Lincoln Electric Named Official Sponsor Of Exxon Flyin' Tiger Aircraft

Lincoln Electric Named Official Sponsor Of Exxon Flyin' Tiger Aircraft Plane Holds 25 Altitude and Time to Climb World Records Reaching an altitude of 20,000 feet in six minutes and 40 seconds after take off may not be for everyone, but for Bruce Bohannon, the pilot and owner of the Exxon Flyin' Tiger, it is just one in many record-breaking flights his aircraft has accomplished. The Exxon Flyin' Tiger of Angleton, Texas, currently holds 25 altitude and time to climb world records. The Lincoln Electric Company has recently become an official sponsor of this specially modified kit plane. According to the National Aeronautics Association's (NAA) World & U.S. Aviation & Space Records publication, the Exxon Flyin' Tiger currently is the world's fastest climbing piston aircraft in the unlimited class to 20,000, 30,000 and 40,000 feet. In the C1-B weight class, which includes aircraft from 1,100 to 2,200 pounds, the plane holds every altitude and time to climb record. Time to climb is defined as how quickly the plane reaches a specified altitude from the ground. Bohannon performs these record-breaking flights in conjunction with Experimental Aircraft Association (EAA) events such as the annual AirVenture in Oshkosh, Wis., and the Sun ‘N Fun fly-in in Lakeland, Fla. During these attempts, an NAA official is present to certify the results. A video camera in the plane's cockpit is positioned at the instrument panel to verify altitude. An official clock on the panel records the time a specific altitude is reached. According to Bohannon, for working on an aircraft this special, he only wants the best equipment and that's why he turned to Lincoln Electric. "For a high performance plane, you don't want to be second guessing the weld quality, especially at high altitudes where temperatures can be 70 degrees below zero and the engine is being pushed to the limit," said Bohannon. Previously, Bohannon and his crew chief Gary Hunter were using an oxyacetylene process to weld the mostly aluminum body of the Exxon Flyin' Tiger, but recently have made the switch to a TIG process and Lincoln's Invertec® V205-T AC/DC. "TIG offers much higher quality, less corrosion and a strong weld," noted Bohannon. "When you are pushing a plane to its limits, quality can't be compromised." For years now, Bohannon has used Lincoln equipment around his farm and air field for repairs and building farm implements. He recently began using the Power MIG 255. "It's fantastically easy to use and reliable. This is the first MIG machine I've ever owned and it is so much easier compared to Stick." Lincoln's Ranger® 250 engine-driven welder / generator also proves handy on the farm, since it generates its own power for welding and can be used anywhere. The Bohannons have also used the Ranger's ability to generate AC auxiliary power to run lights, tools and other necessities during power outages. But the equipment is not the only thing that has impressed Bohannon about Lincoln. "The company's service has been absolutely impeccable," said Bohannon. "Delivery has always been on time and I appreciated all the help provided by Lincoln's Scott Skrjanc in specifying machines that would work best for us." What's next for the Exxon Flyin' Tiger? Bohannon has two goals in mind. The first is to be the highest flying piston airplane in American history. That record is currently held by a World War II B-29 Bomber at 47,910 feet. The second goal is to hold the unlimited class' time to climb record in the 10,000 feet category. http://www.lincolnelectric.com

Shop Gains Productive Edge with Robotic Welding

Shop Gains Productive Edge with Robotic Welding

F.R. Custom Metal Fabricating Ltd. made a sound investment in the future with the recent purchase of its first robotic welding cell. Faced with a contract to produce a large volume of pallet truck handles, the fabricating shop found it increasingly difficult to maintain the skilled workforce of welders needed to produce consistent, high quality parts at the necessary volume. By adding a two-station Lincoln Electric automated welding system, the firm is now able to meet production and quality goals without trying to find employees willing to work overtime.

Robotics Help Custom Fabricator Tackle a Production Job

F.R., a custom fabricator founded 28 years ago by its President, Alfred Nonnewitz, traditionally has specialized in lower volume, higher quality fabrications, particularly those involving tubular components. For the last three or four years, the company has been producing pallet truck handles on a contract that calls for increasingly higher volumes, now generally between 700 and 1,000 parts per week, according to Bill Nonnewitz, the founder's son.

As with most manufacturing firms throughout North America, F.R. was finding it increasingly difficult to hire the skilled workers needed to maintain the quality and volume of its production. And with today's busy lifestyle, employees were less willing to work long overtime hours to keep up with the demand.

Robotics Not Just for Larger Shops

After meeting with representatives of The Lincoln Electric Company's Automated Systems Group (ASG), Alfred and Bill Nonnewitz concluded that the benefits of automating the handle-welding operation would be worth the investment.

The result is a complete two-station work cell that incorporates a six-axis Fanuc ARC Mate™100i robot equipped with a SYSTEM R-J3™ controller, a Lincoln Power Wave® 450 power source, and a Binzel ROBO-WH-455-22 water-cooled torch.

Safety was built into the welding cell with the addition of safety zone rings (limit switches) that prevent the robot and welding torch from going to the station where the operator is working on the next setup until the area is cleared. In addition, each station has a safety mat that prevents the robot from coming to that station if the operator is standing on the mat. Further safety protection is provided by a breakaway nozzle that minimizes damage in case the torch hits any part of the workstation or the parts being welded.

All components are mild steel, with the handle and brackets being 16 gage and the tube being 14 gage. Welds are made with .035" diameter Lincoln SuperArc® L-56™ (AWS ER70S-6) electrode, which includes extra deoxidizers that provide cleaning action and improve weld quality. Since the handles are used to move pallet trucks that weigh up to 5000 lbs., weld integrity is critical to meeting the stresses they must withstand. All welds are fillets, but the welds that join the round handle to the square tube are especially critical. Bill Nonnewitz explains, "The welding power source is capable of making a full regulated controlled weld without spatter or burn-through. Because we only have 1/16" on a side, the welds can't extend out very much. They have to be good, and the penetration has to be consistent."

A Packaged Approach to Automated Welding

Jim Grant explains that the entire workstation is modular and can be moved with a forklift. "It's essentially a plug-and-play robot that was placed on the floor as a complete unit, pre-programmed for the parts they make. Everything is mounted on a platform that keeps the units in proper relationship to one another and allows the cell to be moved easily to another location if needed."

