank case oil of slow speed engines as well as large medium speed diesel engines water free and this has to be a continuous process , even continued when engines are idle. Apart from removing the water the purifiers also remove the sludge that is generated especially if the system is operating on a medium speed engine. Water finds its way from various sources and they are:
Lub oil separators which work as purifiers are very essential in maintaining the crank case oil of slow speed engines as well as large medium speed diesel engines water free and this has to be a continuous process , even continued when engines are idle. Apart from removing the water the purifiers also remove the sludge that is generated especially if the system is operating on a medium speed engine. Water finds its way from various sources and they are:
- Condensation of vapour from the atmosphere stagnant in the lube oil sump.
- Occasional leaks from lub oil coolers especially due to cooling water on with leaking water valves when the engines are idle.
- Leakage of water from liners which are unnoticed.
- Improper purification resulting in water remaining in the oil, till it is discovered.
- Leakage of heating steam in sumps and heaters for the purifier.
- Continuous operation of the purifier even during idle time of the engines is necessary to prevent bacterial degradation
(c) role of Magnetic filters:- They are often used in lubricating oil systems, where a large permanent magnet collects any ferrous particles which are circulating in the system. The magnet is surrounded by a cage or basket to simplify cleaning. Magnetic filters play a very important role in filtering ferrous debris collected in the oil as abrasion particles of the liner or piston rings especially in medium speed engines In crank case oils it may be the grit from crank pins and journals which cause wear of these components.
It is an indicative device of detecting a faulty bearing when conducting a crank case examination.
(d) Role of Visual Inspection:-Aim of inspection and test of lube oil is to monitor deterioration of oil, consumption of oil, wear of machinery parts being lubricated further use or rejection of lube oil. monitoring of lube oil condition is a indirect indication of the health of machinery.
Many basic lubrication problems can be found just by simple visual inspections such as level, pressure, temperature, colour and odor monitoring of the lube oil.
additionally following tests can be carried out on board.
alkalinity test:- a drop of methyl orange and phynopthaline solution on blotting paper followed by a drop of sample oil at the center if previous drop. colour change arround the oil spot can be compared for the results
- red colour is indication of acid
- blue/green colour is an indication if alkalinity
- yellow colour indicates neutral
Water Crackle test:- this method is to determine water presence in the lube oil where the oil sample drops are heated in an aluminium container over a flame. If water is present crackling sound will come.
Spot test:- In this test a drop of lube oil is put on the blotter paper and it is then dried for few hours.
- irregular shape of spot indicates presence of water.
- uniform distribution of contaminants indicates good dispersiveness.
- contaminants concentrated at center indicates the poor dispersiveness.
- black colour of the spot indicates heavy contamination.
Odor of oil test:- Rotten egg smells is an indication of microbial degradation of oil , also sliminess of the oil in the crankcase painted surfaces can be observed, additional problems may be observed like increased acidity and water content, filter choking more frequently poor heat exchanger performance, black staining of white metal bearings and corrosion of exposed steel surfaces.
Viscosity Test:- This test is performed by using a Flow stick in which two paths are provided for flow of oil side by side. In one path fresh oil is filled and in other side path used sample oil is filled. Now the flow stick is tilted allowing oil on both paths flowing in the direction of the tilt due to gravity. A finish point is provided along with reference points along the flow stick and the position of used oil is checked when fresh oil reaches the finish point.
- reduced viscosity indicates dilution with distillate fuel
- increased viscosity indicates contamination with heavy oil, carbon or oxidation of oil.
(e) Role of Periodic laboratory tests. laboratory test of lube oil is helpful in knowing the fluid properties, contamination and wear debris.
Various test like Foaming characteristics, water separability, air release value, rust prevention characteristics, oxidation stability, flash point, corrosion test, particle sizing and counting, TAN, Moisture, viscosity measurements etc are carried out by shore based laboratory.
Typically, an oil analysis report comes with a written summary section that attempts to put the results and recommendations in layman’s terms. But, since the laboratory has never seen the machine or know its full history, these recommended actions are generic and not tailored to your individual circumstances. Therefore, it is the responsibility of the personnel who receive the lab report to take the proper action based on all known facts about the machine, the environment and recent lubrication tasks performed.
Microbial degradation.
A. What is microbial degradation of lubricating oil and how is it prevented?
The term microbial degradation is sometimes referred to as biodegradation. It is the name given to the process whereby micro-organisms increase in number and decompose a hydrocarbon fuel or lubricant and eventually render it unfit for its duty.
This form of decomposition requires the presence of water together with other favorable environmental conditions including temperature, acidic conditions (pH value), and nutrients. With favorable environmental conditions the increase in microbial count may take place very quickly and cause rapid breakdown of the fuel or lubricant.
In the case of lubricating oils the additives in the oil may function as the nutrients.
The indications of attack may be seen as follows.
Creation of sulphurous gases having a smell similar to bad eggs.
Build up of yellowish-coloured film on the inside of crankcases and the polished steel surfaces at the sides or unworn parts of bearings.
The colour of the oil darkening.
The oil tending to become opaque with a milky appearance.
Inability of the lubricating oil centrifuge to separate water from the oil due to the creation of stable emulsions.
Plugging of lubricating oil filters due to thick sludges.
The effect of degradation usually shows up on bearings and bearing journals as a corrosive attack in the form of pitting in both the journal and the bearing, or a breakdown of the bearing surface. This may show itself as staining and in extreme cases as a breakdown of the bearing lining alloy.
This form of decomposition requires the presence of water together with other favorable environmental conditions including temperature, acidic conditions (pH value), and nutrients. With favorable environmental conditions the increase in microbial count may take place very quickly and cause rapid breakdown of the fuel or lubricant.
In the case of lubricating oils the additives in the oil may function as the nutrients.
The indications of attack may be seen as follows.
Creation of sulphurous gases having a smell similar to bad eggs.
