welding lincoln guide

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ASME Code Calculator:- Information

This page calculates the approval range for both welding procedures and welder approvals. It was developed for groove welds but fillet welds follow the same basicrules except parent metal thickness is not considered, but welding positions for

performance qualification should be correct and also diameter limits.{Note Diameter limits don't apply to fillet welds if qualified by a groove weld}

Enter test piece data above horizontal line. Click the 'Calculate Approval Range' buttonand the range of approval willappear below it.

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The ABC's of Nondestructive Weld ExaminationReprinted courtesy of Welding Journal magazine.

An understanding of the benefits and drawbacks of each form of nondestructive examination can help you choose the best method for yourapplication

By Charles Hayes

The philosophy that often guides the fabrication of welded assemblies andstructures is "to assure weld quality." However, the term "weld quality" is relative.The application determines what is good or bad. Generally, any weld is of goodquality if it meets appearance requirements and will continue indefinitely to do the

job for which it is intended. The first step in assuring weld quality is to determinethe degree required by the application. A standard should be established based onthe service requirements.

Standards designed to impart weld quality may differ from job to job, but the use of appropriate weld techniques can provide assurance that the applicable standardsare being met. Whatever the standard of quality, all welds should be inspected,even if the inspection involves nothing more than the welder looking after his ownwork after each weld pass. A good-looking weld surface appearance is many timesconsidered indicative of high weld quality. However, surface appearance alone doesnot assure good workmanship or internal quality.

Nondestructive examination (NDE) methods of inspection make it possible to verifycompliance to the standards on an ongoing basis by examining the surface andsubsurface of the weld and surrounding base material. Five basic methods arecommonly used to examine finished welds: visual, liquid penetrant, magneticparticle, ultra-sonic and radiographic (X-ray). The growing use of computerizationwith some methods provides added image enhancement, and allows real-time ornear real-time viewing, comparative inspections and archival capabilities. A review
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of each method will help in deciding which process or combination of processes touse for a specific job and in performing the examination most effectively.

Visual Inspection (VT)Visual inspection is often the most cost-effective method, but it must take placeprior to, during and after welding. Many standards require its use before othermethods, because there is no point in submitting an obviously bad weld tosophisticated inspection techniques. The ANSI/AWS D1.1, Structural Welding Code- Steel, states, "Welds subject to nondestructive examination shall have been foundacceptable by visual inspection." Visual inspection requires little equipment. Asidefrom good eyesight and sufficient light, all it takes is a pocket rule, a weld sizegauge, a magnifying glass, and possibly a straight edge and square for checkingstraightness, alignment and perpendicularity.

Before the first welding arc is struck, materials should be examined to see if theymeet specifications for quality, type, size, cleanliness and freedom from defects.Grease, paint, oil, oxide film or heavy scale should be removed. The pieces to be

joined should be checked for flatness, straightness and dimensional accuracy.Likewise, alignment, fit-up and joint preparation should be examined. Finally,process and procedure variables should be verified, including electrode size andtype, equipment settings and provisions for preheat or postheat. All of theseprecautions apply regardless of the inspection method being used.

During fabrication, visual examination of a weld bead and the end crater mayreveal problems such as cracks, inadequate penetration, and gas or slag inclusions.Among the weld defects that can be recognized visually are cracking, surface slaginclusions, surface porosity and undercut.

On simple welds, inspecting at the beginning of each operation and periodically aswork progresses may be adequate. Where more than one layer of metal filler isbeing deposited, however, it may be desirable to inspect each layer beforedepositing the next. The root pass of a multipass is most critical to weld soundness.It is especially susceptible to cracking, and because it solidifies quickly, it may trapgas and slag. On subsequent passes, conditions caused by the shape of the weldbead or changes in the joint configuration can cause further cracking, as well asundercut and slag trapping. Repair costs can be minimized if visual inspectiondetects these flaws before welding progresses.

Visual inspection at an early stage of production can also prevent underwelding andoverwelding. Welds that are smaller than called for in the specifications cannot betolerated. Beads that are too large increase costs unnecessarily and can causedistortion through added shrinkage stress.

After welding, visual inspection can detect a variety of surface flaws, includingcracks, porosity and unfilled craters, regardless of subsequent inspectionprocedures. Dimensional variances, warpage and appearance flaws, as well as weldsize characteristics, can be evaluated.

Before checking for surface flaws, welds must be cleaned of slag. Shotblastingshould not be done before examination, because the peening action may seal finecracks and make them invisible. The AWS D1.1 Structural Welding Code, forexample, does not allow peening "on the root or surface layer of the weld or thebase metal at the edges of the weld."

Visual inspection can only locate defects in the weld surface. Specifications orapplicable codes may require that the internal portion of the weld and adjoining


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determined by the smallest diameter of wire that can be clearly seen on theradiograph.

A penetrameter is not an indicator or gauge to measure the size of a discontinuityor the minimum detectable flaw size. It is an indicator of the quality of theradiographic technique.

Radiographic images are not always easy to interpret. Film handling marks andstreaks, fog and spots caused by developing errors may make it difficult to identifydefects. Such film artifacts may mask weld discontinuities.

Surface defects will show up on the film and must be recognized. Because the angleof exposure will also influence the radiograph, it is difficult or impossible to analyzefillet welds by this method. Because a radiograph compresses all the defects thatoccur throughout the thickness of the weld into one plane, it tends to give anexaggerated impression of scattered type defects such as porosity or inclusions.

An X-ray image of the interior of the weld may be viewed on a fluorescent screen,as well as on developed film. This makes it possible to inspect parts faster and at alower cost, but the image definition is poorer. Computerization has made it possibleto overcome many of the shortcomings of radiographic imaging by linking thefluorescent screen with a video camera. Instead of waiting for film to be developed,the images can be viewed in real time. This can improve quality and reduce costson production applications such as pipe welding, where a problem can be identifiedand corrected quickly.

By digitizing the image and loading it into a computer, the image can be enhancedand analyzed to a degree never before possible. Multiple images can besuperimposed. Pixel values can be adjusted to change shading and contrast,bringing out small flaws and discontinuities that would not show up on film. Colorscan be assigned to the various shades of gray to further enhance the image andmake flaws stand out better. The process of digitizing an image taken from thefluorescent screen - having that image computer enhanced and transferred to aviewing monitor - takes only a few seconds. However, because there is a timedelay, we can no longer consider this "real time." It is called "radioscopy imagery."

Existing films can be digitized to achieve the same results and improve the analysisprocess. Another advantage is the ability to archive images on laser optical disks,which take up far less space than vaults of old films and are much easier to recallwhen needed.

Industrial radiography, then, is an inspection method using X-rays and gamma raysas a penetrating medium, and densitized film as a recording medium, to obtain aphotographic record of internal quality. Generally, defects in welds consist either of a void in the weld metal itself or an inclusion that differs in density from thesurrounding weld metal.

Radiographic equipment produces radiation that can be harmful to body tissue inexcessive amounts, so all safety precautions should be followed closely. Allinstructions should be followed carefully to achieve satisfactory results. Onlypersonnel who are trained in radiation safety and qualified as industrialradiographers should be permitted to do radiographic testing.


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Selecting Filler Metals: Low HydrogenKey Concepts in Welding Engineeringby R. Scott Funderburk

This is part two in a series on selecting filler metals. When selecting filler metals,

the specifier may elect to require "low hydrogen electrodes." Such electrodes maybe required to minimize the possibility of hydrogen related cracking. In some casesthe engineer may specify low hydrogen electrodes because he believes theseelectrodes will also provide weld deposits exhibiting a high minimum level of notchtoughness. While this may be true, it can not be assumed. This article will addressspecifying filler metals that resist hydrogen related cracking while also providinggood mechanical properties.

The term "low hydrogen" has been around for about 60 years. It was firstintroduced to differentiate this classification of shielded metal arc welding (SMAW)

electrode (e.g., E7018) from other non-low hydrogen SMAW electrodes (e.g.,E6010). They were created to avoid hydrogen cracking on high strength steels,such as armor plate.1

Confusion About the Term

Although so-called "low hydrogen electrodes" have been around for many years,there is some confusion about what is meant by the term. Many codes andspecifications use the designation, however, neither "low hydrogen" nor "lowhydrogen electrodes" are listed in the American Welding Societys (AWS) StandardWelding Terms & Definitions (AWS A3.0-94)2. This may come as a surprise tosome, especially to engineers that have been specifying that "only low hydrogen

electrodes shall be permitted," or "all welds shall be low hydrogen", or that "allwelding processes shall be low hydrogen." Without a formal definition, the term"low hydrogen" can be understood differently by engineers, contractors, orinspectors, which can lead to confusion and conflicts.