The Lincoln PowerWave® 450 is a sophisticated power source that gives the company significant advantages, with cost savings that are expected to more than offset a slightly higher initial investment. First is the unit's capability for Pulsed MIG welding, an advanced welding mode that combines the best qualities of all other metal transfer modes without their disadvantages. Its lower heat input prevents burn-through on thin metals. Spatter and fume are reduced as well, which improves the working environment and reduces costs. Since only one wire size is required, wire and gas costs are also lower, and the process delivers higher deposition rates than other processes, so productivity is greater. In addition, the power source can be updated easily with new software, an important advantage that protects the company's investment.

The Fanuc ARC Mate™100i robot is designed with integral utilities to improve reliability and setup time. The wire feed motor cable, gas line and air line are all inside the robot arm. Its high motion speeds help improve productivity, and advanced servo-control features allow faster and smoother point-to-point motion.

The FANUC Robotics System R-J3 controller is completely integrated with the robot itself, which allows flexible work cell layout and easy installation. It utilizes the most advanced software with features that include welding restart, scratch start, and on-the-fly weld adjustment. Mirror image utility allows the programmer to shift an existing program and also to invert it, which is extremely useful with F.R. Custom Metal's two-station mirror-image cell. The program also allows starting and stopping the programmed welding sequence from the Teach Pendant, which features commands in English for ease of use.

The Binzel ROBO-WH-455-22W torch includes a wire-cutting feature that helps speed up maintenance and maintain productivity. Lincoln Electric's Jim Grant explains, "If the operator has to pull the nozzle out for cleaning or adjustment, it is designed to cut the wire cleanly. There is a key that releases the whole bottom nozzle assembly and cuts the wire, so you can make any adjustments on the bench instead of trying to make them while the nozzle is on the robot or having to cut the wire to remove the nozzle."

While no comparative figures were kept, the improvements in product quality and productivity have been significant since the company added the robotic cell, and the labor shortages it experienced earlier have been minimized. Bill Nonnewitz says that, since installing the robotic system a few months ago, the company has already seen significant savings, both in reduced overtime costs and in rework and scrap losses.

http://www.lincolnelectric.com

Extensive Use of Wire Welding Speeds Productivity on Cheyenne Plains Gas Pipeline Project

Extensive Use of Wire Welding Speeds Productivity on Cheyenne Plains Gas Pipeline Project
First Major X-80 Grade Pipe Project in U.S. Utilizes New Lincoln Wire

During the summer and fall of 2004, the plains of the west were busy with the hustle and bustle of cranes, trucks, heavy equipment and supplies to lay pipe for the Cheyenne Plains Gas Pipeline Project. The 380-mile, 36-inch natural gas pipeline runs from the Cheyenne hub in Colorado to existing pipelines near Greensburg, Kan. Once operational in early 2005, the pipeline will export 560 million cubic feet of natural gas per day from Wyoming to growing markets in the mid-continental U.S. and further east.

The $425 million pipeline, owned by El Paso Corporation, was being constructed in three spreads which were connected in the final phase of the project. Spread one was contracted to Associated Pipelines while spreads two and three were handled by U.S. Pipeline, Inc.

The Cheyenne Plains Gas Pipeline Project was the first major pipeline in the U.S. to use X-80 grade pipe. Already a standard in other parts of the world, the X-80 pipe provides higher strength with a thinner wall.

As on any pipeline project, welding plays a critical role in the construction process. But what made this project unique was the extensive use of wire welding to provide high productivity. A new consumable from the Lincoln Electric Company, the Pipeliner® G80M gas-shielded flux-cored wire, was selected by the evaluation team at U.S. Pipeline, Inc. for use on the pipe tie-ins at connection points and road crossings near populated areas. These welds, completed manually by independent pipeline contractors, connect the mainline pipe to the thicker walled pipe of the tie-ins.

For the mainline pipe, a CRC-Evans® automated welding system was used in combination with Lincoln’s premium SuperArc® L-56 copper-coated gas metal arc wire.

An Overview of the Pipe Installation Process
More than 140,000 tons of pipe and 25,000 individual sections were used to complete this project. Each section of pipe is 78-feet long and per industry standards, was buried at least 30 inches below the ground through a trenching process.

Much like an assembly line where each worker is responsible for a certain portion of the job, construction crews in each spread followed after each other along the length of the pipe to complete specialized tasks. Crews at the front staked the area and prepared the right-of-way. Those following behind aligned the pipe, welded and inspected the pipe and then lowered it into the trench. Finally, the construction crews at the rear were responsible for conducting hydrostatic pressure testing, backfilling the trench and restoring the land as close as possible to its original condition.

Welding Connection Points and Road Crossings
After a lengthy process of evaluating solid and flux-cored electrodes for the job, U.S. Pipeline, Inc. selected a .045-inch diameter Pipeliner G80M wire as the consumable of choice for the vertical up welding of the pipe tie-in fill and cap passes. The Cheyenne Plains Pipeline Project marked the first time this new consumable was used in the field and for many of the pipeline contractors, it was also the first time they had made the switch from a traditional Stick process to complete the tie-ins for the job.

“We chose the Lincoln Pipeliner G80M wire for this project for a number of reasons. First, it met the mechanical requirements of the job and also offered a crisper arc,” said Dana Bratcher, Welding Foreman, U.S. Pipeline, Inc. “In addition, we felt that the Lincoln product flowed better and was more durable for outdoor use. We also were attracted to the fact that the pipe supplied from the manufacturer was welded using a Lincoln consumable.”

This electrode, specifically designed for pipeline welding, is easier for the operator to use and provides a smooth arc, lower spatter levels and less frequent clogging of gun nozzles when compared to other flux-cored wire electrodes.

All tie-in welds were performed manually because of the specialized skills needed to handle fit-up issues between the thinner mainline pipe and thicker tie-ins. Each manual welding team consists of two welders, one on each side of the pipe performing one-half of the welding pass – root, hot, fill and cap. Each welder also had an assistant who performed tasks such as preheating the joints, setting the clamp to align the two lengths of pipe, setting up the welding equipment and completing the finish wire brushing on the joint.

Every tie-in weld was inspected with a radiographic process and throughout the job the weld quality had been excellent. “We had a low repair rate with the Lincoln wire. It was consistent and worked wonderfully,” noted Bratcher. “Our welding operators liked the fact that they were able to see how the puddle flowed.”

The use of Pipeliner G80M wire to weld the spiral seam pipe’s fill and cap passes provided significantly increased productivity and high quality welds. “The wire is about three to five times faster than stick welding,” said Ray Edwards, an independent pipeline welder from the Pipeliners Union 798 and one of the welders on Spread Two of the project. “The same length of weld bead that would take up to five minutes with stick welding is now taking me about one minute.”

