How to Evaluate Compatibility When Switching TBM Greases

For a TBM Chemicals Supplier, changing from one tunnel boring machine grease to another is not simply a matter of comparing price or dropping a new product into the lubrication system. The new grease must be compatible with the existing base oil, thickener, additives, seals, automatic lubrication equipment, ground conditions, and environmental requirements. Huadingcheng provides this practical evaluation framework to help purchasing, engineering, maintenance, and site teams reduce risk before switching TBM greases.

1. Start With the Real Compatibility Questions

Why grease compatibility matters in TBM applications

TBM grease is used in demanding areas such as the main bearing, tail seal, wire brush seal, articulation seal, screw conveyor, shield skin, and other high-load or water-exposed components. A grease change can affect lubrication performance immediately or several weeks later.

Incompatible greases may cause:

• Thickener separation or hardening.
• Oil bleeding and loss of lubricant from the contact zone.
• Blocked progressive distributors, pumps, hoses, or grease lines.
• Reduced water resistance in wet or high-pressure ground conditions.
• Seal swelling, shrinking, cracking, or softening.
• Higher bearing temperature and torque.
• Abnormal consumption of sealing grease.
• Unexpected wear, leakage, or premature component failure.
• Difficulty proving whether a problem came from the grease or the machine.

What purchasing teams need to confirm before approving a new grease

Purchasing teams usually need more than a technical data sheet. They need a clear answer to whether the new product can be introduced without increasing operational, supply, or warranty risk.

• Can the new grease be mixed with the grease already in the system?
• Does the new grease use a compatible base oil and thickener?
• Will it work with the existing pumps, metering units, hoses, and injectors?
• Can it protect the TBM under water, soil, rock dust, pressure, and vibration?
• Will it remain stable during storage and transport?
• Is the product available in the required packaging and delivery schedule?
• Does it satisfy project environmental, safety, and disposal requirements?
• Is there reliable technical support if the performance changes underground?
• Can the supplier provide batch consistency, test reports, and traceability?
• Is the total cost lower after considering flushing, waste, downtime, consumption, and maintenance?

2. Collect Complete Data on the Existing and Replacement Greases

First step: identify the exact product currently in use

Do not evaluate compatibility using only a commercial product name. The same brand may offer different grades for different TBM components, and formulations may change over time. Record the exact product name, grade, manufacturer, batch number, and application.

Collect the following information for the existing grease:

• Product name and product code.
• NLGI consistency grade.
• Base oil type, such as mineral oil, synthetic hydrocarbon, ester, or another fluid.
• Thickener type, such as lithium, lithium complex, calcium sulfonate complex, aluminum complex, polyurea, or clay.
• Base oil viscosity at the relevant test temperatures.
• Operating temperature range.
• Water resistance and water washout results.
• Extreme pressure and anti-wear performance.
• Four-ball weld load or other load-carrying test results.
• Oil separation and mechanical stability data.
• Corrosion protection data.
• Compatibility statements for elastomers, plastics, coatings, and metals.
• Safety data sheet and technical data sheet.

Second step: define the intended use of the replacement grease

A TBM may use different greases in different locations. A main bearing grease should not automatically be treated as equivalent to a tail seal grease or a general assembly grease. Define the exact component and service condition before comparing products.

Record the following operating conditions:

• Component name and lubrication point.
• Grease feed method and pump type.
• Line length, hose diameter, and distribution system.
• Estimated pressure at the injection point.
• Operating temperature and possible temperature peaks.
• Water pressure, groundwater level, and water chemistry.
• Soil type, rock dust, abrasive particles, and chemical contaminants.
• Component speed, load, vibration, and movement.
• Required grease consumption rate.
• Expected relubrication interval.
• Seal material and age.
• Required environmental classification and disposal method.

Third step: request formulation and performance information from both suppliers

Ask both suppliers for written confirmation rather than relying on verbal statements such as compatible, equivalent, or universal. The replacement supplier should identify the product limitations and the recommended conversion procedure.

