1. Weld Quality & Weld Testing

2. What is unique about the Eisenhower Interstate Highway System?
One in every 5 miles is straight, this can be used as airstrips in times of war and other emergencies

4. Weld Quality and Weld Testing
Learning Activities
View Slides;
Read Notes,
Listen to lecture
Do on-line workbook
Do homework
Lesson Objectives
When you finish this lesson you will understand:
Causes and prevention of discontinuities
Testing for assessing the effect of discontinuities when present in a weld
Keywords
Discontinuity, Porosity, Slag Inclusion, Lack of Fusion, Incomplete Root Penetration, Overlap, Undercut, Excessive Penetration, Root Concavity, Spatter, Cracks, Tensile Test, Bend Test, Fatigue Test, Corrosion Test

5. Each Weldment Should Be:
Adequately Designed to meet the intended service for the required life
Fabricated with specified materials and in accordance with the design concepts
Operated and maintained properly
The quality of any weldment depends on a number of factors:
Was it designed adequately to meet its intended purpose?
Was it fabricated with care selecting appropriate materials and welding procedures to avoid defects?
Was it operated and maintained as originally intended?
Only when all of these conditions are met can one say that weldment was of sufficient quality.

6. Welds are examined in regard to: Size Shape Contour Soundness
Other Features as Specified
To assure quality of weld workmanship the welds are examined with the factors listed above in mind.

7. Effect of Discontinuities on Properties
Welding Code
Effect of Discontinuities on Properties
Discontinuities in a welded joint can influence mechanical properties
Codes establish size limits for acceptable discontinuities
Discontinuities unacceptable by a given code are called defects and are subject to repair
Stress applied to a material is magnified by flaws in the material, e.g., cracks. A stress intensity factor quantifies this magnification of the applied stress. The fracture toughness of a material is the critical value of this stress intensity factor that causes fracture.
The term Engineering Critical Assessment is used for the analysis of a structure that has flaws (cracks) and will be subjected to stress. Several factors must be considered in order to make a realistic prediction of the likelihood of catastrophic (brittle) failure of such a structure: temperature, crack geometry, magnitude of the stress, strain rate, and yield strength of the material.

8. Classification of Weld Joint Discontinuities
Welding Process or Procedure Related Discontinuities
Metallurgical Discontinuities
Design Related Discontinuities
When discontinuities are discovered in a weldment, they can be generally sorted into one of the three classification listed above. Did they occur as a result of the selection of the wrong process or procedure, did they occur because of some metallurgical inconsistency, or did they occur because of a miscalculation in the design process? It should be noted that even though a discontinuity is detected, is is not classified as a defect unless it of sufficient size or severity to render the weldment unserviceable or suspect in service. Codes and standards are clear on the point where discontinuities become defects and they should be consulted for quality concerns.

9. Classification of Weld Joint Discontinuities
Welding Process or Procedure Related Discontinuities
Geometric
Misalignment
Undercut
Concavity or Convexity
Excessive Reinforcement
Improper Reinforcement
Overlap
Burn-through
Backing left on
Incomplete Penetration
Lack of Fusion
Shrinkage
Surface Irregularities
Other
Arc Strikes
Slag Inclusions
Tungsten Inclusions
Oxide Films
Spatter
Arc Craters
The tables above list various discontinuities classified as welding process or procedure related discontinuities. Some examples of these are shown in the next slide.

10. Examples of welding process or procedure related discontinuities.

11. Classification of Weld Joint Discontinuities
Metallurgical Discontinuities
Cracks or Fissures
Hot
Cold or Delayed
Reheat
Stress-Relief
Strain-age
Lamellar Tearing
Heat-Affected Zone Microstructural Alterations
Weld Metal & HAZ Segregation
The above table list various metallurgical related discontinuities.
Porosity
Spherical
Elongated
Worm-hole
Base Plate Laminations

12. Classification of Weld Joint Discontinuities
Design Related Discontinuities
Changes in Section & Other Stress Concentrators
Weld Joint Type
And finally, the above tale lists design related discontinuities.

