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Tube-to-tube sheet mechanizedwelding is not new. The technology— originally developed in the

United States — has been utilized in theheat exchanger fabrication market goingback some 40 years. What is new is theevolution of orbital welding technologyand the role it’s playing in bringing heatexchanger fabrication back to the UnitedStates.

Largely due to competitive pressures,U.S. heat exchanger fabrication begantransitioning overseas about 15 yearsago. Lower labor and material costsdrove companies to look outside theUnited States to build these devices. Re-cently, however, U.S.-based heat ex-changer fabrication has undergone a

resurgence as newer, larger, and morecomplex exchanger designs have comeonline and users have demanded an ever-higher level of performance and quality.

This outsourcing trend took its toll ontube sheet orbital welding manufactur-ers. As the outsourcing trend gatheredsteam, domestic demand for tube-to-tubesheet applications dried up, with the firstgeneration of orbital welding systemslargely disappearing from the market-place. Now that this fabrication is return-ing stateside, many progressive compa-nies are looking at the newest generationof orbital welding systems to deliver thespeed, quality, repeatability, and ruggedduty cycles needed to remain competi-tive in a global economy — Fig. 1.

Today’s orbitalwelding systemsdeliver the speed,quality, and easeof use that canhelp companiesstay competitive

BY MARK LESKA

Technology Drives U.S. Heat Exchanger Resurgence

MARK LESKA(MLeska@ehwachs.com) is sen-ior marketing coordinator, ITWOrbital Cutting & Welding, E. H.Wachs®/Orbitalum Products,

Lincolnshire, Ill.

Fig. 1 — The newest generation of tube-to-tubesheet welding systems are more compact,durable, faster, and easier to operate.

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These orbital welding systems canhelp American companies remain com-petitive in a global marketplace, makingit financially attractive to fabricate in theUnited States. This is particularly truewith complex, restricted space or highlytechnical exchanger applications. Today’sorbital welding systems are more com-pact, powerful, durable, faster, and eas-ier to program and operate than ever be-fore.

Orbital Weld PreparationIn both manual and mechanized weld-

ing, the quality of the finished weld is di-rectly related to the quality of the weldpreparation. Rather than using circularsaws with saw guides or grinding wheelsthat leave burrs, uneven wall thickness,melted tube debris, or a crooked cutline,a precision tube saw such as one of theGF series from Orbitalum Tools pro-duces a finished edge that is ready formany orbital welding applications.

Some applications require squaring(or “facing”) the cut edge further. InFig. 2 — Facing machine tools deliver a perfectly square, burr-free edge with no gaps

or misalignments for orbital welding.

Fig. 3 — Full autofacing machine tools such as shown here speed weld preparation on the hundreds of tube-to-tube sheet weldsused in a typical heat exchanger.

these cases, a facing machine toolis used to create a perfectly square,burr-free edge, eliminating gapsand misalignments to ensure theweld fitup is uniform and consistent— Fig. 2. When the weld joints areproperly prepped, an orbital weld-ing operator can minimize the weldrejection rate, making an orbitalsaw, tube facer, and orbital weldingsystem essential tools for mechani-cal contractors and fabricators.

In specialized tube sheet appli-cations, a consistent extension ofthe tube (“stickout”) may be re-quired before the welding processbegins, and here again automationcan be highly beneficial. An exam-ple is the BRB 2 full autofacing ma-chine tool from Orbitalum, whichis designed with an automatic stopfeature to produce repeatable ex-tension in a production setting. Thismachine automates the clampingprocedure, rotation speed, and feedrate for higher productivity thanmanual beveling — Fig. 3.

E. H. Wachs and OrbitalumTools, divisions of ITW Orbital Cut-ting & Welding, have joined forcesto create a global supplier of orbitaltube and pipe cutting, beveling, andwelding products.

Orbital WeldingBasics

The basic premise of orbital tubesheet welding is simple — utilizinga standard GTAW process, thewelding torch is mechanically ro-tated around the tube end whileadding welding wire (strength weld)or fusion only (seal weld). The or-bital welding system, through itsprogramming, maintains the opti-mum arc to ensure a high-quality,highly repeatable finished weld. Al-though it’s possible for a skilledmanual welder to achieve similarresults, the challenge of producingconsistent, repetitive welds hourafter hour and day after day be-

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Fig. 4 — The challenge of producing consistent, repetitive weldsbecomes greater if operator fatigue becomes a factor.