Request:

• Current technical data sheet.
• Current safety data sheet.
• Certificate of analysis or batch test report.
• Base oil and thickener information.
• Recommended application and operating range.
• Compatibility test results, if available.
• Seal and elastomer compatibility data.
• Storage life and storage temperature requirements.
• Packaging options and minimum order quantity.
• Production lead time and supply continuity plan.
• Technical service contact for the project region.

3. Compare the Formulations Before Performing Physical Tests

Base oil compatibility screening

Base oil compatibility is an important first filter. Mineral oils and synthetic hydrocarbons are often easier to evaluate together than products based on chemically different fluids. Some synthetic esters, polyglycols, silicone fluids, and specialty fluids may require additional testing because they can affect seals, additives, or the stability of the existing grease.

Compare:

• Base oil family.
• Viscosity at operating temperature.
• Volatility and evaporation tendency.
• Resistance to water and oxidation.
• Effect on seal materials.
• Effect on existing additive packages.

Similar base oil type does not prove full compatibility. It only indicates that the products may be suitable for further testing.

Thickener compatibility screening

The thickener controls the structure, consistency, mechanical stability, water resistance, and release of base oil. Two greases with the same NLGI grade may still behave very differently when mixed.

Pay particular attention to these combinations:

• Lithium with lithium complex: potentially workable, but testing is still required.
• Lithium with calcium sulfonate complex: may show changes in consistency or oil release.
• Aluminum complex with other soap thickeners: requires specific compatibility testing.
• Polyurea with soap-based greases: compatibility can vary significantly by formulation.
• Clay or other non-soap thickeners with soap greases: do not assume compatibility.

Thickener type alone is not enough to approve a mixture. Commercial formulations contain additives, polymers, solid lubricants, and other components that can change the result.

NLGI grade and pumpability comparison

The new grease should have a consistency suitable for the existing lubrication system. A grease that is too stiff may increase pump pressure and restrict flow. A grease that is too soft may leak from seals, settle in lines, or fail to remain in the lubrication zone.

Compare:

• NLGI grade.
• Worked penetration.
• Low-temperature pumpability.
• Flow pressure through the actual hose and distributor.
• Oil separation under pressure.
• Behavior after mechanical working.

4. Use a Structured Laboratory Compatibility Test

Required tools and materials

A controlled test requires clean equipment and a representative sample. The following tools are commonly required:

• Clean sample containers with secure lids.
• Labels and permanent marker.
• Digital balance with suitable accuracy.
• Spatulas or mixing tools dedicated to each sample.
• Gloves, safety glasses, and protective clothing.
• Temperature-controlled oven or environmental chamber.
• Penetrometer for worked and unworked penetration.
• Grease worker or mechanical working device.
• Water bath or water contamination test equipment.
• Microscope for observing separation, lumps, and structural changes.
• Viscosity or flow test equipment where applicable.
• Pressure gauge and test hose for pumpability checks.
• Compatible seal coupons or samples from the actual seal material.
• Laboratory data sheets and photographic records.

For critical projects, use an accredited independent laboratory or a laboratory approved by the equipment owner.

Fourth step: prepare representative samples

1. Collect a fresh sample of the existing grease from a clean and active lubrication point.
2. Collect a fresh sample of the replacement grease from the intended production batch.
3. Keep the samples sealed and record product name, batch number, date, and sampling location.
4. Remove visible dirt, metal fragments, and water only if the laboratory procedure requires it. Do not alter the sample without recording the action.
5. Prepare three mixtures at different ratios, such as 90 to 10, 50 to 50, and 10 to 90.
6. Prepare unmixed samples of both products as control samples.
7. Mix each sample thoroughly using a clean tool and avoid cross-contamination.

Fifth step: test consistency and structural stability

Measure the penetration of the unmixed greases and the mixtures before and after mechanical working. A substantial change in consistency may indicate incompatibility, even if the mixture looks normal at room temperature.

Look for:

• Large softening or hardening compared with the control samples.
• Visible lumps or fibrous structure changes.
• Rapid oil release.
• Loss of adhesion.
• Formation of a dry or rubber-like surface.
• Separation into clear oil and thickened material.

Sixth step: perform heat aging and water exposure tests

TBM grease may experience heat from bearings, friction, compression, and surrounding equipment. Water may enter from groundwater, slurry, cleaning, or wet spoil. Test the mixtures under conditions that represent the actual project.

