Refining 01b - Testing Methods

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SECTION 1B

SPECIFICATIONS ANDPRODUCT QUALITY

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SPECIFICATIONS AND PRODUCT QUALITYEach specific ExxonMobil product is identified by a formula number, as well as a name, and the specifications for this product are shown in a Specification Book. These books are proprietary information. There are several volumes, and those used by ExxonMobil Company, U.S.A. are:

AX Fuels and SolventsAY Lube and WaxAZ Grease-and Purchased Ingredients

Books named BX, BY, and BZ contain the same information, plus the formulation or a manufacturing method when it is appropriate.

Properties of products are checked against specifications by laboratory tests. A product must meet all specifications when shipped, unless a specific exception has been granted, The Specification Book shows the allowable limits for each specification and gives a reference for the test method by which the quality is determined. Most of the time it is an ASTM test method number. This refers to a specific test number published in ASTM Standards by the American Society for Testing Materials. In this publication, a detailed procedure for each test method is described, usually along with repeatability and reproducibility information. Other specifications are checked by AM-S tests, which means 'Analytical Methods Specifications', a company confidential series of test procedures. Less frequently, other test methods are quoted, such as military or customer test procedures.

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All laboratory tests are hot made on every batch of a product. There must be, however, 95% confidence that the specifications are met. This can be gained by running the rest, or by running some other test which correlates with the test methods specified, or by experience.

To ensure 95% confidence, we actually blend to limits more restrictive than the specification. For example, if the Research Octane Number specification is 92.0, we will not ship below 92.1 Research Octane Number.

A sample entry from a Specification Book is shown on the following three pages.

SPECIFICATIONS AND PRODUCT QUALITY

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TEST METHODS

Most testing methods are empirical procedures that have been developed and accepted by long experience. The aim generally is to define the method and apparatus precisely. The test results are often of little meaning as absolute properties, but are valid in making comparisons between samples or between a sample and specifications. In some cases, test results are correlated with real physical properties and in some case. approximate test results can be predicted from calculations made from other test -results.

Test methods described below are mostly ASTM methods, described in detail in the literature. Each has a specific number, which appears In the Specification Book, to define the exact test by which each specification was set.

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TEST METHODSAPI Gravity is the nearly universal measurement of density used in the petroleum industry.

ASTM D-287 and ASTN D-1298 are similar tests. The sample is placed in a tall vertical container and a hydrometer is placed in it. The height at which the hydrometer floats and the temperature are listed. Tables are used to correct the scale reading to 60ºF.

Density at 60ºF is related to ºAPI at 60ºF by the formula.

ºAPI = 141.5 - 131.5 Sp. Gr.or

Sp. Gr. = 141.5 ºAPI + 131.5

The term ºAPI is often used to mean ºAPI Gravity. The API Gravity scale goes in the opposite direction from density; that is, low density materials are high API Gravity. Water is 10 ºAPI, and oils heavier than water are less than 10 ºAPI.

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TEST METHODS

Flash Point is important from the standpoint of safety. Minimums on some products are set by law. The flash point of a material is the temperature to which it must be heated under conditions of the test method to give off enough vapour to form a mixture with air that can be ignited momentarily by a specified flame.

ASTM D-56 (“TAG” Closed Cup or TCC). A closed cup method applied to liquids which flash below 175ºF. NOT USED ON PRODUCTS CLASSIFIED AS FUEL OIL.

ASTM D-93 (Pensky-Martins). A closed cup method applied to middle distillates and to fuel oils unless other methods are specified.

ASTM D-92 (Cleveland Open Cup). May be applied to products with flash above 175ºF. NOT USED ON FUEL OILS.

Illustrations of Pensky-Martens and Cleveland open cup apparatus are shown below.

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TEST METHODS

FIGURE 1PENSKY-MARTENS FLASHAPPARATUS, ASTM D-93

FIGURE 2 CLEVELAND OPEN CUP FLASH

APPARATUS, ASTM D-92


TEST METHODSDryness of Propane is a test to ensure flow of propane in service.

