7: Interpreting Results Flashcards
3 problems that occur due to large grain structure, porosity or precipitates.
- Scattering
- Attenuation
- Noise on screen
What are the solutions for scattering, attenuation and noisy screen?
- Lower probe frequency
- Inspect 90 degree to grain structure
- Reduce beam spread (increase probe diameter)
- Test from opposite/adjacent surfaces
What problems could occur with a rough surface? (3)
- Mode conversion/refraction
- Attenuation
- Widening of the IP
What are 3 solutions to rough surface problems (mode conversion/refraction, attenuation and widening of IP)? (3)
- Smooth the surface
- Use thicker couplant
- Lower probe frequency
What are 2 problems that could occur when testing a hot surface?
- Damage to transducer
2. Cannot obtain results
What are 2 solutions to testing on a hot surface?
- Use a hot temp probe
2. Use a high temp couplant
What problem could occur with testing on a vertical or overhead surface? And the solution?
Problem: Couplant runs down
Solution: use thicker couplant
What 2 problems could occur with testing a specimen with unparalleled surfaces?
- Mode conversion at back surface
2. Loss of back surface reflection
What is a solution to testing a specimen with unparalleled surfaces?
Obtain measurements or blueprint of the part
What are 2 problems you could encounter with testing a long thin specimen?
Mode conversion and attenuation.
When testing a long thin specimen, what are two solution to the mode conversion and attenuation you will encounter?
- Reduce beam spread (increase probe diameter or frequency)
2. Inspect from both ends
What are 3 problems you may encounter when testing on a small concave/convex surface?
- Mode conversion and refraction
- Attenuation
- Back wall reflection not clear
What is a solution to the problems you will encounter when testing small concave/convex surfaces?
Use a cylindrical lens that matches contour of the part.
What are two problems you may encounter when testing thin material?
- Defects in the dead zone
2. Hard to read indications
What are 3 solutions to the problems you will encounter when inspecting thin material (defects in dead zone and hard to read indications)?
- Use a delay line or dual probe
- Immersion testing
- Through-transmission technique
What problem will you encounter when inspecting large surfaces?
Time consuming
How can you speed up inspection when testing a large surface?
Use a larger diameter or paintbrush transducer
What problem will you encounter when testing for a discontinuity at an angle?
Small/no signal from discontinuity
How do you fix the problems that will be involved with finding a discontinuity at an angle?
Use an angle-beam transducer
What problem might you encounter when testing a rough discontinuity? And what is the solution?
Problem: reduced signal due to scatter
Solution: increase gain
What problem might you encounter with a discontinuity in the dead zone?
Can’t detect in
What are 6 solutions when trying to detect a discontinuity in the dead zone?
- Increase probe frequency
- Use broad bandwidth probe
- Reduce pulse length
- Use a dual/delay-line transducer
- Test with immersion/through-transmission
- Test from opposite side
Increasing the diameter of probe will do what to penetration power?
Increase it
Increasing diameter of probe will do what to the beam spread?
Decrease it
Increasing the diameter of probe will do what to near field?
Increase it
Increasing the frequency on a probe will do what to penetration power?
Decrease it (more attenuation)
Increasing the frequency will do what to beam spread?
Decrease it
Increasing frequency of a transducer will do what to the near field?
Increase it
Increasing frequency will do what to sensitivity?
Increase it
Increasing frequency will do what to the resolution?
Increase it
Using a broad bandwidth probe will do what to the penetration power?
Decrease it
Using a broad bandwidth probe will do what to the front surface resolution?
Increase it
Using a broad bandwidth transducer will do what to the dead zone?
Decrease it
Using a broad bandwidth probe will do what to the sensitivity?
Decrease it
What are the 3 main variables that affect UT?
- Material variables (composition, sound velocity, attenuation)
- Discontinuity variables
- Equipment and settings (transducer, couplant, instrument setting)
What will slightly increase attenuation by absorption?
Higher frequency
Reducing frequency will increase what that will in turn reduce sensitivity?
