Shield Metal Arc Welding of Pipe

OBJECTIVES

After completing this chapter, the student should be able to

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 groov

on pipe welds.

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 45° fixed inclined position.

KEY TERMS

concave root surface

fixed inclined position

horizontal fixed pipe position

horizontal rolled pipe position

icicles

land

pIpe

INTRODUCTION

pressure range

root face

root gap

root suck back

tubing

vertical fixed pipe position

welding uphill or downhill

104

The pipe welder is considered by some other welders to be one of the most skilled welders'the industry. Often pipe welders share a great deal of pride. Some finished welded piping systeare considered works of art. Mastering the skills required to be a master pipe welder often takes~

large commitment on the pan of the welding student, but this commitment is well rewarded ~

the industry. The rewards of being a quality pipe welder include earning better pay. workingwiuthe best equipment, and often having a helper to do the less glamorous jobs of cleanup and setui

106 Section 2 Shielded Metal Arc Welding

TUBING

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20' x 2' OD x 20 GAUGE LOW CARBON, ROUND, MECHANICAL, COLD DRAWN WELDED TUBING

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2' (51 mm) _ 20 GA [.035' (0.8mm))L.~..--~ WALL THICKNESS

OUTSIDEDIAMETER

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'0' x " OD x 20 GAUGE 304 STAINLESS STEEL, ROUND, HYDRAULIC-LINE, COLD DRAWN, SEAMLESS, SOFT ANNEALED, TU81NG

L-----t~------," l2S mm)

O\1't.\E.1E.R:;:.-.------ 20 GA [.035" (0.8 mm)li WALL THICKNESS /

FIGURE 5-2 Typical specifications used when ordering tubing.

tubing to withstand compression, bending, or twistingloads. Tubing should also be specified as rigid or nexible.

Pipe and tubing are both available as welded (seamed)or extruded (seamless).

Most pipe that will be welded into a system is used tocarry liquids or gases from one place to anot1}er. Thesesystems may be designed to carry large or small quantitiesor materials having a wide range of pressures. Small diameter pipe may be used for some structural applications,but usually only on a limited scale.

Small diameter nexible tubing is commonly used to carrypressurized liquids or gases. Ridged tubing is normally used[or structural applications. Some tubing is designed [or specific purposes, such as electrical mechanical tubing (EMT),which is used to protect electrical wiring. Tubing can be usedto replace some standard structural shapes such as I-beams,channels, and angles [or buildings. Tubing is also available insizes that will slide one inside the other to be used in placeswhere telescoping tubing is required, Figure 5-4.

In this chapter, the term pipe will refer to pipe only.However, it should be understood that the weldingsequence, procedures, and skill can also be used on thickwall round tubing.

Advantages of Welded Pipe Most pipe I 1/2 in.(38 mm) in diameter and all steel pipe 2 in. (51 mm) andlarger are generally arc welded. Welded piping systems,compared to pipe joined by any other method, arestronger, require less maintenance, last for longer periodsof time, allow smoother now I and weigh less.

StrengthThe thickness o[ the pipe and fitting is the same when

they are welded together. Threaded pipe is weakenedbecause the threads reduce the wall thickness o[ the pipe,Figure 5-5.

Less Maintenance RequiredOver much time and use, welded pipe joints are resis·

tant to leaks.

Longer LastingWelded pipe joints resist corrosion caused by electro

chemical reactions because all the parts are made of thesame types o[ metal. Small cracks belween the threads onthreaded pipe are likely spots [or corrosion to start.

Chapter 5 Shielded Metal Arc Welding of Pipe 107

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PIPE

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114' (356 mm)OUTSIDEDIAMETER

10' x 2" SCHEDULE 40, 6061-T6 ALUMINUM, EXTRUDED SEAMLESS, THREADED PIPE

2" (51 mm)INSIDEDIAMETER

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20' x 14" SCHEDULE 10, CARBON STEEL, WELDED, PLAIN END, PIPE

FIGURE 5,) Typical specifications used when ordering pipe.

"rFIGURE 5-4 Space shuttle launch tower is constructed using round and rectangular tubing, much of which slides outof the way during launch preparation. Courtesy of NASA.


PIPEWALL

THICKNESS

WELDEDJOINT

THICKNESS

WELDED JOINT

(A)

THREADED JOINT

+PIPE WALL

THICKNESSt

--------.".--/

{ \I \I I\ J\ I

--------~/

{

II\\

THREAD JOINTTHICKNESS

(8)FIGURE 5-5 The welded joint (A) is thicker than the original pipe; the threaded joint (B) is thinner than the original pipe.

FIGURE 5-6 The flow along a welded pipe is less turbulent than that in a threaded pipe.

piping systems may be several miles in length. Lowereresistance to product Dow can save on operating enercosts.

Lighter WeightThreaded fittings are larger and weigh more lhan

welded fittings and joints. The weight savings whenwelded joints are used for an aircraft means that it can fitlonger and faster and can carry a larger load for Imoney. Buildings and factories will also realize a savingsbecause welded points are less expensive.

Other advantages of welded pipe include the following.

• An ability to make specially angled fittings by CUl

ling existing fittings, Figure 5-7.

• Odd-shaped parts can be fabricaled.

• A lot of highly specialized equipment is notrequired for each di£ferent size of pipe.

• Alignment of parts is easier. It is not necessary toovertighten or undertighten fittings so that they willline up.

