+ 312.476.9292
Log In

ASTM D1401

Standard Test Method for Water Separability of Petroleum Oils and Synthetic Fluids

ASTM D1401 test method is used to determine the ability of petroleum products and synthetic fluids to separate from water. This method may be used to test oils and other types of products with different viscosities at different temperatures than the original method developed for steam-turbine oils with viscosities in the range of 28.8-90 mm2/s at 40 oC. It is recommended the method be run at 82± 1 °C when viscosities are higher than 90 mm2/s at 40 oC.

The values in SI units are to be regarded as standard. No other units of measurement are included in this standard.

A precise and reliable determination of the ability of petroleum oils and other products to separate from water constitutes a valuable tool not only to more precisely determine the specifications of new oils but also to monitor in-service oils and optimize preventive maintenance programs of engines and machinery reducing downtime and repair costs avoiding unnecessary unscheduled maintenance.                                                                                                              

Referenced Documents

ASTM Standards:

D665 Test Method for Water Separability of Petroleum Oils and Synthetic Fluids
D1141 Practice for the Preparation of Substitute Ocean Water of Lubricating Oils
D1193 Specification for Reagent Water
D2711 Test Method for Demulsibility Characteristics of Lubricanting Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products

ISO Standards:

BS EN ISO 3696:1995 Water for analytical laboratory use – Specification and test methods

Summary of Test Method

A 40 mL sample of the test specimen and a 40-mL of distilled water, or 1% sodium chloride (NaCl) solution or synthetic seawater are stirred for 5 min in a graduated cylinder at 54°C or 82°C, depending upon the viscosity of the test specimen or sample specification. The time required for the separation of the emulsion thus formed is recorded either after every 5 min or at the specification time limit. If complete separation or emulsion reduction to 3 mL or less does not occur after standing for 30 min or some other specification time limit, the volumes of oil (or fluid), water, and emulsion remaining at the time are reported.

Significance and Use

This test method provides a guide for determining the water separation characteristics of oils subject to water contamination and turbulence. It is used for specification of new oils and monitoring of in-service oils.


Heat the bath liquid to 54 6 1°C, 82 6 1°C or specified test temperature and maintain it at that temperature throughout the test. Add reagent water to the graduated cylinder to reach the 40-mLmark when at test temperature. Typically, 39.5 mL of water at room temperature will expand to the 40-mLmark once the cylinder is placed in the bath at 54°C; 39 mL if heating the sample to 82°C. Invert the sample several times in the original container. Do not pour, shake, or stir samples to any greater extent than necessary to prevent air entrainment. Pour the oil (or fluid) under test into the same cylinder until the top level of the oil reaches the 80-mL mark on the cylinder when at test temperature.

If initial volumetric measurements are made at room temperature, expansion occurring at the elevated test temperature will have to be considered. For example, there will be a total volumetric expansion of about 2 to 3 mL at 82°C. Corrections to each volume reading at 82°C, therefore, should be made so that the total of the volume readings made for oils (or fluid), water, and emulsion does not exceed 80 mL.  An alternative procedure which would avoid the corrections is to make the initial volumetric measurements at the test temperature.

A 1 % sodium chloride (NaCl) solution or synthetic seawater, as described in Practice D1141 or Test Method D665, may be used in place of distilled water when testing certain oils or fuels used in marine applications.

Secure the cylinder in place directly under the stirring paddle. Lower the paddle into the cylinder until the stop engages at the required depth. Start the stirrer and a stop watch simultaneously and adjust the stirrer, as required, to a speed of 1500 6 15 rpm. At the end of 5 min, stop the stirrer and raise the stirring assembly until it is just clear of the graduate. Wipe the paddle with a spatula or wiper, allowing the liquid thus removed to drop back into the cylinder. At 5-min intervals, or at the specification time limit identified for the product being tested, depending on the type of heating bath utilized, lift the cylinder out of the bath or inspect the sample through the glass panel of the heating bath, and record the volumes of the oil (or fluid), water, and emulsion layers. If necessary, additional lighting, such as a backlight or an indoor flood light, may be used to aid the analyst in the inspection of the sample.

Several samples may be placed in the bath at the beginning of the first analysis. While the first sample is being observed, additional samples may be stirred. At no time during a sample inspection shall an additional sample be added to the heating bath.


Record Measurements at 5–min Intervals—Report the following information:

(1) Type of water used.
(2) Test temperature.
(3) Time, in minutes, to reach 3 mL or less of emulsion.
(4) Time, in minutes, to reach 37 mL of water.
(5) Time, in minutes, to reach a complete break of 0 mL emulsion, 40 mL of oil, and 40 mL of water.

In addition to reporting the time, report the volume of each layer in milliliters. In all cases, report results as follows:

mL oil – mL water –  mL emulsion (time, min)                         (1)

The test may be aborted after 30 min when testing at 54°C and 60 min at 82°C.

