Chapter 9
Testing and Inspection of Welds
Objectives
• Contrast six differences between mechanical or
destructive and nondestructive testing
• List the 12 most common discontinuities and the
nondestructive methods of locating them
• Describe how three mechanical or destructive
and four nondestructive testing methods are
performed
• State five reasons why welds are tested
• Evaluate a weld for compliance with a given
standard or code
Introduction
• Necessary to ensure quality, reliability, and
strength of a weldment
• Active inspections are needed
• Extent of testing and inspection depends upon
the intended service of the product
• A weld that passes for one welding application
may not meet the needs of another
Quality Control (QC)
• Two classifications of methods in quality
control:
– Destructive, or mechanical, testing
– Nondestructive testing
• Mechanical testing (DT) methods destroy the
product
– Hydrostatic testing is the exception
• Nondestructive testing (NDT) does not destroy
the part being tested
Discontinuities and Defects
• Discontinuities and flaws are interruptions in
the typical structure of a weld
• A defect is a discontinuity which renders a part
unable to meet standards
• Many acceptable products may have
discontinuities
• The tolerances for welds have been
established and are available as codes or
standards
Porosity
• Results from gas that was dissolved in the
molten weld pool
• Bubble trapped as metal cools to become solid
• Porosity is most often caused by:
– Improper welding techniques
– Contamination
– An improper chemical balance between the filler
and base metal
Figure 9.1 Uniformly scattered porosities
Figure 9.2 Clustered porosity
Figure 9.3 Linear porosity
Figure 9.4 Piping or wormhole porosity
Inclusions
• Nonmetallic materials, such as slag and
oxides, that are trapped:
– In weld metal
– Between weld beads
– Between weld and base metal
• Sometimes inclusions are jagged
• Can also form a continuous line
• Reduces structural integrity
Figure 9.5 Nonmetallic inclusions
Inadequate Joint Penetration
• Occurs when the depth that the weld
penetrates the joint is less than needed
• Major causes:
–
–
–
–
Improper welding technique
Not enough welding current
Improper joint fitup
Improper joint design
Figure 9.6 Inadequate joint penetration
Figure 9.7 Incomplete root penetration
Incomplete Fusion
• Lack of coalescence
– Between the molten filler metal and previously
deposited filler metal
– Between the molten filler metal and the base metal
• Interpass cold lap
• Lack of sidewall fusion
Figure 9.8 Incomplete fusion
Incomplete Fusion (continued)
• Major causes of lack of fusion:
–
–
–
–
–
–
Inadequate agitation
Improper welding techniques
Wrong welding process
Improper edge preparation
Improper joint design
Improper joint cleaning
Figure 9.9 Gouge removal
Remove gouges along the surface of the joint before welding
Arc Strikes
• Caused by accidentally striking the arc in the
wrong place and/or faulty ground connections
• Even though arc strikes can be ground
smooth, they cannot be removed
• Will always appear if an acid etch test is used
• Can cause localized hardness zones or the
starting point for cracking
Figure 9.10 Arc strikes
Source: Courtesy of Larry Jeffus
Overlap
• Also called cold lap
• Occurs in fusion welds when weld deposits are
larger than the joint is conditioned to accept
• Weld metal flows over the surface of the base
metal without fusing
• Generally occurs on the horizontal leg of a
horizontal fillet weld
• To prevent overlap, the fillet weld must be
correctly sized
• Arc must be properly manipulated
Figure 9.11 Rollover or overlap
Undercut
• Result of arc force removing metal from joint
face
• Can result from excessive current
• A common problem with GMA welding when
insufficient oxygen is used
• Incorrect welding technique can cause
undercut
Figure 9.12 Undercut
Crater Cracks
• Tiny cracks that develop in the weld craters as
the weld pool shrinks and solidifies
• High shrinkage stresses aggravate crack
formation
• Can be minimized by not interrupting the arc
quickly at the end of a weld
• Some GMAW equipment has a crater filling
control
Figure 9.13 Crater or star cracks
Underfill
• Deposited metal inadequate to bring the weld's
face equal to the original plane
• For a fillet weld the weld deposited has an
insufficient effective throat
• Usually corrected by:
– Slowing the travel rate
– More weld passes
Figure 9.15 Underfill
Plate-Generated Problems
• Some problems result from internal plate
defects that the welder cannot control
• Internal defects are the result of poor
steelmaking practices
• Steel producers try to keep their steels as
sound as possible
• Mistakes that occur in steel production are
often blamed on the welding operation
Lamination
• More extensive than lamellar tearing
– Involve thicker layers of nonmetallic contaminants
• Located toward the center of the plate
• Caused by insufficient cropping of the pipe in
ingots
• Slag and oxidized steel in the pipe is rolled out
with the steel
• Can be caused when the ingot is rolled at too
low a temperature or pressure
Figure 9.16 Lamination and delamination
Delamination
• The heat and stresses of the weld may cause
some laminations to become delaminated
• Contamination of the weld metal occurs if the
lamination contained large amounts of:
