How large of a crack or open defect will most codes consider a failure in a guided bend test?

In a guided bend test, the criteria for acceptable defects can vary depending on the specific code or standards being followed. However, many welding codes, including those referenced by the Canadian Welding Bureau (CWB), typically identify a defect greater than 3mm as a significant issue.

A crack or open defect of 3mm is often deemed unacceptable because it can severely compromise the integrity of the weld, potentially leading to failure under service conditions. Defects of this size are indicative of underlying issues in the welding process, such as inadequate fusion, improper technique, or material inconsistencies. The acceptance criterion is designed to ensure that welds can withstand the mechanical stresses and environmental challenges they will face in practical applications.

While smaller defects may sometimes be tolerated, a 3mm crack becomes a critical point of consideration in assessing the quality of the weld. Codes are set to maintain safety and reliability standards, and a defect of this size is viewed as compromising those standards. This is why the 3mm threshold is commonly highlighted in industry guidelines.