1. Advanced Shielded Metal Arc Welding
Chapter 6
Advanced Shielded Metal Arc Welding

2. Objectives Discuss how metal must be prepared before welding
Describe the process, and demonstrate making the root pass, filler weld, and cover pass in all positions and techniques
Explain the purpose of a hot pass
Tell what should be checked with a visual inspection, and describe the appearance of an acceptable weld

3. Objectives (cont'd.) Demonstrate how to make:
A root pass on plate in all positions
A root pass on plate with an open root in all positions
An open root weld on plate using the step technique in all positions
A multiple pass filler weld on a V-joint in all positions using E7018 electrodes
A cover bead in all positions

4. Objectives (cont'd.)
A single V-groove open root butt joint with an increasing root opening
A single V-groove open root butt joint with a decreasing root opening
SMAW welds of plate to plate
SMAW welds of pipe to pipe

5. Introduction SMAW process produces high-quality welds
Welders frequently make welds in difficult situations to a code or standard
Metal edges must be prepared
100% joint penetration
Code-quality welds
Metal thicker than ¼ inch
Preparation improves strength
Prepared joints require more than one weld pass

6. Introduction (cont'd.) Root pass Hot pass
Fuses and seals parts together
Hot pass
Improves weld contour
A test for one company may not qualify a welder for another company
AWS Certified Welder program
Available from AWS's office in Miami, Florida

7. Root Pass First of a multiple pass weld Fuses two parts together
Establishes depth of weld metal penetration
Needed to obtain a sound weld
May be open or closed
Can use a backing strip or backing ring
Backing strip used in a closed root can remain as part of the weld or be removed
Removable backup tapes have been developed
Tape can be peeled off after weld is completed

8. FIGURE 6-2 Root pass maximum deposit 1/4 in. (6 mm) thick.
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9. Root Pass (cont'd.) Widely used in plate and pipe designs
Face side is not as important as root surface on back or inside
If root surface is correct: front side can be ground, gouged, or burned out
Weld is evaluated from root side only
Root face for most grooves will be about the same size

10. FIGURE 6-4 Using back gouging to ensure a sound weld root.
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11. Root Pass (cont'd.)
Control penetration on joints with varying root gaps
Stepping electrode manipulation
Key hole
Electrode is moved in and out of molten weld pool
Metal flows through key hole to root surface
Key hole ensures 100% penetration
Process requires more welder skill

12. FIGURE 6-7 Electrode movement to open and use a key hole.
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13. Hot Pass Surface of a root pass may be irregular
High-strength code welds
Root pass and each filler pass must be ground
Grinding is important when high-strength, low alloy welding electrodes are used
Hot pass
Cleans out trapped slag
Makes a root pass more uniform
Uses high amperage and a fast travel rate
Rapidly melts a large surface area

14. Hot Pass (cont'd.) Small amount of metal should be deposited
Resulting weld is concave
Concave weld is easier cleaned
Failure to clean a convex root leaves wagon tracks
Can be used to repair or fill small spots
Incomplete fusion or pinholes
Normal weave pattern
Straight step or “T” pattern

15. FIGURE 6-19 Slag trapped between passes will show on an X ray.
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16. Hot Pass (cont'd.) Key points
Do not allow molten weld pool to cool completely
Do not blow shielding gas covering away from the molten weld pool
Penetration of the molten weld pool must be deep
Free all trapped slag
All porosity must be burned out

17. Filler Pass Fills groove after root pass Characteristics
Made with stringer or weave beads
Characteristics
Weld beads must overlap
Stringer beads overlap 50%
Weave beads overlap 25%
Finish bead is smooth
Each weld bead must be cleaned before the next bead is started

18. FIGURE 6-24 Filler pass buildup sequence.
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19. Filler Pass (cont'd.) Ways to remove slag between filler weld passes
Chipping, wire brushing, and grinding
Weld can be checked by ultrasonic or radiographic nondestructive testing
Most schools are not equipped to do this testing
Check soundness by destructive testing

20. Cover Pass Last weld bead on a multipass
May use a different electrode weave
Must be uniform and neat looking
Appearance might be the only factor in accepting or rejecting welds
Should not be more than 1/8 inch wider than the groove opening

21. FIGURE 6-26 The cover pass should not be excessively large.
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22. Plate Preparation Weld groove prepares the plate
Can be cut into one side or both sides
May be cut into one or both plates of the joint
Depth, angle, and location
Determined by a code standard
SMA welds on plate 1/4 inch or thicker that need to have a weld with 100% joint penetration
Plate must be grooved
May be ground, flame cut, gouged, or machined

23. Plate Preparation (cont'd.)
Bevels and V-grooves
Best if cut before parts are assembled
J-grooves and U-grooves
Can be cut either before or after assembly
Groove on both sides
Tee joints, welds with little distortion, and welds that will be loaded equally from both sides
Back gouging
Cuts a groove in back side of a joint that has been welded

24. FIGURE 6-29 Typical butt joint preparations.
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25. Preparing Specimens for Testing
Maximum allowable size for fissures in a guided-bend test
Given in codes for specific applications
Some standards are listed
ASTM E190
AWS QC10
AWS QC11
Copies available from appropriate organization

26. Acceptance Criteria for Face Bends and Root Bends
Key points
Weld is uniform
No arc strikes on the plate other than the weld
Free of incomplete fusion and cracks
Penetration must be 100% or as specified
Weld must be free of overlap
Correct weld specimen preparation is essential

27. Acceptance Criteria for Face Bends and Root Bends (cont'd.)
Specimen cut out of test weldment
Abrasive disc
Sawing
Cutting with a torch
Flame-cut specimens
Grind or smooth the edges
All corners must be rounded
Radius of 1/8 inch maximum
Grinding or machining marks must run lengthwise

28. Restarting a Weld Bead Welding bead must be restarted
After stopping to change electrodes
Weld bead near completion
Should be tapered
Increase the travel rate
Before restarting
Chip slag and clean weld crater
Restart the arc in the joint ahead of the weld
Electrodes must be allowed to heat up

29. Restarting a Weld Bead (cont'd.)
Movement to root of weld and back up on bead
Builds up weld
Reheats metal
Avoid starting and stopping weld beads in corners
Tapering and restarting are especially difficult in corners
Often results in defects

30. Preheating and Postheating
Application of heat to metal before welding
Helps to reduce:
Cracking
Hardness
Distortion
Stresses

31. Preheating and Postheating (cont'd.)
Preheating is often required:
On large thick plates
When plate is very cold
When temperature is very cold
When using small diameter electrodes
On high-carbon or manganese steels
On complex shapes
With fast welding speeds

32. Preheating and Postheating (cont'd.)
Applies heat to metal after welding
Used to slow the cooling rate
Reduces hardening
Interpass temperature
Temperature of metal during welding
Given as a minimum and maximum

33. Poor Fitup Some welding must be done on joints that are poorly fitted
Requires a good welder
Skilled welders can watch the molten weld pool and knows how to avoid disaster
Considerations
Amperage setting may have to be adjusted
May be necessary to break and restart the arc
May need to change the electrode angle

34. Summary Grooved welds on one-half inch thick plate Grooved welds
Most common test plates
Grooved welds
Used by many companies in testing
Vertical and overhead positions
Most common positions used in testing
Visually defect-free welds
Assumed to pass destructive testing
Always make welds as uniform as possible