ASTM D4175 Terminology Relating to Petroleum, Petroleum Products, and Lubricants
R - in a distillation column, abbreviation for reflux ratio.
r - in statistics, abbreviation for repeatability.
R - in statistics, abbreviation for reproducibility.
Ra, n - in measuring surface finish, the arithmetic average of the absolute distances of all profile points from the mean line for a given distance.
Ra (C.L.A.), n - in measuring surface finish, the arithmetic average of the absolute distances of all profile points from the mean line for a given distance.

DISCUSSION - C.L.A. means center line average, and it is the synonym to Ra.

radiant energy, n - energy transmitted as electromagnetic waves.
radiant power, P, n - the rate at which energy is transported in a beam of radiant energy.
radio frequency, n - the range of frequencies between 3 kHz and 300 GHz.
random error, n - the chance variation encountered in all test work despite the closest control of variables.
rate of change (or slope), n - the change in temperature reading per percent evaporated or recovered, as described in 13.2.
raw petroleum coke, n - petroleum coke that has not been calcined.
reactivity, n - rate at which another material will form compounds with carbon or graphite.
reading, n - in data acquisition, the reduction of data points that represent the operating conditions observed in the time period as defined in the test procedure.
ream of paper (news and wrapping), n - 500 sheets each 610 by 914 mm (24 by 36 in.).
receiver, n - any individual or organization who receives or accepts the product delivered by the supplier.
reclaiming, n - the use of cleaning methods during recycling primarily to remove insoluble contaminants, thus making the oil suitable for further use. The methods may include settling, heating, dehydration, filtration, and centrifuging.
recycle delay, n - NMR spectrometer parameter setting for the time delay that allows magnetization recovery.
recycling, n - in petroleum technology, the acquisition of oil that has become unsuitable for its intended use, and processing it to regain useful materials.
reference fluid, n - a reference fluid base to which prescribed quantities of a known surface active agent have been added.

DISCUSSION - The known surface active agent is typically bis-2-ethylhexyl sodium sulfosuccinate, commonly referred to as AOT, dissolved in toluene.

reference fuels above 100, n - for octane rating, blended fuels of reference grade isooctane and 3-methylphenylamine.

DISCUSSION - This practice describes reference fuels above 100 MON in terms of isooctane/3-methylphenylamine. Alternate reference fuels may be used if appropriate, for example, MON in Test Method D2700, Section 8, mixtures of tetraethyl lead and reference grade isooctane. Care should be exercised to ensure the reference fuel does not adversely contaminate the engine and influence the results.

reference fuel framework, n - for supercharge method knock rating, the graphic representation of the knock-limited power curves for the specified primary reference fuel blends of isooctane + n-heptane and isooctane + TEL (mL/U.S. gal) that defines the expected indicated mean effective pressure versus fuel-air ratio characteristics for supercharge test engines operating properly under standardized conditions.
reference material (RM), n - a material or substance of which one or more properties are sufficiently well established to enable the material to be used for the calibration of an apparatus, the assessment of a method, or the assignment of values to similar materials.
reference material, RM, n - a material with accepted reference value(s), accompanied by an uncertainty at a stated level of confidence for desired properties, which may be used for calibration or quality control purposes in the laboratory.

DISCUSSION - Sometimes these may be prepared "in-house" provided the reference values are established using accepted standard procedures.

reference oil, n - an oil of known performance characteristics, used as a basis for comparison.

DISCUSSION - Reference oils are used to calibrate testing facilities, to compare the performance of other oils, or to evaluate other materials (such as seals) that interact with oils.

reference viscosity, n - the viscosity of Newtonian standard reference fluids certified at each of several temperatures by the supplier.
refinery, n - a plant at which gasoline or diesel fuel is produced.

DISCUSSION - This definition is from CFR 40 Part 80.2. In the federal definition, a plant not only covers the conventional refinery, but also covers oxygenate blending and other facilities where gasoline is produced.

reflux ratio, R, n - in a distillation column, the ratio of the condensate at the head of the column that is returned to the column (reflux) to that withdrawn as product.
reflux ratio, R, n - the ratio of reflux to distillate.

DISCUSSION - The vapor reaching the top of the column is totally condensed and the resulting liquid is divided into two parts. One part L (reflux), is returned to the column and the other part, D (distillate), is withdrawn as product. The reflux ratio ( R = L/D), can vary from zero at total takeoff (L = 0) to infinity at total reflux (D = 0).

