Test Method for Water in Petroleum Products – Distillation Method
(ASTM D95 / ISO 3733)
The Distillation Method is a widely used technique to determine water content in petroleum products, lubricants, and bituminous materials. This method is ideal for samples with water content ranging from 0.02% to 25%.
1️⃣ Test Standard
✔ ASTM D95 – Standard Test Method for Water in Petroleum Products and Bituminous Materials by Distillation
✔ ISO 3733 – Petroleum products and bituminous materials—Determination of water—Distillation method
2️⃣ Principle of the Distillation Method
🔹 The sample is heated in the presence of a water-immiscible solvent (e.g., xylene or toluene).
🔹 Water in the sample co-distills with the solvent and condenses in a graduated receiver.
🔹 The separated water is measured volumetrically and expressed as a percentage of the sample.
3️⃣ Required Equipment & Materials
🛠 Equipment:
✅ Distillation Apparatus – Includes a flask, condenser, and graduated receiver
✅ Heat Source – Electric heating mantle or gas burner
✅ Water-Immiscible Solvent – Xylene or toluene (higher boiling point than water)
✅ Graduated Receiver – For accurate measurement of collected water
✅ Drying Agents (Optional) – To remove residual water from the apparatus
4️⃣ Test Procedure (ASTM D95 / ISO 3733)
Step 1: Sample Preparation
✔ Weigh 25-100 g of the petroleum sample into the distillation flask.
✔ Add a measured quantity of water-immiscible solvent (typically xylene or toluene).
Step 2: Distillation Process
✔ Assemble the distillation apparatus with the sample flask, condenser, and receiver.
✔ Apply heat gradually until the mixture starts to boil.
✔ Water evaporates with the solvent and condenses in the receiver.
✔ Continue distillation until no more water collects in the receiver.
Step 3: Measurement & Calculation
✔ Allow the receiver to cool and read the water volume (mL).
✔ Calculate the water content (%) using the formula: \text{Water Content (%) } = \frac{\text{Volume of Water (mL)} \times 100}{\text{Sample Weight (g)}}
5️⃣ Advantages & Limitations
✅ Advantages
✔ Effective for high water content samples (up to 25%).
✔ Measures both free and emulsified water.
✔ Suitable for crude oil, fuels, lubricants, and bitumen.
❌ Limitations
✘ Not suitable for trace water detection (<0.02%); use Karl Fischer Titration (ASTM D6304) instead.
✘ Requires high-temperature heating, which may degrade certain samples.
✘ Solvent disposal requires proper handling.
6️⃣ Alternative Water Determination Methods
| Method | Detection Range | Best for |
|---|---|---|
| Distillation (ASTM D95 / ISO 3733) | 0.02% – 25% | Crude oil, fuels, heavy lubricants |
| Karl Fischer Titration (ASTM D6304) | 10 ppm – 5% | Low water content in refined oils, additives |
| Coulometric Karl Fischer (ASTM D6304C) | 1 ppm – 0.5% | Ultra-trace moisture in oils & fuels |
| Crackle Test (Field Test) | >0.1% | Quick on-site screening of lubricants |
A.1.1 The sample should be treated in such a way that its properties and integrity are maintained at the point of extraction, at the laboratory bench or at the point of sample storage.
A.1.2 The method of sample treatment depends on the purpose of sampling. The laboratory analytical method to be used will often require a special treatment method to be combined with it. For this reason, refer to the appropriate test method and give the sampler the necessary instructions concerning sample treatment. If the analytical method to be applied has inconsistent requirements, separate samples should be drawn and the appropriate sampling method should be used for each sample.
A.1.3 Special attention should be paid to the following:
a) Liquids containing volatile substances, which may undergo evaporation losses;
b) Liquids containing water and/or sediments, which have a tendency to separate in the sample container;
c) Liquids with potential wax precipitation, which may precipitate if not kept at an adequate temperature.
A.1.4 When preparing composite samples, special attention should be paid to not causing the volatile liquid to lose light components and not changing its water and sediment content. This is a difficult operation and should be avoided if possible.
A.1.5 Samples of volatile liquids should not be transferred to other containers at the sampling site. Instead, the original sample container should be used to transport the sample to the laboratory for sample transfer. If necessary, the sample container should be cooled and inverted during transfer. When the sample contains volatile components and free water, special care must be taken during transfer.