Editor’s Note: This is the first article in athree-part series on cutting, removing, anddisposing of weld beads. Part I discussesthe reasons to remove the weld bead andequipment parameters that affect thescarfing process. Part II, which willappear in the September issue, will discussmanual and automated removal processes.Part III, which will appear in theOctober/November issue, will discussstrategies for improving ID weld beadremoval and disposal.

MANY commonly used methods ofwelded tube and pipe production create anupset, or weld bead, on both the OD andID. This is true for any variation of electricresistance welding (ERW), whether it useshigh-frequency (HF) or direct current(DC), and regardless of the current trans-fer method, such as contact wheels, shoes,or induction coils. Fusion welding meth-ods, such as gas tungsten arc welding(GTAW), plasma, and laser, can producethickness variations but normally do notproduce weld bead upset zones unless hotforging is used.

The weld upset zone is rough, sharp,and undesirable in the majority of fin-ished goods. Therefore, the weld beadmust be removed or reduced to make theproduct marketable. Consequences ofnot removing the weld bead include per-sonnel injury, lost-time accidents, andproduct rejection. Accidents involvingweld bead scarfing are a leading cause of

lost-time accidents in the tube and pipeindustry.

Bear in mind that weld beads on theoutside of the tube are the easiest toremove. If the removal process goespoorly, the OD can be repaired orreworked. The ID weld bead is far moredifficult to remove, and after the tube ismanufactured, the ID scarf flaw is almostimpossible to repair.

SAFETY IS THE FIRST CONCERNThe top four strategies for reducing acci-dents are training, training, training, andstrict enforcement of safety policies. Besure that every employee understands theprinciples of the manufacturing processesso the hazards are clear. Guarding goesonly so far in protecting people.Knowledge is the best line of defense.

Equip every tube mill operator and allpersonnel working near the tube millwith hardhats, face shields, hearing pro-tection, flame-resistant clothing, andhand and forearm guards made fromNOMEX1 or a similar material to protectagainst cuts and burns.

The next line of defense is plant clean-ness. Keep floors clean and dry, andmaintain clutter-free work areas.

Finally, use your tube mill equipmentthe way it was designed to be used. Donot eliminate guards, defeat interlocks,misuse tools, overload the mill, or ignorethe maintenance schedule.

TIPS TO IMPROVE WELDBEAD TRIM OPERATIONSTo improve the weld bead scarfingprocess, concentrate on the factors thataffect the weld bead. The main factors arethe strip edges and mill parameters.

Strip edge condition affects toolinglife, weld fit-up, and the weld bead. Edgecondition systems can increase setup reli-ability and reduce the weld upset.

Pay particular attention to setupcharts so strip edges are properly set inthe fin passes and you have the right weldapproach angle. The setup must followmaterial requirement guidelines, and thestrip width must be appropriate for theyield strength and thickness. A carefulsetup reduces variations in weld beadupset conditions and contributes tolonger scarf tool life.

Work coils and impeder locationaffect the heat coupling to the skelp edgeand thereby affect weld bead scarfing.Scarfing while the bead is as hot as possi-ble is accomplished by balancing forgeconditions against OD and ID scarfingneeds. The scarfing location should be asclose as possible to the weld forge point.

Equally important as scarfing locationis coolant control. Do not quench theweld bead any more than necessary—thishelps maintain the forge roll life. Rollsand bearings experience heating becauseof their proximity to the induction coils.New carbide and ceramic scarfing toolsare designed to run hot and require

16 TPJ • JULY/AUGUST 2005 A TPA PUBLICATION

P R O D U C I N G R E S U L T S

SCARFING TUBE AND PIPE—CUT TO THE QUICK

PART I: DRAWING A BEAD ON SCARFING CONDITIONS

By W.B. “Bud” Graham, Contributing Writer

16-19 Producing Results 11/14/05 12:36 PM Page 16

P R O D U C I N G R E S U L T S

A TPA PUBLICATION JULY/AUGUST 2005 • TPJ 17

Figure 1The relative strength of steelchanges with temperature, asdoes its resistance to scarfing.Scarfing the weld bead at thehighest possible temperatureputs less stress on the scarf-ing tooling. Degrees F

Rel

ativ

e S

tren

gth

(10

0 =

Str

eng

th a

t 70

Deg

rees

F)

consistent, uniform cooling or no coolingat all. Do not subject the scarf tooling tosplash or submergence cooling because itcannot withstand the thermal shock load.You must shield the cutting inserts fromdirect contact with the coolant on boththe OD and ID.