Build up of yellowish-coloured film on the inside of crankcases and the polished steel surfaces at the sides or unworn parts of bearings.
The colour of the oil darkening.
The oil tending to become opaque with a milky appearance.
Inability of the lubricating oil centrifuge to separate water from the oil due to the creation of stable emulsions.
Plugging of lubricating oil filters due to thick sludges.
The effect of degradation usually shows up on bearings and bearing journals as a corrosive attack in the form of pitting in both the journal and the bearing, or a breakdown of the bearing surface. This may show itself as staining and in extreme cases as a breakdown of the bearing lining alloy.
The effect of degradation usually shows up on bearings and bearing journals
as a corrosive attack in the form of pitting in both the journal and the bearing,
or a breakdown of the bearing surface. This may show itself as staining and in
extreme cases as a breakdown of the bearing lining alloy.
Biocides and fungicides can be used to kill and prevent the spread of organisms within a distillate fuel oil. They can also be used in lubricating oils provided their use is approved by the oil supplier. Most of the treatments available cause some deterioration in the lubricating properties of the oil and their use should be carefully followed and observed.
The known organisms causing degradation are killed by preheating the lubricating oil to a temperature of 82.5°C during continuous separation treatment and when preparing to centrifuge the whole of the system oil charge.
Note The temperature at which lubricating oils are heated prior to centrifuging should never exceed the supplier's recommendations.
Care should be exercised in preventing leakage of cooling water into the system oils in both cross-head and trunk-piston engines. Modern non-toxic anti-corrosion additives may act as a nutrient to the organisms causing degradation.
some of the older additives are toxic to the organisms, but their use is banned in cooling systems used for heating low-pressure distilling plant producing portable water.
as a corrosive attack in the form of pitting in both the journal and the bearing,
or a breakdown of the bearing surface. This may show itself as staining and in
extreme cases as a breakdown of the bearing lining alloy.
Biocides and fungicides can be used to kill and prevent the spread of organisms within a distillate fuel oil. They can also be used in lubricating oils provided their use is approved by the oil supplier. Most of the treatments available cause some deterioration in the lubricating properties of the oil and their use should be carefully followed and observed.
The known organisms causing degradation are killed by preheating the lubricating oil to a temperature of 82.5°C during continuous separation treatment and when preparing to centrifuge the whole of the system oil charge.
Note The temperature at which lubricating oils are heated prior to centrifuging should never exceed the supplier's recommendations.
Care should be exercised in preventing leakage of cooling water into the system oils in both cross-head and trunk-piston engines. Modern non-toxic anti-corrosion additives may act as a nutrient to the organisms causing degradation.
some of the older additives are toxic to the organisms, but their use is banned in cooling systems used for heating low-pressure distilling plant producing portable water.
What methods are employed to ensure correct sampling for shore based testing?
1. Sampling location must not be varied and sample to be collected from the same sampling point, preferably on the main supply line into the main engine.
2. Engine must be in running at continuous rating and in normal operating range of load and temperature.
3. Before sample collection the sampling cock must be thoroughly flushed to remove any sludge accumulation.
4. A new sample bottle provided by the Labs for the sampling purpose of lube oil only must be used every time.
5. The sample should be fully identified with date, vessel name, type/grade of oil.
B. What action will you take If the testing results show abnormal values of water content and TBN for crank case lube oil of a slow speed main engine?
1. Source of water leakage to be traced and eliminated. This can be a cooler tube leaking or a sump drain line leaking.
2. Water can be removed by settling and draining method or by centrifugal purification.
3. Cooling water connections must always be isolated prior to the stopping of lubricating oil circulation. That will prevent the water from leaking cooler tubes to enter into water side.
4. The cause for decrease in TBN value is due to the presence of water and high temperature of the oil resulting in oxidation and subsequent acidity of the oil resulting in decrease of the TBN value. The subsequent action to be taken is to continue purification of the oil with the purifier. The cooler may require cleaning of the tubes to improve the cooling of the oil. By doing these the condition of the oil can be improved.
5. A high TBN value is the indication of leaking Cylinder oil into the sump. The leakage can be traced and rectified.
Used oil analysis.
Used Oil Analysis is one of the important, and maybe the simplest, approaches to diagnosing the health of an engine. It is, however, not easy for engine users or engineers to understand and interpret each analysis parameter correctly and to assess the condition of the oil and the engine. It is an important part of engine maintenance. It provides information about the condition of the oil, its suitability for further use and to a certain extent information about the condition of the machinery lubricated by the oil.
Need of used oil analysis
The purpose of conducting used oil analysis is two-fold:
a. To assess the condition of the oil - to provide recommendations on its suitability for further use and optimisation of the oil change intervals.
b. To assess the condition of the engine - to enable the detection and thus prevention of issues which left unattended may impact the reliable operation of the engine.
Routine Analyses
The physical & chemical characteristics of an in-service oil are obviously linked back to the specific type of oil, its age and the conditions under which it operates. For engine oils, the tests carried out under “Routine Analyses” will typically include:
1) Viscosity
2) Water content
3) Base Number (BN) or Alkalinity reserve
4) Insolubles
5) Flash Point
6) Elements (measuring the concentration of additives and levels of wear metals, etc.)
These tests are typically carried out in highly automated specialised laboratories. Only a small volume of oil is needed- typically less than 250 ml for a full Routine Analysis, and fully automated equipment can be used. This makes Routine Analysis quick, easy & economical to run. Normally the test method used will be according to conventional ISO or ASTM standards but where in-house specialised test methods are used these can have the advantage that the tests are specifically designed for their relevance to ‘used oil’ based on many years field experience. In cases of a dispute the ISO or ASTM methods are used as the referee method.
In cases where a high degree of test precision is needed standard Routine Analysis testing may not be suitable.
Non Routine Analyses
Sometimes more sophisticated testing is needed to investigate an ongoing problem or to obtain a better diagnosis of the condition of the engine or its components. These analyses are known as “Non Routine” analyses. Such tests can be carried out as part of an investigation or indeed be done as part of an oil based condition monitoring programme. Extended analysis suites can include tests carried out on engine deposits, debris & fuel samples as well as the oil samples themselves.