FLOW

FLOW-

WELDED JOINT~

THREADED JOINT

Smoother FlowThe inside of a welded fitting is the same size as the

pipe itself. As material flows through the pipe, less turbulence is caused by unequal diameters, Figure 5-6. Large

PLATE

PIPE HELD IN POSITION BYCLAMPS FOR CUTItNG

PIPE

BASE PLATE

FIGURE 5-9 Turntable built from a front wheel assembly.

FIGURE 5-10 The 37 1120 angled joint may use nearly50% less filler metal, time, and heat, as compared tothe 45 0 angled joint.

FRONT WHEELHUB AND SPINDLE

Final shaping should be done with a grinder so that theroot gap will be uniform.

The bevel on the end of the pipe can be machine cutusing a portable pipe beveling machine, Figure 5-8, or ahand-held torch. Chapter 7 describes how to set up andoperate name-cutting equipment. A turntable, similar to

the one shown in Figure 5-9, can be made in the schoolshop and used for beveling short pieces of pipe. Theturntable can be used vertically or horizontally. By turning the table slowly with pipe held between the clamps, ahand torch can be used to produce smooth pipe bevels.Large-production welding shops may also use machinesdesigned speCifically for beveling pipe. These machineswill accurately cut a 37 1/20 angle on the pipe.

The 37 1/20 angle allows easy access for the electrodewith a minimum amount or Hiler metal required to HII thegroove, Figure 5-10.

The root face will help a welder control both penetration and root suck back. Penetration control is improved

Chapter 5 Shielded Metal Arc Welding oj Pipe 109

~900 FITIING

, ,45° ,

\\\

cUTr>~~:::~'~~,7/"\ I

\ 800\:

75°\ \ \\ I \\ I \I IJ

------ ..., ,I--

FIGURE 5-8 Pipe beveling machine. courtesy of ESCO Tool Co.

• Removing, replacing, or changing parts is easybecause special connections are not needed toremove the parts.

Preparation and FitupThe ends of pipe must be beveled for maximum perre

lrallon and high joint strength. The end can be beveled byname cutting, machining, grinding, or a combinationprocess. It is important that the bevel be at the correClangle, aboUl37 1/20 depending on specifications, and thatthe end meet squarely with the mating pipe. The sharp orfeathered inner edge of the bevel should be ground natforming achamfer. This area is called a root face or land.

FIGURE 5-7 A standard 90 0 fitting can be cut to anyspecial angle that is needed.

ANGLE IRON

TACK WELD

Pradice WeldsOne of the major problems to be overcome in pipe

welding is learning how to make the transition from oneposition to another. The rate of change in welding position is slower with large diameter pipes, but the large

CHAIN CLAMP

Figure 5-1L The root face allows a larger molten weldpool to be controlled, and because of the increased size ofthe molten weld pool, it is not so affected by surface tension, Figure 5-12,

Fitting pipe together and holding it in place for weidingbecome more difficult as the diameter of the pipe ge~

larger, Devices for clamping and holding pipe in place areavailable, or a series of wedges and dogs can be used,Figure 5-13, In the Practices for this chapter, the pieces ofpipe the welder will be using are about 1 1/2 in, (38 mm)in diameter. However, when welding on larger diameterpipe sizes, the weld specimens must be larger than 1 1/2 in,(38 mm), Welds on larger pipe sizes need more metal tohelp absorb the higher heat required to make these weids,

A welder can use a vise to hold the pipes in place forlack welding, If the pipe is not round and does not alignproperly, first tack weld the pipe together and thenquickly hit the tack while holding the pipe over the homon an anvil, Figure 5-14. This action will force the pipeinto alignment. For pipe that is too distorted to be forcedinto alignment in this manner, a welder must grind downthe high points to ensure a good fit.

UNALIGNED PIPE

DOG

ANVIL/

FIGURE 5-14 Hitting a hot tack weld can align a pipe joint,

FIGURE 5-13 Shop fabrications used to align pipe joints,

SURFACETENSION

, I, I

, I\ I

l.-..---------""'1"---~-

'L CONCAVE ROOTSURFACE

FIGURE 5-11 Root surface concavity,

HEAT

FIGURE 5-12 Heat is drawn out of the molten weldpool, and surface tension holds the pool in place,


because there is more metal near the edge to absorb excessive arc heal. This makes machine adjustments less crilical by allowing the molten weld pool to be quickly cooledbetween each electrode movement. Root suck back iscaused by the surface tension of the molten metal tryingto pull itself into a ball, forming a concave root surface,

E7018 USED FORROOT, FILLER,AND COVER PASSES

/

Weld 5tandards Weld quality is very important to thepipe welding industry. Like other welds, the major parts ofthe weld come under a higher level of inspection. However,the surface of the pipe on both sides of the weld is alsoimportant. No arc strikes should be made on this surface.Arc strikes outside of the weld groove are considered to bedefects by much of the pipe welding industry. Arc strikesform small hardness spots, which, if not remelted by theweld, will crack as the pipe expands and contracts with heatand pcessure changes. Thus, they are a defect and must beremoved and the area repaired. This removal under somestandards may simply involve grinding them off, but undersome codes they must be treated like any other defect, anda special weld repair procedure must be followed. Becauseof the importance of not having arc strikes outside the weldgroove on pipe welds, you should try to avoid them from thebeginning. In Chapter 4, Experiment 4-2, several techniques are described to avoid arc strikes outside of the welding zone. You may want to refer back to this section if youhave difficulty in making arc starts accurately.

