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  THE AMERICAN WELDER SEPTEMBER 2009 78 Defects can be reduced or avoided by un-derstanding and controlling the process.Many defects can be eliminated in thepreweld stage. Let’s take a look at theprocess and some common defects andhow they can be avoided. The SAW Process The submerged arc welding (SAW)process was first patented in 1935 and li-censed by Union Carbide a year later.Union Carbide marketed the process andrelated products under the “Unionmelt”trademark. Since that time, many ad- vances have been made to the process, in-cluding multiwire, cored wire, andcladding applications, but the fundamen-tals remain the same: an arc is createdusing a bare wire under a granular flux covering. The flux contributes to the me-chanical properties of the weld, deoxidizesthe base metal, and protects the molten weld metal from atmospheric contami-nants. When the weld is complete, it iscovered by an easily removed layer of slag.Submerged arc welds are typically madeusing some form of automation, althoughit is possible to make a subarc weld witha hand-held torch.Submerged arc welding offers manyadvantages over other welding processes,including the following:ã High weld qualityã High deposition rateã Deep penetrationã High-speed welding on thin sheet steelsã Almost no fume or light emission.Nothing is perfect, however, and sub-arc welding does have its limitations. Thisform of welding is limited to the flat andhorizontal positions, requires precise jointpreparation, and does not allow observa-tion of the arc and the process during the weld. Despite its limitations, the sub-merged arc process is popular in a num-ber of industries, notably shipbuilding, wind tower fabrication, ASME vessel fab-rication, pipe mills, and fabrication of util-ity poles and trailer beams. The Role of Flux  Submerged arc fluxes are generallygrouped into neutral and active fluxes.Many fluxes alloy some Si and Mn to the weld metal while others melt off these el-ements. The intensity of this chemical re-action depends on the quantity of flux in-teracting with the wire. An increase in voltage or arc length will lead to increasedalloying or melt-off of these elements.Neutral fluxes are used in multilayer  welding of unlimited plate thickness withappropriate wires. The alloying of ele-ments, especially Si and Mn, is carefullycontrolled.  Active fluxes add a significant amountof Si, acting as a deoxidizer, and Mn tothe weld metal. They enhance resistanceto porosity and improve bead appearanceand toughness in high-dilution applica-tions. Active fluxes are primarily used for Minimizing Defectsin Submerged Arc Welding Understanding and controlling the submerged arc welding  process can help you reduce or avoid defects BY DAN GERBEC  DAN GERBEC (dgerbec@esab.com) is product manager, Submerged ArcConsumables, ESAB Welding & Cutting  Products, Hanover, Pa.,  www.esabna.com  . Submerged arc welding (SAW) can be a highly productive tool for fabricators, but as with most welding technologies, defects can occur.This leads to rework and a reduction in overall productivity.  Fig. 1 — Excessive voltage or travel speed,insufficient current, or improper joint de- sign can lead to insufficient penetration inthe weld.  THE AMERICAN WELDER 79 WELDING JOURNAL single-pass or multilayer welding with lim-itation of layers, with three to five layersnormally the maximum. Process Variables Submerged arc welding can be done with either direct current (DC) or alter-nating current (AC) power supplies. Di-rect current is the most commonly usedbecause it is easiest to control and pro- vides the best arc starting and stability, ex-cept at high currents, when arc blow canbe a problem. Direct current electrodepositive, or reverse polarity, is used mostoften and yields the deepest penetration.Direct current electrode negative, orstraight polarity, provides up to 25% lesspenetration but offers the highest deposi-tion rates and is useful in cladding appli-cations or applications with poor joint fit-up. The characteristics of AC power fallbetween straight polarity and reverse po-larity but offer the benefit of eliminatingarc blow because the rapidly changing po-larity prevents magnetic fields from forming.Once the polarity of the power supplyis chosen, amperage, voltage, travel speed, wire size, and electrode extension all playa role in the shape, size, and quality of the weld deposit.  