evaluating the merits of a bunker claim...

EVALUATE THE MERITS

OF A BUNKER CLAIM

By the IBIATechnical Working Group

IBIA’S THANKS GO TO COUNCIL MEMBER

CHRIS FISHER

FOR THE RESEARCH AND WORK

IN PRODUCING THIS GUIDE

2

Contents Page Introduction................................................................................................. 3

Background.................................................................................................. 4

Quality characteristics and test methods ……………………………………………….. 4

Density ......................................................................................................... 4

Viscosity....................................................................................................... 5

Flash Point................................................................................................... 6

Pour Point................................................................................................... 6

Micro Carbon Residue (MCR)...................................................................... 6

Ash Content................................................................................................. 7

Water........................................................................................................... 7

Sulphur........................................................................................................ 8

Vanadium.................................................................................................... 8

Aluminum + Silicon.................................................................................... 8

Total Sediment…………………......................................................................... 9

TSE……………….……………………………………………………………………………………. 9

TSA ……………………………………………………………………………………………………. 9

TSP ……………………………………………………………………………………………………. 10

Phosphorous, Calcium and Zinc …………………………………………………………… 10

Cloud Point ………………………………............................................................... 11

Cetane Index................................................................................................ 11

Appearance ……………………………………………………………………………………….. 11

Evaluating a quality problem ……………………………………………………………….. 12

Evaluation of the reliability of the tested sample …………………………………… 12

Evaluation of laboratory test results …………………………………………………….. 14

Using test results to resolve a dispute …………………………………………………… 20

Conclusions ……………………………………………………………………………………….. 21

3

Every day, suppliers, owners, charterers, traders and others engage in transactions involving large quantities of bunkers at locations throughout the world. This is frequently done without the knowledge of the complexities which are involved in the manufacture of bunker fuels. These are generally traded using several readily available product quality specifications. Among these specifications, the most widely used is ISO 8217. Readers are reminded to make sure they use the latest version of this standard. These specifications are often used without proper knowledge of their interpretation. Complicated claims can and do arise from a rash of premature decisions having been taken on the face of a single test result without understanding the inherent limitations of the fuel sampling and testing procedures. These occurrences could be reduced with the help of representative sampling, appropriate testing and proper tools for interpretation of test results. The analyses presented here deal with 8217: 2005 specification and the rules of interpretation of results as set out in ISO 4259.

Submitted Samples

4

Test method ISO 3675 (Equivalent methods - IP – 160, ASTM D 1298)

NB: The above methods are by hydrometer and most laboratories now use the “digital” method ISO 12185 or IP 365. All these methods are considered to be equivalent to the above hydrometer methods. Measured in kg/m3 (SI), density is an important quality characteristic and there are at least three reasons why:-

1. The energy content of the fuel is inversely related to the density. This is a compositional matter. As a general rule, the lower the density, the greater the hydrogen content of the fuel. The more hydrogen in the fuel, the greater the energy content for a given mass.

2. Density is important in that it used to determine the mass of fuel (tonnes) delivered from

the volume figures.

3. The treatment systems on the vessel, used to separate water and solids from the fuel (centrifuges), are dependent on the difference in density between the fuel and these extraneous materials. Fuel treatment systems are designed to handle a range of fuel densities, but conventional systems start having difficulties when the fuel density exceeds 991 kg/m 3

There are some fuel treatment systems that can handle fuel densities up to 1010 kg/m 3

The purpose of any specification is to control to a certain minimum standard, the quality parameters of the commodity, or the service being traded. The primary reasons governing the need for such control revolve around concerns for safety, the environment and equipment requirements. In the case of marine fuels, the establishment of these minimum standards was originally undertaken by the British Standards Institution (BSI) and subsequently by the International Standards Organisation (ISO), the International Council on Combustion Engines (CIMAC), and the American Society for Testing Materials (ASTM). Of these, ISO 8217: 2005 has become the accepted industry standard. In this publication we have described the fuel quality characteristics and the test methods prescribed in the current ISO 8217, 2005. Following this we have highlighted the importance of understanding the precision of the test methods and how the results may be used to evaluate the merit of a bunker quality claim. It is important to remember that test results can only be compared when the test method used is the same or an equivalent method.

