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D2619-21 – Standard Test Method Technical Guide
ASTM D2619‑21, the Standard Test Method for Hydrolytic Stability of Hydraulic Fluids (Beverage Bottle Method), specifies a stringent accelerated aging test to evaluate the resistance of hydraulic fluids to chemical decomposition in the presence of water. This method helps predict the formation of acidic and insoluble contaminants that can lead to corrosion, valve sticking, and viscosity changes in hydraulic systems.
📐 Scope and Summary of the Beverage Bottle Method
The test method applies primarily to petroleum-based and synthetic hydraulic fluids. Water-based or water-emulsion fluids can also be tested but must be run “as is” without the addition of the standard 25 g of distilled water—a condition the requesting party must explicitly communicate to the operator. The core procedure seals a copper test specimen with 75 g of fluid and 25 g of water (or 100 g of a water-containing fluid) inside a pressure-type beverage bottle and rotates it end‑over‑end for 48 hours in a 93 °C oven.
| 🟦 Test Parameter | 📏 Specification |
|---|---|
| Sample Composition (Standard) | 75 g fluid + 25 g water |
| Sample Composition (Water‑based) | 100 g fluid, run “as is” |
| Test Temperature | 93 °C ± 0.5 °C (200 °F ± 1 °F) |
| Test Duration | 48 hours |
| Rotation | End‑over‑end |
| Test Container | Pressure‑type beverage bottle, 200 mL (7 oz) |
| Test Specimen | Copper strip |
⚙️ Apparatus and Critical Safety Procedures
A convection oven capable of maintaining the required temperature tolerance and pressure‑type beverage bottles form the core apparatus. While straight‑sided bottles are available, curved‑side bottles are strongly recommended as they slow the velocity of the copper coupon during rotation, significantly reducing the risk of breakage.
⚠️ Critical Safety Warning
This test involves sealed glass bottles containing approximately 200 kPa (2 atm) of air and water vapor at 93 °C. Operators must wear a full face shield and heavy woven fabric gloves when handling or working with the heated and sealed sample container.
This test involves sealed glass bottles containing approximately 200 kPa (2 atm) of air and water vapor at 93 °C. Operators must wear a full face shield and heavy woven fabric gloves when handling or working with the heated and sealed sample container.
💡 Technical Tip for Water‑Based Fluids
When testing water-containing or water-emulsion fluids, ensure the test operator is explicitly notified so the standard 25 g of additional water is not added to the 100 g sample. Running the fluid “as is” is critical for accurate results.
When testing water-containing or water-emulsion fluids, ensure the test operator is explicitly notified so the standard 25 g of additional water is not added to the 100 g sample. Running the fluid “as is” is critical for accurate results.
📊 Key Measured Properties and Significance
After the 48‑hour rotation, the fluid and water layers are separated. Hydrolytic instability is quantified by measuring the weight change of the copper specimen, the change in acid number of the fluid layer, and the total acidity of the water layer. These results correlate with the fluid’s tendency to form corrosive and insoluble degradation products in service.
| 💡 Property Measured | 🎯 Analysis Method | 📌 Indicator of Instability |
|---|---|---|
| Copper Specimen Mass Change | Direct weighing | Corrosive attack by degradation products |
| Fluid Acid Number Change | ASTM D664 or D974 | Formation of acidic contaminants |
| Water Layer Acidity | Potentiometric titration | Migration of acidic species from fluid |
| Fluid and Copper Appearance | Visual observation | Qualitative degradation and sludge formation |
❓ Frequently Asked Questions
🔍 What specific fluid types are evaluated by D2619‑21?
The standard covers petroleum-based and synthetic-based hydraulic fluids. Water-based and water-emulsion fluids can also be tested but must be run “as is” without any water addition.
💡 How is hydrolytic stability quantified in this test?
Stability is quantified primarily by three metrics: the weight change of the copper coupon, the change in the acid number of the fluid (per D664 or D974), and the total acidity of the separated water layer.
⚡ What is the major safety risk of this method?
The major risk is the pressurized glass bottle (≈200 kPa) at 93 °C. The standard mandates wearing a full face shield and heavy woven fabric gloves whenever handling the sealed, heated container.
📌 Why are curved-sided bottles recommended over straight ones?
Straight-sided bottles have a higher reported risk of breakage because the copper coupon moves with greater velocity during rotation. Curved sides slow the coupon movement, reducing the chance of bottle rupture.