Wear resistant hardbanding alloys for the worldwide petroleum industry

Hardbanding Wear Testing

Mohr Engineering - Drill String Friction and Casing / Riser Wear Testing:

While some manufacturers of hardbanding material, as well as some operators, have developed and employ the use of proprietary wear testing machines, the Mohr Engineering Wear Test is currently an industry benchmark for hardband performance. The test is useful when comparing hardbanding performance across competitive products and is required during most industry certification processes.

Mohr Engineering defines the general scope of the wear test machine as follows: "While in either water or oil based drilling fluid, a lateral load is applied to a rotating tool joint at the sliding surface between the tool joint and the casing/riser. The casing is reciprocated to simulate axial movement of the drill string. Lateral load, torque, and wear are monitored during the tests to evaluate the severity of the wear, contact pressure threshold and the friction factor between the tool joint and casing/riser specimen." It is useful to examine illustrations of the machine and to understand the test data point definitions in order to analyze and interpret these results among competitive products.

In order to compare wear test results across competitive products, it is important to look at the test specifications used to ensure accurate comparisons. The four critical specifications to evaluate in order to ensure the validity of a comparison are: type of drilling fluid used, sideload weight applied to the specimen, rpm at which the test samples rotate and the casing material used for the test. If two leading hardbanding products using Mohr Wear Test results are evaluated for performance , you would need to ensure that they were both tested under the same specifications.

Most leading products have been tested using the standard specifications of - water based drilling fluid / mud (WBM), with 3,000 lb side load, 155 RPM and N-80 casing. Though, as of 2010 Mohr Engineering changed the standard casing sample used from N-80 to T-95. This recent change makes it important to determine whether a product was tested on N-80 or T-95, while also looking to the other specifications used. Once test specs are determined then it evaluation of test results allows an observer to better gauge the performance of a hardbanding product. Below are common performance measures and their definitions.

Mohr Wear Test Result Data Point Definitions:

Casing Wear Percent (%) - The amount of casing material worn during the 8-hour wear test in casing, measured as a percentage of the total casing thickness.  This can range from 2-3% for extremely casing friendly materials, and up to 100% for a complete casing failure.

Casing Wear Factor (Hall Wear Factor) - Hall Wear Factor is the ratio of the volume of steel worn from the casing during the 8-hour wear test by the tool joint to the frictional work done on the casing by the tool joint.  The Hall Wear Factor determinations compensate for any differences between the dimensions of actual test pieces used and standard test dimensions.  Standard dimensions are used with wear factors to calculate "Normalized T-95 Casing Wear".  Normalized T-95 Casing Wear is the wear which would occur in a test using a standard tool joint and T-95 Casing dimensions.  Hall Wear Factor units are 10E-10/psi. 

Hall Wear Factors with low values are typically associated with very slow wear rates; which also implies that it will take a long time to reach a maximum wear depth. 

Friction Factor -  The ratio of frictional forces and contact force between the tool joint and the casing while rotating. 

Friction Factor has been included in wear test results for many years, however, to date, it has been difficult to draw any statistically significant correlation between Friction Factor and either casing or tool joint wear parameters. 

Tool Joint Wear in Casing (in.) - The amount of tool joint material that has worn during the 8-hour testing period in casing, measured in inches.  Typical ranges are from 0" to .025". 

Tool Joint Wear in Open Hole (in.) - The amount of tool joint material that has worn during the 8-hour testing period in the open hole simulator, measured in inches.  Typical ranges are from 0" to .05".

Contact Pressure Threshold -  The minimum pressure exerted by the tool joint on the inside casing wall that will produce casing wear.  Contact Pressure Threshold is calculated as lateral load applied by the tool joint to the casing divided by the area of contact.  Since the lateral load is constant during a wear test, the contact pressure decreases as the wear groove deepens and widens during the wear test. 

As the contact pressure decreases, it will eventually reach a value below which casing wear does not occur.  This limiting value of the contact pressure is the Contact Pressure Threshold.  Higher values for CPT are desirable and can be a good indicator of general wear properties of a hardbanding alloy.  The Contact Pressure Threshold may prove to be a more significant predictor of casing wear than Wear Factor. 

ASTM G-65 Dry Sand Rubber Wheel Abrasion Test:

One of the simplest, though useful and reliable wear tests is the ASTM G-65 Dry Sand Rubber Wheel Abrasion Test. This test measures the weight or volume lost from a test sample in a controlled environment - fixed time parameter, constant load, etc. It simulates what is commonly referred to as "Scratching Abrasion", a uniform condition of wear. During the test, the abrading material is considered a constant due to the sand particles maintaining their original shape throughout the test. An alternative test considering "Grinding Abrasion" would require newly created wear agents. Grinding Abrasion, in this case, would occur if the sand, or other material involved in the high friction environment fractured, introducing highly abrasive particles.

Results are typically returned showing the amount of material lost during the test in milligrams (mg) or grams (g). So, for example, Arnco 300XT, one of the most durable products on the market returns a result of 0.190 grams lost during a test using the standardized parameters of 30lbs of side load and 6,000 revolutions. The illustration below depicts the components associated with the test.