Welding Inspection
Non-Destructive Testing
Characteristics and Comparison between
Methods
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Introduction to NDT
NDT: Definition
• Check of a product by using a non-
invasive technique to determine (NDT)
the integrity of a material, component or
structure
• Some techniques (NDE) can
quantitatively measure some defects or
characteristics of an object
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Introduction to NDT
NDT: Requirements and Purposes
Requirements Purposes
• Capability of non • Locating of both
inducing any alteration superficial and internal
imperfections
• Easy and quick • Sizing of located
execution imperfections (not always
required)
• Possibility of executing • Real time monitoring of a
“in-field” tests “in-service” damage
• Immediate results
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Introduction to NDT
NDT: Applications
Detecting Flaws:
Techniques able to FIND, LOCATE and
SIZE imperfections.
Some techniques are successfully
usable for 2-D (planar) flaws, some
others for 3-D (volumetric) flaws
Investigating Structures:
Techniques able to give some information
about metallurgical (chemical)
characteristics and modifications
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Introduction to NDT
NDT: Methods
Visual Testing (VT)
Penetrant Testing (PT)
Magnetic Particle Testing (MT)
Eddy Current Testing (ET)
Ultrasonic Testing (UT)
Radiographic Testing(RT)
Leak Testing (LT)
Acoustic Emission Testing(AT)
Infrared Thermographic Testing(TT)
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Introduction to NDT
NDT: Metallurgical Investigations
Field Metallography
• To have some information about mechanical & chemical
characteristics’ deterioration of a component, an in situ field
metallographic analysis is used.
• This method investigate the microstructure by means of a
buffing of the surface, a chemical etching and a REPLICATION
(an acetyl cellulose’s film is applied on the surface).
• Replication technique is often used to estimate pressure
components’ remaining life and their maintenance plan.
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Introduction to NDT
NDT: Metallurgical Investigations
Hardness Testing
• Hardness is the mechanical property that values the resistance
a material offers to scratches and represents an indication of
tensile strength and structures.
• This test is made by applying a local load by means of a
penetrator (conical, spherical, pyramidal…) that produces a
elasto-plastic deformation.
• This method is considered a SEMI-DESTRUCTIVE testing
because of the imprints left by the penetrator on the surface.
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Introduction to NDT
NDT: Position of Flaws
According to position of
detectable flaws, we can have:
Superficial Methods Volumetric Methods
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Introduction to NDT
NDT: Superficial Methods
Superficial Methods are methods able to detect
imperfections that are located only on the surface.
Some of these methods can investigate the
surface and a few under layers.
They are:
• Visual Testing
• Magnetic Particle Testing
• Penetrant Testing
• Eddy Current Testing
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Introduction to NDT
NDT: Volumetric Methods
Volumetric Methods are methods able to detect
imperfections that are located on the surface and
in the balk too.
They are:
• Radiographic Testing
• Ultrasonic Testing
• Leak Testing
• Acoustic Emission Testing
• Infrared Thermographic Testing
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Introduction to NDT
NDT: Detected Imperfection’s Characterisation
• Non-destructive Testing Methods can be classified
according to the capability of characterize flaws,
giving some information about not only their
positions but also their nature and typology (and so
about their severity).
• The only method able to give a full characterization
of the detected imperfections is the Ultrasonic
Testing
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Introduction to NDT
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