Which condition could lead to a failure in tensile strength testing according to AWS specifications?

All of the conditions listed can adversely affect the tensile strength of welded joints, as specified by AWS (American Welding Society) standards.

Excessive heat treatment can alter the mechanical properties of materials, leading to undesirable changes in their structure. This can reduce the tensile strength and ductility, making the welded joint susceptible to failure during testing or in service.

Using untested materials is significant as it introduces uncertainty regarding their compatibility and behavior when subjected to welding processes. If the materials do not meet the specified grades or chemical compositions, the resultant weld may not achieve the required strength or integrity, leading to failures in testing.

Improper welding techniques can also directly compromise the quality of the weld. Techniques that do not follow the prescribed procedures can result in defects such as porosity, inadequate penetration, or incomplete fusion, all of which can severely weaken the weld and affect its tensile testing results.

Since each of these factors plays a critical role in maintaining the quality and strength of welded connections, it's clear that any or all of these conditions could lead to failures in tensile strength testing, which validates the correct selection of the answer.