SH/T 0208-1992 Determination of thermal oxidation stability and corrosion of aviation hydraulic oils

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: test method

1. Standard designation, title, English title and supersession

• Standard designation: SH/T 0208-92.
• Title translated from Chinese: Determination of thermal oxidation stability and corrosion of aviation hydraulic oils.
• Official English title: not found in the available source.
• Supersession: replaces ZB E39 005-88.
• Other information: the confirmation-year entry is garbled as (2a“), and remains unverified. Approved by China Petrochemical Corporation on 1992-05-20; implemented on 1992-05-20.

2. Scope and exclusions

• This standard specifies a method for determining thermal oxidation stability and corrosion of aviation hydraulic oils.
• It applies to aviation hydraulic oils.
• Exclusions: not found in the available source.

3. Principle

Place a set of test metal coupons in an oxidation tube containing the sample and test under the specified conditions. Evaluate thermal oxidation stability and corrosion from changes in acid number, kinematic viscosity and metal-coupon corrosion before and after thermal oxidation.

4. Reagents and materials: purity and preparation

4.1 Reagents

• 5.1 Toluene: analytical reagent.
• 5.2 Anhydrous calcium chloride: chemically pure.
• 5.3 Benzene: chemically pure.
• 5.4 Acetone: analytical reagent.
• 5.5 Potassium hydroxide: analytical reagent.
• 5.6 Ethanol, 95%: analytical reagent.
• 5.7 Alkali blue 6B indicator.

4.2 Preparation

• 6.1 Prepare potassium hydroxide in ethanol standard titrant, c(KOH)=0.05 mol/L, according to SH/T 0079. The source extraction reads (KOH) = 0.05m.UL; the concentration unit remains unverified.
• 6.2 Prepare 20 g/L alkali blue 6B indicator solution in ethanol according to SH/T 0079.

4.3 Materials

• 4.2.1 Metal coupons: square, 20 mm × 20 mm × (2–3) mm, with a hole of diameter 2.5–3 mm near one corner, located 3 mm from both edges.
  • Steel coupon: 30CrMnSi.
  • Copper coupon: 12, as recorded in the source; the material designation remains unverified.
  • Aluminium coupon: LY12.
  • Magnesium coupon: ZM5.
• 4.2.2 Compressed air.
• 4.2.3 Medical infusion rubber tubing.
• 4.2.4 Metallographic abrasive paper: 180 grit.
• 4.2.5 Woodworking abrasive paper: 120 grit.
• 4.2.6 Activated carbon: granular.
• 4.2.7 Indicating silica gel: granular.
• 4.2.8 Industrial ethanol.

5. Apparatus

• 4.1.1 Oxidation apparatus: hard glass, comprising an oxidation tube, stopper and condenser (see Figure 1 of the source).
• 4.1.2 Heating bath: an oil bath with electric heating and stirring, capable of stable control over 50℃±0.5℃–200℃±0.5℃. Its depth must allow the sample level in the oxidation tube to be 20–30 mm below the bath liquid level. Other baths meeting these conditions may be used.
• 4.1.3 Thermometers: 50–150℃ and 150–200℃, with scale divisions of 0.5℃.
• 4.1.4 Air rotameter: 0~120 mL/min. The source extraction reads 0-120mUrnino; its unit remains unverified.
• 4.1.5 Gas-drying tower: 250 mL.
• 4.1.6 Gas buffer bottle: 1000 mL.
• 4.1.7 Vernier caliper.
• 4.1.8 Industrial balance: sensitivity 0.1 g.
• 4.1.9 Analytical balance: sensitivity 0.0001 g.
• 4.1.10 Porcelain evaporating dish: 150 or 200 mL.
• 4.1.11 Conical flask: 250 mL.
• 4.1.12 Low-form weighing bottle: 60 mm × 30 mm.

6. Recommended operating conditions

• Oxidation temperature: determined by the oil's technical specification; the available source does not give a fixed numerical temperature.
• Air flow: 5 L/h ± 0.1 L/h.
• Oxidation duration: run for the specified time; the available source does not give a fixed numerical duration.
• Cooling water: supply cooling water to the reflux condenser.
• Air treatment: the card describes three gas-drying towers of 250 mL, charged with sulfuric acid, activated carbon, anhydrous calcium chloride and indicating silica gel. The allocation of these materials among the towers is not explicit in the card and must be checked against the original arrangement. Fill the air filter with alternating layers of absorbent cotton and glass beads, and connect the apparatus in the sequence shown in Figure 2 of the source.
• Note: replace the anhydrous calcium chloride and silica gel when the gel changes from blue to pink; replace sulfuric acid in the drying tower when it becomes transparent brown-red.

