Resistance of grease to water contamination

Resistance of Grease to Water Contamination – Evaluating Lubricant Stability and Performance in Wet Environments

As an ISO/IEC 17025 accredited (CNAS) independent laboratory, we provide specialized testing services for the resistance of grease to water contamination to support industries across Angola, including mining, oil and gas, agriculture, construction, and transportation. Water contamination is one of the most common and destructive forms of lubricant degradation. When water enters a grease‑lubricated system, it can cause oil separation (bleeding), thickening or softening, accelerated oxidation, corrosion of metal surfaces, and loss of adhesion. In extreme cases, water‑contaminated grease may wash out of bearings, leading to premature failure and costly downtime. Our laboratory evaluates grease resistance to water using a range of standardized test methods that simulate real‑world conditions: static water immersion, dynamic water spray (water washout), water absorption (water pick‑up), and emulsion stability. The results help equipment operators and maintenance engineers select the right grease for wet or high‑humidity environments, predict service intervals, and diagnose field failures.

Types of Grease Samples We Test

• Lithium‑based greases (lithium 12‑hydroxystearate, lithium complex) – widely used in general industrial and automotive applications
• Calcium sulfonate greases – known for excellent water resistance and extreme pressure properties
• Aluminum complex greases – often specified for wet environments and food processing
• Polyurea greases – used in electric motors and high‑temperature bearings
• Clay (bentonite) greases – non‑melting, water‑resistant greases for high‑temperature applications
• Synthetic greases (PAO, ester, PAG‑based) – for extreme temperature and demanding wet conditions
• Biodegradable greases (vegetable oil‑based, synthetic ester) – for environmentally sensitive areas (near water bodies, agriculture)
• Marine greases – specially formulated for saltwater and splash conditions
• Field samples – used grease taken from equipment operating in wet environments (post‑failure analysis, condition monitoring)
• Competitor product samples for comparative benchmarking

Key Mechanisms of Water Contamination and Their Effects on Grease

Water can enter grease‑lubricated systems through seals, breathers, washdowns, condensation, or pressure washing. Once inside, water interacts with the grease in several damaging ways:

• Oil separation (bleeding) – Water acts as a solvent for certain base oils and thickener systems, causing the oil to separate from the thickener. The grease loses its consistency and may leak out of the bearing or housing.
• Softening or hardening – Depending on the thickener type, water can either soften the grease (reducing its consistency number) or, in some cases, harden it through chemical reactions (e.g., with lithium greases, water can cause a reversible stiffening).
• Water washout – Under dynamic conditions (rotating bearings, moving parts), water spray or splashing can physically remove the grease from the lubrication points. This is especially critical in food processing, paper mills, mining conveyors, and marine applications.
• Corrosion promotion – Water enables galvanic corrosion of steel surfaces and, when combined with acids or other contaminants, accelerates rust formation on bearings, shafts, and housings.
• Additive extraction – Water can leach out water‑soluble additives (e.g., certain antioxidants, corrosion inhibitors), permanently reducing the grease’s protective properties.
• Microbiological growth – In the presence of water, bacteria and fungi can grow at the oil‑water interface, producing acids and slime that further degrade the grease and promote corrosion.

Sample Preparation and Conditioning for Water Resistance Tests

• Grease sampling – Representative samples are taken from original containers (unused grease) or from field equipment (used grease). For field samples, we record equipment operating conditions (temperature, load, water exposure history).
• Homogenization – The grease sample is stirred (without incorporating air) to ensure uniformity. For used grease, we avoid disturbing water layers; we analyze both the bulk grease and any separated water.
• Test water quality – Unless otherwise specified, we use deionized water (conductivity < 5 µS/cm) to avoid interference from dissolved minerals. When simulating specific environments, we may use synthetic seawater, tap water, or process water provided by the client.
• Temperature control – All tests are performed at specified temperatures (typically 25°C, 38°C, 50°C, 79°C, or 80°C) using thermostatically controlled water baths or ovens.
• Number of replicates – At least three specimens per grease sample to account for material variability. Results are reported as averages with standard deviation.

Test Methods for Grease Resistance to Water Contamination

Our laboratory uses the following core test methods to quantify the effects of water on grease. Each method simulates a different mechanism of water exposure encountered in service.

