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Inspections Day 2

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MIAT106 Inspections

on 1 September 2014

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Transcript of Inspections Day 2





Process Compensated
Resonant Testing -
PCRT

Acoustic Emission Testing
Uses the sound generated within an object to determine the condition of that object
Can be for conditioning monitoring
Can be used as an alarm

Acoustic Testing

Blades can be tested using ultrasound provided the internal layup is known

Complex shapes can be difficult
Small coverage area per scanning
Highly trained personnel to understand readings
Rough surfaces may cause problems

Limitations of Ultrasound

A pulse is sent through the material
When the pulse reaches the opposite side:
It echoes back to the transducer
The scope calibrates the pulse to show depth
When the pulse contacts a defect:
It echoes back in the same manner
Has a shorter echo time
You can track the depth and the length of the defect

Pulse Echo method

Three ways Ultrasonic energy is introduced into test material:
Direct contact: contact on one side only.
Transducer on both sides
one sends and the other receives.
Immersion method.
Test material is immersed in water and transducer beams energy through the water to the test material.
Method of Fault Indications
Pulse Echo Method
Resonance System

Ultrasonic transducers are available in over 5000 variations in frequency

Sound is a product of vibration
Ultrasonic waves vary in frequency from 200 KHz to 25 MHz
Sound energy can be transmitted through most media
Metals, plastics & ceramics
Piezoelectric Effect
Some materials produce electricity when
Struck, Pressed, Bent, or other wise distorted.
These materials are useful as TRANSDUCERS
Transducers can receive or send signals

Ultrasound Inspection

Eddy Current can be used to test new material in a “conveyor belt” style or continuous feed system

Set the circuit to a balanced condition with the sample piece.
The meter should read center scale.
Anything that is not equivalent to the sample will deflect the meter to either side.
This deflection is indicating that the material is either a different material than the sample or has a defect

Eddy Current Set Up

Eddy Current
Very little preparation required
Detects surface and subsurface flaws.
Detects different metals as well as heat treatment
Based on current acceptance into the inspection material
Current flow is effected by four things;
Conductivity
Permeability
Mass,
Voids or faults.

Eddy Current Testing

Inspect Under a UV Light

Apply Penetrant

Mag Particle Machine

PCRT uses an external source to induce a resonant frequency into the object being tested
The resonant frequency is measured
Any deviation from the predetermined frequency indicates a flaw
Degree of shift in resonant frequency correlates to degree of defectiveness
Resonances evaluate the whole part

Process Compensated Resonant Testing (PCRT)

Acoustic Emission Testing

Ultrasonic waves propagate through single or multiple layers of well bonded materials.

Transition through different mediums causes reflection of sound waves and reduces/eliminates signal strength.

Ultrasonic Signal

Ultrasound inspections can be utilized in extremely diversified applications

Ultrasonic Inspection


The ultrasound unit is calibrated for a specific metal thickness.
If the thickness varies it will produce an indication on the monitor screen
This system is used to indicate wear or corrosion of a part or material

RESONANCE SYSTEM

Ultrasound Systems

Angle-Beam Transducer Pulse Reflecting Off A Weld

Can be used on small to large parts
Good for checking for:
Voids
Cracks
Delaminating
Inclusions
Defects in manufacturing
Internal corrosion
Modern day x-ray can render 3D color pictures

Film Radiography

Types of Detectable Defects:
Inclusions
Nonmetallic materials, such as slag that have been trapped in a material
Large inclusions near the surface or open to the surface usually appear elongated or as parallel lines
Fatigue Cracks
Found in highly stressed areas of a part, or where a stress concentration exists
Usually clear, sharp patterns

MAGNETIC PARTICLE

Demagnetize Part

You must check for cracks in every directions

Crack Orientation

Reasons for demagnetization include:
May interfere with welding and/or machining operations
Can effect gauges that are sensitive to magnetic fields if placed in close proximity.
Abrasive particles may adhere to components surface and cause and increase in wear to engines components, gears, bearings etc.