Non routine analyses typically require larger sample volumes (1 litre or so), and the analyses performed are chosen on a case by case basis with guidance from the oil supplier and / or engine manufacturer. Use of a different laboratory may also be required. It is necessary to provide specific and detailed information on the history of the engine & practical working details in order to determine which analysis is most useful to provide the most relevant diagnosis.
As such Non Routine analyses are more time consuming and specialised, they are also more costly so
it is important to provide as much background information on the nature of the problem at the point of
submitting the sample.
Key Actions required for a correct analysis
In order to enable a full and proper routine or non routine analysis it is essential that:
a. The oil sample bottles are clean
b. The oil sample taken is representative of the oil in service,
c. All supporting details (e.g. sampling point, date, oil name and hours of service) are attached to the sample container and so are made available to the laboratory
d. The sample is quickly dispatched to the laboratory
Sampling Procedure
How, when and where a sample is taken from within the lubrication system is very important. This is because only a very small amount of oil is taken during sampling. A 250 ml sample represents only a very small percentage of the total oil capacity which can be up to 100,000 litres. It goes without saying that it is essential to be sure that the sample taken is truly representative of the full oil volume and take the necessary precautions when sampling oils which may be hot and contained within pressurised systems, the use of gloves and face protection is advisory.
Some general, but key points regarding the acquisition of representative oil samples include:
a. Sample when the machine is running at normal operating temperature, never when the equipment is stationary or cold, or after any significant addition of fresh oil.
b. Sample from the main supply line of the engine, if necessary arrange to fit dedicated sampling valves that can be accessed easily and safely.
c. Always sample from the same sampling point for any particular piece of equipment.
d. Sample after flushing a small quantity of oil (0.5 - 1.0l) through the sampling point - and without operating the sampling valve between flushing and sampling.
e. Whenever possible fill the sample directly into the sampling bottle to avoid any unnecessary contamination.
f. Use only dedicated clean and dry sampling equipment intended for the sampling of used oils.
g. To avoid leakage fill the sample bottle to 90% capacity and ensure it is properly sealed before despatch to the laboratory.
Good Sampling Locations
1. System oil
Not all engines are equipped with sampling valves in the main lubricating oil system when delivered. It is therefore sometimes seen that the operator needs to remove e.g. a manometer before being able to take a sample of system oil. It is recommended that a dedicated sampling valve is placed in the circulating system before the engine entry.
The most representative sample of oil of the quality that the engine is exposed to, is taken from the lubricating oil system at the engine inlet. The sample should be taken at a location with a full flow condition to avoid getting the sample contaminated by precipitated sludge. In the case of horizontal piping with a low flow condition hence a risk of sludge forming in the bottom part of the pipe, it is recommended to place the sampling valve in the side or top of the pipe instead of in the bottom.
2. Centrifuges - Purifiers and clarifiers
Routine oil analysis cannot be used to assess the performance of centrifuges, purifiers and clarifiers as the tests normally offered cannot differentiate sufficiently between inlet and outlet conditions, therefore non-routine tests need to be employed which are based upon appropriate sampling and particle analysis techniques.
3. Scavenge drain oil (only 2-stroke engines)
Scavenge drain oil can be collected after each cylinder or in a common drain pipe collecting drain oil from all cylinder units.
Taking samples using the common drain pipe should be avoided as the effect of dilution and contamination between units reduces the opportunity of gaining a useful diagnosis of the effects of combustion and evidence of wear.
For two-stroke scavenge drain oil samples, a 250 ml sample may be difficult to achieve as the engine does not provide large amounts of scavenge drain oil. For this type of sample, 100 ml is usually sufficient. However it must be pointed out that the results of scavenge drain oil analysis are reliant upon the quality of the sampling procedure. In addition, it has been shown that the results can be significantly influenced by contamination with system oil, fuel, partially pyrolysed fuel, water and intercylinder cross contamination, therefore any analysis and subsequent diagnosis must take this into account.
The scavenge drain piping is usually equipped with a closing valve and a sample valve branching off the vertical piping between the engine and the closing valve. The sample is drawn by closing the closing valve and waiting until the piping has filled up sufficiently so that a sample of drain oil can be collected. Unfortunately, it may take quite some time to fill up the piping until the point of the sampling valve is reached due to the relatively low flow rate of scavenge drain oil in the line.
Sample Information
To guarantee that sample will be analysed without delay, it is vital that the label attached to the sample bottle is accurate and complete. Key information includes the name of the ship or power plant, the specific name of the engine, type of lubricant, type of engine, date of sampling and the number of hours of service. Omission or mistakes made in labelling may delay the analysis of the sample and make a correct assessment and recommendation impossible.
Characteristics
Characteristics are those measured by most oil analysis labs. They are the basic things that have to be measured and are detailed below.
1 Viscosity
The kinematic viscosity (kV) is commonly referred to as just ‘viscosity’ and is determined by measuring the time a fluid needs to flow through a defined capillary at a defined temperature. The viscosity describes the flow resistance of a fluid and is typically expressed as a kV@40 or kV@100 test result, where 40 or 100 denotes the test temperature used (°C).
The viscosity of lubricating oil is defined at 100°C according to the SAE J300 Industry Classification System and is expressed in mm2 s-1 or cSt (centistokes). In practice, this parameter is also measured at 40°C and many used oil analysis laboratories report the viscosity measurement at 40°C, 100°C or both. Kinematic viscosity is the absolute or dynamic viscosity in Pa. S divided by the fluid density.
Change to oil viscosity during operation is mainly influenced by oil contamination (Insolubles, fuel, soot, particles and water) and oxidation. In the case of a two stroke engine, the system oil could also be contaminated by the cylinder oil.
