NDT Testing Flashcards
Destructive testing tests include:
- tensile testing
- compressive testing
- torsion testing
- fatigue testing
- hardness testjng
- impact testing
What are the five most common non destructive testing methods?
- visual inspection
- dye penetrant
- magnetic particle
- ultra sonic
- radiography
Eddy current is not the top five most common but it is frequently used for automatic production line inspection.
Welding process can cause internal stress of the parts or the ______ condition of the manufactured component. And must be NDT tested.
Operating conditions
Liquid dye penetrant (LDT) is used to?
Detect discontinuities open to the surface of solid and non porous materials.
What type of NDT testing uses capillary action, blotted to the surface with a developing agent and viewed under a ultra violet light or white light?
Liquid penetrant testing
LPT testing can be done on a wide variety of materials such as:
Some advantages are?
Metals, glass, ceramics and plastics
Portable and can be applied on small and large surfaces
- in practice it is relatively simple and less costly
- good for detecting flaws in non-magnetic materials and inspecting items made from non-ferromagnetic steels
Limitations of liquid penetrant?
- can only detect imperfections that are open to the surface
- rough or porous surfaces will produce false indications
- temperature sensitive
Liquid penetrant process?
1: clean area, must be free of oil, water or other contaminants. For atleast 1” beyond the area being inspected.
2: apply a penetrating coloured liquid dye to the surface of the test piece. Should be left on long enough to along sufficient penetration. (Dwell)
3: Remove all surplus dye. Type of dye will dictate cleaning method. Make sure not to over clean
4: apply thin coat of developer to the surface to provide a contrasting background.
5: inspect with good white light or or black light depending on the penetrant.
Two type of liquid penetrants?
Fluorescent - visible Under ultraviolet light
Visible - red penetrant produces vivid red indications in contrast with the light background
Non flammable cleaners usually contain halogenated solvents which make them unsuitable for some applications. How come?
High toxicity and have undesirable effects on some materials.
Fluorescent dye penetrant test detects surface imperfections such as?
- Surface cracks in in castings, welds and carbide tools
- shrinkage in castings and hot forgings
- cracks in turbine blades and ceramic insulators
Liquid penetrant is widely used in?
Welded thin walled vessels
Magnetic particle testing (MT) is used to detect surface and subsurface discontinuities usually at depths not greater than?
6mm (1/4”)
Magnetic partial testing is commonly used on?
- welds
- Large forgings
- castings
- other parts with rough surfaces
To detect the flaws with magnetic particle testing magnetic field must be orientated in which direction of the defect?
90 degrees
Limitations of magnetic particle testing?
- thin coatings of paint make less sensitive
- non-ferromagnetic materials cannot be tested
- demagnetizations is often required afterwards
- exceedingly large currents are sometime needed
- ## wide cracks may not produce a particle pattern
Three types of unbalance
What current is used for Magnetic particle testing?
Ac - should not be used for searching for subtracted discontinuities.
And
Dc - generally penetrate the cross section of the part.
Two types of magnetic yokes are?
Permanent
Electromagnetic
Radio graphic testing (RT) is?
Penetrating radiation is used to produce a film image of the internal structure of a specimen.
Two different radio graphic testing sources are?
X-ray - accelerating electrons
Gamma ray - radio active materials
Two criteria for measuring the quality of the radio graph are ?
Contrast - different degrees of darkening on the film
Definition - sharpness of the image projected on the film
Radio graphs can pick up:
- gas pockets or porosity
- slag inclusions Or slag lines
- lack of penetration or fusion
- internal or external undercuts
- burn throughs or cracks
What is the best testing method for checking an engine or compressor cylinder head casting for interior cracks?
X-ray
Ultrasonic inspection (UT) has two main types of ultrasonic waves for testing welds?
Longitudinal
Shear waveforms
Which NDT method can measure the length of a stud, locate and measure defects deeper and more accurately and less expensive?
Ultra sonic testing
Most widely used NDT methods of testing
The NDT testing can measure thickness of materials within 1% accuracy?
Ultrasonic thickness gauging
Can test any thickness over 1/8”
Sending transducer does?
Receiving transducer does?
Sending transducer - emits a beam of ultrasonic waves when burst of alternating voltage is applied
Receiving transducer - accepts and converts the output of ultrasonic waves from the test piece to corresponding burst of alternating voltage
Advantages of ultrasonic testing:
- portable
- superior penetrating power 20ft
- high sensitivity
- greater accuracy
- only needs access to one surface
- operation is electronic
- volumetric scanning
- not hazardous
- can measure wall thickness
- can test on almost any kind of metal of any size
Disadvantages of ultrasonic testing?
- manual operation by experienced techs
- exclusive technical knowledge
- rough irregular shapes are hard to inspect
- discontinuities right below surface may not be detected
- reference standards are needed
Eddy current testing applications?
- used as an alternative to magnetic Particle and dye penetrant testing because it is able to detect surface and subsurface cracks beneath even a thick layer of paint.
- ideal for testing non magnetic conductive materials such as copper, bronze, aluminum and Austenitic stainless steels
- economical because of speed of inspection
- used in marine, aerospace, high pressure, high temperature, and corrosive applications where failure of a part would be disastrous
- parts are scanned by moving test probes or passing them through test coils
Disadvantages of Eddy current testing?