Demagnetization

Large Bolt with Service Induced Crack

Drive Shaft with Heat Treatment Induced Cracks

Install Part into Mag Particle Machine
Induce current to cause magnetic flux

Inspect for cracks using a UV light

Magnetic Particle Inspection
The part is magnetized
Finely milled iron particles coated with a dye pigment are then applied to the specimen
Particles are attracted to magnetic flux leakage fields and will cluster to form an indication directly over the discontinuity
Can be visually detected under proper UV lighting conditions
Must be dark
Must have good eyesight



Visual Inspection

Inspections Day 2

Ac current flowing through a coil generates a magnetic field around the coil
When the coil is placed close to a conductive material, eddy currents are induced into that material
If a flaw in the material disturbs the eddy current circulation, the magnetic coupling between the probe and the material is changed
This disturbance can be detected by the impedance variation when measured through the coil

Eddy Current Testing

Inducing magnetic flux around the part will check for cracks oriented perpendicular to the part up to a 45° angle

Creates longitudinal flux
Two methods of Mag Flux testing
Residual
Continuous

Crack Orientation

Parts inspected by the magnetic particle method may sometimes have an objectionable residual magnetic field that may interfere with the service of the component.
After the inspection is complete, you must demagnetize the part
The part is put through a Degausser which neutralizes any magnetic energy retained in the part

Degauss or Demagnetize part

Splined Shaft with Service Induced Cracks

Primitive AE as a conditioning monitoring
tool

Primitive AE as an alarm system

Early uses of AE

Eddy current testing is particularly well suited for detecting surface cracks but can also be used to make electrical conductivity and coating thickness measurements. Here a small surface probe is scanned over the part surface in an attempt to detect a crack or corrosion.

Eddy Current Testing

High pressure always seeks low pressure.
Therefore there are two types of leaks:
Leak out
Process pressure is higher than atmospheric pressure
Leak in
Process pressure is lower than atmospheric pressure

U.A. can be used to detect leaks on the following types of systems:
Leaking Process Valves Steam Traps
Condensers Safety Valves

Ultrasonic Acoustics

Cameras and Ultrasonic transducers on long articulating arms are used to inspect underground storage tanks for damage.

Robotic crawlers use ultrasound to inspect the walls of large above ground tanks for signs of thinning due to corrosion.

Storage Tank Inspection

The failure of a pressure vessel can result in the rapid release of a large amount of energy.
To protect against this dangerous event, the tanks are inspected using radiography.

Pressure Vessel Inspection

Radiographic Images

Gray scale image produced using the sound reflected from the back surface of the coin (inspected from “heads” side)

Gray scale image produced using the sound reflected from the front surface of the coin

High resolution images can be produced by plotting signal strength or time-of-flight using a computer-controlled scanning system.

Ultrasonic Imaging

Electromagnetic devices and visual inspections are used to find broken wires and other damage to the wire rope that is used in chairlifts, cranes and other lifting devices.

Wire Rope Inspection

Ultrasonic Signal

Receiver

Transmitter

SEAL

Pouch seal or package material is placed between ultrasonic transmitter and receiver

Used In Food Packaging

Pipe with damage

Signals produced by various amounts of corrosion thinning.

Periodically, power plants are shutdown for inspection.
Inspectors feed eddy current probes into heat exchanger tubes to check for corrosion damage.

Power Plant Inspection

Probe

Ultrasonic Gun Transducer

Acoustic Lens

LCD

Imaging Array

Target

Source transducer

Corrosion

Water trapped in Honeycomb

Wind Blade Delaminating

Crack in a composite piece

Eddy Current Testing

Magnetic field
Created by a
flaw

Eddy current's

currents

Eddy

magnetic field

Coil's

Coil

Conductive
material

Ultrasonic Inspection

Oscilloscope, or flaw detector screen

back surface
echo

crack
echo

initial
pulse

crack

plate

f

High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws.
Reflected sound energy is displayed versus time, and will display the thickness to the edge. Cracks will indicate a shorter echo time

Radiation
Penetrates
the Sample


Exposure Recording Device

X-ray Generator or Radioactive Source Creates Radiation

+

-

Electrons

High Electrical Potential

The radiation used in radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation can come from an X-ray generator or a radioactive source.

Radiography (X-Ray)

Magnetized

Demagnetized

Demagnetization requires that the residual magnetic field is reversed and reduced by the inspector.
This process will scramble the magnetic domains and reduce the strength of the residual field to an acceptable level.

Demagnetization

1
2
3
Cracks can radiate perpendicular to the part, parallel to the part, or any where in between
Inducing current through the part will check for cracks oriented parallel to the part up to a 45° angle
Creates circular flux
Full transcript