What limits the effectiveness of liquid penetrant tests?

The effectiveness of liquid penetrant tests is significantly limited by the porosity of the materials being tested. Porous materials have tiny openings or voids that can absorb the penetrant, which prevents it from properly filling cracks or surface defects that are located beneath the surface. As a result, the penetrant may not be adequately drawn into all relevant defects, leading to possible missed indications and an inaccurate assessment of the material's integrity.

While high surface tension of the penetrant can affect its ability to spread on a surface, it typically does not negate the overall capacity of the test, as penetrants are formulated to minimize this issue. Excessive dwell time may potentially lead to excessive absorption in porous materials, but it can also improve defect visibility in non-porous materials. High temperatures could cause the penetrant to evaporate or seep out more quickly, but they do not inherently limit the test's ability when appropriate precautions are taken.