–
–
–
–
Slag
Mill scale
Dirt
Other undesirable materials
• Can cause wormhole porosity or lack-of-fusion
defects
Lamellar Tears
• Appear as cracks parallel to and under the
steel surface
• Not in the heat-affected zone
• Have a steplike configuration
• Thin layers of nonmetallic inclusions lie
beneath the plate surface
• These inclusions separate when severely
stressed
Figure 9.17 Lamellar tearing
Figure 9.19 Correct joint design to reduce lamellar tears
Destructive Testing (DT)
• Tensile testing is performed with specimens
prepared as round bars or flat strips
• Two flat specimens are used, commonly for
testing thinner sections of metal
• Weld section
– Machined to specified dimensions
– Placed in tensile testing machine
Figure 9.22 Tensile specimen for flat plate weld
Source: Courtesy of Hobart Brothers Company
Fatigue Testing
• Determine weld resistance to repeated
fluctuating stresses or cyclic loading
• Part is subjected to repeated changes in
applied stress
• Specimen may be bent back and forth
Figure 9.23 Fatigue testing
The specimen is placed in the chucks of the machine. As the machine
rotates, the specimen is alternately bent twice for each revolution
Shearing Strength of Welds
• Two forms of shearing strength of welds:
– Transverse shearing strength
– Longitudinal shearing strength
• Transverse shearing strength:
– Divide the maximum force by twice the width
• Longitudinal shearing strength:
– Divide the maximum force by the sum of the length
of ruptured welds
Figure 9.24 Transverse fillet weld shearing specimen after welding
Source: Courtesy of Hobart Brothers Company
Figure 9.25 Longitudinal fillet weld shear specimen
Welded Butt Joints
• Three methods of testing welded butt joints:
– Nick-break test
– Guided bend-test
– Free bend-test
• A jig is commonly used to bend most
specimens
• Not all guided bend testers have the same
bending radius
• Codes specify different bending radii
Figure 9.26 Nick-break specimens
(A) Nick-break specimen for butt joints in plate and (B) method of rupturing nickbreak specimen
Source: Courtesy of Hobart Brothers Company
Figure 9.27 Root and face bend specimens for 3/8-in. (10-mm) plate
Figure 9.32 Free bend test
(A) The initial bend can be made in this manner; (B) a vise can be used to make
the final bend; and (C) another method used to make the bend
Source: Courtesy of Hobart Brothers Company
Alternate Bend
• Initial bend may be made by placing the
specimen in the jaws of a vise
• Specimen is bent away from the gauge lines
• Specimen is inserted into the jaws of a vise
• Pressure is applied by tightening the vise
• Pressure is continued until a crack or
depression appears on the convex face
Fillet Weld Break Test
• Force is applied to specimen until it ruptures
• Any convenient means of applying the force
may be used
• Break surface should be examined for
soundness
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Slag inclusions
Overlap
Porosity
Lack of fusion
Figure 9.33 Fillet weld testing
(A) Fillet weld break test and (B) method of rupturing fillet weld break specimen
Source: Courtesy of Hobart Brothers Company
Testing by Etching
• Specimens are etched for two purposes:
– To determine the soundness of a weld
– To determine the location of a weld
• Most commonly used etching solutions:
– Hydrochloric acid
– Ammonium persulphate
– Nitric acid
Impact Testing
• A number of tests can determine impact
capability of a weld:
– Izod test
– Charpy test
• Izod test:
– Specimen is gripped on one end, held vertically
– Tested at room temperature
• Charpy specimen:
– Held horizontally, supported on both ends
– Tested at a specific temperature
Figure 9.34 Impact testing
(A) Specimen mounted for Izod impact toughness testing and (B) a typical
impact tester used for measuring the toughness of metals
Source: Courtesy of Tinius Olsen Testing Machine Co., Inc.
Nondestructive Testing (NDT)
• Visual inspection is the most frequently used
nondestructive testing method
• Penetrant inspection locates minute surface
cracks and porosity
• Magnetic particle inspection uses finely divided
ferromagnetic particles to indicate defects
• Radiographic inspection detects flaws inside
weldments
Figure 9.35 Penetrant testing
Source: Adapted from Magnaflux Corporation
Figure 9.36 Magnetic particle inspection
Flaws and discontinuities interrupt magnetic fields
Source: Adapted from Magnaflux Corporation
Figure 9.38 Schematic of an X-ray system
Nondestructive Testing (NDT)
(continued)
• Ultrasonic inspection employs electronically
produced high-frequency sound waves
• Leak checking can be performed by filling the
welded container with either gas or liquid
• Eddy current inspection: a magnetic field
induces eddy currents within the material
• Hardness testing measures the resistance of
metal to penetration
– An index of the wear resistance and strength
Figure 9.43 Ultrasonic testing
Figure 9.44 Rockwell hardness tester
Source: Courtesy of Newage Testing Instruments, Inc.
Summary
• Quality must be built into a product
• A weld must be fit for service
• Important for both the welder and inspector to
know the appropriate level of weld
discontinuities
• Welds to an excessively high standard will
result in an excessively expensive product
• Producing high-quality welds is a matter of skill
and knowledge