Wavelength
What will cause a lot of noise on the screen?
A porous material and large grain structures
In a worked material, how are discontinuities normally orientated?
Same direction as grain boundaries
When you have a hard material to penetrate, what should you consider trying?
Testing from opposite side
How do you improve an inspection of a large casting?
Reduce frequency (though it will also reduce sensitivity)
In what type of material can you reduce scatter by testing at 90 degrees to grain structure?
Worked material
Chlorine based products cause corrosion on what type of alloys?
Nickel based alloys (stainless steel)
Dispersion from rough surface entry causes loss of what?
Loss of signal amplitude from back surface and discontinuity.
Will also increase IP Width.
What is your last resort when working with a rough surface?
Lower probe frequency
With a temperature change, what will that affect in a material?
Density and elasticity
What do you have to be sure of when calibrating for hot surfaces?
The reference blocks are also a raised temperature.
What is to be said about readings taken on hot material?
They will be higher than true value - expansion of material and reduction of velocity
temperature correction charts are available
What happens in long, thin specimens?
Reflection and mode conversion
Where do NON-RELEVANT indications appear in long, thin specimens?
After first back wall as the useful energy has been reduced
How do you calculate beam spread?
Sin theta = 1.22V/Df
Why shouldn’t you reduce probe size to help with inspection on a small contact surface of a round specimen?
It will increase beam spread and may generate surface waves
On inspections of thin specimens, less than approx 10 mm, you should use 1 of these 4 options:
- Delay shoe transducer
- Dual transducer
- Immersion testing
- Through-Transmission technique
Which 2 techniques will only show ONE indication on screen?
Dual transducer and Through-Transmission.
Which 2 techniques will show both the front and back wall indications on the screen?
Delay line transducer and immersion testing.
Increasing what increases sensitivity for small discontinuities?
Frequency
What should you do if reflector is too thin?
Test from another direction.
What should one do when suspecting a sizeable void?
Scan from different directions to determine actual dimensions.
How can you trick the probe when inspecting a rough surface?
Lowering frequency will increase reflection making the probe think the surface is smooth.
To determine if the discontinuity surface is rough or smooth, one should do what?
Vary the frequency.
(Normally this would decrease height if signal… however it’s a rough surface reflector parallel to front surface, it will increase the amplitude)
What is the near field formula?
D^2/4 LAMBDA
A DAC curve is often used to compensate for attenuation when…
Sizing discontinuities that are smaller than sound beam
Inspecting for discontinuities near back surface can be hard if back resolution is not sufficient.. what is the solution and why?
Broader bandwidth will give better resolution because crystal won’t ring as long.
What happens when a crystal is loose?
It becomes detached from backing member
What happens on the screen when there is electrical interference?
Thin, irregular reflectors that move continuously/rapidly across screen.
What are 3 potential causes of electrical interference?
High voltage currents nearby, bad connection between probe and cable or a short in coaxial cable.
6 characteristics of larger diameter transducers:
- Transmits more energy (more penetration)
- Require more reflected energy to vibrate
- More fragile
- Limited to lower frequencies
- Reduce beam spread
- Increase length of near zone
A narrow bandwidth means what type of Q factor?
Large
Broad bandwidth, which is highly dampened, improves what?
Near surface resolution
What happens when you increase pulse length/width?
More energy will be sent to part and sensitivity will increase BUT DECREASE in resolution
What do you need to do with the PRR/PRF for very thick/low attenuation material?
Need to lower
How are “phantom waves” created?
When reflecting wave meets the next incoming wave.
What are 2 reasons a delay shoe is used for?
- Improve front surface resolution
2. Facilitate thickness measurements of thin sections
Why do we use a cylindrical lens?
For contour correction
4 factors that cause attenuation by absorption:
- Friction
- Heat production
- Inelasticity of particles
- Dislocations
How do you reduce attenuation by scatter?
Reduce frequency and increase wavelength
What’s the best option when working with a rough surface?
Smooth it
How do you reduce problems associated with course grain structure?
Reduce beam spread (large diameter probe)
