CSWIP 3.1 Welding Inspection
TWI Training & Examination
Services
Course Reference WIS 5
Course notes section reference 5.0
Copyright © TWI Ltd 2009
Non-Destructive Testing
Non-Destructive Testing
A welding inspector should have a working knowledge of NDT
methods and their applications, advantages and
disadvantages.
Four basic NDT methods
• Dye penetrant inspection (PT)
• Radiographic inspection (RT)
• Ultrasonic inspection (UT)
Copyright © TWI Ltd 2009
• Magnetic particle inspection (MT)
Non-Destructive Testing
Surface Crack Detection
•
Liquid Penetrant (PT or Dye-Penetrant)
•
Magnetic Particle Inspection (MT or MPI)
•
Ultrasonics (UT)
•
Radiography (RT)
Each technique has advantages & disadvantages with respect
to:
•
Technical Capability and Cost
Note: The choice of NDT techniques is based on consideration
of these advantages and disadvantages
Copyright © TWI Ltd 2009
Volumetric Inspection
Copyright © TWI Ltd 2009
Penetrant Testing (PT)
Penetrant Testing
Main features:
• Detection of surface breaking defects only.
• This test method uses the forces of capillary action
• Applicable on any material type, as long they are non porous.
• Penetrants are available in many different types:
• Solvent removable contrast
• Water washable fluorescent
• Solvent removable fluorescent
• Post-emulsifiable fluorescent
Copyright © TWI Ltd 2009
• Water washable contrast
Penetrant Testing
Step 1. Pre-Cleaning
Copyright © TWI Ltd 2009
Ensure surface is very Clean normally with the use of a solvent
Penetrant Testing
Copyright © TWI Ltd 2009
Step 2. Apply penetrant
After the application, the penetrant is normally left on the
components surface for approximately 15-20 minutes (dwell
time).
The penetrant enters any defects that may be present by
capillary action.
Penetrant Testing
Copyright © TWI Ltd 2009
Step 3. Clean off penetrant
the penetrant is removed after sufficient penetration time (dwell
time).
Care must be taken not to wash any penetrant out off any
defects present.
Penetrant Testing
Copyright © TWI Ltd 2009
Step 3. Apply developer
After the penetrant has be cleaned sufficiently, a thin layer of
developer is applied.
The developer acts as a contrast against the penetrant and
allows for reverse capillary action to take place.
Penetrant Testing
Copyright © TWI Ltd 2009
Step 4. Inspection / development time
Inspection should take place immediately after the developer
has been applied.
any defects present will show as a bleed out during
development time.
After full inspection has been carried out post cleaning is
generally required.
Penetrant Testing
Bleed out viewed
under a UV-A light
source
Copyright © TWI Ltd 2009
Fluorescent Penetrant
Bleed out viewed
under white light
Colour contrast Penetrant
Penetrant Testing
•
•
•
•
Simple to use
Inexpensive
Quick results
Can be used on any nonporous material
• Portability
• Low operator skill required
Disadvantages
• Surface breaking defect only
• little indication of depths
• Penetrant may contaminate
component
• Surface preparation critical
• Post cleaning required
• Potentially hazardous
chemicals
• Can not test unlimited times
• Temperature dependant
Copyright © TWI Ltd 2009
Advantages
Penetrant Testing
Comparison with Magnetic Particle Inspection
ADVANTAGES
•easy to interpret results
•no power requirements
•relatively little training required
DISADVANTAGES
•good surface finish needed
•relatively slow
•chemicals - health & safety issue
Copyright © TWI Ltd 2009
•can use on all materials
Penetrant Testing
Copyright © TWI Ltd 2009
Any Questions
Copyright © TWI Ltd 2009
Magnetic Particle testing (MT)
Magnetic Particle Testing
Main features:
• Surface and slight sub-surface detection
• Relies on magnetization of component being tested
• Only Ferro-magnetic materials can be tested
• A magnetic field is introduced into a specimen being tested
• Fine particles of iron powder are applied to the test area
• Any defect which interrupts the magnetic field, will create a
leakage field, which attracts the particles
• Any defect will show up as either a dark indication or in the
case of fluorescent particles under UV-A light a green/yellow
indication
Copyright © TWI Ltd 2009
• Methods of applying a magnetic field, yoke, permanent magnet,
prods and flexible cables.
