The area of the base material adjacent to a weldLocalized coalescence of metals produced by heating the materials to the welding temperature, with or without the application of pressure, or by the application… where its microstructure and mechanical properties have been altered due to the heat generated during the welding process. This critical area in a weld jointA single section (also pipe spool) of pipe that is circumferentially welded to form a pipeline. may have different characteristics compared to the base material and the weld metal.