Which aspect of the fillet weld is most critical for inspection?

The aspect of complete penetration and fusion in a fillet weld is crucial for inspection because it directly affects the weld's strength and integrity. A fillet weld must ensure that the base metals are adequately joined, which requires the weld metal to fully penetrate and fuse with the base materials. This completeness prevents issues such as incomplete fusion or lack of penetration, which can lead to significant weaknesses in the structure and potential failure under load.

Inspection focuses on this aspect because it is essential for ensuring the reliability and safety of welded joints in pipelines and related facilities. If a weld does not meet the requirements for complete penetration and fusion, it may not be able to withstand environmental factors or operational pressures, leading to potential leaks or catastrophic failures. While the other aspects such as weld thickness, color, and length are also important, they are secondary to the fundamental need for thorough blending of the weld metal with the base materials.