2 BN (Base Number)
The alkalinity of lubricating oil is defined as the quantity of hydrochloric acid or perchloric acid required to neutralize one gram of oil, expressed in terms of the equivalent number of milligrams of potassium hydroxide (mg KOH/g). The BN is measured by titration with acid.
The BN (formerly called TBN total base number) is a measure of the alkalinity reserve. It shows the potential of the lubricating oil to neutralize acids caused by combustion products condensing on the cylinder walls and elsewhere within the engine. For example sulphur in the fuel is converted to sulphur oxides during combustion - mainly SO2 along with a small proportion of SO3. Together with the water formed during the combustion process, the sulphur oxides condense on the cylinder walls as sulphuric acid, this acid is then neutralized by the alkalinity of the lubricant.
BN depletion is mainly influenced by the sulphur content of the fuel used, the oil consumption of the engine and the operating conditions of the engine.
3 Water content
The water content of used oil is typically measured by Karl-Fischer titration or by infrared spectroscopy rather than by the more commonly referenced distillation method.
Water can originate from various sources and can cause fresh or sea water contamination of the oil. Water in lubricating oil is a pollutant and is potentially harmful to the engine even in low quantity. Unfortunately traces of water in used lubricating oil tend to be unavoidable - they can result from internal leakages (water jacket, coolers), build up of condensation, or, through use of an incorrectly set separator.
4 Flash Point
The temperature at which a spark or a flame can ignite the oil vapor is called the flash point. This is the lowest temperature, at which vapours from the oil can be ignited. Change of flash point is mainly influenced by fuel contamination and to a certain extent by oil degradation.
There are different Industry flash point test methods including the “Open Cup” and “Closed Cup” type
methods.
It must be noted that due to evaporation losses the result with the Closed Cup method is generally lower than the result with the Open Cup method. NB: Flash Point is NOT a measure of flammability.
5 Insolubles
Insolubles can be defined as solid material that can be isolated from the oil by filtration or by centrifugation after a solvent (pentane, heptane or toluene) has been added.
However it should be realised that this is not the amount of insoluble material (particles) in the oil! It’s important to know that different insolubles analysis methods will generate different values and so only the analyses made by the same test method are reliably comparable with one another.
The amount of Insolubles is increased in case of oil contamination (e.g. fuel) and by degradation of additives.
6 Metallic elements
The metallic elements in the oil are measured by spectroscopic methods. This can be atomic emission, atomic absorption or X-ray fluorescence spectroscopy.
The elements measured include additive elements, wear metals, combustion products and external contaminants e.g. from cooling water or intake air. Therefore these values are influenced by the additive package of the oil, component wear and fuel combustion.
Mostly Plasma Emission Spectrometry (ICP - Inductively Coupled Plasma) is used to determine the metal contents of used lubricating oils. However particles bigger than 5 - 7 μm are not detected by this method as they are not fully vaporised in the plasma due to mass effects and so wear element concentration can be underestimated in cases of particularly high wear. Here non-routine analysis like x-ray fluorescence spectroscopy, ashing of the sample before ICP measurement (to collect 100% of the material within the sample), ferrography, ferrometry, PQ (Particle Quantifier) and similar methods can help.
It must be realised that - according to the type of apparatus and way of sample preparation, the results obtained can be very different. When comparing and plotting results for trend analysis, therefore, it is important to ensure that the data are generated by the same laboratory, the same apparatus and the same method.
The accuracy and lower detection limits of the methods have to be considered carefully before any alarm or alert condition is applied to the analysis- especially low values (below 5 ppm) should be interpreted with caution.
7. AN (Acid number)
The AN formerly called Total Acid Number (TAN) describes the amount of acidic components in the oil. It is measured by titration with a base such as Potassium Hydroxide (KOH). The acidity of a lubricant is measured by the amount of KOH required for neutralization and is expressed in mg KOH/g.
The AN is relevant for lower BN oil and mainly in engines operated on gas. It is influenced by oil degradation.
8. Oxidation
The oxidation is measured by infrared spectroscopy. Oxidation products within the oil have an absorption at 1710 cm-1. The number reported is the absorption value at this wavelength. Oxidation is a process in which oxygen reacts with hydrocarbon molecules to form insoluble carbonaceous residues and resins. The oxidation of an oil is influenced by temperature and contamination.
9. Nitration
The principle of measuring Nitration is very similar to oxidation but uses a different infrared wavelength (1620 cm-1). The nitration is influenced by oil degradation and results from the reaction of the oil with NOx. This
value is typically only measured for gas engine oils and high-speed engine oils.
10. Sulphation
Sulphation is measured at an infrared wavelength of 1150 cm-1. Sulphate by-products are typically formed from the oxidation of Sulphur components of the additives or fuel contamination and results from the reaction of the oil with SO2. Typically as BN reduces, absorption peaks indicative of Sulphation increase.
For any or all of the above measurements a fresh oil sample is needed in order to create a baseline for determining the rate and degree of degradation that has subsequently occurred. Only the results from same laboratory and the same analysis method should be compared with each other in this respect.
11. Particle Count
Particle counting is done in order to determine and trend the level of particulate or dirt loading within an oil.
This can be determined by light obscurance or light scattering techniques or by image analysis of particles that have been filtered from the oil. The result is expressed as the amount of particles of different sizes.
Typically, the particle counting is done using optical evaluation using standard industry methods (like ISO 4406, NAS 1638). Basically, these methods were developed for hydraulic oils and are not very suitable for used engine lube oils which are much darker and as such more difficult to assess due to the presence of soot and pollution This means that it is necessary to dilute the sample as much as1:10, which will lead to significant variation in the results, as such this type of test is not routinely carried out for engine oils.
When it is necessary to determine the particle count within used lubricants a number of laboratories have developed in-house methods which are non-routine but are acceptable for determination of the particle population and size distribution. These methods will in time become acceptable standards as experience develops and confidence increases.
The size and amount of particles is influenced by wear condition, contamination of the oil with particles (e. g. through charge air), and products of combustion and of course by oil treatment.