1. Place control and mixed samples in clearly labeled containers.
2. Expose the samples to the selected operating temperature for the planned test period.
3. Inspect the samples for oil separation, hardening, skin formation, and color change.
4. Expose separate samples to the expected water type or a justified laboratory water solution.
5. Observe emulsion formation, washout, corrosion, and loss of adhesion.
6. Compare the results with the performance of the existing grease.

Seventh step: check corrosion, load, and wear performance

Compatibility is not only a physical mixing issue. The mixture must still protect metal surfaces. Use appropriate standardized tests for corrosion, extreme pressure, wear, and water resistance.

Depending on the application, evaluate:

• Four-ball wear and weld load.
• Timken or equivalent load-carrying performance.
• Rust and corrosion protection.
• Water washout and spray-off resistance.
• Oil separation under static and elevated-temperature conditions.
• Mechanical stability after repeated working.

Test results should be compared against the existing grease, the replacement grease, and the project acceptance criteria. A pass or fail decision should not be based on one test only.

Eighth step: test seal and elastomer compatibility

Grease can affect nitrile rubber, fluorocarbon rubber, polyurethane, EPDM, silicone, and other seal materials differently. Use actual seal samples from the TBM whenever possible.

1. Identify the seal material from the equipment documentation or supplier.
2. Record the original dimensions and mass of each test coupon.
3. Immerse or contact the coupons with the existing grease, replacement grease, and mixtures.
4. Age the coupons at the expected temperature for the defined period.
5. Measure changes in mass, volume, hardness, and dimensions.
6. Inspect for swelling, shrinkage, cracking, softening, or loss of elasticity.
7. Obtain approval from the seal manufacturer if the results are uncertain.

5. Verify Pumpability and Equipment Compatibility on the TBM

Why laboratory compatibility does not guarantee system performance

A mixture may be stable in a container but fail in a long automatic lubrication line. TBM systems can include long hoses, narrow passages, progressive distributors, check valves, filters, and multiple injection points. Pressure loss can increase if the replacement grease is stiffer or releases solids.

Ninth step: inspect and measure the existing lubrication system

Before introducing the new grease, document the system condition.

• Inspect the reservoir, pump, follower plate, and suction area.
• Check for hardened grease at the bottom or around the pump inlet.
• Inspect hoses for blockage, cracking, and leakage.
• Check distributors and metering units for restricted movement.
• Record normal pump pressure and operating cycle.
• Record grease consumption at each important lubrication point.
• Confirm that the new grease packaging fits the existing filling equipment.

Tenth step: perform a controlled flow and pressure test

1. Use a clean test hose and the actual pump or an equivalent test pump.
2. Fill the system carefully and remove avoidable air pockets.
3. Measure the pressure required to move the new grease through the hose.
4. Compare the pressure with the existing grease under similar temperature conditions.
5. Operate the distributor or metering unit through several cycles.
6. Check whether grease reaches every outlet at a consistent rate.
7. Inspect fittings for leaks, separation, or pressure pulses.
8. Repeat the test at the lowest expected site temperature if possible.

Do not increase pump pressure simply to force a questionable grease through the system. Excessive pressure may damage hoses, fittings, seals, or distributors.

6. Create a Safe Conversion and Flushing Plan

When a full cleaning is recommended

Full cleaning or extensive flushing is recommended when the products have different thickener systems, different base oil families, unknown formulation details, visible contamination, or a history of unstable mixtures. It is also advisable for critical main bearing systems where a blockage could cause severe downtime.

When controlled displacement may be acceptable

Controlled displacement may be considered when laboratory testing shows acceptable compatibility, the grease feed system is simple, the residual volume is known, and the equipment owner approves the conversion. The old grease should still be displaced from accessible lines and outlets as far as practical.

Eleventh step: calculate the residual grease volume

1. Measure the internal diameter and length of each main hose.
2. Calculate the approximate internal volume of the hoses and distribution components.
3. Add the estimated volume in the pump, reservoir, fittings, and lubrication chamber.
4. Determine how much new grease is needed to displace the old grease.
5. Define the disposal volume and cleaning materials required.