DDDDENSITYENSITYENSITYENSITY

QQUUAALLIITTYY CCHHAARRAACCTTEERRIISSTTIICCSS AANNDD TTEESSTT MMEETTHHOODDSS

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Test Method ISO 3104 (Equivalent methods IP-71, ASTM D445)

Recorded in mm 2/sec (a.k.a. - cSt), this parameter measures a fluid’s resistance to flow. The viscosity of petroleum products is greatly affected by temperature, so it is very important to know the reference temperature at which it is measured.

For residual fuel oils, viscosity is most commonly measured at 50 °C and, for distillates, at 40 °C. In most cases, viscosity is not a critical parameter, but viscosity at the point of injection into the engine cylinder is important for a proper fuel atomization and combustion. Most vessels are able to modify the injection temperature to compensate for minor variances in fuel viscosity. Suppliers control the viscosity of intermediate fuel oils by blending quantities of distillate that has low viscosity with residual components that have high viscosity. Residual fuels for bunkers have a viscosity range between 30 and 700cSt at 500C.

VVVVISCOSITYISCOSITYISCOSITYISCOSITY

Viscosity TestViscosity TestViscosity TestViscosity Test

6


Recorded in degrees Celsius, this parameter measures the temperature at which sufficient vapour is generated to yield a combustible mixture in a closed environment of the test apparatus. The ISO 8217 minimum flash point for all marine fuels is 60 °C (except for ISO DMX, used only for emergency equipment, which has a minimum flash of 43 °C). There are safety and legal requirements to meet this specification and it is therefore a critical limit. Storage temperatures for fuel oils should be kept well (10 degrees °C) below the flash point. It must be stressed that there is no correlation between flash point and explosivity. Fuels with flash points above 60C can produce flammable gas when stored in tanks and sources of ignition must always be avoided with all bunker fuels.


Recorded in degrees Celsius, the pour point is the lowest temperature at which the fuel will still flow (3 °C above the solidifying temperature). This parameter is a factor primarily with fuels having a high wax content, but it can also be a factor with normal fuels in very cold conditions. Generally, this characteristic is not critical as the majority of vessels have the heating capacity to handle most fuels available in the marketplace. However, if the fuel is allowed to solidify, reliquifying the fuel will be difficult as the liquid fuel around the heating coils can have an insulating effect. Particular care is needed on ships which have little or no tank heating capacity and use low viscosity grades.

Test Method ISO 10370 (Equivalent method ASTM D4530) Recorded in percent mass, MCR

measures the tendency of a fuel to deposit carbon (as coke) under specified conditions of temperature, pressure and environment. Among the factors affecting the MCR content of fuels are fuel grade (lower viscosity grades have more diluents, and these generally have lower MCR values), processing, and crude source. These last two influence, among other things, the asphaltene content which historically has a directional correlation to carbon deposition. High carbon content may lead to fouling of fuel injectors, cylinder components and turbo chargers

FFFFLASHLASHLASHLASH PPPPOINTOINTOINTOINT

PPPPOUROUROUROUR PPPPOINTOINTOINTOINT

MMMMICROICROICROICRO CCCCARBONARBONARBONARBON RRRRESIDUEESIDUEESIDUEESIDUE

(MCR)(MCR)(MCR)(MCR)

7


Recorded in percent mass, the ash is the amount of material remaining after the combustion of the fuel takes place at a very high temperature to remove carbon. For marine fuels, the typical levels of ash range between 0.02 and 0.09 percent. Primarily, the ash is composed of trace metals in the fuels. These metals are either naturally occurring in the fuel or are introduced by various contamination sources. Most common among the naturally found metals in fuels are vanadium and nickel. Sodium is most commonly present as a result of salt water contamination in transport, but can also be introduced during crude processing (ie. as a treatment to neutralize acids or reduce hydrogen sulphide.) Aluminium and silicon are two other metals commonly found in marine fuels. The source of these is usually catalytically cracked fuel components used for the purpose of blending. Finally, there can be extraneous solids such as rust and dirt, primarily from tank bottoms, etc. If the ash content of the fuel is significantly greater than might otherwise be explained by the vanadium, sodium, aluminium and silicon, additional testing may be warranted.