12. VI (Viscosity Index)
The VI is calculated from the two measurements of viscosity at 100°C and 40°C and describes the viscosity-temperature relationship of the oil. A high VI indicates a small change of viscosity with temperature.
The VI is mainly defined by the base oil properties and by additives used. A high VI is important for multi-grade oils where a restricted range of viscosity over a large temperature range is required to meet specification. Such a high VI enables optimum performance under varying temperature conditions.
13. Sulphated Ash
To measure sulphated ash content the oil is burned to remove the hydrocarbons and the remaining ash is converted into sulphates by reaction with sulphuric acid. The resulting sulphated ash represents the amount of ash building additives in the oil.
This technique measures the amount of detergent and anti-wear additives in new lubricating oil and so is not typically applied to used oils.
14. Soot
The amount of soot is measured by infrared absorption. The value is influenced by combustion, oil degradation and of course by the quality of the oil treatment.
15. Asphaltene Content
The asphaltene content can be measured by a chromatographic method, separating molecules according their molecular size. Asphaltenes are heavy molecules originating from the heavy fuel oil. The asphaltene content
represents the amount of unburned heavy fuel components. Such components can enter the oil
through fuel leakages or as unburned fuel via the combustion chamber.
16. PQ (Particles Quantifier) Index
The PQ Index determines the relative quantity of ferrous metals in an oil sample as a function of the quantity of ferromagnetic debris in the sample. As the oil sample is brought into close proximity to the controlled magnetic flux field within the apparatus, this field will distort proportionally to the amount of ferromagnetic debris within the sample. The amount of distortion is expressed as the "PQ Index" and is independent of particle size. This value is then used in conjunction with spectrometric or other ferrographic analysis data.
Generally, as a wear situation deteriorates within a given system, more large particles tend to be generated. As a result, emission spectroscopy or atomic absorption test results which only capture data from particles typically less than 5-7 μm in size, will be seen to flatten or even reduce over time against an increasing PQ index value. The sensitivity of the PQ index is most effective where particles are in excess of approximately 20μm, meaning that there is however a dip in sensitivity between 7 and 20μm but wear debris under aggressive tribological conditions tends to produce a wear debris population over a wide size range up to and in excess of the critical clearance dimensions of interacting surfaces.
17. Ferrography
In Analytical Ferrography a ferrogram is created by either rotary particle deposition or by linear gravity slide. Both methods require the sample to move through a magnetic field which has the effect of aligning the ferrous particles in size order.
The resultant a ferrogram is then studied by an expert to quantify the type, concentration, size and morphology of ferrous particles. Here aspects such as the processes involved in the formation can be described such as cutting, fatigue, adhesion, fretting etc. thus giving further understanding of the wear situation within the machine. It is extremely important to ensure that the experts dealing with the Ferrography are fully familiar with the type of equipment being assessed. The sump volumes of large engines can be significantly greater compared to smaller equivalents and a period of learning must be built into any relationship with a new oil analysis laboratory. Furthermore, trending of Ferrography is potentially misleading as the samples need to be extremely representative and taken in such a way as to ensure good repeatability and reproducibility.
18. Ferrometry
Ferrometry, a similar technique to the PQ Index, measures all the ferrous particles (100% efficient for particles size > 0.1 μm) of a fluid. The principle is to precipitate all magnetic particles by creating a strong magnetic field trough a glass tube. A fibre optic bundle directs light at two locations where large (> 5 μm) and small particles are deposited by the magnet. The measure is obtained by a reduction of light, proportional to the quantity of particles captured. Two sets of readings are made: one for the large particles (L), one for the small particles (S). From these values, the following calculation can be made:
Wear Particles Concentration (WPC) is derived by adding L+S, divided by the volume (V) of sample (L + S)/V
Percentage of large Particles (PLP). When volume of sample is 1ml
WPC = L+S and the PLP can be calculated as follows; PLP = 100xL/(S+L)
Wear Severity Index; WSI =(L² + S ²)/ V
19. Blotter Tests
There are a number of “Blotter” or “Patch” test methods which can be used to quickly reference the condition of used engine oil. They rely upon the relative density and film forming properties of the various constituents of the used lubricant. More specifically, as an oil ages and the dispersancy and detergency capabilities deteriorate, it is possible to detect these via the different types of pattern that are left behind.
A small quantity of used oil sample and the corresponding fresh oil is dropped onto a sheet of special filter paper and allowed to spread. For simple tests it is used purely for comparison. For the basic analysis the droplet will behave in a number of ways. Firstly the insolubles will separate from the oil thus allowing a basic comparison to be made. Quantification of this can be assessed by the trained analyst but should not be quoted as there are no statistical qualitative or quantative controls which apply in this regard.
For a more quantitative assessment of insolubles there is a more detailed analysis based upon a photometric measurement. After patch development is complete, the sheet is then transferred to a special photometer which has been adjusted to zero using the spot of the fresh oil. The absorbance of used oil spot is measured automatically over concentric zones. Absorbance in the central zone provides a measure of the amount of sooty insoluble material present in the used oil and the radial distribution of absorbance relates to the lubricant’s dispersancy.
Need of used oil analysis
The purpose of conducting used oil analysis is two-fold:
a. To assess the condition of the oil - to provide recommendations on its suitability for further use and optimisation of the oil change intervals.
b. To assess the condition of the engine - to enable the detection and thus prevention of issues which left unattended may impact the reliable operation of the engine.
Routine Analyses
The physical & chemical characteristics of an in-service oil are obviously linked back to the specific type of oil, its age and the conditions under which it operates. For engine oils, the tests carried out under “Routine Analyses” will typically include:
1) Viscosity
2) Water content
3) Base Number (BN) or Alkalinity reserve
4) Insolubles
5) Flash Point
6) Elements (measuring the concentration of additives and levels of wear metals, etc.)