When the test method is performed to determine if the sample meets a specification, report the test temperature. Report the time when either:

(1) The product passes the product separability requirements against which it is being tested, or

(2) The test limit for water separability is exceeded (usually 3–mL emulsion or less for 30 min at 54°C and 60 min at 82°C). In addition to reporting the time, report the volume of each layer in millilitres. In both cases, report results as follows:

mL oil –  mL water – mL emulsion (time, min)                         (2)

Some samples may produce a hazy oil layer without an emulsion layer. In situations where the water layer is ≥37 mL, report the upper layer as the oil layer. If there are two layers, and the water layer is <37 mL, that is, the upper layer is >43 mL, report the upper layer as the emulsion layer.

For uniformity, test results may be reported in the manner shown in the examples provided above i.e:

40-40-0 (20)        Complete separation occurred in 20 min. More than 3 mL of emulsion had remained at 15 min.

39-38-3 (20)         Complete separation had not occurred, but the emulsion reduced to 3 mL so the test was ended.

39-35-6 (60)        More than 3 mL of emulsion remained after 60 min—39 mL of oil, 35 mL of water, and 6 mL of emulsion.

41-37-2 (20)          Complete separation had not occurred but the emulsion layer reduced to 3 mL or less after 20 min.

43-37-0 (30)         The emulsion layer reduced to 3 mL or less after 30 min. The emulsion layer at 25 min exceeded 3 mL, for example, 0-36-44 or 43-33-4.

The appearance of each layer may be described in the following terms:

Oil (or Oil Rich) Layer:

1 Clear.

2 Hazy (Note 2).

3 Cloudy (or milky) (Note 2).

4 Combinations of 1-3.

Water or Water-Rich Layer:

1 Clear.

2 Lacy or bubbles present, or both.

3 Hazy (Note 2).

4 Cloudy (or milky) (Note 2).

5 Combinations of 1 – 4.


1 Loose and lacy.

2 Cloudy (or milky) (Note 3).

3 Creamy (like mayonnaise) (Note 3).

4 Combinations of 1-3.

NOTE 2—A hazy layer is defined as being translucent and a cloudy layer opaque.

NOTE 3—The principal difference between cloudy and creamy emulsions is that the former is quite fluid and probably unstable while the latter has a thick consistency and is probably stable. A cloudy emulsion will readily flow from an inclined graduate while a creamy emulsion will not.

The appearance of the oil/emulsion and water/ emulsion interfaces may be described in the following terms:

1 Well-defined, sharp.

2 Ill-defined, bubbles.

3 Ill-defined, lace.

Report the test temperature if other than 54°C and the aqueous medium if other than distilled water.


Heating Bath, sufficiently large and deep to permit the immersion of at least two test cylinders in the bath liquid up to their 85-mL graduations as illustrated in two versions in Figure 1. The bath shall be capable of being maintained at a test temperature to within 61°C. The cylinder shall be secured in a position so that the longitudinal axis of the paddle corresponds to the vertical center line of the cylinder during the stirring operation. It is recommended that the bath be constructed with at least one transparent side that allows for clear visual inspection of the oil (fluid), water, and emulsion layer volumes while the cylinder remains immersed in the bath.

Cylinder, 100-mL, graduated from 5 to 100 mL in 1.0-mL divisions, made of glass, heat-resistant glass, like borosilicate glass, or a chemical equivalent. The inside diameter shall be no less than 27 mm and no more than 30 mm throughout its length, measured from the top to a point 6 mm from the bottom of the cylinder. The overall height of the cylinder shall be 225 to 260 mm. The graduation shall not be in error by more than 1 mL at any point on the scale.

Precision and Bias

Precision—An interlaboratory study performed in 2008 by 13 laboratories (9 using glass baths and 4 using metal baths).At 54°C, the following samples were included: Turbine Oil, Mineral Turbine Oil ISO 32, 150 N Base oil (in duplicate), Mineral Circulating Oil ISO 32 , Synthetic Gear Oil ISO 32 , Industrial Oil ISO 68, Industrial Oil ISO 68, Synthetic Compressor ISO 46, Multi-Purpose Oil ISO 32. At 84°C, the following samples were included: 600 NS Base oil , Synthetic Gear Oil ISO 320 (in duplicate), Synthetic Paper Machine Oil ISO 220, Industrial Oil ISO 100, Hydraulic oil ISO 150, Synthetic Compressor ISO 100, Multi-Purpose Oil ISO 100, Circulating Oil, Circulating Oil. The mineral oil samples were Group I or Group II based. The synthetic samples were primarily PAO based but may have contained some amount of a Group V oil, however no specific details on any co-base oil was disclosed. This precision is for the determination of the time in minutes to 3 mL of emulsion or 37 mL of water.

Repeatability—The difference between successive test results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty.

at 54°C                    15 min

at 82°C                    10 min

Reproducibility—The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty:

at 54°C                    20 min

at 82°C                    25 min

Bias—The procedure in this test method for measuring water separability has no bias because the value for water separability is defined only in terms of the test method.

We offer the following items that cover this method:


Herschel Demulsibility and Foaming


Semi-Automatic Herschel