Recorded in volume percent, water is commonly found in marine fuels. Water is present during processing and transport. It is also the outcome of tank condensation. Industry standards for this parameter are generally well accepted, and in most cases vessels have the ability to handle even greater than the max 0.5% which the ISO specification allows. In practice, most fuels (80%) contain 0.3% or less. In instances of excessive water, an appropriate quantity adjustment is warranted.

AAAASHSHSHSH CCCCONTENT ONTENT ONTENT ONTENT

WWWWATERATERATERATER

Water by Distillation

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Reported in percent mass, sulphur (next to carbon and hydrogen) is one of the most common elements found in all petroleum-based fuels. The sulphur content of the vast majority of marine residual fuels ranges from 1.0 to 4.0 percent, although there are some locations in the world where the sulphur can be below 1%. The world average is currently around 2.7%. The potential problems associated with the combustion of sulphur (especially in the presence of water) to form sulphurous and sulphuric acids, has been virtually eliminated by the development and use of high TBN (Total Base Number) cylinder lubricating oils. The sulphur content of fuel is now of prime concern with respect to environmental legislation. Readers must check the latest international, regional and local regulations which limit the level of sulphur in marine fuels.

Test Method ISO 14597 (Equivalent methods IP 501, IP470)

Recorded in mg/kg (commonly referred to as ppm), vanadium is a metal naturally found in crude oil. Vanadium is found in the form of organic complexes which are soluble / miscible in oils and have high boiling points. The result is that the vanadium in the crude ends up in the residual used to make marine fuels. Vanadium content in residual fuel oils range from less than 10 mg/kg to greater than 450 mg/kg, depending on the source crude oil. When the fuel is burned, the hydrocarbon portion of the compound is combusted and the vanadium becomes part of the remaining ash component. With the proper conditions of temperature and composition, vanadium combines with sodium, and the oxides of sulphur, to form corrosive compounds which can be detrimental to engine components. The effect of these conditions can be significantly reduced by the use of engines equipped with nimonic valves and with adjustments to valve cooling temperatures.

Test Method ISO 10478 (Equivalent methods IP-501, IP 470)

Recorded in mg/kg (commonly referred to as ppm), the sum total of Aluminium plus Silicon is a critical parameter. The primary source of these metals is cycle or slurry oils, from catalytic cracking, used as blend components. The catalytic refining process has become one of the most important, if not the most important, process in the refining industry. Its primary purpose is to make gasoline components, but catcracking also generates distillate and residual components. The catalyst used in this process is composed of alumina and silicates (which contain aluminium and silicon). Refiners do their best to separate and reclaim as much of the catalyst as possible. Nonetheless, some still ends up in the slurry components from this process. These metals are abrasive but, since they tend to be heavier than the fuel, proper fuel centrifuging and filtration should significantly reduce even high concentrations. Most engine makers suggest that the maximum combined aluminium, plus silicon, at the engine inlet is 15mg/kg to minimize wear of engine components.

SSSSULPHURULPHURULPHURULPHUR

VVVVANADIUMANADIUMANADIUMANADIUM

AAAALUMINIUM & LUMINIUM & LUMINIUM & LUMINIUM & SSSSILICONILICONILICONILICON

9

ISO 8217:2007 sets a maximum of 80 mg/kg for the sum of the two metals (Al + Si) for all residual fuel grades and 25 mg/kg for MDO grade DMC.