These tests are typically carried out in highly automated specialised laboratories. Only a small volume of oil is needed- typically less than 250 ml for a full Routine Analysis, and fully automated equipment can be used. This makes Routine Analysis quick, easy & economical to run. Normally the test method used will be according to conventional ISO or ASTM standards but where in-house specialised test methods are used these can have the advantage that the tests are specifically designed for their relevance to ‘used oil’ based on many years field experience. In cases of a dispute the ISO or ASTM methods are used as the referee method.
In cases where a high degree of test precision is needed standard Routine Analysis testing may not be suitable.
Non Routine Analyses
Sometimes more sophisticated testing is needed to investigate an ongoing problem or to obtain a better diagnosis of the condition of the engine or its components. These analyses are known as “Non Routine” analyses. Such tests can be carried out as part of an investigation or indeed be done as part of an oil based condition monitoring programme. Extended analysis suites can include tests carried out on engine deposits, debris & fuel samples as well as the oil samples themselves.
Non routine analyses typically require larger sample volumes (1 litre or so), and the analyses performed are chosen on a case by case basis with guidance from the oil supplier and / or engine manufacturer. Use of a different laboratory may also be required. It is necessary to provide specific and detailed information on the history of the engine & practical working details in order to determine which analysis is most useful to provide the most relevant diagnosis.
As such Non Routine analyses are more time consuming and specialised, they are also more costly so
it is important to provide as much background information on the nature of the problem at the point of
submitting the sample.
Key Actions required for a correct analysis
In order to enable a full and proper routine or non routine analysis it is essential that:
a. The oil sample bottles are clean
b. The oil sample taken is representative of the oil in service,
c. All supporting details (e.g. sampling point, date, oil name and hours of service) are attached to the sample container and so are made available to the laboratory
d. The sample is quickly dispatched to the laboratory
Sampling Procedure
How, when and where a sample is taken from within the lubrication system is very important. This is because only a very small amount of oil is taken during sampling. A 250 ml sample represents only a very small percentage of the total oil capacity which can be up to 100,000 litres. It goes without saying that it is essential to be sure that the sample taken is truly representative of the full oil volume and take the necessary precautions when sampling oils which may be hot and contained within pressurised systems, the use of gloves and face protection is advisory.
Some general, but key points regarding the acquisition of representative oil samples include:
a. Sample when the machine is running at normal operating temperature, never when the equipment is stationary or cold, or after any significant addition of fresh oil.
b. Sample from the main supply line of the engine, if necessary arrange to fit dedicated sampling valves that can be accessed easily and safely.
c. Always sample from the same sampling point for any particular piece of equipment.
d. Sample after flushing a small quantity of oil (0.5 - 1.0l) through the sampling point - and without operating the sampling valve between flushing and sampling.
e. Whenever possible fill the sample directly into the sampling bottle to avoid any unnecessary contamination.
f. Use only dedicated clean and dry sampling equipment intended for the sampling of used oils.
g. To avoid leakage fill the sample bottle to 90% capacity and ensure it is properly sealed before despatch to the laboratory.
Good Sampling Locations
1. System oil
Not all engines are equipped with sampling valves in the main lubricating oil system when delivered. It is therefore sometimes seen that the operator needs to remove e.g. a manometer before being able to take a sample of system oil. It is recommended that a dedicated sampling valve is placed in the circulating system before the engine entry.
The most representative sample of oil of the quality that the engine is exposed to, is taken from the lubricating oil system at the engine inlet. The sample should be taken at a location with a full flow condition to avoid getting the sample contaminated by precipitated sludge. In the case of horizontal piping with a low flow condition hence a risk of sludge forming in the bottom part of the pipe, it is recommended to place the sampling valve in the side or top of the pipe instead of in the bottom.
2. Centrifuges - Purifiers and clarifiers
Routine oil analysis cannot be used to assess the performance of centrifuges, purifiers and clarifiers as the tests normally offered cannot differentiate sufficiently between inlet and outlet conditions, therefore non-routine tests need to be employed which are based upon appropriate sampling and particle analysis techniques.
3. Scavenge drain oil (only 2-stroke engines)
Scavenge drain oil can be collected after each cylinder or in a common drain pipe collecting drain oil from all cylinder units.
Taking samples using the common drain pipe should be avoided as the effect of dilution and contamination between units reduces the opportunity of gaining a useful diagnosis of the effects of combustion and evidence of wear.
For two-stroke scavenge drain oil samples, a 250 ml sample may be difficult to achieve as the engine does not provide large amounts of scavenge drain oil. For this type of sample, 100 ml is usually sufficient. However it must be pointed out that the results of scavenge drain oil analysis are reliant upon the quality of the sampling procedure. In addition, it has been shown that the results can be significantly influenced by contamination with system oil, fuel, partially pyrolysed fuel, water and intercylinder cross contamination, therefore any analysis and subsequent diagnosis must take this into account.
The scavenge drain piping is usually equipped with a closing valve and a sample valve branching off the vertical piping between the engine and the closing valve. The sample is drawn by closing the closing valve and waiting until the piping has filled up sufficiently so that a sample of drain oil can be collected. Unfortunately, it may take quite some time to fill up the piping until the point of the sampling valve is reached due to the relatively low flow rate of scavenge drain oil in the line.
Sample Information
To guarantee that sample will be analysed without delay, it is vital that the label attached to the sample bottle is accurate and complete. Key information includes the name of the ship or power plant, the specific name of the engine, type of lubricant, type of engine, date of sampling and the number of hours of service. Omission or mistakes made in labelling may delay the analysis of the sample and make a correct assessment and recommendation impossible.
Characteristics
Characteristics are those measured by most oil analysis labs. They are the basic things that have to be measured and are detailed below.
1 Viscosity
The kinematic viscosity (kV) is commonly referred to as just ‘viscosity’ and is determined by measuring the time a fluid needs to flow through a defined capillary at a defined temperature. The viscosity describes the flow resistance of a fluid and is typically expressed as a kV@40 or kV@100 test result, where 40 or 100 denotes the test temperature used (°C).