13. Supplemental
Work
Open the web page under “Demonstrations” and do the exercise entitled “Discontinuities

14. Supplemental
Work
Pages 364 through 367 of the Welding Handbook list table of Common Causes and Remedies like the one on the Right. Review these tables to gain insight about Discontinuities

15. Questions?
Turn to the person sitting next to you and discuss (1 min.):
From a general point of view, how would you rank the following discontinuities in their severity to weld properties: Hot Cracks, Change in section size, Porosity, ? Why

16. Welding Discontinuities
Porosity
Porosity is the entrapment of small volumes of gas in solidifying weld metal
Prevention
Drying consumables
Cleaning, degreasing material being welded
Electrode or filler metals with higher level of deoxidants
Sealing air leaks, reducing excess shielding gas flow
Molten weld metal is able to hold more gas than solid weld metal. For this reason, gas bubbles tend to evolve as the liquid metal solidifies. These gas bubbles trapped within the solid weld metal are referred to as porosity. Although porosity is sometimes noted at the surface of a weld, visual inspection cannot detect internal porosity. Radiography and ultrasonic methods are required. Localized regions of porosity can be cut from a weld; a repair is then made. For general porosity throughout a weld, the entire weld must be gouged out and rewelded. T

17. Welding Discontinuities
Slag inclusions
Slag inclusions are irregularly shaped, not spherical like porosity
Prevention
Position work and/or change electrode/flux to increase slag control
Better slag removal between passes
Dress weld surface smooth if it is likely to cause slag traps
Remove heavy mill scale on plate
Slag inclusions, as the name implies, are small pieces of welding slag which are trapped in the weld metal. Unlike porosity, which is usually spherical, slag inclusions are irregularly shaped. Since these are internal discontinuities, radiography or ultrasonic testing is required for detection. Weld regions containing slag inclusions must be cut out and rewelded. T

18. Welding Discontinuities
Lack of Fusion
Lack of fusion is caused by incorrect welding conditions
Prevention
Procedure for complete fusion should be verified by testing
Increased energy input
Correct electrode angle and work position
Lack of fusion can occur at the weld sidewall, root, or between individual passes. Magnetic particle and dye or fluorescent penetrant may be used to detect this discontinuity if it reaches the surface. Otherwise, radiography or ultrasonic methods must be used. Affected regions must be cut out and rewelded. T

19. Incomplete Root Penetration
Welding Discontinuities
Incomplete Root Penetration
Incomplete root penetration can be caused by
Excessively thick root face, insufficient root gap
Incorrect welding conditions
Misalignment of second weld
Prevention
Improved joint preparation
Test weld verifications for correct parameters
Reassessment of back gouging
Incomplete root penetration is the failure of a weld to extend into the root of a joint. For a double weld, it is an internal discontinuity and can be detected only by radiography or ultrasonic testing. It can be detected by magnetic particle, and dye or fluorescent penetrant methods if the root side is accessible. A long pipeline would be an example of when the weld root (inside the pipe) would not be accessible. This defect is repaired by cutting it out and rewelding. T

20. Welding Discontinuities
Overlap
Overlap is an imperfection at the weld toe or root caused by metal flowing onto the surface of the base metal without fusing to it
Prevention
Adjust electrode manipulation to ensure fusion of base metal
Limit size of fillet to 9-mm leg length
Overlap is often associated with horizontal welding; welding in the flat position can help to eliminate this problem. Overlap can be detected visually and can be supplemented with dye penetrant. It is corrected by cutting back to sound weld metal. Rewelding may be necessary. T

21. Welding Discontinuities
Undercut
Undercut is an irregular groove at the weld toe in the parent metal or previous pass caused by
excessive weaving
melting of top edge of fillet weld with high current
Prevention
Weld in flat position
Change shielding gas to one which produces better wetting
Terminate welds so they don’t finish at a free edge
Undercut is another defect that can be associated with horizontal welding among other factors such as high current and excessive weaving. Flat position welding can aid in eliminating this discontinuity. It is detected visually and measured by a depth gauge. Deep undercut is ground out and weld repaired. T

22. Excessive Penetration
Welding Discontinuities
Excessive Penetration
Excessive penetration is caused by
Incorrect assembly or preparation
Edge preparation too thin to support weld underbead
Excessive root gap
Energy input too high
Lack of operator skill
Prevention
Control of preparation, backing bars
Maintaining uniform root penetration requires great skill on the part of the welder, especially when welding butted pipe ends. Excessive root penetration is detected visually; however in the case of pipelines, radiography is used if the pipe bore cannot be examined. Excessive penetration is corrected by such dressing operations as grinding. In piping, it is corrected by broaching. T