refractive dispersion, n - the difference between the refractive indexes of a substance for light of two different wavelengths, both indexes being measured at the same temperature. For convenience in calculations, the value of the difference thus obtained is usually multiplied by 10 000.
refractive index, n - the ratio of the velocity of light (of specified wavelength) in air, to its velocity in the substance under examination. This is the relative index of refraction. If absolute refractive index (that is, referred to vacuum) is desired, this value should be multiplied by the factor 1.00027, the absolute refractive index of air.
refractive index, n - the ratio of the velocity of light (of specified wavelength) in air, to its velocity in the substance under examination. It may also be defined as the sine of the angle of incidence divided by the sine of the angle of refraction, as light passes from air into the substance. This is the relative index of refraction. If absolute refractive index (that is, referred to vacuum) is desired, this value should be multiplied by the factor 1.00027, the absolute refractive index of air. The numerical value of refractive index of liquids varies inversely with both wavelength and temperature.
Reid vapor pressure (RVP), n - resultant total pressure reading, corrected for measuring error, of a specific empirical test method (Test Method D323) for measuring the vapor pressure of gasoline and other volatile products.
relative density, n - the ratio of the density of a material at a stated temperature to the density of water at a stated temperature.
relative density (specific gravity), n - the ratio of the mass (weight in vacuo) of a given volume of material at a temperature, t1, to the mass of an equal volume of water at a reference temperature, t2; or it is the ratio of the density of the material at t1 to the density of water at t2. When the reference temperature is 4.00°C, the temperature at which the relative density of water is unity, relative density (specific gravity) and density are numerically equal.
relative density (specific gravity), n - the ratio of the mass of a given volume of liquid at a specific temperature to the mass of an equal volume of pure water at the same or different temperature. Both reference temperatures shall be explicitly stated.

DISCUSSION - Common reference temperatures include 60/60°F, 20/20°C, 20/4°C. The historic deprecated term "specific gravity" may still be found.

relative molar response, n - the measured area of a compound divided by the moles present in the synthetic mixture relative to an arbitrarily chosen component.
relative volume response factor (RVRF), n - the volume response factor of a component i relative to the volume response factor of n-heptane.
relaxation time constant (T1), n - a numerical value which is a measure of magnetization relaxation time following an excitation pulse of an NMR spectrometer.
repeatability, n - the quantitative expression of the random error associated with a single operator in a given laboratory obtaining repetitive results by applying the same test method with the same apparatus under constant operating conditions on identical test material within a short interval of time on the same day. It is defined as the difference between two such results at the 95 % confidence level.

DISCUSSION - Interpret as the value equal to or below which the absolute difference between two single test results obtained in the above conditions may expect to lie with a probability of 95 %.

DISCUSSION - The difference is related to repeatability standard deviation but is not the standard deviation or its estimate.

repeatability (r), n - quantitative expression of the random error associated with a single operator in a given laboratory obtaining replicate results with the same apparatus under constant operating conditions on identical test material within a short period of time. It is defined (3.1.8.1) as that difference between two such single results as would be exceeded in the long run in only 1 case in 20 in the normal and correct operation of the test method (3.1.8.3). (This is known as the 95 % confidence level.)

DISCUSSION - The repeatability and reproducibility values should have been determined according to the methods described in ASTM Research Report RR:D02-1007, Manual on Determining Precision data for ASTM Methods of Petroleum Products and Lubricants, Practice D6300, or ISO 4259.

DISCUSSION - Not all standards organizations define repeatability and reproducibility in precisely these same terms, and attention should always be paid to definitions before comparing precision values quoted.

DISCUSSION - This difference is related to the repeatability or the reproducibility standard deviation but is not the standard deviation.

repeatability conditions, n - conditions where mutually independent test results are obtained with the same test method in the same laboratory by the same operator with the same equipment within short intervals of time, using test specimens taken at random from a single sample of material.
repeatability conditions, n - conditions under which test results are obtained with the same test method in the same laboratory by the same operator with the same equipment in the shortest practical period of time using test units or test specimens taken at random from a single quantity of material that is as nearly homogeneous as possible (see 10.3 of Practice E 691).

DISCUSSION - The same operator, same equipment requirement means that for a particular step in the measurement process the same combination of operator and equipment is used for every test result. Thus, one operator may prepare the test specimens, a second measure the dimensions, and a third measure the mass in a test method for measuring density.

DISCUSSION - By in the shortest practical period of time is meant that the test results, at least for one material, are obtained in a time period not less than in normal testing and not so long as to permit significant change in test material, equipment, or environment. See Terminology E 456.

repeatability conditions, n - conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.

DISCUSSION - In the context of this test method, a short time interval between two ratings on a sample fuel is understood to be not less than the time to obtain at least one rating on another sample fuel between them but not so long as to permit any significant change in the sample fuel, test equipment, or environment.

representative sample, n - a part of a homogeneous material, or a part of the composited and mixed portions of a material, which carries all the true properties and physical characteristics of the whole material.
reproducibility, R, n - quantitative expression of the random error associated with operators working in different laboratories, each obtaining single results on identical test material when applying the same method.
reproducibility, n - a quantitative expression of the random error associated with different operators from different laboratories, using different apparatus, each obtaining a single result by applying the same method on an identical test sample. It is defined as the 95 % confidence limit for the difference between two such single and independent results.