The viscosity of lubricating oil is defined at 100°C according to the SAE J300 Industry Classification System and is expressed in mm2 s-1 or cSt (centistokes). In practice, this parameter is also measured at 40°C and many used oil analysis laboratories report the viscosity measurement at 40°C, 100°C or both. Kinematic viscosity is the absolute or dynamic viscosity in Pa. S divided by the fluid density.
Change to oil viscosity during operation is mainly influenced by oil contamination (Insolubles, fuel, soot, particles and water) and oxidation. In the case of a two stroke engine, the system oil could also be contaminated by the cylinder oil.
2 BN (Base Number)
The alkalinity of lubricating oil is defined as the quantity of hydrochloric acid or perchloric acid required to neutralize one gram of oil, expressed in terms of the equivalent number of milligrams of potassium hydroxide (mg KOH/g). The BN is measured by titration with acid.
The BN (formerly called TBN total base number) is a measure of the alkalinity reserve. It shows the potential of the lubricating oil to neutralize acids caused by combustion products condensing on the cylinder walls and elsewhere within the engine. For example sulphur in the fuel is converted to sulphur oxides during combustion - mainly SO2 along with a small proportion of SO3. Together with the water formed during the combustion process, the sulphur oxides condense on the cylinder walls as sulphuric acid, this acid is then neutralized by the alkalinity of the lubricant.
BN depletion is mainly influenced by the sulphur content of the fuel used, the oil consumption of the engine and the operating conditions of the engine.
3 Water content
The water content of used oil is typically measured by Karl-Fischer titration or by infrared spectroscopy rather than by the more commonly referenced distillation method.
Water can originate from various sources and can cause fresh or sea water contamination of the oil. Water in lubricating oil is a pollutant and is potentially harmful to the engine even in low quantity. Unfortunately traces of water in used lubricating oil tend to be unavoidable - they can result from internal leakages (water jacket, coolers), build up of condensation, or, through use of an incorrectly set separator.
4 Flash Point
The temperature at which a spark or a flame can ignite the oil vapor is called the flash point. This is the lowest temperature, at which vapours from the oil can be ignited. Change of flash point is mainly influenced by fuel contamination and to a certain extent by oil degradation.
There are different Industry flash point test methods including the “Open Cup” and “Closed Cup” type
methods.
It must be noted that due to evaporation losses the result with the Closed Cup method is generally lower than the result with the Open Cup method. NB: Flash Point is NOT a measure of flammability.
5 Insolubles
Insolubles can be defined as solid material that can be isolated from the oil by filtration or by centrifugation after a solvent (pentane, heptane or toluene) has been added.
However it should be realised that this is not the amount of insoluble material (particles) in the oil! It’s important to know that different insolubles analysis methods will generate different values and so only the analyses made by the same test method are reliably comparable with one another.
The amount of Insolubles is increased in case of oil contamination (e.g. fuel) and by degradation of additives.
6 Metallic elements
The metallic elements in the oil are measured by spectroscopic methods. This can be atomic emission, atomic absorption or X-ray fluorescence spectroscopy.
The elements measured include additive elements, wear metals, combustion products and external contaminants e.g. from cooling water or intake air. Therefore these values are influenced by the additive package of the oil, component wear and fuel combustion.
Mostly Plasma Emission Spectrometry (ICP - Inductively Coupled Plasma) is used to determine the metal contents of used lubricating oils. However particles bigger than 5 - 7 μm are not detected by this method as they are not fully vaporised in the plasma due to mass effects and so wear element concentration can be underestimated in cases of particularly high wear. Here non-routine analysis like x-ray fluorescence spectroscopy, ashing of the sample before ICP measurement (to collect 100% of the material within the sample), ferrography, ferrometry, PQ (Particle Quantifier) and similar methods can help.
It must be realised that - according to the type of apparatus and way of sample preparation, the results obtained can be very different. When comparing and plotting results for trend analysis, therefore, it is important to ensure that the data are generated by the same laboratory, the same apparatus and the same method.
The accuracy and lower detection limits of the methods have to be considered carefully before any alarm or alert condition is applied to the analysis- especially low values (below 5 ppm) should be interpreted with caution.
7. AN (Acid number)
The AN formerly called Total Acid Number (TAN) describes the amount of acidic components in the oil. It is measured by titration with a base such as Potassium Hydroxide (KOH). The acidity of a lubricant is measured by the amount of KOH required for neutralization and is expressed in mg KOH/g.
The AN is relevant for lower BN oil and mainly in engines operated on gas. It is influenced by oil degradation.
8. Oxidation
The oxidation is measured by infrared spectroscopy. Oxidation products within the oil have an absorption at 1710 cm-1. The number reported is the absorption value at this wavelength. Oxidation is a process in which oxygen reacts with hydrocarbon molecules to form insoluble carbonaceous residues and resins. The oxidation of an oil is influenced by temperature and contamination.
9. Nitration
The principle of measuring Nitration is very similar to oxidation but uses a different infrared wavelength (1620 cm-1). The nitration is influenced by oil degradation and results from the reaction of the oil with NOx. This
value is typically only measured for gas engine oils and high-speed engine oils.
10. Sulphation
Sulphation is measured at an infrared wavelength of 1150 cm-1. Sulphate by-products are typically formed from the oxidation of Sulphur components of the additives or fuel contamination and results from the reaction of the oil with SO2. Typically as BN reduces, absorption peaks indicative of Sulphation increase.
For any or all of the above measurements a fresh oil sample is needed in order to create a baseline for determining the rate and degree of degradation that has subsequently occurred. Only the results from same laboratory and the same analysis method should be compared with each other in this respect.
11. Particle Count
Particle counting is done in order to determine and trend the level of particulate or dirt loading within an oil.
This can be determined by light obscurance or light scattering techniques or by image analysis of particles that have been filtered from the oil. The result is expressed as the amount of particles of different sizes.