"Low Hydrogen Electrode" Means SMAW Electrode

The closest thing to a formal definition for lowhydrogen SMAW electrodes is found in the AWSA5.1 filler metal specification3. This specificationlists several electrode classifications with "lowhydrogen" coatings. These classifications must

have a coating moisture level of less than 0.6%when tested at 1800 F (980 C), according toAWS A5.1. This moisture level corresponds to a relatively low diffusible hydrogen

Figure 1. "Fish-eyes" on an all-weld-metal tensile specimen

fracture surface.

EXX15-xEXX16-xEXX18-x

Table 1. AWS SMAW

Electrodes with Low HydrogenCoverings


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level in the deposited weld metal, typically less than 16 mL/100g. For example,AWS A4.3, Standard Methods for Determination of Diffusible Hydrogen4, shows thatwhen E7018 is welded at 70 F and 60% relative humidity a 0.6% coating moistureequates to approximately 12 mL/100g of diffusible hydrogen. Many of todaysE7018 products have actual coating moisture content levels much lower than themaximum of 0.6% in the as-received condition. Table 1 lists the SMAW electrodeswith low hydrogen coating contained in A5.1.

Can Hydrogen Affect Mechanical Properties?

The influence of hydrogen can be observed in mechanical testing; however, itseffects on the test results are limited. A high hydrogen content in a tensilespecimen can produce "fish-eyes" on the fracture surface as seen in Figure 1.

Additionally, the presence of hydrogen can reduce ductility (as expressed byelongation and reduction in area). Hydrogen, however, does not typically influencethe impact toughness, ultimate tensile strength or yield strength results. It is onlyin severe cases that it can influence the ultimate tensile strength.

Since low hydrogen SMAW electrodes like E7018 are also required to have aminimum specified level of Charpy V-notch (CVN) impact energy, low hydrogen issometimes equated with a minimum CVN level. This has led some people to specifylow hydrogen when the real desire is for notch toughness. The better approach is tospecify notch toughness requirements since there is no automatic link between lowdiffusible hydrogen content in the weld and CVN values. Actually, some depositswith high hydrogen levels can deliver relatively high levels of notch toughness. Forexample, the E6010 classification (non-low hydrogen, 30-50 mL/100g) has aminimum CVN requirement of 20 ft-lbs at minus 20F.

Use of the Term in Codes and Specifications

Some codes and specifications refer to hydrogen control in terms of either (1)requiring low hydrogen SMAW electrodes or (2) placing specific limits on diffusiblehydrogen. The Structural Welding Code Steel (AWS D1.1-2000)5 has provisionsrelated to hydrogen in the preheat table (Table 3.2). In the table, Category "A" isapplicable to "shielded metal arc welding with other than low hydrogen electrodes."The minimum preheat temperatures listed in Category "A" are higher than Category"B" because Category "B" is for "shielded metal arc welding with low hydrogenelectrodes, submerged arc welding, gas metal arc welding, flux cored arc welding."

In the Interim Guidelines: Evaluation,Repair, Modification and Design of Welded Steel Moment FrameStructures6 published by the FederalEmergency Management Agency(FEMA), a comparison between lowhydrogen SMAW electrodes andFCAW and SAW is made. Thisdocument states, "All of the electrodes that are employed for flux cored arc welding(both gas shielded and self shielded), as well as submerged arc welding, areconsidered low hydrogen." Implied is the assumption that FCAW and SAW willprovide weld deposits with diffusible hydrogen levels similar to SMAW electrodeswith low hydrogen coverings.

Weld Deposit Hydrogen Levels

Diffusible Hydrogen,

mL/100gH8 8H4 4H2 2

Table 2. Optional Hydrogen Designators


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As mentioned above, no definition exists for a "low hydrogen weld deposit." Theword "low" is an imprecise description. The preferred method of controlling the levelof hydrogen in a weld deposit is to use the optional hydrogen designators asdefined by the American Welding Society. These designators are in the form of asuffix on the electrode classification (e.g., H8, H4, and H2). The filler metalmanufacturer may choose to add the hydrogen designator to the electrodeclassification if the filler metal meets the diffusible hydrogen requirements in theapplicable AWS A5.x filler metal specification. Following are examples of thedesignator requirements:

To avoid hydrogen induced cracking, the hydrogen level in the material must beheld to a certain maximum level. This level is a function of the microstructuresusceptibility, constraint (or restraint), and residual stresses. Microstructuresusceptibility to hydrogen induced cracking often increases with increasing steelstrength. Therefore, for higher strength steels lower levels of hydrogen arerequired. To simply state "use low hydrogen" is not enough. For example, "low" fora 50 ksi steel may not be "low" for a 100 ksi steel. Rather than require that "onlylow hydrogen electrodes can be used," engineers and fabricators are should usestatements such as, "only electrodes or electrode-flux combinations capable of depositing weld metal with a maximum diffusible hydrogen content of 8 mL/100g(H8) are permitted."

Codes That Use Hydrogen Designators

The AWS D1.1 Structural Welding Code also has several provisions that utilizehydrogen designators (e.g., H8). For example, Category "D" in the minimumpreheat and interpass temperature table (Table 3.2) allows only "electrodes orelectrode-flux combinations capable of depositing weld metal with a maximumdiffusible hydrogen content of 8 mL/100 g (H8)." This is a good example of properlyusing the H-designators.

The AWS D1.1 Code also has an alternate method to determine the minimumpreheat temperature (Annex XI) that uses three levels of diffusible hydrogen. InAnnex XI, category H1 is called an "extra low hydrogen" at less than 5 mL/100g.Category H2 is labeled as "low hydrogen" at less than 10 mL/100g. The thirdcategory, H3, is a hydrogen level that is not controlled. Although category H2 islabeled "low hydrogen," this does not define low hydrogen electrode as less than 10mL/100g. The actual diffusible hydrogen value can also be used to calculate theminimum preheat temperature with this method instead of using the H1, H2 and H3categories.

The Fracture Control Plan of the AWS Bridge Welding Code7 (AWS D1.5-95) isanother fine example of hydrogen control. This code requires the following forwelding Fracture Critical Members:

H16, H8 or H4, when the minimum specified yield strength is 50 ksi or less. H8 or H4, when the minimum specified yield strength is greater the 50 ksi.

Furthermore, SMAW electrodes can be used for tack welding without preheat if theelectrode has an H4 designator, according to AWS D1.5.

Other agencies such as the United States Military8 and the American Bureau of Shipping9 also set limits on the diffusible hydrogen levels. Both use limits of 15, 10

and 5 mL/100g, and the military specification has a stricter limit of 2 mL/100g forsome applications. Today, a logarithmic system (i.e., H16, H8, H4, and H2) ispreferred in the United States.


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Other Issues

Using an H8, or even an H4, electrode with controlled diffusible hydrogen aloneprovides no guarantee of eliminating problems related to hydrogen during or afterwelding. In addition to the electrode, several other factors can influence thediffusible hydrogen level and the potential for cracking. These should be consideredas well.

base metal surface condition (contamination from oils, grease, dirt,moisture, acid, rust and other hydrogen containing materials can increasehydrogen levels);

relative atmospheric humidity (humid conditions generally lead to higherhydrogen levels);

welding shielding gas (higher moisture content results in higher hydrogenlevels);

consumable storage conditions (improper or prolonged storage can lead tohigher hydrogen levels);

welding procedures (electrical stickout, arc voltage, wire feed speed andother parameters can influence diffusible hydrogen).

Conclusions

1. A "low hydrogen electrode" refers only to a SMAW electrode that has acoating moisture of less than 0.6%.

2. The maximum diffusible hydrogen level associated with low hydrogen SMAWelectrodes has been a point of confusion because SMAW electrodes with lowhydrogen coatings are not tied to any specific hydrogen level.

3. "Low hydrogen" should not be specified in order to achieve specific impactproperties. If notch toughness is required, then it should be listed separately

from the hydrogen limits (if any).4. Job specifications should be written clearly and precisely regarding the useof "low hydrogen." The intent of the specifier should be listed in such a waythat the contractor will understand what is required.

5. If a contractor has any questions regarding in the intent of the engineer, orif the specifications are not clear, the contractor should seek clarificationbefore welding. For example, if "use low hydrogen electrodes only" is listedon the contract, then the contractor may want to ask: "Is only SMAWallowed, or can other processes also be used?"

6. Supplemental hydrogen designators (e.g., H8 and H4) are the preferred wayto define a specific level of diffusible hydrogen in the weld deposit andshould be used when needed.

7. Finally, there are applications where low hydrogen electrodes are notrequired or where non-low hydrogen SMAW electrodes, like E6010, arepreferred. Therefore, utilizing the blanket statement "use low hydrogen"should be avoided.