DISCUSSION - Interpret as 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 standardized test may be expected to lie with a probability of 95 %.

DISCUSSION - The difference is related to the reproducibility standard deviation but is not the standard deviation or its estimate.

DISCUSSION - In those cases where the normal use of the test method does not involve sending a sample to a testing laboratory, either because it is an in-line test method or because of serious sample instabilities or similar reasons, the precision test for obtaining reproducibility may allow for the use of apparatus from the participating laboratories at a common site (several common sites, if feasible). The statistical analysis is not affected thereby. However, the interpretation of the reproducibility value will be affected and therefore the precision statement shall, in this case, state the conditions to which the reproducibility value applies.

reproducibility, n - quantitative expression of the random error associated with operators working in different laboratories, each obtaining single results on identical test material when applying the same method. It is defined (3.1.8.1) as that difference between two such single and independent results as would be exceeded in the long run in only 1 case in 20 in the normal and correct operation of the test method. See 3.1.8.3.
reproducibility conditions, n - conditions under which test results are obtained in different laboratories with the same test method, using test specimens taken at random from the same sample of material.
reproducibility conditions, n - conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment.
re-refining, n - the use of refining processes during recycling to produce high quality base stocks for lubricants or other petroleum products. Re-refining may include distillation, hydrotreating, or treatments employing acid, caustic, solvent, clay, or other chemicals, or combination thereof.
residual fuel, n - a liquid fuel containing bottoms remaining from crude distillation or thermal cracking; sometimes referred to as heavy fuel oil.

DISCUSSION - Residual fuels comprise Grades 4, 5, and 6 fuel oils, as defined in Specification D396.

residual fuel oil, n - any liquid or liquefiable petroleum product having a kinematic viscosity at 100°C between 5.0 and 50.0 mm2/s, inclusive, burned for the generation of heat in a furnace or firebox or for the generation of power in an engine.
residual fuel oil, n - a fuel oil comprising a blend of viscous long, short, or cracked residue from a petroleum refining process and lighter distillates blended to a fuel oil viscosity specification.
residuum, n - a liquid or semi-liquid product obtained as residue from the distillation of petroleum and consisting primarily of asphaltic hydrocarbons.

DISCUSSION - Also known as asphaltic oil, asphaltum oil, liquid asphalt, black oil, petroleum tailings, and residual oil.

response factor, n - a constant of proportionality that converts area to liquid volume.
rest conductivity, n - the reciprocal of the resisitivity of uncharged fuel in the absence of ionic depletion or polarization.

DISCUSSION - It is the electrical conductivity at the initial instant of current measurement after a dc voltage is impressed between electrodes, or a measure of the average current when an alternating current (ac) voltage is impressed.

result, n - the value obtained by following the complete set of instructions of a test method.
result, n - the value obtained by following the complete set of instructions of a test method. It may be obtained from a single determination or several determinations, depending on the instruction of the test method.
reticulated foam, n - in carbon and graphite technology, a foam with a ligamentous structure rather than a spherical pore structure.
RF, n - reference fuel above 100
ridging, n - on ring and pinion gears, an alteration of the tooth surface to give a series of parallel raised and polished ridges running diagonally in the direction of sliding motion, either partially or completely across the tooth surfaces of gears.
riffle - a manual sample divider which splits the sample stream into a number of alternate elements.
rippling, n - on ring and pinion gears, an alteration of the tooth surface to give an appearance of a more or less regular pattern resembling ripples on water or fish scales.
RON - in gasoline knock testing, abbreviation for Research octane number.
rosin oil, n - a viscous, oily liquid obtained as a condensate when the residue (rosin) from turpentine production is subjected to dry, destructive distillation.

DISCUSSION - Also used to describe specially compounded oils having a rosin base.

Rpk, n - Reduced peak height according to DIN EN ISO 13565-2:1998. Rpk is the mean height of the peak sticking out above the core profile section.
rpm, n - revolutions per minute
running torque, n - the 15-s average value of the torque after rotation for a specified period of time (60 min).
rust, n - of ferrous alloys, a corrosion product consisting primarily of hydrated iron oxides.
rust (coatings), n - of ferrous alloys, a corrosion product consisting of hydrated iron oxides.
rust (coatings), n - the reddish material, primarily hydrated iron oxide, formed on iron or its alloys, resulting from exposure to humid atmosphere or chemical attack.
Ry, n - in measuring surface finish, the vertical distance between the top of the highest peak and the bottom of the deepest valley in one sampling length.
Ry, n - in measuring surface finish, the vertical distance between the top of the highest peak and the bottom of the deepest valley in one sampling length of the roughness profile.
Rz, n - in measuring surface finish, the average of all Ry values (peak to valley heights) in the assessment length.
Rz (DIN), n - in measuring surface finish, the average of all Ry values (peak to valley heights) in the assessment length.