Root Weld A root weld is the first weld in a Jomt,Figure 5-16. It is part of a series of welds that make up amultiple pass weld. The root weld is used to establish thecan lOur and depth of penetration. The most importantpart of a root weld is the internal root face, or, in the caseof pipe, the inside surface. The face, or outside shape, orcontour of the roo I weld is not so important.

INCOMPLETE ROOTFACE PENETRATION

CONCAVE ROOT FACE

POOR ROOT PASSES

E7018 USED FOR FILLERAND COVER PASSES

/

E6010 OR E6011 USED E6010 OR E6011 USEDFOR ROOT, FILLER, FOR ROOT PASSAND COVER PASSES

FIGURE 5·15 Single or multiple types of electrodes may be used when producing a pipe weld. The electrode selectedis most often controlled by a code or specification.

COMPLETE ROOTFACE PENETRATION

FIGURE 5·16 Root pass.

GOOD ROOT PASS


diameter pipes require more time to weld. When a welderfirst starts welding, a large diameter pipe should be usedin order LO make learning this transition easier. As weldersd"'e!op skill and the technique of pipe welding, they canchange to the small diameter pipe sizes. Pipe as small as 3m. (76 10m) can be welded quickly. It is large enough forthe welder to be able to cut oul test specimens.

Pipe used for these practice welds should be no shorterthan I 112 in. (38 mm). Pipe that is shorter than 1 1/2 in.(38 mm) rapidly becomes overheated, making weldingmore difficult.

To progress more quickly with pipe welds, a weldershould master grooved plate welds. Once plate welding ismastered in all positions. pipe skills are faster and easierto develop.

Pipe welding is either performed with E6010 or E6011electrodes for the complete weld, or these electrodes areused for the root pass, and E7018 electrodes are used tocomplete Ihe joint. Pipe welding can also be done usingthe E7018 electrode for the entire weld, Figure 5-15.

The practice pieces of pipe used in the school shopare much shorter than the pieces of pipe used in industry. When learning to weld on short pipe, it is a goodIdea to avoid positioning oneself where longer pipewould eventually be located. Ohen it is easier to standat the end of a pipe rather than to one side; however,thiS cannot be done if the weld is being made on a fulllenglh of pipe,


FIGURE 5-18 Filler pass using stringer beads. Courtesy of

Larry Jeffus.

FIGURE 5-19 Filler pass using weave bead. The beadwidth should not be more than two times the roddiameter. Courtesy of Larry Jeffus.

BEAD WIDTH

1"4 (6 mm)

5"16 (8 mm)

3"8 (10 mm)

ELECTRODEDIAMETER

1"8 (3 mm)

5"32 (4 mm)

3"16 (4.8 mm)

In order for cleaners (pigs) to be used in a pipeline, theinside of each welded joint must be smooth, Figure 5-17.Excessive penetration, known as icicles, gets in the wayof cleaning, adds resistance to now, and will cause weakened points on the weld. On some piping systems, consumable inserts or backing rings are used to controlpenetration and the inside contour. Most pipe welds aremade without these devices to control penetration.

The face of a root weld is not important if the root surfaceis clean, smooth, and uniform. A grinder is used to removeexcessive buildup and reshape the face of the root pass. Thisgrinding removes slag along the sides of the weld bead andmakes it easier to add the next pass. Not all root passes areground. Pipe that is to be used in low- and medium-pressuresystems is not usually ground. Grinding each root pass takesextra time and does not give the welder the experience ofusing a hot pass. Most slag must be completely removed bychipping and wire brushing before the hot pass is used.

If you need morc experience or practice in making anopen root weld, refer to Chapter 4.

Hot Pass The hot pass is used to quickly burn out smallamounts of slag trapped along the edge of the root pass.This is slag that cannot be removed easily by chipping orwire brushing. The hot pass can also be used to reshapethe root pass by using high current settings and a fasterthan normal travel speed.

Slag is mostly composed of silicon dioxide, whichmelts at about 3100°F (l705°C). Steel melts at approximately 2600°F (l440°C). A temperature of more than500°F (2700C) hotter than the surrounding metal isrequired to melt slag. The slag can be floated to the surface by melting the surrounding metal. A high current willquickly melt enough surface to allow the slag to float free;a fast travel speed will prevent burnthrough. The fasttravel speed [onus a concave weld bead that is easy toclean for the welds that will follow.

FIGURE 5·17 The root face must be uniform. Courtesy of

Larry Jeffus.


Filler Pass After thoroughly removing slag from the weldgroove by chipping, wire brushing, or grinding, it is ready tobe filled. The finer pass(es) may be either a series of stringerbeads, Figure 5-18, or a weave bead, Figure 5-19. Stringerbeads require less welder skill because of the small amountof metal that is molten at one time. Ifdone correctly, stringerbeads are as strong as weave beads.

The weld bead crater must be cleaned before the nextelectrode is started. Failure to clean the crater will resullIn slag inclusions. On high-strength, high-pressure pipe

fiGURE 5·20 The weld crater should be filled to prevent cracking and cleaned of slag before restarting thearc. Courtesy of larry Jeffus.

welds, the crater should be slightly ground to ensure ilScleanliness, Figure 5-20. When the bead has gone completely around the pipe, it should continue past the starting point so that good fusion is ensured, Figure 5-21. Thelocations of starting and stopping SPOlS for each weld passmust be staggered. The weld groove should be filled levelwith these beads so that it is ready for the cover pass.

