Flash and Fire Point Test for Asphalt by Cleveland Open Cup Tester

Job 6:

Flash and Fire Point Test for Asphalt by Cleveland Open Cup Tester

Code: ASTM: D 92-12

SCOPE & SIGNIFICANCE:

This test method describes the determination of the flash point and fire point of petroleum products by a manual Cleveland open cup apparatus

This test method is applicable to all petroleum products with flash points above 79°C and below 400°C except fuel oils.

• Flash point measures the tendency of time sample to form a flammable mixture with air under controlled laboratory conditions. It is only one of a number of properties that must be considered in assessing the overall flammability hazard of a material.
• Flash point is used in shipping and safety regulations to define ‘‘flammable’’ and ‘‘combustible’’ materials.
• Flash point can indicate the possible presence of highly volatile and flammable materials in a relatively nonvolatile or nonflammable material. Fire point measures the characteristics of the sample to support combustion.
• Bituminous materials give rise to volatiles at high temperature as they are basically the hydrocarbons. These volatiles catch fire causing a flash which is very hazardous.
• During construction of bituminous pavements, the engineer may restrict the mixing or application temperatures well within the limits. The test therefore gives indication of critical temperature at and above which suitable precautions should be taken to eliminate fire hazards during use of asphalts. In other words, heating should be limited to a temperature well below the flash point.

RELATED THEORY:

FLASH POINT:

The lowest temperature corrected to a barometric pressure of 101.3 kPa (760 mm Hg), at which application of an ignition source causes the vapors of a specimen of the sample to ignite under specified conditions of test.

The material is deemed to have flashed when a large flame appears and instantaneously propagates itself over the surface of the specimen.

Note: Occasionally, particularly near the actual flash point, the application of test flame will cause the blue halo or an enlarged flame; this is not a flash and should be ignored.

FIRE POINT:

The lowest temperature corrected to a barometric pressure of 101.3 kPa (760 mm Hg), at which application of an ignition source causes the vapors of a test specimen of the sample to ignite and sustain burning for a minimum of 5 s under specified conditions of test.

DIFFERENCE BETWEEN FLAMMABLE & COMBUSTIBLE MATERIAL:

A flammable material is the one which can give/form flames but does not sustain fire while a combustible material is the one which sustains fire and burns itself.

SOURCES OF BITUMEN:

• Naturally occurring

The refined lake asphalt typically contains 55 % bitumen, e.g. in Trinidad lake.

• Extracted from Limestone and Sandstone

Limestone and sandstone are impregnated with 5- 15 % of natural bitumen.

• From Oil Refineries

Bitumens that are produced artificially from petroleum crudes

This is the major source of bitumen in Pakistan

ASPHALT CEMENT:

Asphalt Cement shall be oil asphalt or a mixture of refined liquid asphalt and refined solid asphalt, prepared from crude asphaltic petroleum. It shall be free from admixture with any residues obtained by the artificial distillation of coal, coal tar or paraffin and shall be homogeneous and free from water.

Temperature Condition	* Asphalt Grade
Cold, mean annual air temperature < 7 °C (45 °F)	AC-10 AR-4000 80 / 100 pen
Warm, mean annual air temperature between 7 °C (45 °F) and 24 °C (75 °F)	AC-20 AR-8000 60 / 70 pen
Hot, mean annual air temperature > 24 °C (75 °F)	AC-40 AR-16000 40 / 50 pen

GRADES OF BITUMEN:

Bitumen is usually characterized in the following three types of grades;

1. Viscosity grades
2. Penetration grades
3. Density grades

FLASH POINT OF DIFFERENT GRADES OF ASPHALT:

VISCOSITY GRADES

Source: Petroleum fuels manufacturing handbook by Surendar Prakash PHD

Note: AC – 10 is most commonly used in Pakistan

ASPHALT CEMENT GRADE OF BITUMEN CORRESPONDING TO FLASH POINT IN COC TEST IN ⁰C (VISCOSITY GRADES)

Grade	AC-2.5	AC-5	AC-10	AC-20	AC-30	AC-40
Min. Flash Point  0C	163	177	219	232	232	232

 

RELATIONSHIP BETWEEN AC AND AR GRADES:

Viscosity grades	Rolling thin film oven test grades
Asphalt Cement (AC)	Aged Residue (AR)
AC 2.5	AR 1000
AC 5	AR 2000
AC 10	AR 4000
AC 20	AR 8000
AC 40	AR 16000

Source: “Pavement Engineering: Principles and Practice, Second Edition”

edited by Rajib B. Mallick, Tahar El-Korchi

APPARATUS:

1. Cleveland Open Cup Apparatus:

This apparatus consists of the test cup, heating plate, test flame applicator, heater, and supports.

