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On site hardness testing also referred to as Portable Hardness Testing is carried out by means of a portable hardness-testing unit. (Leeb Model TIME HLN-11A) This unit is capable of converting values such as Brinell, Vickers, Rockwell and Shaw. On site hardness testing is required to compare the 3 zones associated with such items as production welds. These zones are referred to as in the Parent Metal (PM), Weld Metal (WM) and Heat Affected Zone (HAZ).  Hardness testing is usually performed after Post Weld Heat Treatment (PWHT) has been carried out to ensure the hardness values are acceptable within each zone of the weld joint. Usually 3 spots are testing within each zone and an average reading qualified.  The advantage of on site hardness testing is you are able to ensure that welder has adhered to all the parameters associated the Welding and that Post Weld Heat Treatment has been performed as per the specifications.