Stick Electrodes: Low Hydrogen Group

References

1. Robert OCon. "Welding with Low Hydrogen Electrodes: A Look at the Pastwith Tips for Today." Practical Welding Today. March/April 2000, pp. 33-35.

2. American Welding Society. Standard Welding Terms and Definitions.(ANSI/AWS A3.0-94), 1994.
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3. American Welding Society. Specification for Carbon Steel Electrodes forShielded Metal Arc Welding. (ANSI/AWS A5.1-91), 1994.

4. American Welding Society. Standard Methods for Determination of DiffusibleHydrogen Content of Martensitic, Bainitic, and Ferritic Steel Weld MetalProduced by Arc Welding. (AWS A4.3-93), 1993, p. 16.

5. American Welding Society. Structural Welding Code Steel. (AWSD1.1:2000), 2000.

6. Federal Emergency Management Agency. Interim Guidelines: Evaluation,Repair, Modification and Design of Welded Steel Moment Frame Structures.(FEMA 267), August 1995, p. 8-11.

7. American Welding Society. Bridge Welding Code. (AWS D1.5-95), 1995.8. United States Military. Military Specification Electrodes Welding, Flux

Cored, Ordinary Strength and Low Alloy Steel, (MIL-E-24403/1D), November14, 1985.

9. American Bureau of Shipping. Rule Requirements for Materials and Welding,Part 2, 1997.

Technology Gets to the Root of Pipe WeldingBy Elliott K. Stava, Technical Advisor-Advanced Welding Technology, The LincolnElectric Company

Open root welds on pipes can be made three to four times faster than GTAW by using the Surface Tension Transfer process. When integrated with an internal spacer clamp into a new automatic orbital pipe welding system, even faster

production is possible, with no lack of fusion.

Pipe welding codes, whether for applications in the field or in the plant, requirehigh-quality root pass welding. To ensure that the joints will not leak, especially forsteam or pressurized applications, a weld must penetrate completely through thepipe.

In the past, pipe welding was done by one of three methods, each of which has itsadvantages and disadvantages. These are the methods that have been used.

Gas tungsten arc welding (GTAW) is popularly known as TIG. Travel speeds areslow, heat input is usually high, and it requires high operator skill level.

Gas metal arc welding (GMAW) - also known as MIG - is a much faster process thanGTAW. However, because operator skill level is hight and heat input difficult tocontrol, fusion may not always be 100 percent.

Shielded metal arc welding (SMAW), also known as stick, can be cost effective interms of equipment but requires high operator skill. Frequent starts and stops areanother potential problem.


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By contrast, the Surface Tension Transfer(STT) process makes it possible to completeopen root welds three or four times fasterthan GTAW, with low heat input and no lackof fusion. The STT process uses highfrequency inverter technology with advancedwaveform control to produce a high-qualityweld with less spatter and smoke. For pipewelding, the process also makes it easier toperform open gap root pass welding, withbetter back beads and edge fusion. It iseasier to operate than other processes, yetproduces consistent, X-ray quality welds. TheSTT process results in a complete back beadwithout shrinkage from the 12 to 6 o'clock

weld positions. Also, because current control is independent of wire feed speed, theprocess allows greater flexibility under all conditions.

Controlling Spatter and Smoke

STT is a proprietary Lincoln Electric process that makes use of Wave Form ControlTechnology to control current precisely and rapidly during the entire weldingcycle. It is unique in that it is neither constant current (CC) nor constant voltage(CV). Instead, the power source adjusts current automatically to the instantaneousheat requirements of the arc.

Spatter and smoke are reduced with this process, whether the arc shielding gas is100 percent CO2, blends of argon and CO2 or helium mixtures for use withstainless steel. Reducing spatter minimizes final weld surface preparation andallows the operator more welding time before the gun nozzle must be cleaned of accumulated spatter.

Reduced spatter also translates into significant cost savings because more of theelectrode is applied to the weld joint, not as spatter on the pipe and surroundingfixtures. Further cost savings are realized because larger diameter wire can beused.

At the start of the cycle, when the electrode shorts, the current is reducedimmediately, eliminating the incipient short. This low-level current is maintained fora short time so that the surface tension forces can begin transferring the drop to

Smoke and Spatter are reduced when pipe joints are welded by means of the Surface

Tension Transfer (STT) process.

In open root pass pipe welding, the STTprocess controls the wave form of the

welidng current for excellent penetrationcontrol, fusion, and back bead.


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the puddle, forming a solid mechanical bridge. A high level of pinch current is thenapplied to accelerate the transfer of the drop. The necking down or squeezing of theshorted electrode is monitored. When a specific value is reached, the pinch currentis reduced quickly to a low value before the fuse separates. When a short breaks, itdoes so at a low current, which produces very little spatter.

Next, the arc is reestablished and a high current known as peak current is applied.This momentary pulse of current establishes the arc length and causes the arc tobroaden and melt a wide surface area, which eliminates cold lapping and promotesgood fusion.

Better Pipe Welding Results

The constant voltage GMAW process normally used for pipe welding does not

control the current directly. Instead it controls the average voltage. This can causethe weld puddle temperature or fluidity to be too high, and the internal bead maybe flat or shrink back into the root. This is known as "suck back." Also, when usingconventional short arc GMAW, the operator must concentrate the arc on the lip orleading edge of the puddle to ensure proper penetration and fusion. If the arc is toofar back on the puddle, penetration will be incomplete. If the arc is too far ahead,the electrode shoots through the gap and causes whiskers to form inside the pipe.

Because Surface Tension Transfer controls the welding current independently of wire feed speed, the process makes it easy to control the temperature or fluidity of the puddle to ensure proper penetration and fusion. This is what makes it soattractive for open root pipe welding applications. In the 5G position, the operator

simply has to stay in the puddle. Experienced pipe welders almost always find theprocess a welcome improvement, both in ease of welding and comfort. Theyparticularly appreciate the reduction in spatter when welding in the 6 o'clockposition.

Spacer clamp and weldingshed on-site and ready for set

up.


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As the decision process evolves, the vendorand the fabricator will continue workingtogether to determine the appropriatesystem accessories, including safetydevices, the optimal layout for the roboticcell, manpower and training requirements,and service and maintenance requirements(internal vs. outside vendor support).

The STT process is gaining acceptance in pipe welding and similar applications,which require precise control of heat input as well as smoke and spatter reduction.Since the heat is controlled directly, the internal backbead profile is also controlled.Welders find that not only are open root welds easier to make, but their mechanicaland metallurgical properties are excellent. Superior welding bead profiles can beattained with improved properties in the heat affected zone. Moreover, open rootwelds are made without the use of ceramic or copper internal backup. In the caseof copper, corrosion is thus eliminated by avoiding the possibility of copperinclusions.

The process is effective for welding mild and high-strength steels, as well asstainless steel and related alloys. On steel, it offers the advantages of low hydrogenand 100 percent CO2 shielding with low spatter. When welding duplex stainless,critical pitting temperature is significantly better with STT than with GTAW, andtravel speeds three or four times that of GTAW can be obtained, with much lessskill.

A Guide to Aluminum WeldingReprinted courtesy of Welding Design and Fabrication magazine.

Equipment Selection, Material Prep, Welding Technique...A Guide to Aluminum WeldingReprinted courtesy of Welding Design and Fabrication magazine.

Follow the rules of thumb offered here for selecting welding equipment, preparingbase materials, applying proper technique, and visually inspecting weldments toensure high-quality gas-metal-and gas tungsten-arc welds on aluminum alloys.Even for those experienced in welding steels, welding aluminum alloys can presentquite a challenge. Higher thermal conductivity and low melting point of aluminum

alloys can easily lead to burnthrough unless welders follow prescribed procedures.Also, feeding aluminum welding wire during gas-metal-arc-welding (GMAW)presents a challenge because the wire is softer than steel, has a lower columnstrength, and tends to tangle at the drive roll.

To overcome these challenges, operators need to follow the rules of thumb andequipment-selection guidelines offered here...

Gas-metal-arc-welding:Base-metal preparation : To weld aluminum, operators must take care to cleanthe base material and remove any aluminum oxide and hydrocarbon contaminationfrom oils or cutting solvents. Aluminum oxide on the surface of the material melts

at 3,700 F while the base-material aluminum underneath will melt at 1,200 F.Therefore, leaving any oxide on the surface of the base material will inhibitpenetration of the filler metal into the workpiece.


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To remove aluminum oxides, use a stainless-steel bristle wire brush or solvents andetching solutions. When using a stainless-steel brush, brush only in one direction.Take care to not brush too roughly: rough brushing can further imbed the oxides inthe work piece. Also, use the brush only on aluminum work-don't clean aluminumwith a brush that's been used on stainless or carbon steel. When using chemicaletching solutions, make sure to remove them from the work before welding.To minimize the risk of hydrocarbons from oils or cutting solvents entering theweld, remove them with a degreaser. Check that the degreaser does not containany hydrocarbons.