7. Sampling and sample preparation

• 7.1 Place 100 mL of sample in a clean, dry oxidation tube.
• 6.3 Cleaning the oxidation apparatus: soak and clean carefully using a mixture of industrial ethanol and benzene at a volume ratio of 1:4. Rinse with ethanol and tap water, then soak in chromic acid solution for 2~3 h. Rinse successively with tap water and distilled water until neutral. Dry in an oven, cover with clean, dry filter paper and set aside.
• 6.4 Preparation of metal coupons:
  • 6.4.1 Polishing: use 180-grit metallographic abrasive paper for steel and copper coupons, and 120-grit woodworking abrasive paper for aluminium and magnesium coupons. Do not use the same sheet for different metals, and do not touch the coupons directly by hand. Polish until all six faces are fresh, without depressions or marks, and show straight polishing lines. Measure each coupon with a caliper and calculate its surface area.
  • 6.4.2 Washing and weighing: carefully wash polished coupons twice with toluene and twice with acetone. Dry on filter paper or with a blower, place in low-form weighing bottles and transfer to a desiccator. Keep in the balance room for 30~40 min, then weigh to 0.0002 g. Use tweezers throughout; do not touch coupons by hand.

8. Procedure

• 7.1 Place 100 mL of sample in a clean, dry oxidation tube.
• 7.2 Suspend the coupons prepared under 6.4.2 from the stopper's glass hook in the order steel, copper, aluminium and magnesium. Insert them into the sample-filled oxidation tube and seal the stopper joint with 2~3 drops of sample. Place the apparatus in the bath preheated to the specified test temperature, with oxidation conditions determined by the oil's technical specification. Immerse the sample level below the bath level, keep the apparatus vertical and gas-tight, and supply cooling water to the reflux condenser. Pass air through the drying system and flowmeter into the oxidation tube. Stabilize the air flow at 5 L/h ± 0.1 L/h and record the start of oxidation.
• 7.3 At the specified end time, switch off bath heating and close the air and cooling-water valves. Lift the apparatus from the bath and cool at room temperature for 30~40 min. Remove the oxidation tube, carefully take out the coupons and place them in groups on filter paper. Pour the sample into a clean conical flask for subsequent tests.
• 7.4 Wash coupons successively with toluene and acetone, dry them in groups on filter paper, and place them in low-form weighing bottles in a desiccator. After 30 min in the balance room, weigh to 0.0002 g.
• 7.5 Determine the oxidized sample's kinematic viscosity at 50℃ and -50℃ according to GB/T 265, and its acid number according to GB/T 264.

9. Identification, quantification and calculations

8.1 Calculate metal-coupon corrosion X (mg/cm²) using equation (1):

X = (m₁ - m₂) / S × 1000 ………………(1)

Where:

• m₁: coupon mass before oxidation, g;
• m₂: coupon mass after oxidation, g;
• S: total area of the coupon's six faces, cm².

8.2 Calculate the percentage change in kinematic viscosity at 50℃ before and after oxidation using equation (2):

The formula is incomplete in the source extraction and remains unverified. No missing formula has been reconstructed here.

Where:

• v₁: kinematic viscosity before oxidation at 50℃, mm²/s;
• v₂: kinematic viscosity after oxidation at 50℃, mm²/s.

10. Precision

Assess the reliability of results using the following provisions at a 95% confidence level.

• 9.1 Repeatability: the difference between two repeated results obtained by the same operator must not exceed the following limits.
  • 9.1.1 Difference in corrosion for each metal coupon: no more than 0.05 mg/cm².
  • 9.1.2 Kinematic viscosity at 50℃ and -50℃: follow the precision provisions in GB/T 265.
  • 9.1.3 Acid number: follow the precision provisions in GB/T 264.

11. Reporting

Report the arithmetic mean of two repeated determinations.

12. Referenced documents

• GB/T 264: determination of acid number of petroleum products.
• GB/T 265: determination of kinematic viscosity and calculation of dynamic viscosity of petroleum products.
• SH/T 0079: preparation of reagent solutions for petroleum-product testing.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference