I’ve had the opportunity to use my Telebrineller a couple times recently. It’s a field hardness tester that most people don’t seem to be aware of. Just opening that case with the sweet purple felt is a joy! Whoever decided on that made a fine choice.

The instrument is made by a company named Teleweld. I believe they work primarily on railroad rails and developed the Telebrineller to allow their welders to perform quick and easy hardness tests. It works great when you just need to take a few tests on relatively large things. The photo above shows the entire kit with the exception of the engineer’s hammer that’s needed. It weighs all of about 10 pounds total and requires no electric power; it’s purely mechanical.

The theory behind it is real simple.

This is the working end. After preparing the test surface (remove coatings/corrosion, may need to grind smooth), place the hardened steel ball (visible within the black rubber piece) onto the surface. The bar on the far left is moveable/removable and is a bar of steel with known hardness. The bar should be similar hardness to the test piece.

In this case it is 192 BHN (or whatever Brinell hardness is abbreviated as now). Each bar can be used for 80 individual tests. Bars are available for a wide hardness range and come with the requisite material certificates.

Give the instrument a good strong blow with the hammer on the silver disc on the instrument. Not on the hardwoods of course:)

The hammer blow forces the ball onto both the surface being tested and the bar of known hardness, leaving a round impression in both. Physics tells us that the force against both is equal.

The black cylindrical piece in the photo of the kit in that sweet purple case is a microscope. Looking through it, a scale is visible that is used to measure the diameter of the impression in the part being tested.

And the diameter of the impression in the bar of known hardness.

The kit originally came with a device that allowed you to compare the two diameters and determine the hardness of the test piece relative to the hardness of the bar. That device has been lost to time in my kit. I use a formula saved into a spreadsheet where the inputs are the two diameters and the bar hardness. The output is the test piece hardness. The formula comes from an ASTM standard.

Carbon steel hardness can be used to approximate tensile strength. Again, there is an ASTM standard involved.

I typically use the Telebrineller to determine steel grades for pressurized equipment built of unknown materials. This is a critical variable for calculations involving pressurized equipment. Hardness testing is often used along with field positive material identification (PMI) to get a real good idea of what unknown carbon steels are. It’s very important to remember that an appropriate level of conservatism needs to be employed when making decisions based on field tests like these. That appropriate level is largely based on risks of failure and the consequence of such.