HARDNESS TESTING

The object of this nondestructive testing method is to identify hardness of materials. The most common micro and macro hardness testing methods include:

• Brinell - forcing a ball between a known standard and the specimen being tested and calculating the hardness of the material by the relative amount of metal displaced.



• Microdur - electronic analysis of resonance frequency changes relative to the size of a micro indentation area.
• Equotip - electronic analysis of impact and rebound velocities.



• Rockwell - hardness is determined by the depth of the indentation in the test material resulting from application of a given force on a specific indenter.



• Vickers - hardness is determined by measuring the indentation in the test material from an application of a given force. Loads from 1g (micro hardness) to 50 Kg (macro hardness) can be used.

Hardness testing can be performed on all ferrous and non-ferrous metals and alloys, and select non-metallic materials.

Hardness tests are commonly performed on welds and weld overlays, weld heat affected zones (HAZ's), castings and forgings, their components, piping, stress relieved material, machined parts, pressure vessels, and structural steel. Hardness tests are also performed on damaged material or when performing failure analysis. Hardness tests are performed on components requiring certification to NACE MR0175/ISO 15156. /p>

Some limitations when performing hardness tests are:

• Brinell hardness tests cannot be performed on thin material, in weld heat affected zones, and on surfaces where indentations are unacceptable such as finished machined surfaces.



• Microdur measurements require a surface polished to almost a mirror-like finish.



• The Equotip should only be used on parts with a thickness of 1/2" or greater.



• When electric hardness testing equipment is in use, the temperature of the test material cannot exceed approximately 200°F.

Test results are summarized in an inspection report.