Static Water Immersion Test (Water Stability)

This test evaluates the ability of a grease to resist oil separation and consistency change when in prolonged contact with standing water. A grease sample (typically 50–100 g) is placed in a glass beaker or metal cup and covered with deionized water. The assembly is stored at a controlled temperature (usually 25°C, 50°C, or 80°C) for a specified period (24 hours, 72 hours, 1 week, or 4 weeks). After exposure, we examine:

• Oil bleeding – Visual observation of oil floating on the water surface or separated from the grease body. The amount of separated oil is estimated (e.g., <5%, 5–20%, >20% of grease volume).
• Consistency change – The grease is removed, and its worked penetration (a measure of softness) is measured before and after water exposure using a grease worker and penetrometer. An increase in penetration indicates softening; a decrease indicates hardening.
• Appearance changes – Discoloration, cracking, crumbling, or emulsion formation are noted.
• Weight change – The grease sample is weighed before and after water exposure (after careful surface drying) to determine water absorption. Water absorption is expressed as percentage of initial grease mass.

A grease with good water resistance shows minimal oil separation (<5%), penetration change within ±20 units, and no visible surface deterioration after exposure.

Dynamic Water Washout Test (Water Spray Resistance)

This test simulates the washing action of water spray on grease applied to a rotating bearing. It is critical for applications where bearings are exposed to water jets, high‑pressure washdowns, splashing, or rain.

The test apparatus consists of a specially designed bearing housing with a ball bearing (typically 6204 or 6304 size). The bearing is packed with a known mass (e.g., 25 g) of test grease. The bearing is rotated at a specified speed (often 1000 rpm or 2000 rpm) while a stream of water (or synthetic seawater) is directed at the bearing seals at a controlled flow rate (e.g., 5 mL/s). The test runs for a defined duration (usually 1 hour, 6 hours, or 24 hours). After the test, the remaining grease on the bearing and in the housing is collected, dried, and weighed. The percentage of grease washed out is calculated:

• Washout (%) = (Initial grease mass – final grease mass) / Initial grease mass × 100.
• Pass/fail criteria – Depending on the application, a grease is considered acceptable if washout is less than 10% (for severe washdown), 20% (for moderate splashing), or 50% (for light moisture exposure).
• Observations – The condition of the bearing (rust, corrosion, noise during rotation) is also recorded. The test can be modified to simulate saltwater (using 3.5% NaCl solution), high‑temperature water (50°C, 80°C), or high‑pressure spray (up to 10 bar).

This test is particularly important for industries in Angola: mining equipment (conveyor idlers, crushers), fishing and maritime vessels (deck machinery, winches), agricultural machinery (tractors, harvesters exposed to rain and irrigation), and food processing plants where daily washdowns are routine.

Water Absorption (Water Pick‑up) Test

This test measures the maximum amount of water that a grease can absorb before it loses its lubricating properties. It is performed by gradually adding water to a sample of grease while mixing, and observing the change in consistency.

A known mass of grease (e.g., 100 g) is placed in a mixer. Deionized water is added dropwise (e.g., 1% increments) while the mixture is stirred at a controlled speed and temperature. After each addition, the mixture is allowed to stabilize, and the consistency (penetration) is measured. The test continues until the grease becomes too soft (penetration exceeds 400 units) or until oil separation becomes evident. The water pick‑up capacity is reported as the percentage of water absorbed at the point of failure. Alternatively, a simpler method involves storing a grease sample over water (not submerged) in a sealed humidity chamber at 100% RH for 7 days, then measuring the weight gain and consistency change. This simulates condensation or high‑humidity storage.

Typical values: lithium greases absorb 5–15% water before breaking down; calcium sulfonate greases can absorb 20–40% water while maintaining consistency; polyurea greases may absorb only 1–5%.

Emulsion Stability Test (Oil‑Water Emulsion Formation)

Water can form stable emulsions with the base oil and thickener, creating a milky‑white, low‑viscosity fluid that cannot retain grease‑like properties. This test quantifies the tendency to form emulsions.

A mixture of grease and water (e.g., 50 g grease + 50 g water) is agitated vigorously in a sealed container (often using a paint shaker or high‑speed stirrer) for a set time (5 minutes, 30 minutes, or 2 hours). After mixing, the mixture is allowed to settle. The time taken for the oil, water, and grease phases to separate is recorded. If the mixture remains homogeneous (emulsified) after 24 hours, the grease is considered emulsion‑prone. We also measure the oil separation from the emulsion by centrifuging a sample of the mixture. This test is relevant for gearboxes, centralized lubrication systems, and circulating oil systems where water ingression can lead to emulsification and loss of lubrication.

