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© 2012 Delmar, Cengage Learning Chapter 5 Shielded Metal Arc Welding of Pipe
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Introduction 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Introduction (cont'd.) Pipe uses –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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Figure 5-2 Typical specifications used when ordering tubing. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning Figure 5-3 Typical specifications used when ordering pipe. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Advantages of Welded Pipe Advantages –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
© 2012 Delmar, Cengage Learning Figure 5-6 The flow along a welded pipe is less turbulent than in a threaded pipe. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Practice Welds Major challenge –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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Figure 5-16 Root pass. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning Filler Pass After removing slag from weld groove –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
© 2012 Delmar, Cengage Learning FIGURE 5-20 The weld crater should be filled to prevent cracking and cleaned of slag before restarting the arc. Larry Jeffus
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning FIGURE 5-34 2G position. The pipe is fixed vertically, and the weld is made horizontally around it. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning FIGURE 5-39 5G horizontal fixed position. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning 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
© 2012 Delmar, Cengage Learning 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. © Cengage Learning 2012
© 2012 Delmar, Cengage Learning Summary Pipe welding –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
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