Preheating : Preheating the aluminum workpiece can help avoid weld cracking.Preheating temperature should not exceed 230 F-use a temperature indicator toprevent overheating. In addition, placing tack welds at the beginning and end of the area to be welded will aid in the preheating effort. Welders should also preheata thick piece of aluminum when welding it to a thin piece; if cold lapping occurs, tryusing run-on and run-off tabs.

The push technique : With aluminum, pushing the gun away from the weld puddlerather than pulling it will result in better cleaning action, reduced weldcontamination, and improved shielding-gas coverage.

Travel speed : Aluminum welding needs to be performed "hot and fast." Unlikesteel, the high thermal conductivity of aluminum dictates use of hotter amperageand voltage settings and higher weld-travel speeds. If travel speed is too slow, thewelder risks excessive burnthrough, particularly on thin-gage aluminum sheet.

Shielding Gas : Argon, due to its good cleaning action and penetration profile, isthe most common shielding gas used when welding aluminum. Welding 5XXX-seriesaluminum alloys, a shielding-gas mixture combining argon with helium - 75 percenthelium maximum - will minimize the formation of magnesium oxide.

Welding wire : Select an aluminum filler wire that has a melting temperaturesimilar to the base material. The more the operator can narrow-down the meltingrange of the metal, the easier it will be to weld the alloy. Obtain wire that is 3/64-or 1/16- inch diameter. The larger the wire diameter, the easier it feeds. To weldthin-gage material, an 0.035-inch diameter wire combined with a pulsed-weldingprocedure at a low wire-feed speed - 100 to 300 in./min - works well.

Convex-shaped welds : In aluminum welding, crater cracking causes mostfailures. Cracking results from the high rate of thermal expansion of aluminum andthe considerable contractions that occur as welds cool. The risk of cracking isgreatest with concave craters, since the surface of the crater contracts and tears asit cools. Therefore, welders should build-up craters to form a convex or moundshape. As the weld cools, the convex shape of the crater will compensate forcontraction forces.

Power-source selection : When selecting a power source for GMAW of aluminum,first consider the method of transfer -spray-arc or pulse.Constant-current (cc) and constant-voltage (cv) machines can be used for spray-arc welding. Spray-arc takes a tiny stream of molten metal and sprays it across thearc from the electrode wire to the base material. For thick aluminum that requireswelding current in excess of 350 A, cc produces optimum results.Pulse transfer is usually performed with an inverter power supply. Newer powersupplies contain built-in pulsing procedures based on and filler-wire type anddiameter. During pulsed GMAW, a droplet of filler metal transfers from theelectrode to the workpiece during each pulse of current. This process produces


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positive droplet transfer and results in less spatter and faster follow speeds thandoes spray-transfer welding. Using the pulsed GMAW process on aluminum alsobetter-controls heat input, easing out-of-position welding and allowing the operatorto weld on thin-gage material at low wire-feed speeds and currents.

Wire feeder : The preferred method for feeding soft aluminum wire long distancesis the push-pull method, which employs an enclosed wire-feed cabinet to protectthe wire from the environment. A constant-torque variable-speed motor in thewire-feed cabinet helps push and guide the wire through the gun at a constantforce and speed. A high-torque motor in the welding gun pulls the wire through andkeeps wire-feed speed and arc length consistent.In some shops, welders use the same wire feeders to deliver steel and aluminumwire. In this case, the use of plastic or Teflon liners will help ensure smooth,consistent aluminum-wire feeding. For guide tubes, use chisel-type outgoing andplastic incoming tubes to support the wire as close to the drive rolls as possible toprevent the wire from tangling. When welding, keep the gun cable as straight aspossible to minimize wire-feed resistance. Check for proper alignment betweendrive rolls and guide tubes to prevent aluminum shaving.Use drive rolls designed for aluminum. Set drive-roll tension to deliver an evenwire-feed rate. Excessive tension will deform the wire and cause rough and erraticfeeding; too-little tension results in uneven feeding. Both conditions can lead to anunstable arc and weld porosity.

Welding guns : Use a separate gun liner for welding aluminum. To prevent wirechaffing, try to restrain both ends of the liner to eliminate gaps between the linerand the gas diffuser on the gun.Change liners often to minimize the potential for the abrasive aluminum oxide tocause wire-feeding problems.Use a contact tip approximately 0.015 inch larger than the diameter of the fillermetal being used - as the tip heats, it will expand into an oval shape and possibly

restrict wire feeding. Generally, when a welding current exceeds 200 A use a water-cooled gun to minimize heat buildup and reduce wire-feeding difficulties

Arc-Welding FundamentalsThe Lincoln Electric Company, 1994.

Arc welding is one of several fusion processes for joining metals. By applyingintense heat, metal at the joint between two parts is melted and caused to intermix- directly, or more commonly, with an intermediate molten filler metal. Uponcooling and solidification, a metallurgical bond is created. Since the joining is anintermixture of metals, the final weldment potentially has the same strengthproperties as the metal of the parts. This is in sharp contrast to non-fusionprocesses of joining (i.e. soldering, brazing etc.) in which the mechanical andphysical properties of the base materials cannot be duplicated at the joint.


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In arc welding, the intense heat needed tomelt metal is produced by an electric arc.The arc is formed between the actual workand an electrode (stick or wire) that ismanually or mechanically guided along the

joint. The electrode can either be a rod withthe purpose of simply carrying the currentbetween the tip and the work. Or, it may bea specially prepared rod or wire that not onlyconducts the current but also melts andsupplies filler metal to the joint. Most welding in the manufacture of steel productsuses the second type of electrode.

Basic Welding Circuit

The basic arc-welding circuit is illustrated in Fig. 1. An AC or DC power source,fitted with whatever controls may be needed, is connected by a work cable to theworkpiece and by a "hot" cable to an electrode holder of some type, which makesan electrical contact with the welding electrode.

An arc is created across the gap when the energized circuit and the electrode tiptouches the workpiece and is withdrawn, yet still with in close contact.

The arc produces a temperature of about 6500F at the tip. This heat melts boththe base metal and the electrode, producing a pool of molten metal sometimescalled a "crater." The crater solidifies behind the electrode as it is moved along the

joint. The result is a fusion bond.

Arc Shielding

However, joining metals requires more than moving an electrode along a joint.Metals at high temperatures tend to react chemically with elements in the air -oxygen and nitrogen. When metal in the molten pool comes into contact with air,oxides and nitrides form which destroy the strength and toughness of the weld

joint. Therefore, many arc-welding processes provide some means of covering thearc and the molten pool with a protective shield of gas, vapor, or slag. This is calledarc shielding. This shielding prevents or minimizes contact of the molten metal withair. Shielding also may improve the weld. An example is a granular flux, whichactually adds deoxidizers to the weld.

Fig. 1 The basic arc-welding circuit


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Figure 2 illustrates the shielding of thewelding arc and molten pool with a Stickelectrode. The extruded covering on the fillermetal rod, provides a shielding gas at thepoint of contact while the slag protects thefresh weld from the air.

The arc itself is a very complex phenomenon. In-depth understanding of thephysics of the arc is of little value to the welder, but some knowledge of its generalcharacteristics can be useful.

Nature of the Arc

An arc is an electric current flowing between two electrodes through an ionizedcolumn of gas. A negatively charged cathode and a positively charged anode createthe intense heat of the welding arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated rate.

In welding, the arc not only provides the heat needed to melt the electrode and thebase metal, but under certain conditions must also supply the means to transportthe molten metal from the tip of the electrode to the work. Several mechanisms formetal transfer exist. Two (of many) examples include:

1. Surface Tension Transfer - a drop of molten metal touches the moltenmetal pool and is drawn into it by surface tension.

2. Spray Arc - the drop is ejected from the molten metal at the electrode tip byan electric pinch propelling it to the molten pool. (great for overheadwelding!)

If an electrode is consumable , the tip melts under the heat of the arc and moltendroplets are detached and transported to the work through the arc column. Any arcwelding system in which the electrode is melted off to become part of the weld isdescribed as metal-arc . In carbon or tungsten (TIG) welding there are no moltendroplets to be forced across the gap and onto the work. Filler metal is melted intothe joint from a separate rod or wire.

More of the heat developed by the arc is transferred to the weld pool with

consumable electrodes. This produces higher thermal efficiencies and narrowerheat-affected zones.

Since there must be an ionized path to conduct electricity across a gap, the mereswitching on of the welding current with an electrically cold electrode posed over itwill not start the arc. The arc must be ignited . This is caused by either supplying aninitial voltage high enough to cause a discharge or by touching the electrode to thework and then withdrawing it as the contact area becomes heated.