The parts of apparatus should conform to the following requirements:

• Test Cup, cup shall be made of brass or other non-rusting metal of equivalent heat conductivity. The cup may be equipped with a handle.
• Heating Plate, shall be of sufficient dimension and materials to ensure that thermal heat to the test cup is only applied to the bottom of the test cup and that extraneous heat to the test cup other than to the bottom is minimized.
• Ignition Source Applicator, The device for applying the test flame may be of any suitable type. When using a test flame, it is suggested that the tip be 1.6 ± 05 mm (¹⁄16 in.) in diameter at the end, and that the orifice be approximately 0.8 ± 0.05 mm (¹⁄32 in.) in diameter. The device for operating the test flame applicator may be mounted in such a manner as to permit automated duplication of the sweep of the test flame, the radius of swing being not less than 150 mm (6 in.). The center of the test flame should be supported so that it swings in a plane not greater than 2 mm (⁵⁄64 in.) above the plane of the rim of the cup. It is desired that a bead, having a diameter of 3.2 to 4.8 mm (¹⁄8 to ³⁄16 in.), be mounted in a convenient position on the apparatus so that the size of the test flame can be compared to it.
• Heater, Heat may be supplied from any convenient source. The use of a gas burner or alcohol lamp is permitted, but under no circumstances are products of combustion or free flame to be allowed to come up around the cup. An electric heater which can be controlled automatically or controlled by the user is preferred. The source of heat shall be centered under the opening of the heating plate with no local superheating. Flame-type heaters may be protected from drafts or excessive radiation by any suitable type of shield that does not project above the level of the upper surface of the heating plate.
• Temperature Measuring Device Support, Any convenient device that will hold the temperature measuring device in the specified position during a test and that will permit easy removal of the temperature measuring device from the test cup upon completion of a test may be used.
• Heating Plate Support—Any convenient support that will hold the heating plate level and steady may be employed.

2. Thermometer:

A thermometer having temperature range from -6 to 400⁰ C

3. Shield:

A shield 460mm square and 610mm high and having an open front is used.

4. Test flame:

Natural gas (methane) flame and bottled gas (butane, propane) flame have been found acceptable for use as the ignition source.

PREPARATION OF APPARATUS:

1. Support the manual on a level steady surface, such as a table.
2. Tests are to be performed in a draft-free room or compartment. Tests made in a laboratory hood or in any location where drafts occur are not to be relied upon.
3. Wash the test cup with the cleaning solvent to remove any test specimen or traces of gum or residue remaining from a previous test. If any deposits of carbon are present, they should be removed with a material such as a very fine grade of steel wool. Ensure that the test cup is completely clean and dry before using again. If necessary, flush the test cup with cold water and dry for a few minutes over an open flame or a hot plate to remove the last traces of solvent and water. Cool the test cup to at least 56°C (100°F) below the expected flash point before using.
4. Support the temperature measuring device in a vertical position with the bottom of the device located 6.4 ± 1 mm (¹⁄4 ± ¹⁄50 in.) up from the bottom of the inside of the test cup and located at a point halfway between the center and the side of the test cup on a diameter perpendicular to the arc (or line) of the sweep of the test flame and on the side opposite to the test flame applicator mounting position.