Cover Pass The final covering on a weld is referred to asthe cover pass or cap. It may be a weave or stringer bead.The cover pass should not be too wide or have too muchreinforcement, Figure 5-22. Cover passes that are excessively large will reduce the pipe's strength, not increase it.

A large cover pass will cause the stresses in the pipe to beconcentrated at the sides of the weld. An oversized weld

FIGURE 5·21 AVDid starting and stDpping all weldpasses in the same area. Courtesy of larry Jeffus.

MAX. COVER PASS

REINFORCEMENT r (3 mm)

t- GROOVE WIDTH .....,

COVER PASS MAX.,.1+-_ WIDTH = 8 (3 mm) _~

WIDER THAN

THE GROOVE

COVER PASS

FILLER PASS

ROOT PASS

fiGURE 5·22 Excessively wide Dr built-up welds restrict pipe expansion at the joint, which may cause premature failure. Check the appropriate code or standard for exact specifications.


- ~ '---'>(

i5°•-- -

15'

,~ rJ /

FIGURE 5·23 Uniformity in each pass shows a highdegree of welder skill and increases the probability theweld will pass testing. courtesy of Larry Jeffus.

FIGURE 5·24 lG position. The pipe is rolled horizontally.

ANGLEV IRON

WELDING TABLE SURFACEFIGURE !I'·2S Angle iron pipe support.

""" '\

~ 17 /I

will not allow the pipe to expand and contract uniformlyalong its length. This concentration is similar to the restriction a rubber band would have on an inflated balloon if itwere put around its center.

The cover pass should be kept as uniform and as neatlooking as possible, Figure 5-23. A visual checking isoften all that low- and medium-pressure welds receive,and a nice-looking cover will pass testing each time. Agood cover pass, during a visual inspection, will indicatethat the weld underneath is sound.

FIGURE 5·26 1G pipe welding area.

position, stopping at the I o'clock position, Figure 5-26.Roll the pipe until the end of the weld is at the 11 o'clockposition. Clean the weld crater by chipping and ",rirebrushing.

Strike the arc again and establish a molten weld poolalthe leading edge of the weld crater. With the molten weldpool reestablished, move the electrode back on the weldbead just short of the last full ripple, Figure 5-27. Thisaction will both reestablish good fusion and keep the weldbead size uniform. Now that the new weld bead is tiedinto the old weld, continue welding to the 1 o'clock posi·tion again. Stop welding, roll the pipe, clean the crater,and resume welding. Keep repeating this procedure untilthe weld is completely around the pipe. Before the lastweld is started, clean the end of the first weld so that theend and beginning beads can be tied together smoothlyWhen you reach the beginning bead, swing your electrodearound on both sides of the weld bead. A poor beginningof a weld bead is always high and narrow and has liulepenetration, Figure 5-28. By swinging the weave pattern(the "C" pattern is best) on both sides olthe bead, you can

1Ci Horizontal Rolled PositionThe horizontal rolled pipe position is commonly used

in fabrication shops where structures or small systems canbe positioned for the convenience of the welder, Figure5-24. The consistent high quality and quantity of welds produced in this position make it very desirable for both thewelder and the company.

The penetration and buildup of the weld are controlledmore easily with the pipe in this position. Weld visibilityand welder comfort are improved so that welder fatigue isless of a problem. The pipe can be rolled continuouslywith some types of positioners, and the weld can be madein one continuous bead.

Because of the ease in welding and the level of skillrequired, welders who are certified in this position maynot be qualified to make welds in other posit.ions.

PRACTICE 5-1

Beading. 1G Position. Using EG010 orEG011 Electrodes and E7018 Electrodes

Using a properly set up and adjusted arc weldingmachine, proper safety protection, E6010 or E6011 andE7018 arc welding electrodes, having a 1/8-in. (3-mm)diameter, schedule 40 mild steel pipe 3 in. (76 mm) orlarger in diameter, you will make a straight stringer beadaround a horizontally rolled pipe.

Place the pipe horizontally on the welding table in avee block made of angle iron, Figure 5·25. The vee blockwill hold the pipe steady and allow it to be moved easilybetween each bead. Strike an arc on the pipe at the 11o'clock position. Make a stringer bead over the 12 o'clock

11 1

..--- STOP

ROLL


y- STRIKE THE

'\\ yARe HERE., \\ \ ~,- f

r~~>~'":=::::-I

1ST WELD _-.....

UNIFORMBEAD

\

fiGURE 5-27 Keeping the weld uniform is important when restarting the arc.

--------~_{==~1~S~T=;)

,I ,..~

I II ~ II~I

I OJ II Ir'l )_;>\:c_~

... 1 y~~ ......"-' ,,, ,-

fiGURE 5-28 Restarting the weld.

make the bead correctly so the width is uniform. Theadded heat will give deeper penetration at the startingpoint. Hold the arc in the crater for a moment until it isbuill up but do not overfill the crater.

Cool, chip, and inspect the bead for defects. Repeat thebeads as needed until they are mastered. Turn off thewelding machine and clean up your work area when youare finished welding.

Compiete a copy of the "Student Welding Report"listed in Appendix I or provided by your instructor. •

PRACTICE 5-2

Butt Joint, 1G Position. Using E6010 orE6011 Electrodes

Using a properly set up and adjusted arc weldiugmachine, proper safety protection, E6010 or E6011 arcweiding electrodes having a lI8-in. (3-mm) diameter, andtwo or more pieces of schedule 40 mild steel pipe 3 in. (76mm) or larger in diameter, you will make a pipe butt jointin lhe lG horizontal rolled position, Figure 5-29.