Corrosion Protection in Presence of Water (Water Washout Corrosion Test)

This test assesses the ability of a grease to protect metal surfaces from rust when exposed to water. Steel panels or bearing races are coated with a thin layer of test grease and then exposed to water (static immersion or water spray) for a defined period (24–168 hours). After exposure, the panels are inspected for rust. The degree of corrosion is rated (0 = no rust, 1 = trace rust, 2 = light rust, 3 = moderate rust, 4 = severe rust). This test is particularly important for bearings that stand idle in wet environments (e.g., shipboard cranes, wind turbines in coastal Angola, outdoor mining equipment).

Factors Affecting Grease Resistance to Water

• Thickener type – Calcium sulfonate and aluminum complex greases generally offer the best water resistance. Lithium greases have moderate water resistance, while sodium and clay greases are more susceptible to water washout.
• Base oil viscosity – Higher viscosity base oils tend to resist water washout better than low‑viscosity oils.
• Additive package – Specialized tackifiers, adhesion promoters, and corrosion inhibitors improve water resistance. Some additives, however, are water‑soluble and may be leached out over time.
• Temperature – Higher temperatures accelerate water diffusion into grease and promote oil separation. Most water resistance tests are performed at elevated temperatures to accelerate aging.
• Water chemistry – Saltwater is more corrosive and may accelerate grease degradation compared to fresh water. Acidic or alkaline process water (pH <6 or >8) can chemically attack the thickener.
• Mechanical agitation – Dynamic conditions (rotation, vibration, high‑pressure spray) dramatically increase water ingression and washout compared to static immersion.

Quality Control and Interpretation of Results

• All tests are performed in triplicate. The coefficient of variation (CV) for washout percentage and water absorption should be <15% for homogeneous greases; higher CV indicates sample non‑uniformity.
• Reference greases with known water resistance are tested periodically to verify apparatus calibration and operator technique.
• Results are compared against client‑supplied acceptance criteria (e.g., “maximum washout <10% after 6 hours at 50°C”). If no criteria are provided, we report measured values with an interpretation of typical performance grades (excellent, good, moderate, poor).
• For field used grease samples, we correlate lab test results with observed field performance (e.g., bearing corrosion, washout) to help diagnose root causes of failure.

Reporting and Deliverables

Each grease water resistance test report includes the following information:

• Sample identification (grease brand, type, NLGI grade, batch number, age, and any known field history for used samples)
• Test methods used (static immersion, dynamic washout, water absorption, emulsion stability, corrosion protection) with key parameters (temperature, duration, water type, rotation speed, flow rate)
• Results for each test: oil separation (%), penetration change (units), washout loss (%), water absorption (%), emulsion behavior, corrosion rating
• Photographs of test samples before and after exposure (especially for static immersion and corrosion tests)
• Comparison with client‑supplied specification (if provided) – pass/fail statement
• General interpretation: classification of the grease’s water resistance as excellent, good, moderate, or poor based on typical industrial benchmarks
• Raw data (weight measurements, penetration values, test logs) archived for 10 years

No statement of compliance with any external standard or regulation is made unless the client has provided specific acceptance criteria in writing. The report is intended for maintenance engineering and procurement decisions.

Practical Recommendations for Angolan Industries

• Mining (diamond, iron ore, gold): Conveyor bearings exposed to wet ore and dust – use calcium sulfonate or aluminum complex greases with high water washout resistance (washout <10% at 1 hour). Regularly test used grease for water content (by Karl Fischer titration) to plan regreasing intervals.
• Oil and gas (onshore and offshore): Wellhead equipment, BOPs, and cranes in coastal environments – choose marine greases with excellent saltwater resistance. Perform dynamic water washout tests using synthetic seawater at 50°C.
• Agriculture: Tractors and harvesters operating in humid, rainy conditions – use lithium complex greases with good water resistance and corrosion inhibitors. Monitor for water ingression through seals and breathers.
• Construction: Excavators, loaders, and concrete pumps – equipment often washed with high‑pressure water jets. Select greases with <5% washout in the dynamic spray test after 6 hours.
• Food processing: Bearings and chains subject to daily hot water washdowns – use NSF H1 registered aluminum complex or polyurea greases that resist water washout and do not emulsify with steam.