Typically, the particle counting is done using optical evaluation using standard industry methods (like ISO 4406, NAS 1638). Basically, these methods were developed for hydraulic oils and are not very suitable for used engine lube oils which are much darker and as such more difficult to assess due to the presence of soot and pollution This means that it is necessary to dilute the sample as much as1:10, which will lead to significant variation in the results, as such this type of test is not routinely carried out for engine oils.
When it is necessary to determine the particle count within used lubricants a number of laboratories have developed in-house methods which are non-routine but are acceptable for determination of the particle population and size distribution. These methods will in time become acceptable standards as experience develops and confidence increases.
The size and amount of particles is influenced by wear condition, contamination of the oil with particles (e. g. through charge air), and products of combustion and of course by oil treatment.
12. VI (Viscosity Index)
The VI is calculated from the two measurements of viscosity at 100°C and 40°C and describes the viscosity-temperature relationship of the oil. A high VI indicates a small change of viscosity with temperature.
The VI is mainly defined by the base oil properties and by additives used. A high VI is important for multi-grade oils where a restricted range of viscosity over a large temperature range is required to meet specification. Such a high VI enables optimum performance under varying temperature conditions.
13. Sulphated Ash
To measure sulphated ash content the oil is burned to remove the hydrocarbons and the remaining ash is converted into sulphates by reaction with sulphuric acid. The resulting sulphated ash represents the amount of ash building additives in the oil.
This technique measures the amount of detergent and anti-wear additives in new lubricating oil and so is not typically applied to used oils.
14. Soot
The amount of soot is measured by infrared absorption. The value is influenced by combustion, oil degradation and of course by the quality of the oil treatment.
15. Asphaltene Content
The asphaltene content can be measured by a chromatographic method, separating molecules according their molecular size. Asphaltenes are heavy molecules originating from the heavy fuel oil. The asphaltene content
represents the amount of unburned heavy fuel components. Such components can enter the oil
through fuel leakages or as unburned fuel via the combustion chamber.
16. PQ (Particles Quantifier) Index
The PQ Index determines the relative quantity of ferrous metals in an oil sample as a function of the quantity of ferromagnetic debris in the sample. As the oil sample is brought into close proximity to the controlled magnetic flux field within the apparatus, this field will distort proportionally to the amount of ferromagnetic debris within the sample. The amount of distortion is expressed as the "PQ Index" and is independent of particle size. This value is then used in conjunction with spectrometric or other ferrographic analysis data.
Generally, as a wear situation deteriorates within a given system, more large particles tend to be generated. As a result, emission spectroscopy or atomic absorption test results which only capture data from particles typically less than 5-7 μm in size, will be seen to flatten or even reduce over time against an increasing PQ index value. The sensitivity of the PQ index is most effective where particles are in excess of approximately 20μm, meaning that there is however a dip in sensitivity between 7 and 20μm but wear debris under aggressive tribological conditions tends to produce a wear debris population over a wide size range up to and in excess of the critical clearance dimensions of interacting surfaces.
17. Ferrography
In Analytical Ferrography a ferrogram is created by either rotary particle deposition or by linear gravity slide. Both methods require the sample to move through a magnetic field which has the effect of aligning the ferrous particles in size order.
The resultant a ferrogram is then studied by an expert to quantify the type, concentration, size and morphology of ferrous particles. Here aspects such as the processes involved in the formation can be described such as cutting, fatigue, adhesion, fretting etc. thus giving further understanding of the wear situation within the machine. It is extremely important to ensure that the experts dealing with the Ferrography are fully familiar with the type of equipment being assessed. The sump volumes of large engines can be significantly greater compared to smaller equivalents and a period of learning must be built into any relationship with a new oil analysis laboratory. Furthermore, trending of Ferrography is potentially misleading as the samples need to be extremely representative and taken in such a way as to ensure good repeatability and reproducibility.
18. Ferrometry
Ferrometry, a similar technique to the PQ Index, measures all the ferrous particles (100% efficient for particles size > 0.1 μm) of a fluid. The principle is to precipitate all magnetic particles by creating a strong magnetic field trough a glass tube. A fibre optic bundle directs light at two locations where large (> 5 μm) and small particles are deposited by the magnet. The measure is obtained by a reduction of light, proportional to the quantity of particles captured. Two sets of readings are made: one for the large particles (L), one for the small particles (S). From these values, the following calculation can be made:
Wear Particles Concentration (WPC) is derived by adding L+S, divided by the volume (V) of sample (L + S)/V
Percentage of large Particles (PLP). When volume of sample is 1ml
WPC = L+S and the PLP can be calculated as follows; PLP = 100xL/(S+L)
Wear Severity Index; WSI =(L² + S ²)/ V
19. Blotter Tests
There are a number of “Blotter” or “Patch” test methods which can be used to quickly reference the condition of used engine oil. They rely upon the relative density and film forming properties of the various constituents of the used lubricant. More specifically, as an oil ages and the dispersancy and detergency capabilities deteriorate, it is possible to detect these via the different types of pattern that are left behind.
A small quantity of used oil sample and the corresponding fresh oil is dropped onto a sheet of special filter paper and allowed to spread. For simple tests it is used purely for comparison. For the basic analysis the droplet will behave in a number of ways. Firstly the insolubles will separate from the oil thus allowing a basic comparison to be made. Quantification of this can be assessed by the trained analyst but should not be quoted as there are no statistical qualitative or quantative controls which apply in this regard.
For a more quantitative assessment of insolubles there is a more detailed analysis based upon a photometric measurement. After patch development is complete, the sheet is then transferred to a special photometer which has been adjusted to zero using the spot of the fresh oil. The absorbance of used oil spot is measured automatically over concentric zones. Absorbance in the central zone provides a measure of the amount of sooty insoluble material present in the used oil and the radial distribution of absorbance relates to the lubricant’s dispersancy.
Bunkering - standing instructions, checklists and BDN
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