Introduction

When sourcing lined pipe fittings for abrasive slurry or wear-prone service, you will often see material datasheets citing ASTM G65 or ASTM G99 test results. These standards are valuable for ranking materials, but they are frequently misunderstood. This guide explains what each test measures, how to interpret the numbers, and what to verify before you rely on them for procurement decisions.

ASTM G65: Dry Sand/Rubber Wheel Abrasion Test

ASTM G65 measures resistance to scratching abrasion using a dry sand/rubber wheel apparatus. The test involves a rubber wheel pressing a specimen against a stream of dry sand. The result is reported as volume loss in cubic millimetres; lower volume loss means higher abrasion resistance.

The standard includes five procedures (A through E) that vary test severity and duration. Procedure A is a relatively severe test that ranks materials from low to extreme abrasion resistance. Procedure B is a short-term variation for medium- and low-abrasion-resistant materials. Procedure C is for thin coatings. Procedures D and E use lighter loads for specific applications.

According to the standard, the test is designed to produce data that reproducibly ranks materials in their resistance to scratching abrasion under a specified set of conditions. It does not attempt to duplicate all process conditions such as abrasive size, shape, pressure, impact, or corrosive elements. Therefore, it should not be used to predict exact resistance in a specific environment. Its value lies in predicting the relative ranking of materials in a similar order of merit as would occur in an abrasive environment.

ASTM G99: Pin-on-Disk Wear Test

ASTM G99 covers wear testing with a pin-on-disk or ball-on-disk apparatus. A pin or ball is pressed against a rotating disk under controlled load and speed. The test measures wear volume and friction coefficient. It is intended for nominally non-abrasive conditions and is used to rank material combinations under sliding contact.

The standard emphasizes that the amount of wear depends on many factors: applied load, machine characteristics, sliding speed, sliding distance, environment, and material properties. The test does not attempt to duplicate all service conditions such as lubrication, load, pressure, contact geometry, removal of wear debris, or corrosive environment. Therefore, it cannot predict wear rate under conditions differing from those in the test.

ASTM G99 includes a specific set of test parameters used in an interlaboratory study (ILS). If you follow the standard exactly, you can compare results to the ILS data. However, users often choose different parameters (load, speed, materials, etc.) to better simulate their application. In such cases, results cannot be compared to the ILS data, and the report must clearly state the chosen parameters.

Comparing G65 and G99: Why They Are Not Interchangeable

G65 and G99 create different contact and wear conditions. G65 involves three-body abrasion with sand particles between a rubber wheel and the specimen. G99 involves two-body sliding wear between a pin and a disk. The wear mechanisms are fundamentally different: scratching abrasion versus adhesive/abrasive sliding wear. Therefore, results from these tests should not be compared as though they measure one universal wear property. A material may rank differently under each test depending on its hardness, toughness, and microstructure.

For lined pipe fittings, the liner material (e.g., ceramic, rubber, or polymer) will respond differently to these tests. For example, a hard ceramic may perform well in G65 (scratching abrasion) but poorly in G99 (sliding wear) if it is brittle. Conversely, a rubber liner may show high volume loss in G65 but excellent performance in slurry service due to its elasticity. Always specify which test method and procedure you require, and understand what it actually measures.

Practical Implications for Lined Pipe Fittings

Neither G65 nor G99 can directly predict slurry-service life. Real-world slurry involves particle shape, impact angle, velocity, corrosion, temperature, liner bonding, and fitting geometry. These factors are not replicated in bench tests. For example, a fitting with a sharp bend will experience higher impact angles and localized wear, which a flat test coupon cannot simulate. Liner bonding quality and thickness also play a critical role; a test on a bare material sample does not reflect the performance of a bonded liner in a fitting.

Therefore, use G65 and G99 results as relative ranking tools, not as absolute life predictors. When comparing materials, ensure the test conditions are identical. If a supplier provides data from different procedures or parameters, you cannot directly compare the numbers.

Procurement Checks and RFQ Inputs

When requesting abrasion or wear test data from suppliers, include the following in your RFQ:

Specify the exact standard and procedure (e.g., ASTM G65 Procedure A).
Ask for the test parameters: load, speed, duration, abrasive type and size, and specimen preparation.
Request the volume loss in mm³ for G65, and wear rate or wear volume for G99.
Ask whether the test was performed by an accredited laboratory and if the report includes the standard's precision and bias statements.
If you need to compare materials, request that all tests be done under identical conditions.
For lined fittings, ask if the test was performed on the liner material alone or on a representative lined sample. Ideally, test the actual liner system.
Inquire about the liner bonding method and quality control procedures, as these affect field performance.

Inspection and Documentation Points

When reviewing test reports, verify the following:

The report clearly identifies the standard and procedure used.
The test parameters are stated, especially if they differ from the standard's default values.
The report includes the specimen material, heat treatment, and surface finish.
For G99, the report states whether the results can be compared to ILS data or if custom parameters were used.
The report includes the date of testing and the laboratory's accreditation.

If the report lacks these details, request clarification. Do not accept vague statements like "tested per ASTM G65" without specifying the procedure.

Common Risks and How to Avoid Them

Risk: Comparing G65 and G99 results as if they measure the same property. Avoid: Always specify which test you require and interpret results accordingly.
Risk: Using bench test results to predict service life. Avoid: Use tests for ranking, and validate with field experience or pilot testing.
Risk: Accepting data from different procedures as comparable. Avoid: Ensure all suppliers use the same procedure and parameters.
Risk: Ignoring the effect of liner bonding and geometry. Avoid: Request additional testing on actual fittings or representative samples.

Conclusion

ASTM G65 and G99 are essential tools for ranking materials under specific wear conditions, but they have limitations. For lined pipe fittings, they provide a starting point for material selection, not a guarantee of performance. Always specify the exact test method, verify the parameters, and combine bench test data with practical experience. For more guidance on selecting and sourcing pipe fittings, visit our products page or contact us for expert advice.