Tack weld two pieces of pipe together as shown inFigure 5-30. Place the pipe horizontally in a vee block on

the welding table. Start the root pass at the 11 o'clockposition. Using a very short arc and high current setting,weld toward the 1 o'clock position. Stop and roll the pipe,chip the slag, and repeat the weld until you have completed the root pass.

Clean the root pass by chipping and wire brushing. Theroot pass should not be ground this time. Replace the pipein the vee block on the table so that the hot pass can bedone. Turn up the machine amperage, enough to remeltthe root weld surface, for the hot pass. Use a stepped electrode pattern, moving forward each time the molten weldpool washes out the slag, and returning each time themolten weld pool is nearly all solid, Figure 5-31. Weldfrom the 11 o'clock position to the 1 o'clock positionbefore stopping, rolling, and chipping the weld. Repeatthis procedure until the hot pass is complete.

The filler pass and cover pass may be the same pass onthis joint. Turn down the machine amperage. Use a "T,"'J," "C," or zigzag pattern for this weld. Start the weld atthe 10 o'clock position and stop at the 12 o'clock position.Sweep the electrode so that the molten weld pool meltsout any slag trapped by the hot pass. Watch the back edgeof the bead to see that the molten weld pool is filling thegroove completely. Turn, chip, and continue the bead

ROOTPASS

ROOT PASS

TRAPPEDSLAG

WELDCRATER

SLAG BEINGMELTED OUT

HOT PASS

1860·

f/

I-+-

I------ ------- -----

L 1" .1. 1"--J1- 1-2 2

(38 mm) (38 mm)

Welding Principles and Applications

MATERIAL:

3" DIAMETER SCHEDULE 40 MILD STEEL PIPEPROCESS:SMAW BUTT JOINT lG

NUMBER: DRAWN BY:

PRACTICE 5-2 GAYL RUNNELS

FIGURE 5-31 Hot pass.

TACK WELDS

FIGURE 5-29 Butt joint in the 1G position.

FIGURE 5-30 The tack welds are to be evenly spaced around the pipe. Use four tacks on small diameter pipe and six (more on large diameter pipe.



/i\600

-G

--------- ---------

+

--------- ---------

L 3' .1. 3" ----J(76 mm) (76 mm)

Welding Principles and Applications

MATERIAL:3" DIAMETER SCHEDULE 40 MILD STEEL PIPE

PROCESS:SMAW BUTT JOINT lG

NUMBER: DRAWN BY:

PRACTICE 5-3 DONNIE AGA

FIGURE 5-32 Butt joint in the 1G position to be tested.

until the weld is complete. Repeat this weld until you canconsistently make welds free of defects. Turn off the welding machine and clean up your work area when you arefmished welding.

Complete a copy of the "Student Welding Report"listed in Appendix I or provided by your instructor. •

PRACTICE 5-3Butt Joint, 1G Position, Using E6010 orE6011 Electrodes for the Root Pass withE7018 Electrodes for the Filler and CoverPasses

Using the same setup, materials, and procedures asdescribed in Practice 5-2, you will make a horizontal rolledbUll joint in pipe, Figure 5-32. The root pass is to have 100%penetration over 80% or more of the length of the weld.

Set the pipe in the vee block on the welding lable andmake the root pass as explained in Practice 5-2. Watch for100% penetration with no icicles. A hot pass or grinder canbe used to clean theface of the root pass. Use an E7018 eleclrode for the filler and cover passes. The E70l8 electrodeshould not be weaved more than 2 1/2 times the diameterof the electrode. Excessively wide weaving will allow themolten weld pool to become contaminated, Figure 5-33.

After the weld is completed, visually inspect it for100% penetration around 80% of the root length. Checkthe weld for uniformity and visual defects on the coverpass. Repeat this weld until you can consistently makewelds free of defects. Turn off the welding machine andclean up your work area when you are finished welding.

FIGURE 5-]] Weave beads more than two and one halftimes the diameter of the electrode may be nice looking, but the atmosphere may contaminate the unprotected part of the molten weld pool. Courtesy of larry Jeffus.

Complete a copy of the "Student Welding Report"listed in Appendix 1 or provided by your instructor. •

2G Vertical Fixed PositionIn the 2G vertical fIXed pipe position, the pipe is verti

cal and the weld is horizontal, Figure 5-34. With thesewelds, the welder does not need to change welding positionsconstantly. The major problem that faces welders whenwelding pipe in this position is that the area to be welded is


HORIZONTALWELD

0°FIGURE 5-34 2G position. The pipe is fixed vertically,and the weld is made horizontally around it.

"'~ } UNIFORM- SHAPE

ELECTRODE HELDAT TRAILING ANGLE "'-"'-t---,OoJ

, ,

FIGURE 5-36 Electrode position and weave pattern fora weld on vertical pipe.

rr

UNDERCUT HOT PASS

ROOT PASS

FIGURE 5-37 Hot pass.

)

NOTE LOWER BEADSPROVIDE A SHELF FORBEADS ABOVE THEM.

FIGURE 5-35 2G pipe welding position.

often located in comers. Because of this location, reachingthe back side of the weld is difficult. In the practices that follow, you may tum the pipe between welds. As a welder gainsmore experience, welds in tight places will become easier.

The welds must be completed in the correct sequence,Figure 5-35. The root pass goes in as with other joints. Toreduce the sagging of the bottom of the weld, increase theelectrode to work angle. As long as the weld is burned inwell and does not have cold lap on the bottom, the weldis correct. Each of the filler and cover welds that will rollow must be supported by the previous weld bead.