TOTAL SEDIMENT EXISTENT (TSE) TOTAL SEDIMENT TOTAL SEDIMENT EXISTENT (TSE) TOTAL SEDIMENT TOTAL SEDIMENT EXISTENT (TSE) TOTAL SEDIMENT TOTAL SEDIMENT EXISTENT (TSE) TOTAL SEDIMENT ACCELERATED (TSA) and TOTAL SEDIMENT POTENTIAL (TSP)ACCELERATED (TSA) and TOTAL SEDIMENT POTENTIAL (TSP)ACCELERATED (TSA) and TOTAL SEDIMENT POTENTIAL (TSP)ACCELERATED (TSA) and TOTAL SEDIMENT POTENTIAL (TSP) The total sediment tests for marine fuels are filtration methods. The results from these tests can be used to evaluate the cleanliness and, to some extent, the stability of the fuel. The result is expressed as % mass. Although only two tests, TSE and TSP, are prescribed in the current (2005) ISO 8217 standard some routine fuel testing laboratories utilise the TSA method as a first screen and only go on to test TSP if the TSA result is higher than expected. In cases of dispute, according to ISO 8217:2005 the reference method for DMB and DMC grades shall be TSE and for all residual grades TSP.

Test Method (ISO 10307-1) This test is used for distillate fuel grade DMC, and for distillate grade DMB, if the sample is not seen to be clear and bright.

Recorded in percent mass, TSE measures the amount of sediment which is inherent in the fuel and is a critical parameter with respect to filter blocking. Fuel sediment may be due to the presence of particulate matter or insoluble hydrocarbon materials. Particulate matter may comprise aluminium plus silicon, rust, coke or other debris. DMB and DMC type marine fuels contain a small amount of residual component and hence a small amount of asphaltenes that in most cases are soluble in the fuel. It is rare to find a distillate fuel grade that has a high sediment value due to the asphaltenes not being soluble in the fuel. A high sediment value in a distillate type fuel is more likely to be due to the presence of a large amount of particulate matter. Testing for ash and elements should reveal the type of particulate matter. Particulate matter can usually be removed by settling, centrifuging and filtration on board.

This method is not prescribed in ISO 8217:2005 but may be used as a fast screening filtration test and if the result is found to be high the TSE and TSP tests can be run to provide an overall evaluation of the cause of the high sediment.

The test follows the same filtration method as for TSE and TSP but prior to filtration the fuel is artificially aged by adding cetane. If the fuel has a reasonable stability reserve the TSA test should produce a low result. If a high result is obtained this could be due to falling out of asphaltenes and/or the presence of particulate matter. The TSA results can be compared with the TSP and TSE results, and the ash and elements results, to reach a conclusion on the cause of the high sediment.

TTTTSESESESE

TTTTSASASASA

10

Test Method ISO 10307-2 (Procedure A)

Fuels containing insoluble asphaltenes have been defined as ‘‘unstable fuels’’.

Unstable fuels can generate significant quantities of sediment that may overload the centrifuges used in the purification process. Asphaltenes are soluble in aromatic fuel components. Catalytic cracked fuel components have a high aromatic content, which is one of the reasons why their use as a diluent for marine fuels has been widely accepted by suppliers. Thermally cracked and hydrocracked fuel components are more prone to instability problems than other fuel components. The TSP method follows the same filtration procedure as for the TSE test, but the fuel sample is heated to 100C for 24 hours prior to the filtration. This method is used to check if the fuel becomes unstable (deposits asphaltenes) after a period of heating, to some extent this simulates heating and storage on board the ship. (This last sentence doesn’t read quite right) Although the current ISO standard does not prescribe testing TSE for residual fuels, the TSE result should be obtained if the TSP result is seen to be high. As mentioned above, a fuel may have a high sediment value for two reasons, particulate matter and/or instability. If the TSE result is low, and the TSP test gives a much higher result, then it may be concluded that there is little particulate matter in the fuel. The high TSP result shows the potential for the fuel to become unstable during heating and storage on board. If both TSE and TSP test are high, and of a similar value, the reason could be that the fuel is dirty, or unstable, or both. The ash and elements test results should show the level of particulate matter and further conclusions may then be drawn.