Arc welding may be done with direct current (DC) with the electrode either positiveor negative or alternating current (AC). The choice of current and polarity dependson the process, the type of electrode, the arc atmosphere, and the metal being

welded.

Fig. 2 This shows how the coating ona coated (stick) electrode provides agaseous shield around the arc and a

slag covering on the hot weld deposit.


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Common Problems and Remedies for GMAWReprinted with permission from the September/October, 1997 issue

of Practical Welding Today magazine, copyright 1997 by The CroydonGroup, Ltd., Rockford, IL

In much the same way that the automatic transmission has simplifiedthe process of driving, Gas Metal Arc Welding (GMAW) has simplified

the process of welding. Of all welding methods, GMAW is said to be one of theeasiest to learn and perform. The main reason is because the power source doesvirtually all the work as it adjusts welding parameters to handle differingconditions; much like the sophisticated electronics of an automatic transmission.

Because less skill is required, many operators are able to GMA weld at an

acceptable level with limited training. These same operators run into trouble,however, when they begin creating inferior welds and are unable to diagnose andcorrect their own problems. The guidelines listed below will help even inexperiencedoperators create high quality welds as well as offering tips for those who have beenusing the GMAW process for a number of years.

Most common welding problems fall into four categories: I. Weld porosity,II. Improper weld bead profile, III. Lack of fusion, and IV. Faulty wire deliveryrelated to equipment set-up and maintenance.

I. Weld Metal PorosityPorosity Problem #1: Improper Surface Conditions

The most common cause of weld porosity is an improper surface condition of themetal. For example, oil, rust, paint or grease on the base metal may prevent properweld penetration and hence lead to porosity. Welding processes that generate aslag such as Shielded Metal Arc Welding (SMAW) or Flux-Cored Arc Welding (FCAW)tend to tolerate surface contaminates better than GMAW since components foundwithin the slag help to clean the metals surface. In GMAW, the only contaminationprotection is provided by the elements which are alloyed into the wire.

RemediesTo control porosity, use a deoxidizer within the wire such as silicon, manganese ortrace amounts of aluminum, zirconium or titanium. Wire chemistry can bedetermined by referring to the American Welding Society (AWS) wire classificationsystem.

Test the various types of wire available to find the right chemistry for a givenapplication. To start, try the most common wire type, ER70S-3 (Lincoln L50) whichcontains 0.9-1.4 percent manganese and 0.45-0.75 percent silicon. If porosity isstill present in the finished weld, increase the amount of silicon and manganesefound in the wire by switching to an ER70S-4 (Lincoln L54) or an ER70S-6 whichhas the highest levels of silicon (0.8 -1.15 percent) and manganese (1.4-1.8percent). Some operators prefer to use a triple deoxidizer such asER70S-2 (Lincoln L52) which contains aluminum, zirconium or titanium in additionto the silicon and manganese.

In addition to changing the wire, further prevent porosity by cleaning the surface of the metal with a grinder or chemical solvents (such as a degreaser.) A word of


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caution though if using solvents, be certain not to use a chlorinateddegreaser such as trichlorethylene near the welding arc -- the fume mayreact with the arc and produce toxic gases.

Porosity Problem #2: Gas CoverageThe second leading cause of porosity in welds is a problem with the shieldinggas coverage. The GMAW process relies on the shielding gas to physicallyprotect the weld puddle from the air and to act as an arc stabilizer. If theshielding gas is disturbed, there is a potential that air could contaminate theweld puddle and lead to porosity.

Remedies Shielding gas flow varies depending on wire size, amperage, transfer mode andwind speed. Typical gas flow should be approximately 30-40 cubic feet per hour.Using a flow meter, check that the shielding gas flow is set properly. There are avariety of flow meters on the market today ranging from simple dial gauges to ballflows all the way up to sophisticated, computerized models. Some operatorsmistakenly think that a pressure regulator is all that is needed, but the pressuremeter will not set flow.

A pure carbon dioxide shielding gas requires the use of special flow metersdesigned specifically for carbon dioxide. These special flow meters are not affectedby the frosting that may occur as the carbon dioxide changes from liquid form to agas.

If high winds are blowing the shielding gas away from the puddle, it may benecessary to erect wind screens. According to the AWS Structural Welding Code, itis advisable not to GMA weld when wind speeds are greater than 5 mph. Indoors,ventilation systems may hamper gas coverage. In this case, redirect air flow awayfrom the puddle. If fume extraction is necessary, use equipment designedspecifically for this purpose such as MAGNUM Extraction Guns from Lincoln

Electric -- they will remove the fume, but not disturb the shielding gas.

A turbulent flow of gas as it exits the gun may also lead to porosity problems.Ideally, the gas will lay over the weld puddle much like a blanket. Turbulent gasflow can be caused by too high a flow, an excessive amount of spatter inside thegun nozzle, or spatter build-up in the gas diffuser.

Other possible causes of insufficient gas flow may be damaged guns, cables, gaslines, hoses or loose gas fittings. These damaged accessories may create what isreferred to as a venturi effect where air is sucked in through these openings andflow is reduced.

Lastly, welding with a drag or backhand technique can lead to gas coverageproblems. Try to weld with a push or forehand technique which lays the gas blanketout ahead of the arc and lets the gas settle into the joint.

Porosity Problem#3: Base Metal PropertiesAnother cause of weld porosity may be attributed simply to the chemistry of thebase metal. For instance, the base metal may be extremely high in sulfur content.

Remedy Unfortunately, if the problem with porosity lies within the base metal properties,there is not much that can be done. The best solution is to use a different grade of steel or switch to a slag-generating welding process.

II. Improper Weld Bead Profile


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If operators are experiencing a convex-shaped or concave-shaped bead,this may indicate a problem with heat input or technique.

Improper Bead Problem #1: Insufficient Heat Input A convex or ropy bead indicates that the settings being used are toocold for the thickness of the material being welded. In other words, thereis insufficient heat in the weld to enable it to penetrate into the basemetal.

RemediesTo correct a problem with running too cold, an operator must first determine if the amperage is proper for the thickness of the material. Charts are available fromthe major manufacturers, including Lincoln Electric, that provide guidelines onamperage use under varying conditions.

If the amperage is determined to be high enough, check the voltage. Voltage that istoo low usually is accompanied by another telltale sign of a problem: a high amountof spatter. On the other hand, if voltage is too high, the operator will haveproblems controlling the process and the weld will have a tendency to undercut.

One way to check if the voltage is set properly is to test it by listening. A properlyrunning arc will have a certain sound. For instance, in short arc transfer at lowamperages, an arc should have a steady buzz. At high amperages using spray arctransfer, the arc will make a crackling sound. The arc sound can also indicateproblems -- a steady hiss will indicate that voltage is too high and the operator isprone to undercut; while a loud, raspy sound may indicate voltage that is too low.

Improper Bead Problem #2: TechniqueA concave or convex-shaped bead may also be caused by using an improperwelding technique. For example, a push or forehand technique tends to create aflatter bead shape than a pull or backhand technique.

Remedy For best bead shapes, it is recommended to use a push angle of 5-10 degrees.

Improper Bead Problem #3: Inadequate Work CableProblems with the work cable can result in inadequate voltage available at the arc.Evidence of a work cable problem would be improper bead shape or a hot workcable.

Remedy Work cables have a tendency to overheat if they are too small or excessively worn.In replacing the cable, consult a chart to determine size based on length and

current being used. The higher the current and longer the distance, the larger thecable needed.

III. Lack of FusionIf the consumable has improperly adhered to the base metal, a lack of fusion mayoccur. Improper fusion creates a weak, low quality weld and may ultimately lead tostructural problems in the finished product.

Lack of Fusion Problem: Cold Lapping in the Short Arc Transfer ProcessIn short arc transfer, the wire directly touches the weld pool and a short circuit inthe system causes the end of the wire to melt and detach a droplet. This shortinghappens 40 to 200 times per second. Fusion problems may occur when the metal inthe weld pool is melted, but there is not enough energy left to fuse it to the baseplate. In these cases, the weld will have a good appearance, but none of the metalhas actually been joined together. Since lack of fusion is difficult to detect visually,


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it must be checked by dye-penetrant, ultrasonic or bend testing.

Remedies:To guarantee correct fusion, ensure that voltage and amperage are set correctly. If the operator is still having problems after making those adjustments, it may requirea change in the welding technique. For example, changing to a flux-cored wire orusing the spray arc transfer method instead. In spray arc transfer, the arc nevergoes out so cold lapping and lack of fusion are not issues. Spray arc welding takesplace at amperages high enough to melt the end of the wire and propel the dropletacross the arc into the weld puddle.

