1. Testing and Inspection of Welds
Chapter 9
Testing and Inspection of Welds

2. 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 2

3. 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 3

4. 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 4

5. 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 5

6. 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 6

7. Figure 9.1 Uniformly scattered porosities
Figure 9.2 Clustered porosity

8. Figure 9.3 Linear porosity
Figure 9.4 Piping or wormhole porosity

9. 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 9

10. Figure 9.5 Nonmetallic inclusions

11. 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 11

12. Figure 9.6 Inadequate joint penetration

13. Figure 9.7 Incomplete root penetration

14. Incomplete Fusion Lack of coalescence Interpass cold lap
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 14

15. Figure 9.8 Incomplete fusion

16. 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 16

17. Figure 9.9 Gouge removal Remove gouges along the surface of the joint before welding

18. 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 18

19. Figure 9.10 Arc strikes Source: Courtesy of Larry Jeffus

20. 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 20

21. Figure 9.11 Rollover or overlap

22. 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 22

23. Figure 9.12 Undercut

24. 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 24

25. Figure 9.13 Crater or star cracks

26. 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 26

27. Figure 9.15 Underfill

28. 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 28

29. 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 29

30. Figure 9.16 Lamination and delamination

31. 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 31

32. 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 32

33. Figure 9.17 Lamellar tearing

34. Figure 9.19 Correct joint design to reduce lamellar tears

35. 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 35

36. Figure 9.22 Tensile specimen for flat plate weld Source: Courtesy of Hobart Brothers Company

37. 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 37

38. 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

39. 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 39

40. Figure 9.24 Transverse fillet weld shearing specimen after welding Source: Courtesy of Hobart Brothers Company

41. Figure 9.25 Longitudinal fillet weld shear specimen

42. 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 42

43. Figure 9.26 Nick-break specimens (A) Nick-break specimen for butt joints in plate and (B) method of rupturing nick-break specimen Source: Courtesy of Hobart Brothers Company

44. Figure 9.27 Root and face bend specimens for 3/8-in. (10-mm) plate

45. 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

46. 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 46

47. 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
Slag inclusions
Overlap
Porosity
Lack of fusion 47

48. 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

49. 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 49

50. 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 50

51. 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.

52. 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 52

53. Figure 9.35 Penetrant testing Source: Adapted from Magnaflux Corporation

54. Figure 9.36 Magnetic particle inspection Flaws and discontinuities interrupt magnetic fields Source: Adapted from Magnaflux Corporation

55. Figure 9.38 Schematic of an X-ray system

56. 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 56

57. Figure 9.43 Ultrasonic testing

58. Figure 9.44 Rockwell hardness tester Source: Courtesy of Newage Testing Instruments, Inc.

59. 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 59