In addition, Lincoln’s Shield-Arc 70+ stick electrode was used to complete the tack welds and vertical down root pass on these tie-ins. This rod was chosen for its ability to accomplish the out-of-position welding required for this job.

On-Site Support and Equipment
For the pipe tie-in welding, Lincoln fully supported the welding efforts from the initial qualifying of the consumables to on-site assistance to ensure the independent contractors weren’t subject to any downtime.

According to Dave Thomas, District Manager in Lincoln’s Tulsa Office, he and representatives from the Cleveland headquarters were present while the Pipeliner G80M consumable was being tested by for the job against competitive consumables. “We watched as U.S. Pipeline officials welded with each of the consumables. The Pipeliner wire product was much more proficient in operator appeal and also created a better looking weld. In addition, it also came out on top after destructive tests on the plate in the lab,” said Thomas.

Thomas also described how once the G80M product was selected, Lincoln representatives qualified the procedures for the wire and were close at hand to answer questions and provide technical assistance as U.S. Pipeline qualified their operators.

During initial start-up of the job in the field, Lincoln representatives were at the site three to four days per week, and at least one day a week on an ongoing basis throughout the project’s duration.

“The Lincoln consumables ran flawlessly on the job with great operator appeal and ease of use,” commented Steve Duren, Technical Sales Representative from Lincoln Electric’s Denver office. “The only issues we addressed with consumables were questions about techniques and proper drag and push angles. On a project of this magnitude, having so few issues was exceptionally good.”

David Fullen, Lincoln Electric Denver District Manager echoed these same words about the Pipeliner G80M electrode. “For many of the welding operators on the job, this was one of the first times they had wire welded. What’s remarkable is that they adapted so well and never had any complaints with the wire. The integration of the wire welding has gone smoothly and the job finished ahead of schedule. Most of our time spent on the job site was addressing equipment issues.”

Although a competitive brand of welding equipment was specified for the job, its alarming failure rate and resulting downtime prompted Lincoln to step in and provide equipment.

“We received an urgent call about equipment when the contractors were struggling with the competitive wire feeders. We were able to answer the call and overnight equipment to the field,” said Fullen. “We sent Lincoln LN-15 wire feeders with accompanying Magnum welding guns to the job which remedied the situation. We also spent time on site providing technical assistance, setting up the equipment and installing wire feed CV modules. We were dedicated to keeping the customer up and running.”

“Throughout this project I received great service from Lincoln,” explained Bratcher. “With a phone call, I would have what I needed either hand delivered or on site the next day.”

For this project, Lincoln Electric partnered with distributor Airgas Intermountain to supply select consumables and equipment to the site as well as an 85 percent/15 percent argon blend shielding gas. According to Mark Duncan, General Manager-East for Airgas Intermountain, Airgas provided additional on-site support to augment Lincoln’s efforts. “We have a strong relation with the Lincoln Denver office and worked as a team. I couldn’t have asked for better support from them,” said Duncan. “I also tip my hat to our field person, Tom McClelland, who did a fantastic job providing technical assistance, process help and service for the equipment when necessary.”

Welding Pipe Mainline
For welding the mainline pipe of the Cheyenne Plains Gas Pipeline, Lincoln consumables also played a prominent role. A CRC-Evans® automated pipe welding system was utilized to automatically weld the circumference of the pipe using a gas metal arc process for high productivity.

The system was used in combination with Lincoln’s premium SuperArc® L-56 copper-coated gas metal arc wire for welding the pipe’s outside diameter, consisting of hot, fill and split cap passes. This .040-inch diameter wire, provided specifically for this project, offers superior feedability and excellent arc characteristics, a result of Lincoln’s manufacturing which uses a strictly controlled chemistry process. All mainline welds are inspected using automatic ultrasonic tests.

“From a business perspective, it was a good decision for us to work with a domestic consumable supplier such as Lincoln Electric,” said Brian Laing, President of CRC-Evans. “From a technical standpoint, the mechanical property requirements for the project were easily met by the SuperArc L-56 wire. Our direct customers, the construction contractors, and ultimately the pipeline owner, were satisfied with the overall quality of the welding and productivity achieved, thanks in part to the Lincoln electrode selected.”

According to Peter Nicholson, Manager of Pipeline Products at The Lincoln Electric Company, providing consumables for the Cheyenne Plains Gas Pipeline required a coordinated effort between many Lincoln entities including its International Division, the Cleveland headquarters, and Lincoln’s Houston district office.

“Six months prior to the start of pipeline construction, consumables were tested in the Houston office to ensure the weld procedures with the consumable complied with the strict industry standards for this job. Lincoln engineers worked closely with CRC-Evans personnel to ensure the right consumable for the job was selected,” said Nicholson.

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Multiple-Wire Welding Creates High Productivity and High Quality