SAMPLING:

1. At least 70 mL of sample is required for each test
2. Erroneously high flash points may be obtained if precautions are not taken to avoid the loss of volatile material. Do not open containers unnecessarily; this will prevent loss of volatile material and possible introduction of moisture. Do not make a transfer of the sample unless the sample temperature is at least 56°C (100°F) below the expected flash point. When possible, flash point should be the first test performed on a sample and the sample should be stored at low temperature
3. Do not store samples in gas-permeable containers since volatile material may diffuse through the walls of the enclosure. Samples in leaky containers are suspect and not a source of valid results.
4. Light hydrocarbons may be present in the form of gases, such as propane or butane, and may not be detected by testing because of losses during sampling and filling of the test cup. This is especially evident on heavy residuums or asphalts from solvent extraction processes.
5. Samples of very viscous materials can be warmed until they are reasonably fluid before they are tested. However, no sample shall be heated more than is absolutely necessary. It shall never be heated above a temperature of 56°C (100°F) below its expected flash point. When the sample has been heated above this temperature, allow the sample to cool until it is at least 56°C (100°F) below the expected flash point before transferring.
6. Samples containing dissolved or free water can be dehydrated with calcium chloride or by filtering through a qualitative filter paper or a loose plug of dry absorbent cotton. Samples of very viscous materials can be warmed until they are reasonably fluid before they are filtered, but they shall not be heated for prolonged periods or above a temperature of 56°C (100°F) below its expected flash point.

Cleaning Solvents:

Use suitable technical grade solvent capable of cleaning out the test specimen from the test cup and drying the test cup. Some commonly used solvents are toluene and acetone

PROCEDURE:

1. Fill the test cup with the sample so that the top of the meniscus of the test specimen is level with the filling mark, and position the test cup on the center of the heating plate. The temperature of the test cup and the sample shall not exceed 56°C (100°F) below the expected flash point. If too much test specimen has been added to the cup, remove the excess using a syringe or similar device for withdrawal of fluid. However, if there is test specimen on the outside of the test cup, empty, clean, and refill it. Destroy any air bubbles or foam on the surface of the test specimen with a sharp knife or other suitable device and maintain the required level of test specimen. If a foam persists during the final stages of the test, terminate the test and disregard any results.
2. Solid material shall not be added to the test cup. Solid or viscous samples shall be heated until they are fluid before being poured into the test cup; however, the temperature of the sample during heating shall not exceed 56°C (100°F) below the expected flash point.
3. Light the test flame and adjust it to a diameter of 3.2 to 4.8 mm (¹⁄8 to ³⁄16 in.) or to the size of the comparison bead, if one is mounted on the apparatus
4. Apply heat initially at such a rate that the temperature as indicated by the temperature measuring device increases 5 to 17°C (9 to 30°F)/min. When the test specimen temperature is approximately 56°C (100°F) below the expected flash point, decrease the heat so that the rate of temperature rise during the last 28°C (50°F) before the flash point is 5 to 6°C (9 to 11°F)/min.
5. Apply the test flame when the temperature of the test specimen is approximately 28°C below the expected flash point and each time thereafter at a temperature reading that is a multiple of 2°C. Pass the test flame across the center of the test cup at right angles to the diameter, which passes through the temperature measuring device. With a smooth, continuous motion, apply the test flame either in a straight line or along the circumference of a circle having a radius of at least 150 ± 1 mm (6.00 ± 039 in.). The center of the test flame shall move in a horizontal plane not more than 2 mm (⁵⁄64 in.) above the plane of the upper edge of the test cup and passing in one direction only. At the time of the next test flame application, pass the test flame in the opposite direction of the preceding application. The time consumed in passing the test flame across the test cup in each case shall be approximately 1 ± 0.1 s.
6. During the last 28°C (50°F) rise in temperature prior to the expected flash point, care shall be taken to avoid disturbing the vapors in the test cup with rapid movements or drafts near the test cup.
7. When a foam persists on top of the test specimen during the last 28°C (50°F) rise in temperature prior to the expected flash point, terminate the test and disregard any results.
8. Meticulous attention to all details relating to the test flame, size of the test flame, rate of temperature increase, and rate of passing the test flame over the test specimen is required for proper results.
9. When testing a sample whose expected flash point temperature is not known, bring the test specimen in the test cup to a temperature no greater than 50°C (122°F), or if the sample required heating to be transferred into the test cup, bring the test specimen in the test cup to that temperature. Apply the test flame, beginning at least 5°C (9°F) above the starting temperature. Continue heating the test specimen at 5 to 6°C (9 to 11°F)/min and testing the test specimen every 2°C (5°F) until the flash point is obtained.
10. Record, as the observed flash point, the reading on the temperature measuring device at the time the test flame causes a distinct flash in the interior of the test cup. The sample is deemed to have flashed when a large flame appears at any point on the surface of the test specimen and instantaneously propagates itself over the surface of the test specimen.
11. The application of the test flame can cause a blue halo or an enlarged flame prior to the actual flash point. This is not a flash point and shall be ignored.
12. When a flash point or fire point is detected during any preliminary test flame application, or on the first application of the test flame, the test shall be discontinued, the result discarded, and the test repeated with a fresh test specimen. The first application of the test flame with the fresh test specimen shall be at least 28°C (50°F) below the temperature found when the flash point was detected under the conditions as explained before.
13. When the apparatus has cooled down to a safe handling temperature, less than 60°C (140°F), remove the test cup and clean the test cup and the apparatus as recommended by the manufacturer.
14. To determine the fire point, continue heating the test specimen after recording the flash point such that the test specimen temperature increases at a rate of 5 to 6°C (9 to 11°F)/min. Continue the application of the test flame at 2°C (5°F) intervals until the test specimen ignites and sustains burning for a minimum of 5 s. Record the temperature of the test specimen when the test flame, which caused the test specimen to ignite was applied. Sustain burning as the observed fire point of the test specimen.
15. When the apparatus has cooled down to a safe handling temperature, less than 60°C (140°F), remove the test cup and clean the test cup and the apparatus as recommended by the manufacturer.