23. Welding Discontinuities
Root Concavity
Root concavity is caused by
Excessively thick root face
Insufficient arc energy for penetration
Excessive backing gas pressure
Prevention
Reduce root face thickness, control backing gas pressure
Establish a procedure by test welding
Root concavity involves the weld metal being forced out of the root by such mechanisms as excessive backing pressure or the wicking action of the joint preparation. It is detected visually if the root is accessible; otherwise, it is detected by radiography. It can be corrected by adding extra weld metal from the root side. If the root is inaccessible, the joint must be cut out and rewelded. T

24. Welding Discontinuities
Spatter
Spatter consists of small droplets of electrode material that land beside the weld and may or may not fuse to the base material
Prevention
Reduce energy input
Shorter arc length
Reposition current return clamp to reduce magnetic arc blow or switch to AC current
As metal drops transfer from the electrode to the weld pool, some are blown clear of the weld and form drops of spatter on the base plate. All open arc consumable electrode processes produce some spatter.
Spatter can occur when the energy input is too high or when the arc length is excessive. Arc blow can also cause spatter, as can insufficient inductance in GMAW or CO2 welding.
Spatter can be detected visually. It can be removed by scraping or by light grinding. Anti-spatter coatings are available on the market that prevent spatter from adhering to the base material. T

25. Questions?
Turn to the person sitting next to you and discuss (1 min.):
We have just looked at a list of discontinuities and preventative measures. How does this information effect the opinions of people involved in writing codes for proper welding conditions?

26. Weld Test Samples Help Reveal Discontinuities and Defects
In the process of determining if an acceptable weld can be made with new materials or by some new process or procedure, it is often helpful to make a test weld and then run some standard mechanical tests on the weld in order to reveal the presence of discontinuities or defects. Following are some of the most common test performed.

27. Tensile tests are perhaps the most often used mechanical test for determining weld quality. As seen from this figure, different size (shape) tensile samples are used depending on if all weld metal properties are required, or cross weld properties, or all base metal properties are required. In addition, often samples are taken in different directions in the plate or weldment as plate rolling often produced anisotropy in mechanical properties and the property in one direction may not be the same as in another.

28. When load carry capacity of weld, particularly fillet welds, are required, weld test coupons like the ones illustrated here are often used. These will give values for the fillet weld strength when loaded longitudinally and transverse.

29. Another test which is often used to determine the quality of test welds is the bend test. In this test, slices are cut across the weld and the slice is then bent in a three point bending unit. The orientation of the slice can be changed from root bend, where the root of the weld is bent so that it is in tension; a face bend, where the face of the weld is in tension; and a side bend where the weld cross section is placed in tension. A root bend will reveal discontinuities in the root such as incomplete penetration. The face bend will reveal discontinuities in the face such as undercut and microcracks. The side bend will reveal lack of fusion and other internal discontinuities.

30. For welds which might find applications in fatigue conditions, a series of fatigue tests might be run. Note that there is a clear distinction between samples welded with different procedures.

31. multiple initiation sites
Fatigue Design
Fatigue Appearance
Distinct fracture surface has a characteristic texture
Concentric line pattern
Smooth portion referred to as clamshell texture
The surface of a fatigue fracture has a characteristic appearance. A concentric line pattern is noted to grow outward from an initiation point. In welding, this initiation point could be associated with a slag intrusion, undercut, or other discontinuity associated with the welding process.
The concentric line pattern provides a visual record of the accumulated crack growth from the initiation site with continued cyclic loading. The fracture surface near the initiation site is generally smooth and is noted to have a clamshell-like texture. If more than one initiation site is present, the fatigue cracks, often growing on different planes, will link up to form a unified crack front.
When the cross section of the material is no longer able to support the load, failure (sometimes sudden, catastrophic) occurs. In these instances, the ends of the fatigue crack can spontaneously start to run at high speeds due to the stress concentration. In cases of brittle fracture in pipelines, longitudinal cracks have been know to run several hundreds of yards before stopping.
multiple initiation sites

32. Welds which must find service in corrosive environments often are immersed in corrosive media and given a corrosion test. Depending upon the location of greatest corrosion, valuable information can be obtained about service life of the weldment.

33. Homework