Magnetic Particle Testing
Collection of ink
particles due to
leakage field
Copyright © TWI Ltd 2009
Electro-magnet (yoke) DC or AC
Prods DC or AC
Magnetic Particle Testing
Copyright © TWI Ltd 2009
A crack like
indication
Alternatively to contrast inks, fluorescent inks may be used
for greater sensitivity. These inks require a UV-A light source
and a darkened viewing area to inspect the component
Copyright © TWI Ltd 2009
Magnetic Particle Testing
Magnetic Particle Testing
Typical sequence of operations to inspect a weld
• Clean area to be tested
• Apply contrast paint
• Apply ferro-magnetic ink to the component during
magnatising
• Interpret the test area
• Post clean and de-magnatise if required
Copyright © TWI Ltd 2009
• Apply magnetism to the component
Magnetic Particle Testing
Advantages
Disadvantages
• Simple to use
• Surface or slight sub-surface
detection only
• Rapid results
• Little surface preparation
required
• Possible to inspect through
thin coatings
• Magnetic materials only
• No indication of defects
depths
• Only suitable for linear
defects
• Detection is required in two
directions
Copyright © TWI Ltd 2009
• Inexpensive
Magnetic Particle Testing
Comparison with Penetrant Testing
ADVANTAGES
• much quicker than PT
• instant results
• less surface preparation needed
DISADVANTAGES
• only suitable for ferromagnetic materials
• electrical power for most techniques
• may need to de-magnetise (machine components)
Copyright © TWI Ltd 2009
• can detect near-surface imperfections (by current flow
technique)
Magnetic Particle Testing
Copyright © TWI Ltd 2009
Any Questions
Copyright © TWI Ltd 2009
Ultrasonic Testing (UT)
Ultrasonic Testing
Main Features:
• Surface and sub-surface detection
• This detection method uses high frequency sound waves,
typically above 2MHz to pass through a material
• The actual display relates to the time taken for the
ultrasonic pulses to travel the distance to the interface and
back
• An interface could be the back of a plate material or a defect
• For ultrasound to enter a material a couplant must be
introduced between the probe and specimen
Copyright © TWI Ltd 2009
• A probe is used which contains a piezo electric crystal to
transmit and receive ultrasonic pulses and display the
signals on a cathode ray tube or digital display
Ultrasonic Testing
Digital
UT Set,
Copyright © TWI Ltd 2009
Pulse echo
signals
A scan
Display
Compression probe
checking the material Thickness
Ultrasonic Testing
initial pulse
Material Thk
defect
0
Compression Probe
10
20
30
40
50
CRT Display
Copyright © TWI Ltd 2009
Back wall
echo
defect
echo
Ultrasonic Testing
UT Set
Copyright © TWI Ltd 2009
A Scan
Display
Angle Probe
Ultrasonic Testing
initial pulse
defect echo
defect
0 10 20 30 40 50
½ Skip
Copyright © TWI Ltd 2009
CRT Display
initial pulse
defect echo
defect
Full Skip
0 10 20 30 40 50
CRT Display
Advantages
Disadvantages
 Rapid results
 Both surface and
 Trained and skilled operator
required
sub-surface detection
 Requires high operator skill
 Safe
 Good surface finish required
 Capable of measuring the
depth of defects
 Defect identification
 May be battery powered
 No permanent record
 Portable
 Calibration Required
 Couplant may contaminate
 Ferritic Material (Mostly)
Copyright © TWI Ltd 2009
Ultrasonic Testing
Ultrasonic Testing
Comparison with Radiography
ADVANTAGES
•good for planar defects
•good for thick sections
•instant results
•can automate
•very portable
•no safety problems (‘parallel’ working is possible)
•low capital & running costs
Copyright © TWI Ltd 2009
•can use on complex joints
Ultrasonic Testing
Comparison with Radiography
DISADVANTAGES
• no permanent record (with standard equipment)
• not suitable for very thin joints <8mm
• reliant on operator interpretation
• good/smooth surface profile needed
• not suitable for coarse grain materials (e.g., castings)
• Ferritic Materials (with standard equipment)
Copyright © TWI Ltd 2009
• not good for sizing Porosity
Ultrasonic Testing
Copyright © TWI Ltd 2009
Any Questions
Copyright © TWI Ltd 2009
Radiographic Testing (RT)
Radiographic Testing
•
X or Gamma radiation is imposed upon a test object
•
Radiation is transmitted to varying degrees dependant upon the
density of the material through which it is travelling
•
Thinner areas and materials of a less density show as darker