Test Method IP 501 or IP 470 Upper limits for these elements have been included in ISO 8217 to limit the amount of waste lubricant in bunker fuels as delivered. Some

research has shown that the presence of waste lubricants in fuels restricts, to some extent, the efficiency of centrifuges with respect to the removal of particulate matter. It is thought that the additives in the waste oil are responsible for this as they tend to hold fine particles tightly in the oil. Results are expressed in mg/kg. For a fuel to be deemed to contain waste lubricants the maximum levels of all the three elements given in ISO 8217 must be simultaneously exceeded. ISO 8217 sets out the same upper limits for these elements in all the residual grades and DMC.

TTTTSPSPSPSP

PPPPHOSPHOROUS, HOSPHOROUS, HOSPHOROUS, HOSPHOROUS, CCCCALCIUM ALCIUM ALCIUM ALCIUM

AND AND AND AND ZZZZINC INC INC INC

11

Test Method ISO 3015 This test is only applicable to gas oil grade DMX. This type of

fuel is only for use in emergency engines such as generators and lifeboats.

For these fuels it is important that the engines start quickly, even in cold conditions. The cloud point test gives an indication of the temperature at which wax starts to develop in the fuel. Wax can block filters and make it difficult, or even impossible, to start the engine. The maximum cloud point for DMX is -16C.

Test Method ISO 4264

This value is calculated from an algorithm using density and distillation measurements and is only applicable to distillate fuel grades DMX, DMA and DMB. It is unusual for these results to be obtained for routine quality screening of marine fuels.

DMX and DMA grades of distillate fuels should be clear and bright to comply with the ISO specification.

CCCCLOUDLOUDLOUDLOUD PPPPOINTOINTOINTOINT

CCCCETANE ETANE ETANE ETANE IIIINDEX NDEX NDEX NDEX

AAAAPPEARANCEPPEARANCEPPEARANCEPPEARANCE

12

EVALUATION OF QUALITY PROBLEM

In the typical sequence of events, a supplier delivers fuel to a vessel a continuous drip sample is taken and from this a number of sub samples are produced. The receiver may send one of these sub samples for testing.

The laboratory tests the sample and issues an analysis report to the ship owner/operator/manager. When one or more of the reported test results exceed the specification limit, a judgment needs to be made on the suitability of the fuel for its intended use and whether or not the buyer should raise a claim with the supplier. The purpose of this next section is to provide guidance on the evaluation of test results, bearing in mind the sampling process and precision of the test methods.

EVALUATION OF THE RELIABILITY OF THE TESTED SAMPLE

All the routine bunker testing agencies rely on ship’s staff to take a representative sample of the fuel as it is pumped on board the vessel. They provide sampling equipment and guidelines for obtaining a representative sample using the equipment. The most widely used sampling device is a continuous drip sampler located either on the barge discharge manifold, or on the ship’s receiving manifold. Operated correctly this device would produce a bulk sample of some 5 to 10 litres throughout the entire delivery process. This bulk sample should then be thoroughly mixed and poured into sub sample bottles. Ideally, these should be labelled, sealed and signed by the supplier and receiver. On the face of it, samples taken by the above method should be representative of the fuel supplied, but sometimes the results found on one of the sub samples cannot be repeated on other sub samples. In addition to this and/or when samples are taken from the ship’s tank that received the fuel, different quality characteristics are found.

Sampling

13

Why should this be the case? There are a number of possible reasons and the most likely are set out below.

The sub samples show different test results

• This can only be due to inadequate mixing of the bulk sample before it is decanted into the sub sample bottles, or incorrect sample preparation and test procedures in the laboratory.