CALCULATIONS AND REPORT:

Observe and record the ambient barometric pressure at the time of the test. When the pressure differs from 101.3 kPa (760 mm Hg), correct the flash point or fire point, or both, as follows:

Corrected flash or fire point, or both = C + 0.033 (760 – P)

where;

C = Observed flash or fire point, or both

P = Ambient barometric pressure, mm Hg.

Using the corrected flash point or fire point, or both, as determined, and round the values to the nearest 1°C and record.    (Ref, ASTM 92)

OBSERVATIONS & CALCULATIONS

TIME	TEMPERATURE	REMARKS
	OC
0	68
1 min	70
2 min	100
3 min	174
4 min	220
5 min	268
6 min	310
6 min 54 s	336	Flash point
7 min 20 s	352	Fire point

Corrected flash or fire point, or both = C + 0.033 (760 – P)

Barometric pressure of laboratory = 738.2 mmHg

Flash point = 336+0.033(760-738.2) = 337⁰C

Fire point   = 352+0.033(760-738.2) = 353⁰C

Result: Grade is AC-40

 

SUMMARY OF TEST:

The test cup is filled to a specified level with the sample. The temperature of the sample is increased rapidly at first and then at a slow constant rate as the flash point is approached. At specified intervals a small test flame is passed across the cup. The lowest temperature at which application of the test flame causes the vapors above the surface of the liquid to ignite is taken as the flash point. To determine the fire point, the test is continued until the application of the test flame causes the material to ignite and burn for at least 5 seconds.

PRECAUTIONS:

• Do not breathe close to the apparatus as the fumes are injurious to health also breathing may cause the fumes to scatter thus altering the results.
• Turn the fans off so that the fumes can be accumulated over the cup.
• The apparatus should not be placed in direct sunlight as it will alter the temperature and will result in absurd results.
• Tip of the thermometer should not touch the bottom or sides of the cup.
• The operator must exercise and take appropriate safety precautions during the initial application of the test flame, since samples containing low flash material may give an abnormally strong flash when the test flame is first applied.

RESULTS & COMMENTS:

• Flash point = 337⁰C
• Fire point = 353⁰C
• Grade is AC-40
• Rate of increase of temperature was not uniform throughout the test as depicted by the above graph. Hence polynomial graph is plotted.
• Barometric correction is applied because when pressure will be less than 760 mmHg, the flash and fire points are higher. This means with decrease in pressure, flash and fire points increases and vice versa.