1. Shielded Metal Arc Welding of Pipe
Chapter 5
Shielded Metal Arc Welding of Pipe

2. Objectives
Discuss three general categories of pipe welds, including how they are used and what type of weld root penetration and strength they require
Compare pipe to tubing
Discuss the advantages of welded pipe
Discuss the preparation needed before welding pipe
Explain the importance of not having arc strikes outside of the weld groove on pipe welds

3. Objectives (cont'd.) Explain the purpose of a hot pass
Describe the purpose of the root, filler, and cover passes for a pipe weld
Name advantages of the horizontal rolled pipe position
Describe the vertical fixed position and give advantages and disadvantages
Discuss how to make a weld in the horizontal fixed position
Describe the 45º fixed inclined position

4. Introduction Pipe welder Rewards of being a quality pipe welder
One of the most skilled welders
Mastering the skills takes a large commitment
Rewards of being a quality pipe welder
Better pay
Working with the best equipment
Having a helper for cleanup and setup

5. Introduction (cont'd.) Shielded metal arc welding
Well suited for pipe systems
Welded steel pipe uses
Factories
Power plants
Refineries
Building to carry liquids and gases

6. Introduction (cont'd.) Pipe uses Pipe welds categories
Ships, planes, and spacecraft
Handrails and building columns
Bicycles and motorcycles
Pipe welds categories
Low-pressure or light structural service
Medium-pressure or medium structural service
High-pressure or heavy structural service

7. Pipe and Tubing Different specifications and uses
Pipe sizes given by inside diameter
Tubing sizes given by outside diameter
Wall thickness of tubing measured in inches
Wall thickness of pipe determined by its pressure range

8. Figure 5-2 Typical specifications used when ordering tubing
Figure 5-2 Typical specifications used when ordering tubing. © Cengage Learning 2012

9. Figure 5-3 Typical specifications used when ordering pipe
Figure 5-3 Typical specifications used when ordering pipe. © Cengage Learning 2012

10. Pipe and Tubing (cont'd.)
Both available as welded or extruded
Most pipe that will be welded into a system carries liquids or gases
Small diameter flexible tubing
Carries pressurized liquids or gases
Rigid tubing
Used for structural appliances
This chapter
Term pipe will refer to pipe only

11. Advantages of Welded Pipe
Thickness and strength of the pipe and fitting is the same when welded
Resistant to leaks
Resist corrosion caused by electrochemical reactions
Less turbulence as material flows through the pipe
Threaded fittings are larger and weigh more than welded fittings

12. Figure 5-6 The flow along a welded pipe is less turbulent than in a threaded pipe.
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13. Advantages of Welded Pipe (cont'd.)
Other advantages
Ability to make specially angled fittings
Odd-shaped parts can be fabricated
Highly specialized equipment is not required
Easier alignment of parts
Removing, replacing, or changing parts is easy

14. Preparation and Fitup Important considerations
Ends of the pipe must be beveled
Bevel must be at the correct angle
Sharp inner edge should be ground flat
Forms a chafer
Final shaping done with a grinder
Root gap will be uniform
Root face
Controls penetration and root suck back

15. Preparation and Fitup (cont'd.)
Root suck back
Caused by surface tension of molten metal
Molten metal tries to pull itself into a ball
Forms a concave root surface
Fitting pipe and holding it in place
More difficult with larger diameter
Hold pipes in place with a vice for tack welding

16. Practice Welds Major challenge Electrodes
Learning how to transition from one position to another
Start with a large diameter pipe
Skills develop: use a smaller diameter pipe
Electrodes
E6010 or 6011 electrodes: complete the weld
E7018 electrodes: complete the joint or entire weld

17. Practice Welds (cont'd.)
Practice pipes used in a school shop
Shorter than those used in the industry
Avoid positioning yourself where longer pipe would eventually be located
Do not stand at the end of a short practice pipe

18. Weld Standards Weld quality is very important to the industry
Major parts of the weld come under a higher level of inspection
No arc strikes should be made on the surface of both sides of a weld
Arc strikes outside the weld area are defects
Try to avoid from the beginning

19. Root Weld First weld in a joint
Part of a series of welds that make up a multiple pass weld
Internal root face is the most important part
Inside of each welded joint must be smooth
Excessive penetration is known as icicles

20. Figure 5-16 Root pass.
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21. Hot Pass Burns out slag trapped on edge of the root pass
Can also reshape the root pass
Slag is mostly composed of silicon dioxide
Floated to surface by melting surrounding metal
Fast travel speed
Prevents burn-through
Forms a concave weld bead

22. Filler Pass After removing slag from weld groove Filler pass
It is ready to be filled
Filler pass
May be a series of stringer beads or a weave bead
Stringer beads require less skill
Done correctly, stringer beads are as strong as weave beads

23. FIGURE 5-20 The weld crater should be filled to prevent cracking and cleaned of slag before restarting the arc.
Larry Jeffus

24. Filler Pass (cont'd.) Weld bead
Must be cleaned before next electrode is started
Failure to clean the crater will result in slag inclusions
High-strength pipe: crater should be slightly ground
Bead goes around the pipe
Should continue past the starting point
Stagger starting and stopping spots for each pipe

25. Cover Pass Final covering on a weld
It may be a weave or a stringer bead
Should not be too wide
Should not have too much reinforcement
Excessively large cover passes reduces strength
Should be as uniform as possible

26. FIGURE 5-22 Excessively wide or built-up welds restrict pipe expansion at the joint, which may cause premature failure. Check the appropriate code or standard for exact specifications. © Cengage Learning 2012

27. 1G Horizontal Rolled Position
Characteristics
Penetration and buildup are more easily controlled
Weld visibility and welder comfort are improved
Welder fatigue is less of a problem
Pipe can be rolled continuously
Weld can be made in one continuous bead

28. 2G Vertical Fixed Position
Characteristics
Pipe is vertical and weld is horizontal
Welder does not need to change welding positions constantly
Area to be welded is often located in corners
Reaching back side of weld can be difficult
Welds must be done in the correct sequence

29. FIGURE 5-34 2G position. The pipe is fixed vertically, and the weld is made horizontally around it.
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30. 5G Horizontal Fixed Position
Characteristics
Root pass can be performed by welding uphill or downhill
Close parallel root opening can be welded uphill or downhill
Root opening that is wide or uneven must be welded uphill
Electrode angle should always be upward
Arc must always be struck inside the joint preparation groove

31. FIGURE 5-39 5G horizontal fixed position.
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32. 6G 45 Degree Inclined Position
Characteristics
Most difficult pipe position
Qualifying in this position will certify welder in other positions using same-size electrodes and pipe sizes
Must continuously change weld pattern, electrode angle, and weld speed
Small multipass stringer beads work best
Weave beads are possible

33. FIGURE 5-43 In the 6G position, the pipe is fixed at a 45º angle to the work surface. The effective welding angle changes as the weld progresses around the pipe.
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34. Summary Pipe welding Experienced welders Good pipe welded joint
Looked upon by many as the pinnacle of the welding trade
Presents its own challenges because of the constantly changing weld position
Experienced welders
Spend a significant amount of time in preparation
Control weld size
Good pipe welded joint
May have many small weld passes