The sub samples all show the same quality characteristics but the tank sample quality is different. This may be due to any or all of the following:

• The tank contained an amount of previous fuel before loading

• Sampling of the tank has not provided a true representation of the entire tank contents

• Sampling at the time of delivery was compromised and did not provide a representative sample of the entire delivery. This may have been due to

� not operating the sampler throughout the entire delivery period for whatever reason.

� The sampler may have stopped delivering at some stage due to a fall in pressure at the sampling point

� or the crew may have started the sampling late or finished it before the delivery was complete

• Incorrect sample preparation and testing at the laboratory

• The fuel supplied was poorly blended and due to the limitations of the drip sampling device a proportionate, representative sample was not obtained

Clarification of the above sampling issues can only be obtained from those present at the time of sampling. If there is any doubt about the reliability of the sample submitted to the laboratory then evaluation of the laboratory test results would be pointless. It is of prime importance that sample takers are properly trained. Qualified and experienced bunker surveyors are now frequently used, not only to perform quantity determination but also to ensure representative samples are taken at the time of delivery.

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EVALUATION OF LABORATORY TEST RESULTS

There are two significant factors to be considered when evaluating laboratory test results, firstly the competence of the laboratory, and secondly the precision of the test methods.

Selection of Laboratory

There are thousands of commercial testing laboratories around the world testing millions of different types of materials. Each will have its own competence in a specific area such as food, metals, chemicals etc and this competence should be demonstrated by the laboratory quality assurance certification. Laboratories are periodically, independently assessed and when they reach the standard required they are issued with appropriate certificates. A laboratory can only use the quality logo of the certification body for tests which have been accredited to the quality system. Many laboratories carry out accredited tests for their main core business but may also carry out tests that are not covered by their certification. When issuing test reports the laboratory has a duty to state if the tests reported are included in their quality accreditation system. The highest quality system for laboratories is encompassed in ISO 17025. So, if a laboratory has attained this level of competence then you should be able to rely on the test results, provided the tests are covered by the scope their accreditation certificate.

Precision of the tests

If you submit the same sample material to a number of accredited laboratories and, for example, request a density test, they should all produce results that are very similar, and at least fall within the precision of the test method. Of course they must all use the same test method or you cannot compare the results.

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So which one is correct?

If you asked a thousand people to do the same measurement it is likely that you would find the vast majority of the results fall within a particular range or band, which is fairly narrow, and some results fall far outside this range. You would likely conclude that all the results within the small band are most likely to be near the true measurement, and those outside this range are probably not reliable. You could then discard the results outside the band and take the average of the results within the band to obtain a “true” value. The acceptable small band of measurements you collected from the tree measurements may be called the precision of the method. If you asked another person to measure the tree, and they came up with a result within the narrow band you originally established, then you would accept that result. However, if their measurement was outside your narrow band you would be unlikely to accept the measurement as being reliable. When laboratory test methods are developed two processes are used to establish the precision of the test method. Firstly, a chemist working in the same laboratory using the same sample material on the same instruments, within a short space of time, is asked to carry out the test a number of times. In a similar way to measuring the tree, the chemist will produce a number of results and most of these are likely to be within a narrow band and some may be outside this band. Data from a number of similar trials is evaluated and from this the acceptable “band”, or variation between results, is established and defined as the precision of the method. For the same chemist working on the same test material, in the same laboratory, with the same instruments, this precision statement is called the Repeatability of the test method. Secondly, data is collected from test results obtained by chemists working in different laboratories, with different instruments, on different days, but using the same sample material and test method.

As in any measurement, all tests are subject to tolerance factors. The allowable tolerance in a test or technique is referred to as the ‘‘statement of precision’’ and some tests are less precise than others. If you take a large tape measure and ask a person to measure the circumference of a tree trunk he or she will provide one measurement. If you then ask a number of other people to measure the same tree trunk, at the same location, with the same tape measure they are all likely to arrive at slightly different results.

