When something breaks, you acknowledge the shock, scratch your head, take stock of the situation, and look for the fastest way to repair the item and put it back into operation. The pressure to repair quickly is understandable, but common sense suggests stopping for a moment and trying to understand what caused the break before attempting the repair. Almost anything can fracture.
The science investigating the origins of fractures is called failure analysis, and it is used to establish responsibilities for fractures and to determine preventive measures for avoiding future occurrences.
The presence of macroscopic deformations and the fibrous or glassy aspect of the surfaces should be assessed to reveal if the failure was ductile (with deformation) or brittle (without deformation).
Specific colors on the surfaces should be remarked; they might be clues about local heating and oxidation. The extent of corrosion, if present, has to be determined and documented.
The presence of arc strikes on the surface, improper starting conditions, or accidental contact may be at the origin of considerable damage.
Hardness testing is a very informative, simple, nondestructive test. However, selecting the proper locations, especially if the weldment must be sectioned for testing, may be beyond what can be expected from a technician not specifically trained for this kind of investigation.
The materials involved should be known and their properties checked for conformance to specifications. No weld repair should be attempted without this essential knowledge. Having this information allows you to select the proper repair procedures and filler metal.