What type of defects can be evaluated using control specimens in penetrant testing?

Control specimens in penetrant testing are specifically designed to contain predefined defects, such as cracks, porosity, or laps that are introduced intentionally. These specimens serve as benchmarks to ensure that the testing process is effective and that the penetrant materials, methods, and procedures are properly calibrated. Using predetermined defects allows the testing personnel to assess the sensitivity of the penetrant system and confirm that it can reliably detect these known discontinuities.

Predefined defects provide a controlled environment for evaluating the effectiveness of the testing procedures and the capabilities of the materials used. They help in establishing criteria for acceptance and ensuring that the testing results are consistent and reproducible. In contrast, the other options do not capture the purpose of control specimens. For instance, while visible surface defects could be part of a control specimen, they are not the only type, making the option too limiting. Additionally, internal defects generally can’t be evaluated using control specimens since they are designed to test sensitivity rather than detect defects that are not accessible or visible at the surface. Lastly, not all control specimens focus on only larger defects, as the size can vary based on the specific testing requirements. Hence, the correct choice emphasizes the importance of predefined defects in evaluating the effectiveness of penetrant testing.