IV. Faulty Wire DeliveryIf the wire is not feeding smoothly or if the operator is experiencing a chatteringsound within the gun cable, there may be a problem with the wire delivery system.Most of the problems related to wire delivery are attributed to equipment set-upand maintenance.

Faulty Wire Delivery Problem #1: Contact TipThere is a tendency among operators to use oversized tips, which can lead tocontact problems, inconsistencies in the arc, porosity and poor bead shape.

Remedies:First, make sure that the contact tip in the gun is in working order and sizedappropriately to the wire being used. Visually inspect the tip and if it is wearing out(becoming egg-shaped), it will need to be replaced.

Faulty Wire Delivery Problem #2: Gun Liner A gun liner, like the contact tip, must be sized to the wire being fed through it. Italso needs to be cleaned or replaced when wire is not being fed smoothly.

Remedy:To clean the liner, blow it out with low-pressure compressed air from the contact tipend, or replace the liner.

Faulty Wire Delivery Problem #3: Worn Out GunInside the gun are very fine strands of copper wire that will eventually break andwear out with time.

Remedy:If the gun becomes extremely hot during use in one particular area, that is anindication that there is internal damage and it will need to be replaced. In addition,be certain that the gun is large enough for the application. Operators like to usesmall guns since they are easy on the hand, but if the gun is too small for theapplication, it will overheat.

Faulty Wire Delivery Problem #4: Drive Roll Drive rolls on the wire feeder periodically wear out and need to be replaced.

Remedies:There are usually visual indications of wear on the grooves of the rolls if replacement is necessary. Also, make sure that the drive roll tension is setproperly. To check tension, disconnect the welding input cable from the feeder orswitch to the cold feed option. Feed the wire and pinch it as it exits the gun withthe thumb and forefinger. If the wire can be stopped by pinching, more drive rolltension is needed. The optimum tension will be indicated by feeding that is notstopped while pinching the wire. If the drive roll tension is too high, it may deform


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the wire leading to birdnesting (tangling) and a burn back (when the arc climbs thewire and fuses the wire to the contact tip.)

Make sure that the drive rolls and the guide tube are as close together as possible.Next, check the path from where the wire leaves the reel to where it enters thedrive rolls. The wire must line up with the incoming guide tubes so there is noscrapping of the wire as it goes through the tube. On some wire feeders, the wirespool position is adjustable -- align it so that it makes a straight path into the tube.

Faulty Wire Delivery Problem #5: Wire Coming Off Reel and TanglingSome wire feeding problems occur because the inertia from the wire reel causes itto coast after the gun trigger is released.

Remedy:If the reel continues to coast, the wire on the reel will loosen and the wire maycome off or become tangled. Most wire feeding systems have an adjustable brakeon the wire reel. The brake tension should be set so that the reel does not coast.

By following these four guidelines, a GMAW operator new to the world of welding oreven someone more experienced should have an easier time diagnosing problemsbefore they affect the quality of the work.

Prevention and Control of Weld Distortion

Beginning welders and even those that are more experienced commonly strugglewith the problem of weld distortion, (warping of the base plate caused by heat fromthe welding arc). Distortion is troublesome for a number of reasons, but one of themost critical is the potential creation of a weld that is not structurally sound. Thisarticle will help to define what weld distortion is and then provide a practicalunderstanding of the causes of distortion, effects of shrinkage in various types of welded assemblies and how to control it, and finally look at methods for distortion

control.

What is Weld Distortion?Distortion in a weld results from the expansion and contraction of the weld metaland adjacent base metal during the heating and cooling cycle of the weldingprocess. Doing all welding on one side of a part will cause much more distortionthan if the welds are alternated from one side to the other. During this heating andcooling cycle, many factors affect shrinkage of the metal and lead to distortion,such as physical and mechanical properties that change as heat is applied. For

Fig. 3-1 Changes in the properties of steel withincreases in temperature complicate analysis of what happens during the welding cycle - and,thus, understanding of the factors contributing toweldment distortion.


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example, as the temperature of the weld area increases, yield strength, elasticity,and thermal conductivity of the steel plate decrease, while thermal expansion andspecific heat increase (Fig. 3-1). These changes, in turn, affect heat flow anduniformity of heat distribution.

Reasons for DistortionTo understand how and why distortion occurs during heating and cooling of ametal, consider the bar of steel shown in Fig. 3-2. As the bar is uniformly heated, itexpands in all directions, as shown in Fig. 3-2(a). As the metal cools to roomtemperature it contracts uniformly to its original dimensions.

But if the steel bar is restrained -as in avise - while it is heated, as shown in Fig.3-2(b), lateral expansion cannot takeplace. But, since volume expansion mustoccur during the heating, the bar expandsin a vertical direction (in thickness) andbecomes thicker. As the deformed barreturns to room temperature, it will stilltend to contract uniformly in alldirections, as in Fig. 3-2 (c). The bar isnow shorter, but thicker. It has beenpermanently deformed, or distorted. (Forsimplification, the sketches show thisdistortion occurring in thickness only. Butin actuality, length is similarly affected.)

In a welded joint, these same expansion and contraction forces act on the weld

metal and on the base metal. As the weld metal solidifies and fuses with the basemetal, it is in its maximum expanded from. On cooling, it attempts to contract tothe volume it would normally occupy at the lower temperature, but it is restrainedfrom doing so by the adjacent base metal. Because of this, stresses develop withinthe weld and the adjacent base metal. At this point, the weld stretches (or yields)and thins out, thus adjusting to the volume requirements of the lower temperature.But only those stresses that exceed the yield strength of the weld metal arerelieved by this straining. By the time the weld reaches room temperature -assuming complete restraint of the base metal so that it cannot move - the weldwill contain locked-in tensile stresses approximately equal to the yield strength of the metal. If the restraints (clamps that hold the workpiece, or an opposingshrinkage force) are removed, the residual stresses are partially relieved as they

cause the base metal to move, thus distorting the weldment.

Shrinkage Control - What You Can Do to Minimize DistortionTo prevent or minimize weld distortion, methods must be used both in design andduring welding to overcome the effects of the heating and cooling cycle. Shrinkagecannot be prevented, but it can be controlled. Several ways can be used tominimize distortion caused by shrinkage:

1. Do not overweld

The more metal placed in a joint, the greater the shrinkage forces. Correctlysizing a weld for the requirements of the joint not only minimizes distortion, but

also saves weld metal and time. The amount of weld metal in a fillet weld canbe minimized by the use of a flat or slightly convex bead, and in a butt joint by

Fig. 3-2 If a steel bar is uniformly heated whileunrestrained, as in (a), it will expand in alldirections and return to its original dimentions oncooling. If restrained, as in (b), during heating, itcan expand only in the vertical direction - becomethicker. On cooling, the deformed bar contractsuniformly, as shown in (c), and, thus, ispermanently deformed. This is a simplifiedexplanation of basic cause of distortion in weldingassemblies.


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proper edge preparation and fitup. The excess weld metal in a highly convexbead does not increase the allowable strength in code work, but it does increaseshrinkage forces.

When welding heavy plate (over 1 inch thick) bevelling or even double bevelling

can save a substantial amount of weld metal which translates into much lessdistortion automatically.

In general, if distortion is not a problem, select the most economical joint. If distortion is a problem, select either a joint in which the weld stresses balanceeach other or a joint requiring the least amount of weld metal.

2. Use intermittent welding

Another way to minimize weld metal isto use intermittent rather thancontinuous welds where possible, as inFig. 3-7(c). For attaching stiffeners toplate, for example, intermittent weldscan reduce the weld metal by as muchas 75 percent yet provide the neededstrength.

3. Use as few weld passes aspossible

Fewer passes with large electrodes,Fig. 3-7(d), are preferable to a greaternumber of passes with small electrodeswhen transverse distortion could be aproblem. Shrinkage caused by eachpass tends to be cumulative, therebyincreasing total shrinkage when manypasses are used.

4. Place welds near the neutralaxis

Distortion is minimized by providing asmaller leverage for the shrinkageforces to pull the plates out of alignment. Figure 3-7(e) illustrates

this. Both design of the weldment andwelding sequence can be usedeffectively to control distortion.

5. Balance welds around theneutral axis

This practice, shown in Fig. 3-7(f),offsets one shrinkage force withanother to effectively minimizedistortion of the weldment. Here, too,design of the assembly and proper

sequence of welding are importantfactors.


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6. Use backstep welding

In the backstep technique, the generalprogression of welding may be, say,from left to right, but each bead

segment is deposited from right to leftas in Fig. 3-7(g). As each beadsegment is placed, the heated edgesexpand, which temporarily separatesthe plates at B. But as the heat movesout across the plate to C, expansionalong outer edges CD brings the platesback together. This separation is mostpronounced as the first bead is laid.With successive beads, the platesexpand less and less because of therestraint of prior welds. Backsteppingmay not be effective in all applications,and it cannot be used economically inautomatic welding.