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It is not surprising that the variation in the results from this process is higher than when the same chemist was working on the same instruments. So the band of results is wider than before, but the majority of results would fall within a new band and outliers could be discarded. This new band is called the Reproducibility of the test method.

REPEATABILITY

Repeat tests from one laboratory – So how does this work in practice? If you send a fuel sample to a single laboratory they will provide a single result. Now, if this result is of concern to you, you may ask the laboratory to repeat the test. Their second test result should be near to their initial result, or the difference between the two results should be within the repeatability (precision) of the method. If not, the laboratory should repeat the tests until they produce at least two results that are within the repeatability of the method, and they may report the average of these two, or more, results. Most good laboratories will repeat a test before reporting a fuel is out of specification.

REPRODUCIBILITY

Evaluation of a single test result and consideration of possible test results from a second laboratory If you are a fuel buyer, and the laboratory has provided you with a rechecked test result that is outside the specification limit, you have to consider the probability of another laboratory, using the same sample material and test method, coming up with a result that is also outside the specification limit. At this stage you will need to look for the reproducibility of the test method and consider how you can use it to evaluate the significance of the single test result.

ISO 8217:2005 contains a very useful Annex (F) “Examples of precision and interpretation of test results”. Readers should make sure they have a complete copy of ISO 8217. This can be purchased on line on the ISO website. Some further explanation of Annex F is given below. Firstly, we refer readers Clause 8 of ISO 8217:2005 “Precision and Interpretation of test results”, which states

‘‘The test methods specified in tables 1 & 2 contain a statement of precision (repeatability and reproducibility). Attention is drawn to ISO 4259:1992, clauses 9 and 10, which cover the use of precision data in the interpretation of test results, and this method shall be used in cases of dispute’

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ISO 4259:1992 provides for the systematic evaluation of the validity of a given result and assumes that the sample being analysed is a ‘‘representative’’ sample of the product delivered/received. Clause 9 of ISO 4259:1992 further establishes a means for the technical & statistical interpretation of ISO test method results. We stress that this evaluation process may be used by the recipient when no other information is available than the one test result. ISO 4259 terminology explained ISO 8217:2005 tables 1 and 2 specify maximum and minimum limits to the true value of a given property.

True value As defined by ISO 4259:1992, true value represents the average of an infinite number of single results obtained by an infinite number of laboratories. Therefore

this true value can never be established exactly.

Reproducibility “The closeness of agreement between individual (test) results obtained in the normal and correct operation of the same (test) method on identical test material but under different test conditions (different operators, different apparatus and different laboratories)... It is the value equal to or below which the absolute difference between two single test results on identical material obtained by operators in different laboratories, using the standardised test method, may be expected to lie within a probability of 95%”

To apply the ISO 4259:1992 (Section 9 & 10) rule to determine, with a high degree of certainty, if the fuel received is out of spec, requires knowledge of the precision statement of the test method used for analysing that parameter. If the test result is more than the specification limit plus 0.59 times the Reproducibility, then the fuel is almost certain (95% confidence) to be out of specification.

Expressed in algebraic terms there is high confidence that the fuel fails the specification if :

Test Result exceeds Max Specification plus 0.59 X the Reproducibility

If the specification is a lower limit such as Flash Point, the sign is changed to minus. Annex F of ISO 8217 provides an example of the calculation for viscosity. It concludes that if the viscosity limit in the specification was 380cSt then we could be 95% confident that the specification limit had been exceeded if the single test result was 396.59cSt or above. This does not mean that the single test result is wrong but due to the precision of the method another laboratory may find a different result and this could be as much as 16cSt different. Some fuel suppliers are tempted to respond to a claim that a certain quality parameter is not out of specification by informing the buyer that to be out of specification the test result must be above

