Hardness Testing shall be conducted by using either a portable Hardness Tester using rebound technique (e.g. Krautkramer DynaMic) or a Telebrineller. The equipment shall be calibrated and verified by checking the hardness of certified metal blocks prior to commencement of hardness testing on the project. Comparative hardness test blocks shall be utilized for comparative purpose to determine Brinell Hardness Number. These test blocks shall be calibrated in accordance with Test Method E10 Section C. The hardness number of the blocks utilized for comparative testing shall be within ± 30 Brinell Hardness Number (BHN) of the maximum limit for the base material being tested. Hardness testing shall be performed on all the full penetration welds whether they have been subjected to local Post Weld Heat Treatment or not, if required by client’s specification.
Hardness Inspection Procedure:
Surface Preparation: The surface on which the impression is to be made shall be ground or polished with abrasive materials so that the edge of the impression shall be defined clearly enough to permit the measurement of the diameter to the required accuracy of 0.1mm divisions by measuring microscope.
Indentation Procedure & Measurement.
Assemble the comparative bar of a Telebrineller making sure a minimum distance of no less than 5 mm will exist between diameter of the impression to be made and any other indentations on the surface.
Krautkramer DynaMic: Place the Hardness Tester on the surface of the weld being tested and apply the impact load by pushing the release button. The ball in the test handle will hit the face of the weld and a hardness number will register on the LCD screen.
Read off the hardness number from the screen in the desired Unit.
Telebrineller: For a Telebrineller place the indenting ball on the surface and hammer the vertical bar by a 5 Lb hammer.Measure the diameters of the indents on the surface of the pipe (vessel) and the comparative bar. Then with the use of the Telebrineller calculator determine the BHN value.