Fig. 3-7 Distortion can be prevented or minimized bytechniques that defeat - or use constructively - theeffects of the heating and cooling cycle.

7. Anticipate the shrinkage forces

Presetting parts (at first glance, Ithought that this was referring tooverhead or vertical welding positions,which is not the case) before weldingcan make shrinkage performconstructive work. Several assemblies,preset in this manner, are shown in

Fig. 3-7(h). The required amount of preset for shrinkage to pull the platesinto alignment can be determined froma few trial welds.

Prebending, presetting or prespringingthe parts to be welded, Fig. 3-7(I), is asimple example of the use of opposingmechanical forces to counteractdistortion due to welding. The top of the weld groove - which will containthe bulk of the weld metal - is

lengthened when the plates are preset.Thus the completed weld is slightlylonger than it would be if it had beenmade on the flat plate. When theclamps are released after welding, theplates return to the flat shape, allowingthe weld to relieve its longitudinalshrinkage stresses by shortening to astraight line. The two actions coincide,and the welded plates assume thedesired flatness.

Another common practice for balancingshrinkage forces is to position identical


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weldments back to back, Fig. 3-7(j),clamping them tightly together. Thewelds are completed on bothassemblies and allowed to cool before

the clamps are released. Prebendingcan be combined with this method byinserting wedges at suitable positionsbetween the parts before clamping.

In heavy weldments, particularly, the rigidity of the members and theirarrangement relative to each other may provide the balancing forces needed.If these natural balancing forces are not present, it is necessary to use othermeans to counteract the shrinkage forces in the weld metal. This can beaccomplished by balancing one shrinkage force against another or by creatingan opposing force through the fixturing. The opposing forces may be: othershrinkage forces; restraining forces imposed by clamps, jigs, or fixtures;restraining forces arising from the arrangement of members in the assembly;or the force from the sag in a member due to gravity.

8. Plan the welding sequence

A well-planned welding sequence involves placing weld metal at differentpoints of the assembly so that, as the structure shrinks in one place, itcounteracts the shrinkage forces of welds already made. An example of this iswelding alternately on both sides of the neutral axis in making a complete jointpenetration groove weld in a butt joint, as in Fig. 3-7(k). Another example, ina fillet weld, consists of making intermittent welds according to the sequencesshown in Fig. 3-7(l). In these examples, the shrinkage in weld No. 1 isbalanced by the shrinkage in weld No. 2.

Clamps, jigs, and fixtures that lock parts into a desired position and hold themuntil welding is finished are probably the most widely used means forcontrolling distortion in small assemblies or components. It was mentionedearlier in this section that the restraining force provided by clamps increasesinternal stresses in the weldment until the yield point of the weld metal isreached. For typical welds on low-carbon plate, this stress level wouldapproximate 45,000 psi. One might expect this stress to cause considerablemovement or distortion after the welded part is removed from the jig orclamps. This does not occur, however, since the strain (unit contraction) fromthis stress is very low compared to the amount of movement that would occurif no restraint were used during welding.

9. Remove shrinkage forces after welding

Peening is one way to counteract the shrinkage forces of a weld bead as itcools. Essentially, peening the bead stretches it and makes it thinner, thusrelieving (by plastic deformation) the stresses induced by contraction as themetal cools. But this method must be used with care. For example, a rootbead should never be peened, because of the danger of either concealing acrack or causing one. Generally, peening is not permitted on the final pass,because of the possibility of covering a crack and interfering with inspection,and because of the undesirable work-hardening effect. Thus, the utility of thetechnique is limited, even though there have been instances where between-pass peening proved to be the only solution for a distortion or crackingproblem. Before peening is used on a job, engineering approval should be


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obtained.

Another method for removing shrinkage forces is by thermal stress relieving -controlled heating of the weldment to an elevated temperature, followed bycontrolled cooling. Sometimes two identical weldments are clamped back to

back, welded, and then stress-relieved while being held in this straightcondition. The residual stresses that would tend to distort the weldments arethus minimized.

10. Minimize welding time

Since complex cycles of heating and cooling take place during welding, andsince time is required for heat transmission, the time factor affects distortion.In general, it is desirable to finish the weld quickly, before a large volume of surrounding metal heats up and expands. The welding process used, type andsize of electrode, welding current, and speed of travel, thus, affect the degreeof shrinkage and distortion of a weldment. The use of mechanized weldingequipment reduces welding time and the amount of metal affected by heat

and, consequently, distortion. For example, depositing a given-size weld onthick plate with a process operating at 175 amp, 25 volts, and 3 ipm requires87,500 joules of energy per linear inch of weld (also known as heat input). Aweld with approximately the same size produced with a process operating at310 amp, 35 volts, and 8 ipm requires 81,400 joules per linear inch. The weldmade with the higher heat input generally results in a greater amount of distortion. (note: I don't want to use the words "excessive" and "more thannecessary" because the weld size is, in fact, tied to the heat input. In general,the fillet weld size (in inches) is equal to the square root of the quantity of theheat input (kJ/in) divided by 500. Thus these two welds are most likely not thesame size.

Other Techniques for Distortion Control

Water-Cooled Jig

Fig. 3-33 A water-cooled jig for rapid removalof heat when welding sheet meta.

Various techniques have been developed tocontrol distortion on specific weldments. Insheet-metal welding, for example, a water-cooled jig (Fig. 3-33) is useful to carry heataway from the welded components. Coppertubes are brazed or soldered to copperholding clamps, and the water is circulated

through the tubes during welding. Therestraint of the clamps also helps minimizedistortion.

Strongback

The "strongback" is another usefultechnique for distortion control during buttwelding of plates, as in Fig. 3-34(a). Clipsare welded to the edge of one plate andwedges are driven under the clips to forcethe edges into alignment and to hold themduring welding.

Thermal Stress Relieving


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Except in special situations, stress relief byheating is not used for correcting distortion.There are occasions, however, when stressrelief is necessary to prevent furtherdistortion from occurring before theweldment is finished.

Summary: A Checklist to Minimize DistortionIn summary, follow the checklist below in order to minimize distortion in the designand fabrication of weldments:

Do not overweld. Control fitup. Use intermittent welds where possible and consistent with design

requirements. Use the smallest leg size permissible when fillet welding. For groove welds, use joints that will minimize the volume of weld metal.

Consider double-sided joints instead of single-sided joints. Weld alternately on either side of the joint when possible with multiple-pass

welds. Use minimal number of weld passes. Use low heat input procedures. This generally means high deposition rates

and higher travel speeds. Use welding positioners to achieve the maximum amount of flat-position

welding. The flat position permits the use of large-diameter electrodes andhigh-deposition-rate welding procedures.

Balance welds about the neutral axis of the member. Distribute the welding heat as evenly as possible through a planned welding

sequence and weldment positioning. Weld toward the unrestrained part of the member. Use clamps, fixtures, and strongbacks to maintain fitup and alignment.

Prebend the members or preset the joints to let shrinkage pull them backinto alignment. Sequence subassemblies and final assemblies so that the welds being made

continually balance each other around the neutral axis of the section.

Following these techniques will help minimize the effects of distortion and residualstresses.

Storing and Re-drying Stick Electrodes


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Electrodes for Shielded Metal Arc Welding(SMAW) or stick electrodes must be properlystored in order to deposit quality welds. Whenstick electrodes absorb moisture from theatmosphere, they must be dried in order torestore their ability to deposit quality welds.Electrodes with too much moisture may leadto cracking or porosity. Operationalcharacteristics may be affected as well. If you've experienced unexplained weld crackingproblems, or if the stick electrode arcperformance has deteriorated, it may be due to your storage methods or re-dryingprocedures.

Follow these simple storage, exposure and re-drying techniques to ensure thehighest quality welds, as well as the best operational characteristics from your stickelectrodes.

Storing Low Hydrogen Stick Electrodes

Low hydrogen stick electrodes must be dry to performproperly. Unopened Lincoln hermetically sealedcontainers provide excellent protection in goodstorage conditions. Opened cans should be stored in acabinet at 250 to 300F (120 to 150C).

Low hydrogen stick electrode coatings that havepicked up moisture may result in hydrogen inducedcracking, particularly in steels with a yield strength of 80,000 psi (550 MPa) and higher.

Moisture resistant electrodes with an "R" suffix in their AWS classification have ahigh resistance to moisture pickup coating and, if properly stored, will be lesssusceptible to this problem, regardless of the yield strength of the steel beingwelded. Specific code requirements may indicate exposure limits different fromthese guidelines.

All low hydrogen stick electrodes should be stored properly, even those with an "R"suffix. Standard EXX18 electrodes should be supplied to welders twice per shift.Moisture resistant types may be exposed for up to 9 hours.

