Department of Materials and Ceramic Engineering
Faculty of Engineering- Imam Khomeini International University
Presenter:
K. Hosseini
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Introduction
Visual examination is used to
determine the quality levels or
conditions of welds, base material
processing discontinuities, bolting,
and other components.
A good weld should be
generally uniform in height.
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Improper welding techniques can
create an excessively uneven weld
with high and low areas.
Improper current, incorrect arc
length, and incorrect welding speed
may create these uneven areas.
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The high-low profile thus created is
undesirable because it makes other
weld
defects
more
difficult
to
interpret during a visual inspection
as well as making nondestructive
examinations
more
difficult
to
interpret.
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Pipe, fittings, valves, and other
parts come in a variety of metals,
alloys, diameters, and wall
thickness.
Materials, components, processes,
and procedures are varied. It is
important to learn and understand
these procedures in order to assure
that all material and work meet the
specified requirements.
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Various criteria are used to judge
the acceptability of welds.
The accept/reject criteria will
determine the acceptable sizes of
specific discontinuities..
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Procedures for welding examination of ASME code stamped
systems are strict, and yet we have tolerances to work with.
Some discontinuities may be acceptable if they do not exceed
allowable tolerances.
The welding specialist must be able to recognize and disposition
base metal and welding defects as required by the project scope.
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When welding is performed
on materials such as beveled
pipe or plate, the first pass
should penetrate to the
underside of the joint.
A flat or slightly convex bead
should
appear
on
the
underside of the plate or on
the inside of the pipe joint.
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When the bead does not penetrate
the required depth, the weld is
considered incomplete.
The bevel and the root gap should
always be in accordance with the
applicable welding procedure.
In addition to inadequate fit-up,
there are other possible causes of
insufficient penetration or excess
reinforcement..
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The welding technique can cause
poor penetration if the welder
moves too fast and excess
reinforcement if he moves to
slowly.
Using the wrong size electrode or
filler
metal
and
incorrect
amperages
can
also
cause
unacceptable root contours.
Using too large of an electrode
prevents penetration into the root
area and incomplete penetration
results.
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Excess Reinforcement
The top of the weld, or cap as it is
sometimes called, is the area where
excessive reinforcement may occur.
Excess reinforcement can be harmful to
piping because it may create an
excessive load at the toe of the weld.
This may induce flexing of the pipe and
premature failure.
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For this reason the reinforcement
should blend
smoothly from the base metal to a
slight crown.
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Excessive Reinforcement
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Excessive Reinforcement
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Underfill
Underfill is a depression on the face of
the weld which is below the height of
the base material.
The welder failed to fill the weld joint
completely.
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Underfill
Underfill is a depression on the face
of the weld which is below the
height of the base material.
The welder failed to fill the weld
joint completely.
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Underfill
This is another example of
underfill..
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Inadequate
Penetration
or
Incomplete
Inadequate
or
incomplete
penetration is the joint penetration
being less than intended or a
condition
created
when
the
penetration and fusion of the filler
material within the joint cavity fails
to reach the specified depth within
the base material cross section.
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Incomplete penetration can result from
insufficient root gap during fit-up or
when weld shrinkage causes the root
opening to close.
Another common cause can be that an
excessive root face or land is provided
during joint preparation that precludes
penetration to the back side of the joint.
For joints welded from both sides,
inadequate back-gouging prior to
welding the second side can result in lack
of penetration.
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Excessive Penetration
Unacceptable root contours can
result from either too much or too
little penetration.
Excessive penetration appears as a
bead that is too high on the
underside of the plate or on the
inside of the pipe.
When this occurs, the welder is
moving or manipulating the weld
rod too slowly or the current is too
high.
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Drop Through
Drop through is an undesirable
protrusion or surface irregularity at
the weld root. When the molten weld
puddle does not solidify quick
enough, it will sag.
Generally, this condition is caused
by too wide of a root gap, excessive
heat, improper welding technique, or
a combination of these.
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Lighting must be at an appropriate level and of the correct
type
lux (lx)
the SI unit for measuring the illumination (illuminance) of a
surface. One lux is defined as an illumination of one lumen per
square meter or 0.0001 phot. In considering the various light
units, it's useful to think about light originating at a point and
shining upon a surface. The intensity of the light source is
measured in candlas; the total light flux in transit is measured in
lumens (1 lumen = 1 candela·steradian); and the amount of light
received per unit of surface area is measured in lux (1 lux = 1
lumen/square meter). One lux is equal to approximately 0.09290
foot candle
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Rigid
Flexible fiber optic
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Borescopes are devices that
permit inspection of internal
surfaces in piping, engines,
air frames etc. They contain
systems of lenses, mirrors,
prisms and lighting which
illuminates the test area and
transmits images to the
inspector.
They may be either rigid or flexible. The flexible type
uses optical fibres, the smallest have outside diameters
of just a few millimetres and can be steered into position
around tight bends.
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Television cameras combined with borescopes, video
recorders and image processing equipment permit the
remote collection and storage of visual images. This
permits inspection in difficult and hazardous sites, e.g.
nuclear installations and underwater pipelines. Image
enhancement by computer is also possible.
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Surface replication using strippable films also permits
the remote inspection of surfaces.
Etching for metallographic examination and to reveal
cracks, inclusions and localised variations in
composition and hardness .
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Surface replication using strippable films also permits
the remote inspection of surfaces.
Etching for metallographic examination and to reveal
cracks, inclusions and localised variations in
composition and hardness .
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Ultimately, visual testing is dependant upon the eyesight
of the inspector. Regular eyesight tests for both visual
acuity and colour differentiation are essential. The time
for continuous viewing must be restricted with frequent
rests to reduce fatigue.
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