ASTM D-2713 provides for allowing liquid propane to escape through an orifice. As it expands, any moisture present freezes and in time blocks the orifice with ice. The time until flow is stopped is recorded as the dryness of the propane. In practice, this method is not used, but a GC water analysis is used instead.

Vapour Pressure is a measure of volatility and is used in calculations of fuel performance indices. It is also important because of safety in storage and transportation.

A sample is charged into a container at 32ºF, in the presence of water saturated air. The container is closed, the temperature raised to 100ºF, and the pressure in PSIA is recorded.

ASTM D-323 (Commonly known as Reid Vapour Pressure “RVP”) Applied to motor gasolines, aviation fuels, natural gasolines, solvents, crudes and Jet fuels.

ASTM D-1267, used for liquefied petroleum gases, essentially the same test, except the air is excluded from the container, and results are expressed in PSIG.


TEST METHODSLIC 10.06 Old type of test now rarely used.

HIVAC - Very high boiling materials. Run under maximum vacuum possible by the apparatus. Results corrected to equivalent temperatures at atmospheric pressure.

Higher fractionating efficiency

True Boiling - An industry term for a test made with good fractionation, but not well defined. The intent is for the boiling point of each component to he reflected in the curve. The term is sometimes used to mean 15/5 (see next item), but this is not precise.

ASTM D-2892, usually called 15/5. The apparatus has 15 theoretical plates and is operated with a 5 to 1 reflux ratio. The sample size is 5 gallons. This distillation is used for many engineering correlations, and makes up part of the crude assay.

A new development is the Gas Chromatograph Distillation, also called Simulated Distillation by Gas Chromatography is in widespread use in the refinery labs; in same cases it has replaced ASTM distillations since it gives essentially a true boiling point (TBP) curve. The results of a gas chromatograph test have been correlated with the results of the conventional laboratory procedures to the extent that they may be substituted. The GCD is much more precise and more effectively automated. The data derived from GCD are used directly on some units for process control.


FIGURE 4ASTM D-1160 10 MM DISTILLATION APPARATUS


TEST METHODSOctane Number is a measure of the burning quality of a fuel in a gasoline engine as it relates to knock. When a fuel detonates in the cylinder of an engine instead of burning smoothly, it causes noise and vibration known as “ping" or “knock”. This is more likely to occur in higher compression engines, and engines under higher load. Engines are built to higher compression ratios to improve efficiency. Therefore, the fuel must be of higher anti-knock quality to perform satisfactorily. To define this property, an empirical scale was developed in 1929 in which isooctane, or 2,2,4 trimethyl pentane is assigned an octane rating of 100, and normal heptane is assigned 0. Then any fuel is rated as having an antiknock quality equal to that of a blend of those two. For example, 85 Octane Number means the fuel has the same anti-knock properties as a blend of 85 percent isooctane and 15 percent normal heptane. This scale has been extended beyond 100 Octane Number by adding tetraethyl lead to isooctane:

cc/gal TEL in Octaneisooctane Number0.5 105.31.0 108.62.0 112.83.0 115.5


TEST METHODSASTM D-2699 (Research Octane Number) is determined using a one-cylinder test engine which has a variable compression ratio. The knock intensity when running on a sample Is compared with that of a reference fuel of know octane number. The results when the engine is run at 600 RPM and about 152ºF air-fuel mixture temperature is reported as Research Octane Number, or RON. This represents performance at relatively mild conditions.

ASTM D-2700 (Motor Octane Number) is determined when the engine is run at 900 RPM and precisely 300ºF air-fuel mixture temperature. The resulting octane number is reported as Motor Octane Number, or MON, and represents performance of engines under more severe conditions.

Cetane Number -is a test for diesel fuel quality that is much the same in concept as the Octane Number test. Reference fuels in this case are hexadecane, or cetane, at 100 and alpha methyl naphthalene at 0 cetane number.

ASTM D-613 provides for a one-cylinder test diesel engine and the comparison is made between the sample and the standards.