Multiple-Wire Welding Creates High Productivity and High Quality at Berg Steel Pipe Corporation Welding Techniques Produce Faster Travel Speeds and Improve Mechanical Properties As a key supplier to the Gulfstream Pipe Project, Berg Steel Pipe Corporation of Panama City, Florida is challenged with producing high-quality, defect-free linepipe at top levels of productivity. To do this, the company employs a number of innovative welding systems, which includes a continuous seam tacking system as well as inside diameter (ID) and outside diameter (OD) pipe welding stations that use multiple wire welding techniques. In comparison to two-wire submerged arc welding (SAW) systems, Berg's techniques have created welding travel speeds that are three times greater for welding the ID and four times greater for OD welding on 0.820" thick pipes. In addition, total heat input has been decreased by 25 percent while overall mechanical weld properties have been improved by these systems. Overall, employing multiple-wire welding has enabled Berg Steel to produce 40 foot long 0.820" thick pipes at a rate of 14 pipes per hour. During 2001, Berg manufactured for the Gulfstream Project, a natural gas pipeline that originates near Pascagoula, Mississippi and crosses the Gulf of Mexico to Manatee County, Florida. Once onshore, the pipeline stretches across south and central Florida to Palm Beach County. This natural gas pipeline will serve Florida utilities and power generation facilities, generating 1.1 billion cubic feet per day of additional natural gas - enough to supply electricity for 4.5 million homes. For Phase One of this project, the offshore portion, Berg Steel Pipe along with its parent company, Europipe GmbH in Germany, supplied 443 miles of pipe in only six months. In Phase Two, Berg will produce 292 more miles for the onshore pipeline. A 40 foot long sheet is being loaded into the planer for edge preparation. Transformation Berg Pipe's welding systems have been supplied by The Lincoln Electric Company and its German subsidiary and system designer, Uhrhan & Schwill. These systems help Berg achieve high production levels. It also makes the company hard to match in terms of welding technology and innovation. "Welding technology has allowed us to transform a facility that was built in 1980 to produce 5,000 tons of pipe per month to a facility that produced more than 40,000 tons per month during the Gulfstream Project," said John Burton, General Manager of Production, Berg Steel Pipe Corporation. "We needed to add the multiple-wire processes because we don't have enough square footage to add more welding stations. We have to make use of the technology on the market to be the most efficient plant possible in the space we have available." Berg is able to service customers that range from oil and gas transmission companies to pipe distributors. The 275-employee company also manufactures structural piling and is even qualified to produce linepipe to arctic specifications with weld metal Charpy requirements to -50° F. Berg Steel Pipe Corporation can supply to this broad range of customers because of the flexibility of its three-roll bending type forming process, which offers a unique advantage to do quick changeovers so the company can accept both small and large projects. Not only does project size vary, but so does the type of pipe produced. Berg can manufacture in diameters ranging from 24" through 64" and wall thicknesses from 0.250" to 1.500". Grades that can be handled at the Berg facility are API Grade B through X80 For purposes of this article, we will look at the pipe produced for the Gulfstream Project in particular, and the productivity and efficiencies achieved during the welding of the pipe as it proceeded through Berg's mill. The majority of the offshore linepipe was 36" diameter, 0.820" (20.8 mm) thick API 5L Grade X70 produced in 40-foot nominal lengths. The 40 foot long sheet is formed into a tube by Berg's Tri-Roll Bender. Preparation of Plates Before welding, Berg planes the plates to the precise required width and bevels the plate edges for longitudinal seam welding. This beveling operation prepares plate edges with a double V groove joint design for the upcoming welding operations. After plate edge preparation, the plate is formed into a rough tubular shape by a three-roll bending machine (pyramid roll). Final tubular forming is subsequently completed by rounding the longitudinal edges of the plate between a hydraulically cushioned top ball and matching hourglass roll. Once the plate is formed into the proper tubular shape, the longitudinal weld is completed in three passes, beginning with a continuous tack weld. For the Gulfstream Project, the longitudinal welding procedures were qualified to both ASME Section IX and Berg's internal standards. Tack Welding The tack welding system is designed to secure the welding edges in proper alignment for welding and to provide continuous backing for subsequent inside submerged arc welding. This process is completed at Berg Steel Pipe using a welding system purchased two years ago to remedy a bottleneck the company was experiencing in this stage of the manufacturing process. The formed tube is tack-welded at the laser-guided continuous tack welding station. In 1999, Berg had a single, DC 1500 power source. For every diameter change in pipe, the system would require 45 minutes to change out the cage that positioned the plate edges for welding. To eliminate this, Berg turned to the expertise of The Lincoln Electric Company. Because of a long, 21-year relationship with Lincoln, Berg looks to the company for innovative solutions to welding challenges and ways to provide higher productivity in its welding operations. At Lincoln's suggestion, Berg installed a continuous tack welding system utilizing two, DC 1000 power sources and a NA-5 control. This new, CNC-controlled tack welder has hydraulic cylinders, which automatically reposition themselves when the pipe diameter changes. This system has reduced changeover time to approximately five minutes. This new system has also eliminated some of the problems with closing the bevel for welding that Berg Pipe was experiencing with its former system. These two DC 1000s create a continuous seam tack using an open arc gas-metal arc welding (GMAW) process at high speeds of 260 inches per minute. Commonly referred to as "buried arc", this process is characterized by low voltage, short arc length, and very high travel speeds allowing for a deep penetrating weld at reduced heat inputs. During tack welding, hydraulic rollers on the system hold the pipe seam together. A laser guidance system from Uhrhan & Schwill is also used to guide the arc in the weld groove and maintain radial alignment of the plate edges. Because this laser guidance was not present on the old tack welding system, it eliminates the time that was needed previously for the operator to stop the weld and adjust these items manually. While some competitors use intermittent tack welds, Berg Steel Pipe Corporation feels there are benefits to a continuous seam technique to close the formed pipe cylinder for welding. "Intermittent tack welds require the use of a backing flux or a copper backing bar during subsequent submerged arc welding, while ours does not," noted Fred Hafner, PE, Chief Metallurgist/QA Manager for Berg Steel Pipe Corporation. "This means that we achieve higher productivity since the backing provided by the continuous seam provides the attributes for fast travel speeds and deep penetration in ID welding." Using a buried arc process allows for the elimination of weld spatter typical of globular transfer because the arc is "buried" in the weld puddle. This process also requires only a CO2 shielding gas, eliminating the need for more expensive argon gas. For the tack welding of 0.820" thick pipe, Berg Steel Pipe Corporation uses Lincoln L-50™ 5/32" diameter wire electrode at 1,500 amps. Since installing the new system, Berg has been extremely pleased with the results. "Our tacking system is very reliable and helped relieve the problem of the arc outage we were experiencing," said Burton. "We also employ the use of CNC controls which can store data on a particular wall thickness so that we can provide rapid changeovers by simply calling up previously-stored information." Inner Diameter Welding After the tacking process is complete, weld tabs are added to the seam areas at both ends of the pipe with a manual GMAW process. This allows the ID and OD systems to start and end welding on the run-off tabs, rather than on the pipe itself. In this way, the large pile of weld metal created at the start of this multiple-wire process will not affect the pipe weld nor will the concave area left at the end of the weld. This tab will be removed after welding so that what is left on the pipe is the best possible weld and not the undesirable weld metal from the start or end of welding. Berg has three, four-wire ID welding systems utilizing Lincoln AC 1200 power sources with NA-4 controllers. This SAW process, run at up to 1,000 amps, is able to produce a large-sized bead all in one pass. Although there is one power source per arc, all four wires are arranged in-line and feed into a single puddle. Since in multiple-arc welding one arc may be deflected by the others, it is necessary to ensure that such deflections are favorable to the weld profile. At Berg, ID submerged arc welding is conducted with constant-current AC power sources arranged such that incoming AC power is successively 90 degrees out of phase. During inside welding, the pipe is moving forward while all the welding equipment is fixed and mounted to a boom that permits travel through the length of the 40-foot pipe. The arcs are buried underneath the granulated flux. For the ID weld, a V-shaped guide wheel rides in the weld seam groove to ensure alignment of the weld head in the weld groove. The ID weld penetrates into the previously laid continuous tack weld that is now serving as weld backing at this stage. The four-wire process on the ID weld creates faster travel speeds - up to 68 ipm on the Gulfstream pipe- and the mechanical properties of the weld improve because there is less heat input delivered per arc. Depending on customer specifications, different types of wires are used at this station. For the Gulfstream Project, 1/8" Lincoln L-61 with a 761 pipe flux are the consumables of choice. This special 761 flux is a special adaptation of the standard Lincoln 761 flux with different-sized particles to create better fluidity, bead shape and edge tie-in to fill in the weld groove on the inside of the pipe. Finished pipe is loaded on the barge for transport to the lay barge. Outer Diameter In the last step of the welding process, Berg uses two, five-wire SAW stations to create OD welds that penetrate into the ID and completely consume the tack weld. There are three main advantages to using a five-wire process: 1) higher weld speeds - the process is four times the speed of the standard, two-wire process; 2) reduced heat input, which reduces grain coarsening in the heat affected zone; and 3) impurities such as slag or porosity have time to escape prior to solidification because of the large weld puddle. The Berg OD systems use a DC lead wire to ensure complete penetration while the trail arcs are AC for fill and travel speed. At one welding cell, Berg uses two Lincoln DC-1000 units in parallel with Lincoln NA-3 controls. At another welding cell, two Lincoln DC-1500 units are used with similar NA-3 controls. In all cases, the AC trailing wire is produced with AC-1200 units from Lincoln and NA-4 controls. Laser seam tracking on the OD ensures that the weld is positioned correctly in the weld groove. Since the arc is buried under a pile of flux and alignment can't be seen, this equipment facilitates positioning of the weld head. For the 0.820" (20.83 mm) thick Gulfstream pipe, the 3/16" DC lead wire operates at 1,550 amps with a weld speed of 90 ipm. Welding consumables were a combination of L-61 and L-70 wire and 995 flux. (L-70 wires are used when higher weld metal Charpy impacts are required - the addition of 0.5 percent Mo L-70 wire results in higher acicular ferrite contents in the weld, and this improves the weld metal Charpy impact energy.) On pipe thinner than 14.3 mm (0.56”), a four-wire process is used while all five-wires are utilized for heavier wall thicknesses. As customers requirements dictate changing wire or flux, Berg Steel Pipe Corporation has called on Lincoln Electric to help run trials at the company's Cleveland headquarters where a five-wire welding station is located for this purpose. In this way, valuable time on Berg's machines doesn't have to be spent on product development. Finishing After welding, the weld tabs are removed manually by operators using oxy-acetylene cutting. Slag is removed the length of the longitudinal weld, typically with a wire brush. Berg Pipe Corporation then sizes the pipe ends between the opposing hourglass rolls to ensure uniform diameters and roundness essential for efficient field constructions. Next, the company simultaneously bevels both ends of the pipe for field girth welding. A stenciling machine labels and barcodes each pipe with its unique identification before shipping via barge or rail to Gulfstream. Inspection Because creating defect-free pipe is so important for high-pressure, natural gas applications, pipes are subject to many nondestructive tests. Testing at Berg Steel Pipe includes automated ultrasonic inspection of the weld seam and film radiography of the seam weld near the pipe ends. Per API 5L, Grade X70 pipes are hydrostatically tested for a minimum duration of ten seconds at a pressure equivalent to at least 90 percent of the specified minimum yield strength. During the Gulfstream project, pipes were tested to higher pressures – for a minimum of 20 seconds at a pressure equivalent to the full 100 percent of the specified minimum yield strength. In addition, dimensional inspection and internal and external visual inspections are completed on each length of pipe. . According to Burton, welding the pipe correctly the first time is critical to achieving high production rates. "In our pipe mill, a pipe that needs rework has to displace a new pipe in the production process," said Burton. "Removing or holding up a new pipe from production to correct a problem can be very costly." Service "We are absolutely pleased with Lincoln Electric and the high level of service we get from our local representative, Troy Gurkin," noted Hafner. "He is always available if we have a problem and we can also refer to pipe welding specialists at Lincoln headquarters. Another advantage we get from Lincoln is that the company keeps a safety stock of consumables in Atlanta. This means that we always have an ample supply nearby." Each finished pipe is hydrostatically pressure-tested to assure the integrity of the welding. Berg Steel Pipe plans to continue its long relationship with Lincoln. "As the company grows and moves into new areas, Lincoln will be directly involved in all phases," explained Burton. Currently, the company is looking to develop seam welding procedures and process controls for Grade X80 pipe. Berg recognizes that Lincoln's Surface Tension Transfer® (or STT®) process will have advantages for field welding of this grade and will help popularize this grade for new pipelines. "Berg is one of the most progressive companies that I have worked with," noted Troy Gurkin, Lincoln Electric area sales representative. "The company is always looking to evaluate new products which can help increase efficiency." Several of Berg's employees have even attended preventative maintenance seminars presented at the local Lincoln office in Birmingham. Multiple wire submerged arc welding of the inside of the pipe. Future "In the future we expect SAW systems to be replaced with software-controlled inverter welding systems that will allow complete manipulation of the waveform and electronic phasing. We will then be able to change the waveform for each wire," said Hafner. "Such systems will provide even better control of weld penetration and arc deflection with higher productivity." http://www.lincolnelectric.com/knowledge/articles/content/bergsteel.asp