PRACTICE 5-4

Stringer Bead, 2G Position, Using EG010or EG011 Electrodes and E7018 Electrodes

Using the same setup, materials, and electrodes aslisted in Practice 5-1, you will make straight stringerbeads on a pipe that is in the vertical position.

The "J" weave pattern should be used so that themolten weld pool will be supported by the lower edge ofthe solidified metal, Figure 5-36. Keep the electrode at anupward and trailing angle so the afC force will help to keepthe weld in place.

Repeat these stringer beads as needed, with bothgroups of electrodes, umil you can consistently makewelds rree or defects. Turn ofr the welding machine andclean up your work area when you are finished welding.

Complete a copy or the "Student Welding Report'listed in Appendix I or provided by your instructor. •

PRACTICE 5-5Butt Joint, 2G Position, Using EG010 orEG011 Electrodes

Using a properly set up and adjusted arc weldingmachine, proper safety protection, E6010 or E6011 arcwelding electrodes having a 1/8-in. (3-mm) diameter, andtwo or more pieces or schedule 40 mild steel pipe 3 in. (76mm) or larger in diameter, you will make a bUll joint ona pipe that is in the vertical pOSition.

Place the pipe on the arc welding table. Strike an arcand make a root weld that is as long as possible. II the rootgap is uniform, a step pattern must be used. After completing and cleaning the root pass, make a hot pass. Thehot pass need only burn the root pass clean, Figure 5-37.Undercut on the top pipe is acceptable.

The filler and cover passes should be stringer beads. Bykeeping the molten weld pool size small, control is easier.


Complete a copy of the "Student Welding Report"listed in Appendix I or provided by your instructor. •

WELD

FIGURE 5-39 5G horizontal fixed position.

The 5G horizontal fiXed pipe position is the mostoften used pipe welding position. Welds produced in nat,vcnical up or vcnical down, and overhead positions mustbe uniform in appearance and of high quality.

When practicing these welds, mark the top of the pipefor future reference. Moving the pipe will make weldingeasier, but the same side must stay on the lOp at all times,Figure 5-39.

The root pass can be performed by welding uphill ordownhill. In industry, the method used to weld the rootpass is determined by established weld procedures. Ifthere are no procedures requiring a specific direction,the choice is usually made based upon fitup. A closeparallel root opening can be welded uphill or downhill.A root opening that is wide or uneven must be weldeduphill. In the following Practices, the welder can makethe choice of direction, but both directions should betried.

The pipe may be removed from the welding positionfor chipping, wire brushing, or grinding. The pipe can beheld in place by welding a piece of nat stock to it andclamping the nat stock to a pipe stand, Figure 5-40.

The electrode angle should always be upward, Figure5-41. Changing the angle toward the top and bottom will

BAR WELDED TOPIPE FOR CLAMPINGTO A PIPE STAND

5Ci Horizontal Fixed Position

ELECTRODE POSITION IFROOT BURNS THROUGH

_J.::---,

J-fl--+-

Butt Joint, 2G Position, Using E6010or E6011 Electrodes for the Root Passand E7018 Electrodes for the Filler andCover Passes

PRACTICE 5-6

Cool, chip, and inspect the completed weld for uniformityand defects. Repeat this weld until you can consistentlymake welds free of defects. Turn off the welding machineand dean up your work area when you are finished welding.

Complete acopy of the "Student Welding Report" listedm\ppendix Ior provided by your instructor. •

l'smg the same setup. materials, and procedures asdt'Sl. nbed in Practice 5-4, you will make a vertical fixedpipe weld. The foot pass is to have 100% penetration overRl1% or more of the length of the weld.

Place the pipe vertically on the welding table. Hold the,hirode at a 90' angle to the pipe axis and with a slighttr.uhng angle, Figure 5-38. The electrode should be heldughth' mto the joint. If a burnthrough occurs, quicklypush the electrode back over the burnthrough whileIncreasing the trailing angle. This action forces the weldmetal back into the opening. When the roOl pass is compl'Ie. chip the surface slag and then clean out the trappedlag bs gnnding or chipping, or use a hot pass.

Use E7018 electrodes for the filler and cover passes~Ilh astringer pattern. The weave beads are not recommended with this electrode and position because theytcnd to undercut the top and overlap the bottom edge.Alter the weld is completed, visually inspect it for 100%penetration around 80% of the root length. Check the~eld for uniformity and visual defects on the cover pass.Repeat the weld until you can consistemly make weldsrrtC of defects. Turn off the welding machine and cleanup '"our work area when you are finished welding.

,

FIGURE 5·38 Electrode position and movement for theroot pass.

FIGURE 5-40 Holding the pipe in place by welding apiece of flat stock to the pipe and then clamping theflat stock to a pipe stand.


Butt Joint. SG Position. Using E6010 orE6011 Electrodes for the Root Pass andE7018 Electrodes for the Filler and CoverPasses

positions. Stop at the 7 o'clock position, Figure 5-42. U'a new electrode, start at the 5 o'clock position and makeuphill straight stringer bead through the 6 o'clock12 o'clock positions. Stop at the 1 o'clock position. Chanthe electrode angle to control the molten weld pool.

Repeat these stringer beads as needed, with eachof electrodes, umil you can consistently make weldsof defects. Turn off the welding machine and clean uyour work area when you are finished welding.

