What condition makes any length of internal concavity acceptable?

The correct choice emphasizes a critical aspect of interpreting radiographic images related to welding defects, such as internal concavities. When assessing these images, the density of the concavity is compared to that of the thinnest adjacent base metal. Acceptable conditions for internal concavity depend on ensuring that its density does not surpass a certain threshold, which, in this scenario, is that it should not exceed the density of the surrounding weld or base material.

This condition ensures that any potential defect represented by the internal concavity is not more pronounced than the inherent characteristics of the surrounding weldment. If the concavity is less dense, it may indicate a dissimilarity in material quality or structure, which can lead to a detrimental effect on the overall integrity and strength of the weld. Therefore, an internal concavity that satisfies this density criterion is considered acceptable within the context of API 1104, as it implies a minimal impact on structural performance.

The other options do not establish the same clarity regarding acceptable conditions. For example, indicating that the density must exceed that of the base metal contradicts the principle of acceptable defect assessment, as it would suggest a defect rather than an acceptable feature. Furthermore, while ultrasonic inspection providing no indications can signify acceptable quality, it