Flashcard · Review PT Principles
What force draws penetrant into a surface crack?
Capillary action, driven by surface tension along the walls of the opening, for a liquid that wets the metal.
Topic: Capillary action, driving force
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- What force draws penetrant into a surface crack?
- Capillary action, driven by surface tension along the walls of the opening, for a liquid that wets the metal.Topic: Capillary action, driving force
- What does a small contact angle tell you about a penetrant?
- It wets the surface well and spreads. Above 90 degrees a liquid beads up and is pushed out of a fine tube instead of rising into it.Topic: Penetrant properties, wetting and contact angle
- Does a narrower opening pull a wetting liquid in harder or more weakly?
- Harder. Capillary rise varies inversely with the bore radius, which is why fine cracks can still fill.Topic: Capillary action, rise height and opening size
- Viscosity controls what: whether penetrant can enter, or how fast?
- How fast. High viscosity means slow filling and a longer dwell; very low viscosity can drain from shallow openings. Cold raises viscosity.Topic: Penetrant properties, viscosity and rate of entry
- Why is high volatility a problem in a penetrant?
- It evaporates during dwell, dries on the part, resists removal and bleeds out poorly.Topic: Penetrant properties, volatility
- How does a fluorescent dye make an indication visible?
- It absorbs UV-A near 365 nm and re-emits longer wavelength visible light, usually yellow-green, which shows against a dark field.Topic: Penetrant properties, fluorescent dye response to UV-A
- What is the one rule for what PT can detect?
- The discontinuity must be open to the surface being tested.Topic: Detection limits, surface-breaking openings
- Why can a machined part hide cracks from PT until it is etched?
- Machining can smear metal over the crack mouth. Etching removes the smeared layer and reopens it.Topic: Detection limits, smeared metal and etching
- Should PT go before or after shot peening, plating or painting?
- Before. Those operations close or cover openings. PT goes after operations that can create cracks, such as grinding or heat treatment.Topic: Detection limits, sequence with other operations
- Can PT find a lamination in plate?
- Only where it reaches a cut edge. A lamination is internal and parallel to the faces, so the faces show nothing.Topic: Detection limits, internal discontinuities
- Does PT need a magnetic material?
- No. It works on almost any nonporous material: steels, aluminum, titanium, glazed ceramics and many plastics.Topic: Applications, material types
- What does a PT indication reliably tell you, and what not?
- Location and surface length. Not depth. Tight cracks hold less liquid and give fainter indications than wider ones of similar length.Topic: Detection limits, what an indication shows