Use return-flow impeders to improveinside bead scarfing. If the ID is too smallto accommodate return-flow units,attach extensions to flow-through imped-ers to carry the coolant downstream pastthe ID scarfing stand or employ offlinesuction to reduce coolant carryout.

Steel’s strength varies with tempera-ture (see Figure 1). As its strength varies,so does its resistance to scarfing. Steelexhibits an increase in apparent strengthas it cools from about 600 degrees F to400 degrees F. When the weld bead upsetis cooled excessively, the work load onthe OD rolling and cutting tooling, theID bead scarf tooling and rolling man-drel, and the stand increases rapidly. Thiscan cause the mandrels to pull apart andthe tooling to shatter. Thus the mantra,“Hotter is better.” Scarf as soon as possi-ble after welding, and don’t do anythingto make life more difficult, like coolingthe weld zone. Also be sure the weldseam doesn’t roll away from the 12

o’clock position.Process speed and tension directly

affect scarf tooling life. Uniform speedand constant pulling through the scarfingzone are mandatory. Worn roll tools,misaligned roll shaft shoulders, and poordrive setup create intermittent push-and-pull shock loading that leads to accelerat-ed scarf tooling wear. A varying millspeed changes the weld approach angleand, therefore, heat penetration into thestrip edge. This, in turn, changes thescarfing cross section. This can lead totwo scarfing strands instead of the nor-mal single strand.

FOCUSING ON THESCARFING PROCESSPoorly maintaining scarfing stands, select-ing improper toolholders, and using thewrong insert grade can affect the scarfingcut finish and, ultimately, tool life.

Poor maintenance of gibs and slidescauses the toolholder to bend under load.This changes the attack angle betweenthe tool and the tube or pipe, and itaffects the tooling work load. Cuttingwith a shallower angle of attack (that is,an angle that is more laid back againstthe direction of travel) puts a lower scarf-ing load on stands and increases tool life.

One clue that belies a shallow attackangle is a rippled appearance (chattermarks) in the scarfing zone. A chatteringsound is a clue that the scarfing toolingrequires maintenance.

As a rule, the angle of attack shouldbe around 15 degrees for most carbonsteel applications for OD scarfing (seeFigure 2) and 30 degrees or more for ID scarfing.

Cutting tools are back-relieved byapproximately 18 degrees so they do notdrag on the scarfed surface. Steeper andshallower back angles have advantagesand disadvantages. Shallower angles cre-ate less tool drag and reduce cuttingforce, but they also have a smaller crosssection and mass in contact with the bead.

Selecting scarf tools for a variety ofmaterial grades and speeds is not easy.Only a dedicated collection of opera-tional data and proper experiment con-trols can provide accurate guidance infinding the best balance. Such workalways pays off, so don’t give in to thenext great craze in inserts. Experimentwith a variety of scarfing tooling, butdepend on actual results to justify toolselection.

Selecting the right radius is also criti-

16-19 Producing Results 11/14/05 12:36 PM Page 17

cal. Using tooling that has a larger radiusthan required can create a flat. Toolingthat has a smaller radius than requiredcan create fluke gouging from the cornersof the tool. Improper radius selection canlead to increased tool consumption, lostuptime because of frequent tool changes,and customers rejecting the finished tube.As a rule of thumb, select a radius that isbetween 110 percent and 150 percent ofthe tube OD.

Bud Graham is president of Welded TubePros, P.O. Box 202, Doylestown, OH44230, 330-658-7070, fax 216-937-0333,budg@bright.net, www.weldedtube-pros.com. He also is the chairman of TPA'sTube Producers Council. Welded TubePros is a consulting engineering firm serv-ing the needs of welded tube producers. Ifyou have a specific question or would liketo see an article on a particular problem,please contact the author or TPJ.

This article is adapted from “Scarf – Cutto the Quick,” a presentation made atTPA’s Tube Producing 2005 conference,April 18-20, 2005, Hamilton, Ontario,Canada.

18 TPJ • JULY/AUGUST 2005 A TPA PUBLICATION

P R O D U C I N G R E S U L T S

Figure 2Select OD scarf tooling that has the proper relief angle (about 18 degrees for most carbon steelapplications) and proper form radius (between 110 percent and 150 percent of the tube’s OD).

Relief Angle

Form Radius

Note1. NOMEX® IIIA is a blend of NOMEXmeta-aramid and Kevlar® para-aramidfiber manufactured by E.I. du Pont deNemours & Co. It is resistant to flames;dissipates static; and is resistant to manychemicals, including organics, acids, and

bases. The fire resistance does not washout during laundering. It is widely used forclothing for military personnel, firefighters,auto racers, and industrial workers.

16-19 Producing Results 11/14/05 12:36 PM Page 18