ASTM D-975 gives a method for calculating Cetane Index from API Gravity and Temperature at 50% off (mid boiling point) in an ASTM D-86 distillation. Cetane Index is close enough to Cetane Number that the ASTM D-613 is never used.


TEST METHODSSmoke Point is an indication of clean burning properties for kerosene or light turbo fuels.

ASTM D-1322 specifies burning a sample in a standard lamp, and measuring the maximum flame height without smoking. A photograph of the lamp is shown on the following page.

Luminometer Number is another test for clean burning of turbo fuel.

ASTM D-1740 measures radiation of certain colour of light from the flame when the sample is burned in a standard lamp. The luminosity is compared to that of two standards, isooctane (2,2,4 trimethyl pentane) at 100 LN and tetralin (1,2,3,4 tetra-hydronaphthalene) at 0 LN. Luminometer Number can be correlated with Smoke Point, and is a measure of aromatics content.

Pour Point is a measure of fluidity at low temperature.

ASTM D-07 describes the procedure. It is the lowest temperature at which a sample will pour or flow under prescribed conditions when it is chilled without disturbance at a standard rate.


FIGURE 5 - SMOKE POINT LAMP ASTM D-1322


TEST METHODS

Freeze Point is a similar test, but used for aviation fuels.ASTM D-2386 is the procedure.

Aniline Point is an indication of the aromatics in a hydrocarbon.

ASTM D-611 provides for mixing equal parts of aniline and the sample, and increasing the temperature until they become miscible. Because aniline is an aromatic, it becomes miscible with highly aromatic samples at a lower temperature than with less aromatic samples. Mixed aniline point is the same test, except two volumes of aniline, one volume of normal heptane, and one volume of the sample are mixed. In this case, a higher temperature will be recorded because of the anti-solvent effect of the heptane.

Heat of Combustion, or Heat Content, is a specification for jet fuels.

ASTM D-240 is a bomb calorimeter test. A sample is burned in oxygen under pressure, and the heat absorbed by water in a surrounding Jacket is measured by temperature rise. This test is seldom run, and heat of combustion is calculated from other test results.


Bromine Number is an indication of the unsaturation of a hydrocarbon sample.

ASTM D-1158 or 1159 is used. It is the number of grains of bromine, determined by titration, that are consumed by 100 grams of the sample. Bromine adds onto double bonds in olefins, but usually does not enter an aromatic ring. When the sample contains much branched chain material, bromine will often substitute for hydrogen, interfering with good test results.

Ash, or ash content, is specified for some oils to detect the possibility of deposits when the oil is burned or vaporised.

ASTM D-482 is the method used. A sample of the oil is heated until it is burned or evaporated fully, and the carbon residue is also burned. The remaining material is weighed and the weight per cent of the original sample is calculated.

Cone Penetration measures the consistency of a grease.

ASTM D-217 is a test in which a cone is allowed to sink into the surface of the grease under a specified weight for 5 seconds. The distance it sinks in tenths of a millimetre is the penetration number of the grease. The next page has a picture of a Cone Penetrometer.

TEST METHODS


FIGURE 6 - CONE PENETROMETER ASTM D-217


Needle Penetration is used for determining the hardness of waxes or asphalt.

ASTM D-1321 uses essentially the same equipment and procedure as cone penetration. The key difference is that a needle is substituted for the cone. Hardness is expressed in tenths of a millimetre that the needle penetrates the sample.

Viscosity is a measure of fluidity of a liquid. There are several tests for Viscosity, but those in common laboratory use measure the time required for a given volume of sample to flow by gravity through a restriction. It is a very important test In specifying lubricating oil quality, and is also related to fuel flow in aircraft and in heating systems. It is an essential consideration in design and operation of refinery equipment. Because viscosity of all oils increases as the temperature drops, close control of temperature is essential in all viscosity tests.

ASTM D-445 is Kinematic Viscosity, and is measured in glass tubes with a capillary section. The most common tube is called a Ubbelohde tube, and each one must be calibrated against a standard. The Ostwald tube is another common type, pictured below, with the constant temperature bath in which it is used. The time required for a given size sample to pass through the capillary is converted to centistokes by calculation. This is density-dependent variable, and to obtain the absolute viscosity in centipoises, it must be multiplied by the density of the sample.

