Weldability test (CTOD)

A CTOD weldability test measures the fracture toughness of a weld or its heat-affected zone by the crack tip opening displacement, the amount a fatigue pre-crack opens before unstable fracture, expressed in millimeters. The specimen is a single-edge-notched bend (SENB) or compact piece with the notch placed in the weld metal, fusion line, or HAZ, tested per BS 7448 and ISO 15653 for welds, often at the design minimum temperature. A higher critical CTOD means more crack-tip plasticity before brittle failure. The result feeds an engineering critical assessment to BS 7910, setting tolerable flaw sizes. Offshore and ice-class steel specifications set CTOD acceptance, for example 0.2 mm or more at the service temperature.