Amperage is directly related to depo-sition rate and depth of penetration, so anincrease in amperage will increase bothdeposition rate and penetration.  Arc voltage is a measure of arc lengthand has an inverse relationship to depthof penetration and a direct relationshipto bead width. An increase in arc voltage,therefore, will cause a decrease in pene-tration and an increase in bead width. Travel speed, also known as feed rate,is inversely related to bead size and pen-etration, so a reduction in travel speed in-creases bead size and penetration.Wire size also affects deposition rateand penetration, but contrary to popularbelief, a larger-diameter wire may not bebetter than a smaller-diameter wire. A small-diameter wire has a smaller cross-sectional area, and therefore, at the samecurrent, a smaller-diameter wire will pro- vide a faster melt-off and consequently ahigher deposition rate and increased pen-etration vs. a larger wire. Electrode extension is the distancefrom the end of the contact tip to the sur-face of the workpiece. As a rule of thumb,electrode extension should be about eighttimes the wire diameter. For example, theelectrode extension for a 1  ⁄  8 -in.-diameter wire should be approximately 1 in. Usinga longer electrode extension will result inreduced penetration and increased depo-sition. The increased deposition is causedby the I 2 R resistive heating of the wire. Identifying Submerged Arc Welding Defects In most cases, a SAW defect has morethan one cause and more than one possi-ble cure. The cure to the problem is oftento do the opposite. For instance, if the de-fect is caused by excess current, simplylowering the current will usually resolvethe defect. But selecting the proper cure will depend on your objective. For exam-ple, melt-through can be resolved by de-creasing the welding current, increasingtravel speed, or reducing the bevel angle.In most cases, reducing the bevel angle isnot a realistic option, so you must eitherreduce the current or increase travelspeed. Since most fabrication applicationsfavor higher productivity, it generallymakes sense to increase travel speed.Here are some common weld defectsand their most likely causes:ã Insufficient penetration. Caused by lowcurrent, high voltage, high travel speed,and/or improper joint design — Fig. 1.ã Melt-through. Caused by high current,too great a bevel angle, too small a rootface or root opening, and/or slow travelspeed.ã Porosity. Caused by joint contaminationby rust or moisture, a shallow flux bur-den, insufficient penetration into thebacking weld, a contaminated backing weld, improper joint fitup, flux fines,and/or flux moisture — Fig. 2. In thecases where porosity is caused by jointcontamination or a high level of atmos-pheric moisture (humidity), the problemmay be solved by using a more active flux or preheating to remove moisture.ã Surface pock marks. Can be caused by joint contamination, moisture on theplate, and/or moisture in the flux. Sur-face pock marks can be avoided by usingan active flux, preheating the plate, andkeeping the flux in an oven at250°–300°F.ã  Arc blow. Caused by an imbalance in themagnetic field surrounding the work-piece. Arc blow is typically experiencedat high DC welding currents and can becured by reducing the current, using AC,and demagnetizing the fixture.ã Reinforcement, or bead, rollover. Typi-cally caused by high current, low volt-age, or low travel speed.ã Undercut. Occurs when there is insuf-ficient molten metal added to the poolto fill the gaps in material created by the voltage — Fig. 3. The simplest ways tofix undercut are to reduce travel speed,increase current, or decrease voltage.Improper wire alignment may also bethe culprit and is easy to remedy.ã Slag sticking. Slag will tend to stick ina deep groove, especially if the weld isconcave. The cure is usually to reduce voltage. Increasing travel speed and de-creasing current may also work.Understanding the SAW process andunderstanding your own objectives inusing that process are the keys to success-fully dealing with submerged arc weldingdefects. ◆  Fig. 2 — Porosity is most commonly caused by the presence of moisture in the weld. Fig. 3 — Undercut generally occurs whenthe amount of wire deposited is not great enough to fill the gaps in the material caused by the voltage. This can be avoided by reducing travel speed, increasing current, or decreasing voltage.
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