TEST METHODS


TEST METHODS

FIGURE 7OSTWALD KINEMATIC VISCOSITY

TUBE ASTM D-445

FIGURE 8CONSTANT TEMPERATURE BATH

FOR KINEMATIC VISCOSITY


Absolute viscosity (CP) Kinematic viscosity (CS) x density.

Kinematic viscosity it most often determined at: 100 and 210ºF.

From these data, viscosities at 40ºC and 100ºC are calculated, since most specifications are at these temperatures. The viscosity of jet fuel is usually determined at 100ºF and converted to viscosity at -30ºF.

ASTM D-88 is Saybolt viscosity. The time required for 60 ml of the sample to flow through an orifice in the bottom of a metal tube is recorded as Saybolt Seconds Universal, or SSU. Pictured below are the tube and the bath used in this test. Standard temperatures for SSU are 100ºF and 210ºF. For heavier oils, a larger orifice is used for the same test method. In this case, the time Is recorded as Saybolt Seconds Furol or SSF -. SSF values are very close to one-tenth of SSU values. Standard temperatures for SSF determinations are 122ºF and 210ºF.

Redwood and Engler are two viscosity tests that are similar to the Kinematic and Saybolt methods. They are little used in ExxonMobil, and tables are available to convert from one determination to another among the four methods.

TEST METHODS


TEST METHODS

FIGURE 9CONSTANT TEMPERATURE

BATH FOR SAYBOLT OR FUROLVISCOSITIES ASTM D-88

FIGURE 10SAMPLE TUBE

SAYBOLT VISCOSITY


ASTM D-2983 is the Brookfield test. It measures the frictional drag on a moving object. A spindle is introduced into the sample, and the energy required to keep it turning at a designated rate is related to the Brookfield Viscosity. Although this is a viscosity-test, it measures a different property from the other tests, and the two types cannot be correlated.

Sulphur is becoming increasingly important as the sulphur level increases in crude oils and as environmental restrictions increase. Sulphur compounds contribute to corrosivity and bad odour in products. Several methods are used for sulphur determinations, and the more important ones are these:

ASTM D-1266, Lamp Sulphur, is designed for testing fuels in the middle distillate range. The sample is burned in a standard lamp, and the combustion products are absorbed in a solution and analysed gravimetrically. Results in PPM of total sulphur are calculated from the data. This method is not used by ExxonMobil.

ASTM D-2622, Sulphur by X-Ray Fluorescence Spectroscopy, is the most frequently used sulphur test at ExxonMobil. The sample is placed in an X-ray bean, and the intensity of the fluorescent sulphur line (5.373Aº) in the resulting spectrum is compared to that of known sulphur content standards. This test is good for determining sulphur at levels between 100 PPM to 90%.

TEST METHODS


ASTM D-3120, Sulphur by Microcoulometry - also called the Dohman Microcoulometer - employs oxidation or reduction of a hydrocarbon sample to form SO2 or H2S. Either of these compounds is titrated electronically in a coulometer to quantify the sulphur content. Used for very low sulphur samples - up to 100 PPM.

ASTM D-484 (Doctor test) is a qualitative indication of H2S and mercaptans in very small quantities. The sample, a pinch of elemental sulphur, and a little doctor solution (sodium plumbite) are shaken together. Discoloration of the sulphur or solution indicates failure.

ASTM D-130 (Copper strip corrosion) is a qualitative test for corrosivity of a sample. A polished copper strip is Immersed in the sample for a specified time at a designated temperature, usually three hours at 122 or 212ºF. The strip is washed and its appearance compared to standards to give a 1, 2, 3, or 4 rating. The most discoloration results in the higher number. Time and temperature are included in the test result.

ASTM D-1838 is the same test, run on LPG and therefore, in a slightly different sample container

TEST METHODS


Gum, Existing is a measure of high boiling polymers that may exist in gasoline, and could cause deposits or varnish when the fuel is evaporated.