When containers are punctured or opened, low hydrogen electrodes may pick upmoisture. Depending upon the amount of moisture, it will damage weld quality inthe following ways:

1. A greater amount of moisture in low hydrogen electrodes may cause porosity.Detection of this condition requires x-ray inspection or destructive testing. If thebase metal or weld metal exceeds 80,000 psi (550 MPa) yield strength, thismoisture may contribute to under-bead or weld cracking.

2. A relatively high amount of moisture in low hydrogen electrodes causes visibleexternal porosity in addition to internal porosity. It also may cause excessive slag

fluidity, a rough weld surface, difficult slag removal, and cracking.
http://www.lincolnelectric.com/knowledge/articles/content/awsclassification.asp%20http://www.lincolnelectric.com/knowledge/articles/content/awsclassification.asp%20


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3. Severe moisture pickup can cause weld cracks in addition to under-beadcracking, severe porosity, poor appearance and slag problems.

Re-drying Low Hydrogen Stick Electrodes

Re-drying, when done correctly, restores theelectrodes' ability to deposit quality welds.Proper re-drying temperature depends uponthe electrode type and its condition.

One hour at the listed final temperature issatisfactory. DO NOT dry electrodes at highertemperatures. Several hours at lowertemperatures is not equivalent to using thespecified requirements.

Electrodes of the E8018 and higher strengthclassifications should be given no more than three one-hour re-dries in the 700 to800F (370 to 430C) range. This minimizes the possibility of oxidation of alloys inthe coating resulting in lower than normal tensile or impact properties.

Any low hydrogen electrode should be discarded if excessive re-drying causes thecoating to become fragile and flake or break off while welding, or if there is anoticeable difference in handling or arc characteristics, such as insufficient arcforce.

Electrodes to be re-dried should be removed from the can and spread out in theoven because each electrode must reach the drying temperature.

Re-Drying Conditions - Low Hydrogen Stick Electrodes

ConditionPre-drying

Temperature(1)

Final Re-drying Temperature

E7018, E7028E8018, E9018,

E10018, E11018

Electrodes exposed to airfor less than one week; nodirect contact with water.

N/A 650 to 750F(340 to 400C)700 to 800F

(370 to 430C)

Electrodes which havecome in direct contactwith water or which havebeen exposed to highhumidity.

180 to 220F(80 to 105C)

650 to 750F(340 to 400C)

700 to 800F(370 to 430C)

(1) Pre-dry for 1 to 2 hours. This will minimize the tendency for coating cracks or oxidation of thealloys in the coating.

Storing and Re-drying Non-Low HydrogenElectrodes

Electrodes in unopened Lincoln cans or cartons retainthe proper moisture content indefinitely when storedin good condition.


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If exposed to humid air for long periods of time, stick electrodes from openedcontainers may pick up enough moisture to affect operating characteristics or weldquality. If moisture appears to be a problem, store electrodes from the openedcontainers in heated cabinets at 100 to 120F (40 to 50C). DO NOT use highertemperatures, particularly for electrodes from the "Fast Freeze" group.

Some electrodes from wet containers or long exposure to high humidity can be re-dried. Adhere to the procedures in the following table for each type.

Re-Drying Conditions - Non-Low Hydrogen Stick Electrodes

Stick Electrode Electrode Group

Final Re-drying

Temperature Time

E6010: Fleetweld 5P, 5P+E6011: Fleetweld 35, 35LS, 180E7010-A1: SA-85(1)E7010-G: SA-HYP+(1)E8010-G: SA-70+(1), SA-80(1)E9010-G: SA-90(1)

Fast Freeze - Excessivemoisture is indicated bya noisy arc and highspatter, rusty core wireat the holder end orobjectionable coatingblisters while welding.

Re-baking of thisgroup of stickelectrodes is notrecommended.

NotRecommended N/A

E7024: Jetweld 1, 3E6027: Jetweld 2

Fast Fill - Excessivemoisture is indicated bya noisy or "digging" arc,high spatter, tight slag,or undercut. Pre-dryunusually dampelectrodes for 30 - 45minutes at 200F to230F (90 - 110C)before final drying tominimize cracking of thecoating.

400 to 500F(200 to 260C)

30 - 45minutes

E6012: Fleetweld 7E6013: Fleetweld 37

E7014: Fleetweld 47E6022: Fleetweld 22

Fill Freeze - Excessivemoisture is indicated by

a noisy or "digging" arc,high spatter, tight slagor undercut. Pre-dryunusually dampelectrodes for 30 - 45minutes at 200 - 230F(90 - 110C) beforefinal drying to minimizecracking of the coating.

300 to 350F(150 to 180C)

20 - 30minutes

(1) Pre-dry for 1 to 2 hours. This will minimize the tendency for coating cracks or oxidation of thealloys in the coating.


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Using longer drying times or higher temperatures can easily damage the electrodes.For drying, remove the electrodes from the container and spread them out in thefurnace because each stick electrode must reach the drying temperature.

Product Comparison: Stick Electrodes - Mild and Low Alloy SteelsClick on Trade Name to view all Products offered in the Product family.

TradeName

AWSClass Polarity Description

Fast Freeze, Out-of-Position, Mild Steel Stick Electrodes

Fleetweld35 E6011

AC,DC+,DC-

Operators consistently give this electrode high marks. This qualityLincoln product is a proven performer for AC pipe welding applicationsand sheet metal welding. Fleetweld 35 is a great electrode to use on jobswhere the steel isnt clean.

Fleetweld35LS E6011

AC,DC+,DC-

Great for making tack welds under Innershield deposits. Use Fleetweld

35LS with confidence on plated, dirty, painted, or greasy steel. It's anoutstanding stick choice for AC pipe welding, for applications that requiredeep penetration, and in jobs where x-ray quality welds are required.

Fleetweld180 E6011

AC,DC+,DC-

Got a small AC welder? Here's your electrode! Fleetweld 180 offersexcellent arc stability for excellent performance with power sources aslow as 50V open-circuit voltage (OCV). A great stick electrode with theability to start easily on low open circuit voltage welders.

Fleetweld22 E6022 AC, DC-

Developed specifically for roof decking and other applications whereburnthrough spot welding on sheet metal is required. Fleetweld 22 isgreat for galvanized or plated steel, as well as on steel that is painted ordirty.

Fast-Fill, High Deposition, Mild Steel Stick Electrodes

Jetweld 2 E6027AC,

DC+,

DC-

When the job demands x-ray quality welds, high deposition rates, andexcellent wash-in, reach for Jetweld 2. Weve designed Jetweld 2 for

peak performance on multiple pass welds, and fast-fill single pass welds.

Jetweld 3 E7024AC,

DC+,DC-

Jetweld 3s high deposition rates, and smooth ripple-free beads make ita great choice for welding on mild steel. It is especially effective formulti-pass welds and fast-fill single pass welds.

Jetweld 1 E7024-1AC,

DC+,DC-

When the project involves large welds, you cant pick a more user-friendly electrode! Operators appreciate Jetweld 1s smooth bead andhigh deposition rates. A great general purpose electrode for single ormulti-pass applications.

Fill Freeze, High Speed, Mild Steel Stick Electrodes

Fleetweld7 E6012 AC, DC-

Got a variety of jobs that a single all-position electrode has to handle?Choose Lincoln Electrics Fleetweld 7. This versatile, high-speedelectrode is a real workhorse on sheet metal lap and fillet welds. Its a lsoa great choice for welding poor fit-up welding jobs.

Fleetweld37 E6013AC,

DC+,DC-

Heres a terrific all-position electrode for low amp welding on sheetmetal -- especially in applications where appearance is important. Wevedesigned Fleetweld 37 for excellent performance with smaller AC welderswith low open-circuit voltages. Its an excellent choice for jobs involvingirregular or short welds that require a change in position.

Fleetweld47 E7014

AC,DC+,DC-

Fleetweld 47 features high deposition rates for fast performance.Operators love this easy-to-use, all-position electrode! Choose Fleetweld47 for sheet metal lap joints and fillet welds, general purpose platewelding and maintenance jobs.

Low Hydrogen, Mild Steel Stick Electrodes

Excalibur7018 MR

E7018H4R AC, DC+

Theres a long list of reasons why operators are so loyal to Excalibur7018 MR. They tell us they love the clean puddle, the square coatingburnoff, the easy all-position handling and the excellent wash-incharacteristics. Its a terrific choice for jobs that involve steels with poorweldability.

Excalibur7018-1

MRE7018-1H4R AC, DC+

When the job involves critical, out-of-position welding, reach for Lincoln

Electrics Excalibur 7018-1 MR. It offers a beautifully clean weld puddle,uniform slag follow, and superior wash-in with no undercutting. Alsogreat for welding on steels with marginal weldability.
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