Challenges and Solutions for the Retention of Field Production Rates in High Strength Pipe

Challenges and Solutions for the Retention of Field Production Rates in High Strength Pipe

Abstract

New, high strength steels are offering many advantages to the pipeline industry. These steels allow for the use of thinner pipe at higher operating pressures. These steels can also drive down total construction costs. However, as pipeline owners and designers look to these new steels, they are presenting a challenge for the welding and fabricating industry that must respond with cost-effective ways of joining them. To complicate the matter, these high performance steels have surpassed conventionally fabricated weld metal in terms of hydrogen crack resistance and fracture toughness.

The latest evolution in these high strength pipe steels is X-80, carrying a specified minimum yield of 80 ksi. With even more advanced steels expected soon, unique opportunities are being created for the arc welding industry to introduce new welding consumables and processes capable of welding these high strength steels
The welding industry’s priority is quality. All pipeline fabricators need to provide repeatable, high quality welds – the first time.

Since SMAW has been adequate to produce safe, economic pipelines, the industry has been slow to adopt the more recent advances in welding process development. SMAW i.e. Cellulosic electrodes has remained the most common process for welding pipelines and has a greater ability than other processes to accommodate non-ideal conditions such as poor fit-up to a change in terrain. However, as the strength of the steel increases there has become a greater risk of failure, either due to hydrogen cracking or reduced toughness. It is this risk of hydrogen cracking that is the main issue with the cellulosic SMAW electrodes in higher strength applications.