18

the specification limit by 0.59 X the Reproducibility. This is not correct. As stated above this is a confidence limit, not an allowance. Many suppliers forget the precision data when it comes to blending and testing fuels for compliance with ISO 8217 quality characteristics. Annex F of ISO 8217 points out that if a supplier wants to be 95% confident that a fuel meets a viscosity limit of 380 cSt then he should not exceed a test viscosity of 363.4 cSt on his blend tests. The following table has been compiled using the reproducibility of the test methods and contain all ISO 8217:2005 fuel category quality parameters and ISO 4259:1992 interpretative values at 95% confidence level. The applicable ISO test methods may be found in ISO 8217. NB: It is stressed that the table below may only be used when only a single test result is known. If a sample has been tested by more than one laboratory and two or more test results are known then please refer to the section below on dispute resolution. ISO 4259 :

95% Confidence that Product Fails Specification based upon a single test result

TESTS

Specification

limit

95% confidence that the specification limit is exceeded when a single test result is

at this value

Density 890.0 890.9 900.0 900.1 920.0 921.0 960.0 960.9 975.0 975.9 980.0 980.9 991.0 991.9 1010.0 1010.9 Viscosity at 40C Min

1.4

1.34

1.5 1.43

Viscosity at 40C Max

5.5

5.74

6.0 6.26 11.0 11.5 14.0 14.6

Viscosity at 50C Max

30

31.3

80 83.5 180 187.9 380 396.6 700 730.6

19

Flash Point Min C

43

41

60 56.5 Pour point Max C

-6

-3

0 3 6 9 24 27 30 33 Sulphur Max

1.0

1.1

1.5 1.58 2.0 2.1 3.5 3.7 4.0

4.5 4.2 4.72

TESTS Specification limit

95% confidence that the specification limit is exceeded when a single test result is

at this value

Micro carbon on 10%

0.3

0.36

Micro carbon Max

0.3

0.36

2.5 2.77 10 10.7 14 14.8 15 15.9 18 19 20 21.1 22 23.1 Water Max

0.3

0.38

0.5 0.6 Vanadium Max

100

106

150 170 200 224 300 330 350 383 500 541 600 646

20

Aluminiun + Silicon Max

25

30

80 96 Total Sediment Existent and Potential Max

0.10

0.16

Zinc Max

15

17

Phosphorous Max

15

18

Calcium Max

30

34

Using more than one test result to resolve a dispute

Very few disputes are settled on the basis of a single test result. If the single test result indicates that the fuel is not in accordance with the specification the same sample, material should be sent to another laboratory for testing by the same method. The two results should not differ by more than the reproducibility of the test method. If there is a larger difference, both laboratories should be asked to repeat their tests.

ICP Flame

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Witnessing of the tests by competent chemists is often carried out to verify compliance with laboratory and test procedures. If the two results do fall within the reproducibility of the method then the parties in dispute may agree to accept the average value as the true and binding result. If the two laboratories cannot obtain test results within the reproducibility of the method an umpire laboratory may be appointed. It is not unusual in bunker disputes for the buyer and seller to submit their own samples to a laboratory for testing, and for the dispute to then involve not only the test results but also the validity of the samples. As mentioned above the precision of test methods can only be applied to tests on the same sample material. If the parties are to accept test results from a laboratory as binding they should of course be satisfied, and agree before the testing that the submitted sample is representative of the fuel supplied. If the testing confirmed that the product quality did not meet the specification, the next step in a bunker quality dispute is to evaluate the impact of this on the value of the fuel and the consequences of consuming it. Readers in this position should refer to the IBIA publication “Avoiding and Resolving Bunker Disputes”.

This publication has been produced by IBIA to assist those involved in bunker quality disputes. Proper evaluation of test results and educated decision making on what further action may be required should help to resolve such disputes in a professional expedient manner. Industry fuel experts, testing services, and engine manufacturers are all good resources to obtain factual opinion regarding the interpretation of ISO test results, the application of ISO 4529:1992 and the impact on engine performance resulting from test results that appear outside the specifications.

evaluating the merits of a bunker claim...

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