Under what condition is a nonaqueous wet developer generally preferred?

A nonaqueous wet developer is generally preferred under conditions where it is essential to use the most sensitive developers. This is because nonaqueous developers typically have a higher ability to absorb and retain penetrant, which enhances the visibility of any indications present. They are often formulated to provide the finest contrast against the background and maximize the detection of surface discontinuities, particularly in applications where high sensitivity to defects is critical.

Using a nonaqueous wet developer allows the inspection process to be more effective in revealing defects that may otherwise go undetected with less sensitive developers. This aspect is especially important in industries where failure can lead to serious safety issues or costly repairs, thereby necessitating the highest level of detection capability available.

While the other conditions may suggest appropriate scenarios for different developer types, they do not specifically align with the unique sensitivity advantage that nonaqueous wet developers provide in nonaqueous liquid penetrant testing.