Hydrogen dissolves in the molten puddle during welding. Upon cooling, diffusable, as opposed to chemically bound, hydrogen can cause porosity during solidification and cracking in the finished weldment. This moisture originates primarily from the moisture and organic components
Attempts to adapt welding processes and procedures to X-80 and higher strength steels must be assessed. To take advantage of the pipe strength, the weld metal must either match the strength of the pipe or exceed it. The welding process and consumables must be controlled to minimize the risk of brittle fracture in the weld during pipeline fabrication and the resulting risk of hydrogen cracking. In addition, the demands of higher productivity

Introduction

Low hydrogen manual processes suitable for the pipeline girth welding have been available for some time, but despite their availability and advantages in terms of reduced crack susceptibility, they have rarely been used in production up to the present time.

With the advent of the new high strength steels such as X-80, any large pipeline project will, consider if not use, these grades of pipe steel, and therefore contractors and engineers must accept the advancements in the welding processes.

New, high strength steels are offering many advantages to the pipeline industry. These steels allow for the use of thinner pipe at higher operating pressures. These steels can also drive down total construction costs. However, as pipeline owners and designers look to these new steels, they are presenting a challenge for the welding and fabricating industry that must respond with cost-effective ways of joining them. To complicate the matter, these high performance steels have surpassed conventionally fabricated weld metal in terms of hydrogen crack resistance and fracture toughness.

Manufactured using a combinations of heat treatment and mechanical treatment that produce higher strength without significant higher alloy. Such advancements in thermomechanical processing in steels (TMCP) make it possible to achieve the balance in strength and toughness, but with a greater resistance to heat affected zone cracking.

With all the positive factors regarding the higher yield materials the biggest challenge is how to weld these steels. The pipe steel is no longer the limiting metallurgical factor. For example, steels are no longer as sensitive to hydrogen cracking as are conventional weld materials. This is why it is important to examine hydrogen cracking and potential solutions in relation to the weld metal.

Hydrogen Cracking

It is the main issue with cellulosic SMAW electrodes in higher strength applications. This hydrogen originates primarily from the burning of the electrode coating, which contains moisture and organic components Hydrogen dissolves in the molten puddle during welding. Upon cooling, diffusable, as opposed to chemically bound, hydrogen can cause porosity during solidification and cracking in the finished weldment. That is why it is critical that hydrogen levels be minimized for the weld to be considered sound.

With respect to the hydrogen issue, the challenge is to minimize the risk of weld metal cracking by controlling the factors know to be influential.

1. Minimize the amount of hydrogen that is available through judicious selection of consumable and/or welding process controls.

2. Minimize stresses, both residual and applied.

3. Minimize weld metal strength, thus controlling the susceptibility of the microstructure. Some industries have successfully employed undermatching strength weld metals, contingent upon design requirements.

It should be noted that with respect to hydrogen, the risk of cracking might be minimized, but it is impossible to eliminate. Since all steel microstructures are susceptible somewhat to cracking, it simply becomes a question of controlling hydrogen and stress levels simultaneously.

A report published in 1996 by The Welding Institute titled “ Evaluation of Low Hydrogen Processes For Pipeline Construction in High Strength Steel”, (PR-164-9330) which investigated suitable processes for the welding of X80 grade pipe reported,

“ The most successful root welding performance was obtained using the Lincoln Electric STT® power source and the LA90 electrode wire. The STT power source provided very precise control of short circuiting metal transfer, which resulted in good handling characteristics, well-fused beads, minimal spatter and lower fume emissions. The TWI welder involved in the trials was depositing satisfactory root beads within two hours of being introduced to the welding machine. The root welding speeds were comparable with cellulosic."

What is the Proper Way of Joining Pipe?

It depends on many variables, including fit-up, accessibility, terrain, if it’s a tie-in or crossing, whether it is a repair weld, the welder skill and a number of other factors.

Each possible welding process has its own merits, and there is no single clear-cut answer for every application. Attempts to adapt welding processes for higher strength steels must be considered. In addition, the demands of higher productivity and quality are always present.

Root Pass Welding

Traditionally the welding of the root and hot pass have been completed using a high hydrogen cellulosic electrode.
However on X-80 type material, restrictions do apply. Deposition of small weld passes at high travel speeds are possible with sufficient preheat temperature control.

Preheat is required to slow the rate at which the weld cools, thus allowing hydrogen to diffuse, in addition, the use of preheat can also help control residual stresses in the weld zone.

While this approach sacrifices nothing in terms of deposition rate compared with current practices on lower yield pipe, the need for potentially high levels of preheat can limit overall productivity.

It is currently not advisable to weld with cellulosic electrodes on X-80 that is more than 10mm in thickness.

The use of basic coated “low hydrogen” electrodes for the root pass weld as productivity issues. Albeit they can produce one-tenth the level of hydrogen compared to a cellulosic electrode, the major disadvantage is that the process is slow compared to any other process, apart from Gas Tungsten Arc Welding (GTAW).

Whilst SMAW as been used, and can be used to create acceptable quality welded joints in the high yield steels, productivity issues make SMAW less attractive than welding with a continuous wire process. Since there is a strength ceiling for the cellulosic electrodes because of the high hydrogen levels, and the poor productivity levels with the basic low hydrogen electrodes, alternatives are required.

Welding Productivity

For field welding of pipelines, it is the elapsed time to remove the pipe clamp, which is the critical indicator of welding productivity. The elapsed time will depend on a number of factors including the strength of the weld deposit, the dimension of the welded ligament and the level of hydrogen present.

The root pass welding speed determines the advancement of the construction, and therefore it is the focal point that lends itself best to technological advances. Mechanized systems can weld faster than manual or semi-automatic, provided the requisite care is taken in joint preparation and fit-up to ensure proper process control.

Preparation and Presentation

In Manual and Semi – Automatic welding, the journeymen or pipe fitter has a tolerance in which the welder can compensate for variation in the joint fit – up. In automatic welding that tolerance is more critical, therefore the bevel geometry, and the line – up and spacing needs to be addressed mechanically.

Preparation – Pipe Facing Machines (PFM’s). The roundness and consistency of the joint are more important when making welds using an automated system. Therefore, the use of a PFM in the field is critical to the success and quality of weld, regardless of whether an internal or external root pass machine is used.

Presentation – After preparation two approaches maybe adopted. One approach is to have the root pass welded in the short arc mode on the inside of the pipe with multiple torches. Production rates can be high, but the process requires great care in joint preparation and fit-up. If this is not perfect, then there is a greater chance that many poor quality welds will be made in a very short period of time.

