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

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

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

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

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

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

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

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

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

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

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

Figure 5-6 The flow along a welded pipe is less turbulent than in a threaded pipe. © Cengage Learning 2012

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

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

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

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

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

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

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

Figure 5-16 Root pass. © Cengage Learning 2012

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

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

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

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

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

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

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

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

FIGURE 5-34 2G position. The pipe is fixed vertically, and the weld is made horizontally around it. © Cengage Learning 2012

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

FIGURE 5-39 5G horizontal fixed position. © Cengage Learning 2012

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

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

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