Fig. 5 — Micro processor-controlled welding heads shown weld-ing tube-to-tube sheet on a heat exchanger.

Fig. 6 — Split frame rotating ring cutting equipmentsectioning welded shell, leaving a beveled, weld-ready finish.

comes greater if operator fatigue be-comes a factor — Fig. 4.

A key point to remember is that or-bital welding systems are mechanized,and not automatic in the truest sense.They’re not AI (artificial intelligence)smart like in a science fiction movie.Even the best orbital welding systems arenot a substitute for a skilled welder — infact, skilled welders become the best can-didates to quickly master the equipment.

Skilled welders have the ability to“read” a weld pool, allowing them to

make any needed adjustments in the pro-gram development phase. They adaptquickly to the equipment, in effect be-coming a supervisor directly monitoringand managing the welding process as op-posed to a slave to it, attempting to end-lessly replicate exacting, tedious, andrepetitive eye, hand, and arm motions.

All the changes a welder normallymakes in a relatively uncontrollable man-ner regarding amps, arc voltage, wirefeed, and travel speed while manualwelding becomes easily controllable with

orbital welding systems by using simpleinputs into a prequalified program.

Tube-to-Tube SheetWelding Basics

While tube-to-tube sheet welding canbe complex (particularly in the contextof box header applications), the basicconcept is fairly simple: A series of tubesis welded to a (typically circular) endplate called the tube sheet — Fig. 5. The

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Fig. 7 — Flush welds are usually fusion seal welds; recessed and extendedare typically strength welds with wire added.

Fig. 8 — Box header applications require customlength mandrels based on the reach or R dimen-sion.

Fig. 9 — Box header applicationsare one of the more difficult man-ual welding operations.

entire tube and tube sheet assembly(called the bundle) is then enclosed in anouter vessel (called the shell), creating afinished heat exchanger.

A significant portion of this work isrepair and refurbishing, taking an exist-ing device, opening the shell, replacingsome or all the tubes in the bundle, andreinstalling it back into the shell. Thisouter shell can be either bolted togetheror welded, and is typically reused on re-pair and refurbishing projects.

For welded shells, exterior-mountedsplit frame rotating ring cutting machines(Fig. 6) and other types of cutting ma-chines are useful for sectioning (open-ing) them for repair. These machinesproduce a precision beveled, weld-readysurface that facilitates quick onsite re-assembly without the hot work permitstorches and hand grinding may require.

Due to the repetitive nature of thetube-to-tube sheet welding task, heat ex-changer fabrication and repair is a prime

candidate for mechanized orbital weld-ing. In building or refurbishing thesecomponents, hundreds and even thou-sands of tubes require weld prep andwelding. These tube-to-tube sheet weldsgenerally fall into one of three types:flush, recessed, or extended, also knownas protruding or stickout — Fig. 7.

The flush profile is usually a “seal”weld, an autogenous fusion weld with nowire added. Recessed and extended aretypically “strength” welds, where wire isadded for additional strength or to joindissimilar metals. On extended profiles,the dimension (D) of the extension typi-cally must be uniform. Heat exchangerengineers specify the weld profile basedon the usage and pressures under whichthe unit will operate.

The high quality and consistency of-fered by microprocessor-controlled or-bital welding leads directly to enhancedproductivity with fewer defects. Orbitalwelding systems are often the best solu-tion where repeatability, quality, andstrength of the finished welds are critical.

Orbital welding systems enhance pro-ductivity in other less obvious ways. Or-bital systems allow your entire workforcethe opportunity to deliver near-perfect,defect-free welds on a consistent basis.It also frees up welders for tasks that sim-ply cannot be economically mechanized.Orbital welding systems are designed tobe operated by workers of all skill levels,from novices to industry pros, althoughtraining is recommended for every skilllevel to minimize the learning curve.

Box Header ApplicationsA specialized application related to

heat exchanger work is the box headerdesign, where an outer box used for heattransfer purposes requires the use of spe-cialized equipment for mechanized weld-ing. In this application, the torch must“reach” through access holes in the outerwall of the box, referred to as the plugsheet, to the inner tube sheet where theactual weld is performed. This processrequires weld heads with custom lengthmandrels for the “R” or reach dimension— Fig. 8.

Box header tube-to-tube sheet weld-ing is one of the more difficult manualwelding operations. It requires an ex-traordinary level of dexterity, skill, expe-rience, and a healthy dose of patience —Fig. 9. In these applications, orbital welding solutions can yield huge im-provements in weld consistency and productivity.u

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