A second option is to weld the root pass from the outside utilizing an internal line-up spacer clamp, shown above. The sequence of operation is somewhat different to conventional internal clamps were as the Internal line – up / Spacer clamp, is first located into the pipe, and the first set of internal chucks are expanded into a hard chuck. This aligns the clamp with the ID of the pipe, and takes out any ovality.

The second step is to bring into close proximity the next section of pipe. The second set of chucks are then engaged, which grabs the piece of pipe in a soft chuck. Once in a soft chuck, the clamp is spaced in, which forces the two pipes together.

With one set of the chucks been in a soft state, they allow the pipe to move, so that the two faces of the pipe are butted up tight together. The second set of chucks are then actuated into a hard chuck, which again takes out any ovality. The final stage is to space the clamp out, giving the journeymen/fitter a predetermined uniform gap around the pipe.

Gas Metal Arc Semi-Automatic / Automatic welding processes provide an opportunity for increased productivity and deposition rates by virtue of fewer stop/starts. However, traditionally the short-circuit mode as been identified as having a risk of lack of fusion.

Normal short arc welding is considered to be low heat input. However, the current, which is proportional to wire feed speed, can be increased to give higher input and increased penetration. This can result in a fine balance between too little and too much, and requires considerable operator skill so to avoid defects like internal “whiskers”. There needs to be enough heat to fuse the inside edges but not so much as to “blow through”. The operator has to ride the puddle with the arc to achieve the correct penetration and does not have much room for deviation.

These defects can easily be detected by industry standard non-destructive evaluation, such as radiography and ultrasonic inspection. On the other hand, GMAW does have its advantages. Since hydrogen levels with GMAW are typically low, pre-heat requirements are minimal and cracking is rarely an issue.

Controlled Short Circuit Transfer (STT)

One area of recent innovation that as provided operational advantage on high strength pipe, is on external open gap root pass utilizing the controlled short circuit transfer mode

The controlled short circuit transfer mode is different in several ways from the conventional CV process. The STT power source operates neither in constant current (CC) nor constant voltage (CV), rather it is a wide – band width, current – controlled machine wherein the power to the arc is based on the instantaneous arc requirements.

In principle, it is a power source, which has the capability of delivering and changing electrode current in the order of microseconds.

How Does It Work.The electrode current supplied by the SurfaceTension Transfer power source is guided by the state of the arc voltage.

• Background current (T0 – T1). This is the current level of the arc prior to shorting to the weld pool. It is a steady current level between 50 and 100A.
  
• Ball time (T1 – T2). When the electrodes initially shorts, the “arc voltage” detector provides a signal that the “arc” is shorted. The background is further reduced to 10A for approximately 0.75 m/s.



• Pinch mode (T2 - T3). Following the ball time, a high current is applied to the shorted electrode in the form of an increasing, dual – slope ramp. This accelerates the transfer of the molten metal from the electrode to the weld pool by applying electric pinch forces.
  
• dv/dt calculation (T2- T3). This calculation is included within the pinch mode. It is the calculation of the rate of change of the shorted electrode vs. time, when this calculation indicates that a specific dv/dt value has been attained, indicating that fuse separation is about to occur, the current is then reduced to 50 A in microseconds. (Note this event occurs before the shorted electrode separates. T4 indicates the separation has occurred, but at a low current.)



• Plasma boost (T5 – T6). This mode follows immediately the separation of the electrode form the weld pool. It is a period of high arc current where the electrode is quickly “melted back.”



• Plasma (T6 – T7). This is the period of the cycle where the arc current is reduced from plasma boost to the background current level.

The process can be applied to either semi-automatic or automatic applications. It operates in the short circuiting region with various shielding gas blends including 100% carbon dioxide for mild steel, as well as various blends of argon/oxygen, argon/carbon dioxide and argon/helium for stainless steel.

Fill / Cap Pass Welding

Cellulosic covered electrodes may still be used if care is taken in controlling preheat and interpass temperatures, with pipe wall thickness up to and including 10mm on X-80. It is not currently advisable to attempt to weld on thickness greater than 10mm because increased restraint and cooling rates are expected to increase the risk of weld metal hydrogen cracking.
Low hydrogen vertical-up electrodes are not normally used for transmission pipeline production welds, due to the low productivity.

It is now become more common, especially in Europe, to use the basic Low Hydrogen vertical Down electrodes for the weld of high yield pipe.

LH-D electrodes are designed for any vertical down welding application where low-hydrogen weld metal is demanded, such as high strength pipe welding.

Although these are designed specifically for vertical down welding of pipe joints, the LH-D are useful in any vertical down application where a low-hydrogen deposit is required.

The low-temperature impact properties are superior to cellulosic electrodes that possess the same level of strength. As downhill electrodes, they have significantly greater deposition rates than both vertical - up electrodes and downhill cellulosic electrodes of equal diameter; this increases the potential for greater productivity, while meeting high strength requirements.

Semi-Automatic processes can be categorized into, gas shielded and shelf shield.

Gas shield GMAW would typically be fully mechanized, because the welding area needs to be protected from the elements. If the contractor is prepared to protect the welding area, it is more feasible to use a fully automatic set-up.

This leaves FCAW-S (self-shielded) as the only serious semi – automatic welding for consideration, the obvious advantage is that you gain from the reduction in stop starts, without the need for ancillary shielding.

Mechanized Processes

GMAW and FCAW-G are the most common means of mechanized welding for fill and cap passes on pipe. The current techniques are based on either short arc or pulsed spray transfer with high wire feed speeds.

The advancement and development of welding power source technology could conceivably yield significant productivity improvement
Along with the improvements and welding characteristics of solid or cored electrodes, it will be possible to improve the welding performance and deposition.

Mechanized GMAW holds tremendous potential for the future, because it requires less training, and results in lower hydrogen levels, higher productivity and better quality.

Conclusions
The direction of the welding community must follow two clearly define channels.

1. Enhancement of current welding processes: by advancing the designs of current basic low hydrogen manual and semi-automatic consumables, to better control hydrogen, strength and toughness. Although this methodology may prove successful for the X-80 applications, the increasing demand for greater hydrogen control and higher toughness, will likely drive the industry to new technological advances in consumables and processes.



2. Innovation in welding consumables and welding power source design. Pipe contractors and fabricators have much to benefit by adopting these new technologies.
• The development of the Controlled Short Circuit Transfer utilizes the latest technology to enable previously unattainable control over several arc variables.



