Standard Test Method for Rust-Preventing Characteristics of Inhibited Mineral Oil in the Presence of Water
(ASTM D665 / ISO 7120)
🔹 Purpose of the Test
This method evaluates the rust-preventing characteristics of inhibited mineral oils, such as lubricating oils, hydraulic fluids, and turbine oils, when mixed with water. It determines whether an oil can protect metal surfaces (typically steel) from rust formation under controlled conditions.
📌 Applicable Industries:
✔ Automotive & Engine Oils
✔ Industrial Lubricants
✔ Hydraulic & Turbine Oils
✔ Metalworking Fluids
🔹 Test Methods & Variants
The test follows ASTM D665 / ISO 7120, which has two main methods:
| Method | Application | Water Type |
|---|---|---|
| Procedure A | Fresh Lubricants | Distilled Water |
| Procedure B | Used Oils & Harsh Conditions | Synthetic or Salt Water |
📌 Procedure B is used for more aggressive testing, such as marine environments.
🔹 Test Equipment & Materials
✔ Test Beaker – 400 mL glass beaker
✔ Metal Test Rod – 12.7 mm steel rod (Polished, Mild Steel)
✔ Temperature Control Bath – Maintains 60°C (140°F)
✔ Stirring Mechanism – Rotates test sample at 1000 rpm
✔ Test Liquids – Oil sample, distilled/salt water
🔹 Test Procedure
🔹 1. Preparation of the Steel Test Rod
- Polish with abrasive paper until smooth
- Clean with solvent to remove residues
🔹 2. Sample & Water Mixing
- Mix 300 mL of oil with 30 mL of water
- Place the steel rod in the solution
🔹 3. Temperature & Stirring
- Heat to 60°C (140°F) in a water bath
- Stir at 1000 rpm for 24 hours
🔹 4. Rust Evaluation
- Remove and inspect the steel rod
- Pass: No rust or slight staining
- Fail: Visible rust or corrosion
📌 If rust appears, the oil fails as a rust-preventing lubricant.
🔹 Key Factors Affecting Results
✅ Oil Formulation – Presence of rust inhibitors like calcium sulfonates
✅ Water Quality – Salt water is more corrosive than distilled water
✅ Temperature & Stirring Rate – Must be consistent to ensure accurate results
✅ Steel Rod Surface Preparation – Proper polishing ensures repeatability
🔹 Interpretation of Results
| Rust Appearance | Rating | Performance |
|---|---|---|
| No Rust | Pass | Excellent Protection |
| Slight Staining | Conditional Pass | Needs Further Evaluation |
| Heavy Rust | Fail | Poor Rust Prevention |
📌 Oils that fail may require additional corrosion inhibitors.
🔹 Applications in Industry
✔ Lubricant Development – Ensures rust inhibitors work effectively
✔ Quality Control – Confirms oil batches meet performance specs
✔ Used Oil Monitoring – Detects depletion of rust inhibitors over time
✔ Marine & Industrial Use – Tests performance in water-contaminated environments
Step-by-Step Test Execution for Rust-Preventing Characteristics of Inhibited Mineral Oil (ASTM D665 / ISO 7120)
🔹 Purpose
This test determines the ability of a lubricating oil, hydraulic fluid, or turbine oil to prevent rust formation on steel surfaces when mixed with water under controlled conditions.
🔹 Required Equipment & Materials
1️⃣ Test Apparatus
✔ 400 mL Glass Beaker – Holds oil and water mixture
✔ Temperature-Controlled Water Bath – Maintains 60°C (140°F)
✔ Steel Test Rod (Mild Steel, 12.7 mm diameter) – Polished and pre-cleaned
✔ Stirring Mechanism – Stirring paddle rotates at 1000 rpm
✔ Thermometer – To monitor bath temperature
✔ Tongs & Gloves – For handling steel rods safely
2️⃣ Test Liquids
✔ Lubricating Oil Sample – 300 mL
✔ Water Sample (30 mL):
- Distilled Water (for Procedure A)
- Synthetic Sea Water (NaCl Solution) (for Procedure B)
🔹 Step-by-Step Test Procedure
Step 1: Steel Test Rod Preparation
1️⃣ Polishing – Sand the steel rod with abrasive paper to remove oxidation and scratches.
2️⃣ Cleaning – Wash thoroughly with solvent (e.g., heptane or acetone) to remove residues.
3️⃣ Drying – Allow the rod to air dry before testing.
📌 Why? Proper polishing ensures a clean test surface and accurate results.
Step 2: Sample & Water Preparation
4️⃣ Measure 300 mL of the oil sample and pour it into the test beaker.
5️⃣ Add 30 mL of water (distilled or synthetic seawater, depending on the method).
6️⃣ Insert the polished steel rod vertically into the solution.
📌 Why? The oil-water mixture simulates conditions where rust formation can occur.
Step 3: Heating & Stirring
7️⃣ Place the beaker in the water bath, maintaining 60°C (140°F).
8️⃣ Start stirring at 1000 rpm using the paddle mechanism.
9️⃣ Let the test run continuously for 24 hours.
📌 Why? Controlled temperature and stirring ensure proper exposure to test conditions.
Step 4: Post-Test Inspection
🔟 After 24 hours, remove the steel rod using tongs.
1️⃣1️⃣ Rinse the rod with solvent (heptane or acetone).
1️⃣2️⃣ Dry with lint-free cloth and examine for rust.
📌 Why? A clean, dry surface makes rust easier to evaluate.
🔹 Evaluation & Interpretation of Results
Rust Classification (Pass/Fail Criteria)
| Rust Appearance | Result | Interpretation |
|---|---|---|
| No Rust | Pass | Oil provides excellent rust prevention |
| Slight Staining | Conditional Pass | Needs further evaluation |
| Visible Rust Spots | Fail | Poor rust prevention |
| Heavy Corrosion | Fail | Oil is ineffective in preventing rust |
📌 If rust appears, the oil fails as a rust-preventing lubricant.
🔹 Key Factors Affecting Results
✅ Oil Formulation – Presence of rust inhibitors (e.g., calcium sulfonates)
✅ Water Type – Saltwater (Procedure B) is more aggressive than distilled water
✅ Temperature Consistency – Keep at exactly 60°C (140°F)
✅ Proper Stirring – Ensures uniform exposure to test conditions
✅ Steel Rod Preparation – Surface condition affects rust formation
🔹 Common Issues & Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| Rust Forms Quickly | Weak rust inhibitors | Reformulate oil with better additives |
| Inconsistent Results | Improper rod polishing | Use consistent sanding technique |
| Excessive Foaming | Oil contains surfactants | Use anti-foam agents |
| No Rust but Heavy Staining | Contamination in solvent or oil | Use fresh solvent and clean beakers |