Complete a copy of the 'Student Welding Reponlisted in Appendix I or provided by your instructor.•

PRACTICE 5-8

/tI, I

I II I

I

\ \\ \\ ,\

~

\-f.,\\\\ , ,\ \

\ \

-++---+----+-

FIGURE 5-41 Electrode angle. Using the same setup, materials, and procedures aslisted in Practice 5-2, you will make a horizontal fixe<! X;

pipe weld. The root pass is to have 100% penetration 0'

80% or more of the length of the weld.Mark the top of the pipe and mount it horizontall)

between waist and chest level. Weld the root pasuphill or downhill using E6010 or E6011 electrodesEither grind the root pass or use a hot pass to clean ou!trapped slag.

Use E7018 electrodes for the filler and cover pass<s

wiLh stringer or weave patLerns. When the weld is completed, visually inspect it for 100% penetration aroun80% of the root length. Check the weld for uniformity anvisual defects on the cover pass. Repeat the weld umil youcan consistently make welds free of defects. Turn off thewelding machine and clean up your work area when youare finished welding.

Complete a copy of the 'Student Welding Repon'listed in Appendix I or provided by your instructor.•

VERTICAL_______ DOWN

+-+----+---

help control the bead shape. The bead, if welded downhill, should stan before the 12 o'clock position and continue pasllhe 6 o'clock position to ensure good fusion andlie-in of the welds. The arc must always be struck insidethe joint preparation groove.

PRACTICE 5-7

Stringer Bead. SG Position. Using E6010or E6011 Electrodes and E7018 Electrodes

Using the same setup. materials, and electrodes aslisted in Practice 5-1, you will make straight stringerbeads in the horizontal fixed SG position using bothgroups of electrodes.

Clamp the pipe horizontally between waist and chestlevel. Starting at the 11 o'clock position, make a downhillstraight stringer bead lhrough the 12 o'clock and 6 o'clock

PRACTICE 5-9

Butt Joint. SG Position. Using E6010 orE6011 Electrodes

Using a properly set up and adjusted arc weldingmachine, proper safety protection, E6010 or E6011 arcwelding electrodes having a 1I8-in. (3-mm) diameter, andtwo or more pieces of schedule 40 mild steel pipe 3 in. (76mm) or larger in diameter, you will make a butt joint ona horizontally fixed 5G pipe.

Mark the top of the pipe and mount it between waistand chest level. Depending upon the root gap, make aroot weld uphill or downhill using E6010 or E6011electrodes. Check the root penetration to determine ifit is better in one area than in another area. Chip andwire brush the weld and set the machine for a hOl pass.Start lhe hot pass at the boltom and weld upward on


HORIZONTAL

Butt Joint, GG Position, Using EG010 orEG011 Electrodes for the Root Pass andE7018 Electrodes for the Filler and CoverPasses

Butt Joint, GG Position, Using EG010 orEG011 Electrodes

PRACTICE 5-12

Using a properly set up and adjusted arc weldingmachine, proper safety protection, E6010 or E6011 arcwelding electrodes having a 1I8-in. ()-mm) diameter, andrwo or more pieces of schedule 40 mild steel pipe) in. (76mm) or larger in diameter, you will make a butt joinl ona pipe in the 45° fixed inclined position.

Starling at the LOp, make a vertical down root pass thatends just beyond the boltom. Repeat this weld on theother side. Chip and wire brush the siag so that an uphillhot pass can be made. The hot pass must be kept small andconcave so that more slag will not be trapped along thedownhill side. Clean the bead, turn down the machineamperage, and complete the joint with stringer beads,Figure 5-44.

Cool, chip, and inspect the completed weld for uniformity and defects. Repeat this weld until you can consistently make welds free of defects. Turn off the weldingmachine and clean up your work area when you are finished welding.

Complete a copy of the "Student Welding Repon"listed in Appendix I or provided by your instructor. •

Using the same setup, materials, and procedures aslisted in Practice 5-11, you will make a 45° fixed inclinedpipe weld. The root pass is to have LOO% penetration over80% of rhe root length of the weld.

Make the root pass as either a vertical up or down weld,depending upon the root opening. Chip the slag and cleanthe weld by grinding or by using a hot pass. If a hot passis used, chip and wire brush the joint. Using the E7018electrode, start slightly before the center on the bottomand make a small stringer bead in an upward direction.

angle should stay to the downhill side with a trailing(pulling) angle. When the weld passes beyond the side,the downhill and trailing angles are decreased. This isdone so that, when the weld reaches the top, the electrodeis perpendicular to the top of the pipe. Repeat this procedure on the opposite side.

Repeat these stringer beads as needed, with bothgroups of electrodes, until you can consistently makewelds free of defeets. Turn off the welding machine andclean up your work area when you are finished welding.

Complete a copy of the "Student Welding Report"listed in Appendix I or provided by your instructor.•

PRACTICE 5-11

OVERHEAD

CHANGING WELDING POSITIONS

,

/

WElD J ---

VERTICAL

FIGURE 5·43 In the 6G position, the pipe is fixed at a45' angle to the work surface. The effective weldingangle changes as the weld progresses around the pipe.

both SIdes. The bead should be kept uniform with lillIebUildup.

t.:sing stringer or weave beads, make the filler andCOler welds. If stringer beads are used, downhill weldscan be made. Cool, chip, and inspect the weld for uniformity and defects. Repeat this weld until you can consIStently make welds free of defects. Turn off the weidingmachine and clean up your work area when you are finIShed welding.