ASTM D-381 provides for evaporating 100 ml of the sample in a stream of hot air, and the weight of the residue is the gum.

Gum. Potential is intended to predict the possibility of forming gum in storage.

AM-S 130.1 is an ExxonMobil test in which the sample is evaporated in a copper dish to catalyse the formation of gum. The residue is weighed as above.

Conradson Carbon is intended to he an indication of the sooting tendency when a fuel is burned in a heating system. However, this test is used for many other purposes, such as to predict Coker yields and carbon forming tendency in catalytic cracking.

ASTM D-189 (Con Carbon) uses 10 grams of sample. It is heated at a controlled rate with a deficiency of air, and the-residue-is weighed. The weight percent of the original sample is calculated and reported. A drawing of the apparatus used is shown on the next page.

TEST METHODS


FIGURE 11CONRADSON CARBON APPARATUS ASTM D-189


Component Analyses - Several tests are available to give information on compound types in a hydrocarbon.. Among the important ones are these:

Gas Chromatograph - Gas chromatography is used extensively to determine individual compounds in a complex mixture of hydrocarbons. Absorption and elution phenomena permit separation of hydrocarbons in a packed column with helium or hydrogen gas providing the driving force. At least 15 ASTM procedures employ GC techniques.

Mass Spectroscopy - Used for the identification and quantification of individual compounds in a mixture. The Mass Spec technique can be applied to liquids and gases as well as heavy material. The analysis of heavy samples is usually reported as type analyses.

MS-9 and MS-50 are sophisticated mass spectrometer analyses used to obtain input data for catalytic cracking correlations (Standard Flexicracking Procedure). Results show percent paraffins, naphthenes, aromatics, number of rings, and length and number of side chains on rings.

Fluorescent Indicator Adsorption (FIA), ASTM D-1319, uses a silica-gel packed column to analyse for component types. The sample, dyed with a fluorescent dye, separates into paraffins, olefins, and aromatics, detectable and ultra-violet light as colour bands.

TEST METHODS


Colour is important for many products for customer acceptance. There are many tests for colour, most of which correlate with each other to some degree. The more common ones used by this refinery are:

ASTM D-156-- Saybolt is used for a very light range of colours. Two tubes, side-by-side, are illuminated from -the bottom. One tube contains a standard colour disk, and the other contains the sample. The sample is withdrawn until the appearance, looking down through both tubes, is the same. The colour is determined by the height of the sample and the disk selected when the colours match. Colours go from +30 to - 16. +30 is colourless and -16 is called "extra pale". Higher numbers describe lighter oils. The photo on the next page shows a Saybolt calorimeter.

ASTM D-1500, ASTM Colour, is used for darker oils. It is run by keeping the depth of the sample column constant and comparing the colour to that of one of 16 standard colour disks. The ASTM colour scale runs from 0, or lily white (about -8 Saybolt), up to 8, which is very dark. Higher numbers represent darker oils. A photo of an ASTM calorimeter is shown on the next page.

TEST METHODS


Tag-Robinson is the name of another test, run by a method similar to Saybolt, except that the depth of sample observed is changed by an immersion tube. This test, as used by ExxonMobil, is designated AM-S 40.01E. However, the same test is used industry wide. Colours are referred to as T-R colour. The Robinson colour scale runs from 25, which is about 0 on the Saybolt scale, to 0, which is opaque. Higher numbers, like the Saybolt test, represent lighter coloured oils. A Tag-Robinson colorimeter-is shown on the next page.

There are other colour tests, such as lovibond, N.P.A., and Union, but these are not as commonly used as the above tests. Tables exist which permit reasonably good conversion from one colour value to another.

TEST METHODS


FIGURE 12SAYBOLT COLOURIMETER

ASTM D-156

TEST METHODS

FIGURE 13ASTM COLOURIMETER

ASTM D-1500

FIGURE 14TAG ROBINSONCOLOURIMETER

AM-S 40.01E

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Refining 01b - Testing Methods