areas on the radiograph
•
Thicker areas and materials of a greater density show as lighter
areas on a radiograph
•
Applicable to metals,non-metals and composites
Copyright © TWI Ltd 2009
The principles of radiography
X – Rays
Gamma Rays
Electrically generated
Generated by the decay of
unstable atoms
Copyright © TWI Ltd 2009
Radiographic Testing
Radiographic Testing
Source
Radiographic film
Image quality indicator
Test specimen
Copyright © TWI Ltd 2009
Radiation beam
Radiographic Testing
Source
Image quality indicator
Test specimen
Radiographic film with latent image after exposure
Copyright © TWI Ltd 2009
Radiation beam
Radiographic Testing
Densitometer
Contrast - relates to the degree of difference
Definition - relates to the degree of sharpness
Sensitivity - relates to the overall quality of the radiograph
Copyright © TWI Ltd 2009
Density - relates to the degree of darkness
Copyright © TWI Ltd 2009
Radiographic Sensitivity
7FE12
Step / Hole type IQI
Wire type IQI
Radiographic Sensitivity
Copyright © TWI Ltd 2009
Step/Hole Type IQI
Wire Type IQI
Radiographic Techniques
Single Wall Single Image (SWSI)
•
film inside, source outside
Single Wall Single Image (SWSI) panoramic
film outside, source inside (internal exposure)
Double Wall Single Image (DWSI)
•
film outside, source outside (external exposure)
Double Wall Double Image (DWDI)
•
film outside, source outside (elliptical exposure)
Copyright © TWI Ltd 2009
•
Single Wall Single Image (SWSI)
Film
IQI’s should be placed source side
Copyright © TWI Ltd 2009
Film
Film
• IQI’s are placed on the film side
• Source inside film outside (single exposure)
Copyright © TWI Ltd 2009
Single Wall Single Image Panoramic
Film
• IQI’s are placed on the film side
• Source outside film outside (multiple exposure)
• This technique is intended for pipe diameters over 100mm
Copyright © TWI Ltd 2009
Double Wall Single Image (DWSI)
Double Wall Single Image (DWSI)
• Identification
• Unique identification
EN W10
• Pitch marks indicating
readable film length
A
B
ID MR11
Radiograph
Copyright © TWI Ltd 2009
• IQI placing
Copyright © TWI Ltd 2009
Double Wall Single Image (DWSI)
Radiograph
Double Wall Double Image (DWDI)
• IQI’s are placed on the source or film side
• Source outside film outside (multiple exposure)
• A minimum of two exposures
• This technique is intended for pipe diameters less than 100mm
Copyright © TWI Ltd 2009
Film
Double Wall Double Image (DWDI)
• Identification
4
• Unique identification
3
EN W10
• Pitch marks indicating
readable film length
1
2
ID
MR12
Shot A Radiograph
Copyright © TWI Ltd 2009
• IQI placing
4
3
1
2
Elliptical Radiograph
Copyright © TWI Ltd 2009
Double Wall Double Image (DWDI)
Radiography
PENETRATING POWER
Question:
What determines the penetrating power of an X-ray ?
Question:
What determines the penetrating power of a gamma ray ?
•the type of isotope (the wavelength of the gamma rays)
Copyright © TWI Ltd 2009
•the kilo-voltage applied (between anode & cathode)
Radiography
Isotope
Typical Thickness Range
• Iridium 192
10 to 50 mm (mostly used)
• Cobalt 60
> 50 mm
• Ytterbium
< 10 mm
• Thulium
< 10 mm
• Caesium
< 10 mm
Copyright © TWI Ltd 2009
GAMMA SOURCES
Radiographic Testing
Permanent record
• Little surface preparation
• Defect identification
Disadvantages
Expensive consumables
• Bulky equipment
• Harmful radiation
• Not so reliant upon operator
skill
• Defect require significant
depth in relation to the
radiation beam (not good
for planar defects)
• Thin materials
• Slow results
• No material type limitation
• Very little indication of
depths
• Access to both sides
required
Copyright © TWI Ltd 2009
Advantages
Radiographic Testing
Comparison with Ultrasonic Examination
ADVANTAGES
good for non-planar defects
good for thin sections
gives permanent record
can use on all material types
high productivity
direct image of imperfections
Copyright © TWI Ltd 2009
easier for 2nd party interpretation
Radiographic Testing
Comparison with Ultrasonic Examination
DISADVANTAGES
• health & safety hazard
• not good for thick sections
• not good for planar defects
• X-ray sets not very portable
• requires access to both sides of weld
• frequent replacement of gamma source needed (half life)
Copyright © TWI Ltd 2009
• high capital and relatively high running costs
Radiographic Testing
Copyright © TWI Ltd 2009
Any Questions