Twelfth step: execute the conversion under written control

1. Obtain approval from engineering, maintenance, procurement, and the equipment owner.
2. Schedule the conversion during a controlled maintenance window.
3. Isolate the lubrication system according to the equipment safety procedure.
4. Remove old grease from the reservoir and accessible areas.
5. Clean the reservoir, pump inlet, follower plate, and filling tools.
6. Flush or replace hoses and distributors where required.
7. Fill the system with the approved replacement grease.
8. Run the pump at a controlled rate and verify grease at every outlet.
9. Collect the first discharged grease for inspection and retention.
10. Label the system with the new product name, batch number, and conversion date.
11. Record pressure, consumption, temperature, and operating conditions.

How to manage mixed grease during the transition

Do not treat the first weeks after conversion as normal operation. The system may contain a changing ratio of old and new grease. Monitor discharge appearance, consistency, oil separation, line pressure, and consumption until the old material has been displaced.

7. Run a Controlled TBM Field Trial

Thirteenth step: select a limited trial area

Start with a manageable lubrication circuit or a defined group of points rather than changing every TBM grease at the same time. Avoid introducing multiple variables during the trial, such as changing the grease, pump setting, seal type, and lubrication interval simultaneously.

Choose a trial area that allows:

• Reliable access for inspection.
• Separate tracking of grease consumption.
• Comparison with an unchanged control area.
• Measurement of pump pressure and lubrication frequency.
• Inspection of seals, outlets, and discharged material.

Fourteenth step: define measurable acceptance criteria

Acceptance criteria should be agreed before the trial starts. This prevents the team from changing the evaluation standard after seeing the results.

Possible criteria include:

• No blocked hoses, distributors, or injection points.
• No abnormal increase in pump pressure.
• No unacceptable leakage from seals.
• No abnormal bearing temperature or torque.
• No significant increase in grease consumption without a clear operating reason.
• No visible hardening, separation, or water washout.
• No accelerated seal wear or metal wear.
• Stable performance during the defined advance length or operating period.
• Acceptable environmental and waste-handling performance.

Fifteenth step: monitor the trial consistently

1. Record the starting condition of the equipment.
2. Record the grease batch and quantity loaded.
3. Measure pump pressure at consistent operating intervals.
4. Track grease consumption by shift, day, or advance length.
5. Inspect grease at outlets for water, soil, metal particles, or structural change.
6. Check seal leakage and visible wear.
7. Record bearing temperature, motor load, vibration, and abnormal noise where available.
8. Photograph important findings using the same inspection locations.
9. Compare the trial data with historical data and the control area.
10. Stop the trial if there is a risk of equipment damage or loss of sealing performance.

8. Evaluate the Total Purchasing and Operating Cost

Why unit price is not the complete cost

A lower purchase price may be offset by higher consumption, difficult pumping, increased flushing labor, additional waste, longer delivery times, or unplanned downtime. Purchasing decisions should use total cost of ownership rather than price per kilogram alone.

Cost items to include in the comparison

• Purchase price per kilogram or drum.
• Required order quantity and minimum order quantity.
• Freight, import charges, and local handling.
• Storage and temperature-control requirements.
• Flushing and cleaning materials.
• Labor required for conversion.
• Disposal cost for old and mixed grease.
• Expected grease consumption.
• Cost of replacement hoses, distributors, or seals.
• Technical testing and independent laboratory fees.
• Risk of production delays and unplanned maintenance.
• Supplier response time and technical support cost.

Supply security questions for the supplier

Purchasing teams should evaluate whether the supplier can support the complete project, not only the first delivery.

• Where is the product manufactured?
• What is the normal and emergency lead time?
• Can the supplier reserve production capacity for the project?
• Are replacement batches consistent with the approved sample?
• Can the supplier provide batch certificates for each delivery?
• Is local stock available near the project site?
• Can the supplier provide application training and troubleshooting support?
• What is the procedure for handling a quality complaint?

9. Avoid These Common Mistakes

Mistake 1: assuming the same NLGI grade means compatibility

NLGI grade describes consistency, not complete formulation compatibility. Two NLGI 2 greases may have different base oils, thickeners, additives, water resistance, and seal effects.