- laminar flaws not detected
- must be electrically conductive
- testing is best done at or near the surface
Causes of imbalance?
- Corrosion or abrasion
- distortion
- eccentricity
- bent shaft
- clearances
- keys and keyways
- non homogenous machined parts
- asymmetry
- material buildup
- shaft flexing
- shifting parts
- temperature
What are the three types of imbalance?
Static - shafts weight is evenly distributed along its length but unevenly from side to side
Dynamic imbalance - extra weight unevenly distributed
Couple imbalance - extra weight at each end of the shaft but opposite sides of the shaft
What is a major result of imbalance?
Vibration
Static equalibrium
8oz x 2” = 16
2oz x 8” = 16
Parts can balance
Imbalance shows up at how many times the rpm?
1x
Why should rotors operate at RPM’s 20 to 30% outside of the critical speed?
Equipment will experience resonance. (Marked increase/implication in vibration) once out of this critical speed range (above/below) vibration will lesson again
Vibration in rotating equipment is?
The result in any force that moves a shaft from its reference
By changing the mass or stiffness of an object you will change its?
Vibratory signature
What are the three terms/meaning to describe vibration?
These are a series of forms called sine waves.
Frequency - how often an event happens in a unit of time or cycle.
- cycles per second (Cps, HZ)
- cycles per minute (cpm)
Amplitude - how much the machine is vibrating. Three
- imperial measurement 1mil = .001”
- metric measurement 1micron = .001mm
Phase - the relationship between displacement, velocity and acceleration
Frequency on a signature is?
The most prominent frequency is the one with the spike. (This is the predominant or fundamental frequency.
What are the three measurements of amplitude?
Displacement - total distance a vibrating part moves either side of its neutral axis
Velocity - rate of change of displacement for a given time
Acceleration - rate of change in velocity for a given time
Displacement (see image)
Imperial measurement 1mil=.001”
Metric 1 micron = .001mm
Velocity see image
Imperial inches per second (in/sec or IPS)
Metric millimetres per second (mm/s)
Best overall indicator of machine condition
Acceleration (see image)
Measure in g forces
Natural frequency?
A frequency at which an object or system naturally vibrates when a forcing function has been introduced
Resonant frequency?
The system amplifies the energy from the forcing function frequency causing large amplitude. RESONANCE OCCURS IN ANY SYSTEM IF THE FORCING FUNCTION FREQUENCIES ARE NOT KEPT AT ATLEAST 20% outside the natural frequency’s range
Critical speed?
Critical speed of a shaft or rotor occurs when the rotor rotates at or near its natural critical speed. At critical speed the rotor reaches a point of resonance and there is a marked increase in vibration. This will damage the machine and should be kept 20-30% outside of the critical speed
Synchronous vibration?
Correspond to a frequency that is a whole multiple of the rotating speed (velocity) of the machine. These are phase locked to the rpm of the machine such as: 1x rpm and 2x rpm
Non-synchronous vibration
Frequencies that are not whole multiples of the rotating speed of the machine
Sub-synchronous vibration?
Frequencies that occurs at less than the rotating speed of the machine
What are some tools for measuring vibration?
- vibration pencils
- portable handheld meters
- portable vibration meters with graphs
- monitors
- analyzers
Most important part of any vibration measurement system is the?
Transducer
If the transducer gives the analyzer immaculate information the analyzer cannot give a accurate analysis.
Three basic categories of transducers are:
- displacement transducers
- velocity transducers
- acceleration transducers
Each has different degree of sensitivity at various frequencies. No single type is able to reliably measure all parameters of amplitude over all the frequency ranges.
Displacement transducers?
Non contact Eddy current transducers measure the relative resistance bearing housing and bearing journal.
They do not generate their own power. And need a high frequency dc electical signal
Velocity transducers?
Used for general vibration measurements and balancing.
Generate their own power
Primarily used to measure velocity but the analyzer can differentiate or interstate the signal making it capable of measuring displacement and acceleration through the machine
Acceleration transducers (Accelerometers)
Most common used with vibration analysis equipment.
Generate their own power but often use an amplifier to increase signal strength.
What are the pickup mounting locations for the transducers?
HVA or XYZ
Water in oil can?
Change viscosity, lubricity and load carrying characteristics. The chemical properties of fluid can also be affected by water.
Water can cause additive depletion, which creates oxidation due to the formation of acids from chemical reaction
The main cause of oxidation is heat. That are the effects of the products oxidation creates?
Gum and varnish
Sludge
Acids
Gum and varnish - sticky valves
Sludge - blocked pilot passages
Acids - corrosion of parts
Where should the sample of oil be taken from in a circulating oil system?
At a point where the fluid is well mixed. A live zone sample
Live zone should have a quick coupler or a valve to take the sample without allowing contamination to enter
Oil taken for sampling on a circulating oil system is taken from the live zone when the machine is?
Running at its normal operating temperature, pressure, speed and load
- from live zones in the piping
- downstream of system components
- upstream from filters or separators
When getting an oil sample from a non circulating system(ring oilers, splash lubricated gear box) how do you get it?
Use a short tube that extends inward and up into the sump.
Make sure not to collect fluid from dead legs (where fluid is not moving)