Complete a copy of the "Student Welding Report"lISted 10 Appendix I or provided by your instructor. •

The45' Hxed inclined position is thought to be themoSl difficult pipe position. Qualifying in this positionWIll certify the welder in the other positions using thesame-size electrodes and pipe sizes. The weld must beuniform and not have defects even though its positionIS changing in more than one direction at a time,Figure 5-43.

During this weld, it is necessary to continuouslychange the weld pattern, electrode angle, and weld speed.mall multipass stringer beads work best. With experi

ence, however, weave beads are possible.

6G 45° Inclined Position

lsing the same setup, materials, and electrodes aslisted in Practice 5-1, you will make straight stringerbeads on a pipe in the 45° fixed inclined position.

UslOg the straight stepped "T" or whipping pauern,start at the boltom of the pipe with a keyhole technique.Keep the molten weld pool small and narrow for easiercontrol. As the bead moves up to the side, the electrode

Stringer Bead, 6G Position, Using EG010or EG011 Electrodes and E7018 Electrodes

PRACTICE 5·10


FIGURE 5-44 Weld bead positions for 6G pipe weld.

Keep a trailing and a somewhat uphill e1eclrode angle sothat the weld is deposited on the bottom of the lower pipe.The next pass should use a downhill eleclrode angle sothat the bead is on the uphill pipe. Alternate this processuntil the bead is complete. Clean the weld and inspect itfor 100% penelration over 80% of the rool length. Check

for uniformity and visual defects on the cover pass. Repe.athe weld untll you can consistently make welds free 0

defects. Turn off the welding machine and clean up youwork area when you are finished welding.

Complete a copy of the "Student Welding Reponlisted in Appendix I or provided by your instructor. •

Pipe welding is looked upon by many in the weldingindustry as the pinnacle of the welding trade. Pipe welding presents its own challenges La the welder because ofthe constantly changing weld position. With practice youlearn to control the molten weld pool as it transitionsthrough the various weld positions. As yOll will learn torecognize the subtle changes in the weld pool, you canmake the welding technique changes as second nature.

As you observe a pipe welder in the field, you willnotice that the welder spends a signiHcant amount of

time in the preparation of the equipment and pipebefore any welding begins. Being properly set up andhaving the weld joint properly aligned before welding are essential in producing quality welded pipejoints.

Often there is a tendency to overweld pipe joints.You must also learn to control weld size. This is veryimportant with pipe welds because too large a weld canput more stresses on the joint. Also a good pipe weldedjoint may have many small weld passes.


The X-34 reusable launch vehicle attached to the underside of a Lockhead Tri-$tar airplane. (Photo courtesy of Orbital

Sciences Corp.)

porosity in a weld and can-in some cases, such as withmixed gases-almost eliminate poroSity. Also, shielding gasis used to purge possible contaminants from a weld area,and manipulation of purge pressure can be used to supporta weld while it is molten. Some of the more difficult applications in the X-34 demanded mixed welding gases toachieve the proper weld quality.

Electrodes. Electrode geometry has always been animportant orbital welding parameter because it has such astrong effect on weld shape and penetration. The use ofproperly prepared tungsten helps ensure repeatable welds.The typical geometry is a 22' taper with a 0.010 to 0.020flat tip. A tip without a flat point may create an unstable arcand produce welds that wander from side to side.

Tube Preparation. As in all welding, fitup is critical to suc·cessfully producing repeatable welds. It is especially critic,with orbital welding because specific parameters, such astravel speed, welding amperes, and arc volts, are preset. Th<tubing used for square butt joints must be cut square andthe end face machined perpendicular to the tube centerlill€using a facing tool.

Why Welding Was Chosen forthe X·34

NASA did not require welding for the X-34 RLV subl»tems, but the RLV program required low maintenance andreliability. The company also wanted to achieve a low fluidleakage rate. The X-34 uses SOOO-pound-per-square-inchpneumatic systems. If tubing were to fail, a considerablesafety hazard would be presented. If a weld were to fail ona tube adjacent to the X-34's large pressure tanks, it wou~represent a major explosion hazard. The weld developmentwork was done with this in mind.

The engineers and technicians also relied on real-timedata acquisition to ensure weld quality and repeatability.The team needed to have high confidence in the quality ofthe work done. Before long, the X-34 will take center stageamong the lead stories in newspapers and on televisionnews. It is expected to be an important element in NASA',more economical space launch program.

Pharos and ort.icle courtesy of the American Welding Society,

1. List some applications that use low-pressurepIping.

2. List some applications that use medium-pressurepIping.

3. List some applications that use high-pressurepIping.

4. Describe the differences between pipe and tubing.

5. What are the advantages of welded piping systemsover other joining methods?

6. Why must the ends of pipe be beveled before beingwelded?

7. How can the ends of a pipe be beveled'

8. Why is the end of a pipe beveled at a 37 112° angle'

9. What causes root suck back or a concave root face?

10. Why are arc strikes outside the welding zone considered a problem on pipe?

11. What are the purposes of backing rings?

12. What is the purpose of a hot pass'

13. Why must the weld crater be cleaned before starting a new electrode?

14. What is the maximum width of the coverpass' Why'

15. When is the IG welding position used'

16. How can the start of a weld be made less narrowand more uniform?

17. What supports the welds on a 2G pipe joint?

18. On 5G welds, what usually determines the direction of the root pass?

19. What three welding pOSitions are incorporated inthe 6G welding position?

20. Why are small multipass stringer beads best for6G welds?

Shield Metal Arc Welding of Pipe

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