Mistake 2: mixing products without a laboratory test

Visual mixing in a small container is not a sufficient approval method. A mixture may look acceptable but fail after working, heating, water exposure, or extended storage.

Mistake 3: relying only on the supplier's word

Supplier guidance is useful, but critical TBM applications require documented data and approval based on the actual equipment, operating conditions, and residual grease in the system.

Mistake 4: changing all TBM greases at the same time

Changing main bearing, tail seal, articulation, and assembly greases simultaneously makes troubleshooting difficult. Use a controlled sequence and document each change.

Mistake 5: ignoring residual grease in hoses and distributors

Even after emptying a reservoir, substantial old grease may remain in long hoses, progressive distributors, fittings, and lubrication chambers. This residual volume can determine the behavior of the mixture.

Mistake 6: failing to account for temperature

A grease that pumps well in a warm warehouse may become difficult to pump during a cold shift. Test and monitor the lowest expected site temperature as well as normal operating temperature.

Mistake 7: increasing pump pressure without investigating the cause

High pressure may indicate incompatible grease, a blocked line, hardened material, excessive hose length, low temperature, or a failing pump. Increasing pressure can create a secondary equipment failure.

Mistake 8: evaluating only short-term appearance

Good appearance during the first few hours does not prove long-term compatibility. Continue monitoring consumption, pressure, water resistance, seal condition, temperature, and wear during the full trial period.

10. Use a Practical Approval Checklist

Technical approval checklist

• Existing grease identity and formulation data confirmed.
• Replacement grease identity and batch data confirmed.
• Base oil comparison completed.
• Thickener comparison completed.
• NLGI grade and pumpability reviewed.
• Mixed-ratio compatibility tests completed.
• Heat and water exposure tests completed.
• Corrosion, wear, and load performance reviewed.
• Seal material compatibility reviewed.
• Automatic lubrication system flow test completed.
• Flushing or displacement method approved.
• Field trial acceptance criteria defined.
• Trial results documented and approved.

Purchasing approval checklist

• Price and total conversion cost calculated.
• Required packaging confirmed.
• Delivery schedule confirmed.
• Safety and environmental documents received.
• Batch traceability confirmed.
• Supply continuity plan accepted.
• Technical support contact assigned.
• Complaint and replacement procedure documented.

Final decision categories

Use one of the following decision categories:

• Approved for direct replacement: suitable only when compatibility and equipment tests are satisfactory and residual mixing risk is low.
• Approved with controlled flushing: suitable when the products can be used after the old grease is substantially displaced.
• Approved for limited field trial: suitable when laboratory results are promising but operating data is still required.
• Not approved: suitable when the mixture is unstable, pumpability is poor, seal risk is high, or performance data is insufficient.

11. Recommended Content for a TBM Grease Compatibility Report

Executive summary

State the reason for the grease change, the current product, the proposed product, the application, the main risks, and the final recommendation in a short section.

Product comparison table

Evidence and records

Attach technical data sheets, safety data sheets, laboratory results, photographs, pump pressure records, consumption records, field trial reports, supplier declarations, and approval signatures. A complete record helps prevent repeated testing on future projects.

12. Make the Final Switch Only After Evidence-Based Approval

A reliable decision sequence

1. Define the TBM component and operating conditions.
2. Collect verified data on the existing and replacement greases.
3. Screen base oil, thickener, consistency, additive, and seal compatibility.
4. Perform controlled mixture and aging tests.
5. Test pumpability through representative equipment components.
6. Choose full cleaning, flushing, or controlled displacement.
7. Run a limited field trial with measurable acceptance criteria.
8. Compare technical performance and total cost.
9. Document the decision and update the lubrication procedure.
10. Continue monitoring after full implementation.

The safest grease change is one that treats compatibility as a process rather than a single product claim. Product data, laboratory testing, equipment trials, conversion control, and field monitoring should all support the final decision. A qualified TBM Chemicals Supplier such as Huadingcheng can help purchasing and engineering teams compare formulations, prepare samples, arrange testing, and develop a practical conversion plan that protects TBM reliability and project continuity.