• Advances in pipe spacing, clamping, Bug and Band systems and multiple arc equipment can save time, increase quality and reduce costs for pipeline projects.



• Advancements in solid and cored electrodes will limit hydrogen and will enable manufacturing flexibility.
  

With quality and productivity in mind, Lincoln Electric is in the forefront of pipe welding processes and is constantly seeking solutions for these high strength steel challenges.

Reference:

TWI: Evaluation of Low Hydrogen Processes for pipeline Construction in High Strength Steel – PR-164-9330

Elliot K. Stava: 1993 The Surface Tension Transfer® power source, A New, Low –Spatter Arc Welding Machine. Welding Journal 72(1): 25-29

Common Mistakes Made in the Design of Aluminum Weldments

Common Mistakes Made in the Design of Aluminum Weldments
By Frank G. Armao, Senior Application Engineer, The Lincoln Electric Company, Cleveland, Ohio

Figure 1

Background

As a rule, designers of metallic structures have learned to design using steel. When designing with aluminum, however, the engineer must not base the design on prior experiences with steel or any other material. The alloy selection, proper joint design and the choice of an optimal welding process may all be a function of the base material. While aluminum obviously obeys the same laws of mechanics as all other materials, it must be approached differently than steel when welded. Aluminum structures are not necessarily more difficult to design or weld than steel structures, they are just different.

Don’t Just Choose the Strongest Alloy

Aluminum is often chosen as a structural material for applications in which weight savings are important. Very often, the designer will choose the very strongest alloy available. This is a poor design practice for several reasons. First, the critical design limitation for many structures often is deflection, not strength. In such cases, the modulus of elasticity, not the tensile properties, will govern the design. The modulus of most aluminum alloys, weak and strong alike, is approximately the same (one-third the modulus of elasticity of steel), so no benefit accrues from using the strongest alloy. Second, and most importantly, many of the strongest aluminum alloys are not weldable using conventional techniques.

When we speak about aluminum alloys being "weldable" or "non-weldable," we are usually referring to the alloy’s ability to be welded without hot cracking. Alloys that are extremely susceptible to hot cracking are not considered appropriate for structural (load-carrying) applications, and are generally put in the non-weldable category. Hot cracking in aluminum alloys is primarily due to the chemistry of the alloy and the weld bead. For virtually every alloying addition, the cracking sensitivity varies as alloy content increases as shown in Figure 1. Weldable alloys have a composition that falls either well above or well below the maximum cracking sensitivity. In some cases, such as that of 6061, which is very crack-sensitive if welded without filler material, the weld cracking sensitivity can be reduced to acceptable levels with the addition of a high silicon or high magnesium filler metal. The additional silicon or magnesium pushes the solidifying weld metal below the cracking sensitivity level. In other alloys, such as 7075, it is not possible to design a weld filler alloy that results in a crack-resistant chemistry. These are considered to be non-weldable.

Alloys are broken into two groups: heat-treatable alloys and non-heat-treatable alloys. A relative assessment of weldability is also given for each of these.

The non-heat-treatable alloys are composed of the 1XXX, 3XXX, 4XXX, and 5XXX series. It is not possible to strengthen these alloys by heat treatment. They can only be strengthened by cold working (also called strain hardening). The 1XXX alloys, such as 1100, 1188, or 1350, are essentially pure aluminum (99+% purity). They are relatively soft and weak, with good corrosion resistance, and are usually used where high electrical conductivity is required, such as for bus bars or as electrical conductors. They are also used in certain applications that require a high degree of resistance to corrosion. All of these alloys are readily weldable.

The 3XXX series of alloys have various levels of manganese (Mn) added to strengthen them and improve their response to cold work. They are of moderate strength, have good corrosion resistance, and are readily weldable. They are used for air conditioning and refrigeration systems, non-structural building trim, and other applications.

The 4XXX series of alloys have silicon (Si) added as an alloying element to reduce the melting point and increase their fluidity in the molten state. These alloys are used for welding and brazing filler materials and for sand and die castings. They are the least crack-sensitive of all the aluminum alloys.

The 5XXX series of alloys have magnesium (Mg) added in order to increase their strength and ability to work-harden. They are generally very corrosion resistant and have the highest strengths of any of the non-heat-treatable alloys. Increasing magnesium content in these alloys results in increasing strength levels. These alloys are commonly available in the form of sheet, plate and strip, and are the most common structural aluminum alloys. They are generally not available as extruded sections, because they are expensive to extrude. They are readily weldable, in most cases, with or without filler metal. However, there is an Al-Mg cracking peak at approximately 2.5% Mg, so care must be used in welding alloys such as 5052. It should not be welded autogenously (i.e., without adding filler metal). Weld filler metal with a high Mg content, such as 5356, should be used to reduce the crack sensitivity.

The heat-treatable alloys are contained in the 2XXX, 6XXX, and 7XXX alloy families. The 2XXX family of alloys are high strength Al-Cu alloys used mainly for aerospace applications. In some environments, they can exhibit poor corrosion resistance. In general, most alloys in this series are considered non-weldable. A prime example of a non-weldable alloy in this series, which is attractive to designers because of its high strength, is alloy 2024. This alloy is commonly used in airframes, where it is almost always riveted. It is extremely crack-sensitive and almost impossible to weld successfully using standard techniques.

Only two common structural alloys in the 2XXX series are weldable: 2219 and 2519. Alloy 2219 is very easily weldable and has been extensively welded in fabricating the external tanks for the U.S. space shuttle. This alloy gets its good weldability because of its higher copper content, approximately 6%. A closely related alloy, which is also very weldable, is 2519. It was developed for fabrication of armored vehicles. Although there are detailed exceptions to this rule, the designer should probably consider all other alloys in the 2XXX series to be non-weldable.

The 6XXX series of alloys are the alloys probably most often encountered in structural work. They are relatively strong (although not as strong as the 2XXX or 7XXX series) and have good corrosion resistance. They are most often supplied as extrusions. In fact, if the designer specifies an extrusion, it will almost certainly be supplied as a 6XXX alloy. 6XXX alloys may also be supplied as sheet, plate and bar, and are the most common heat treatable structural alloys. Although all alloys in this series tend to be crack-sensitive, they are all considered weldable and are, in fact, welded every day. However, the correct weld filler metal must be used to eliminate cracking. Additionally, these alloys will usually crack if they are welded either without, or with insufficient, filler metal additions.

The 7XXX alloys are the ones that usually trip designers up. They are the very high strength Al-Zn or Al-Zn-Mg-Cu alloys that are often used in aerospace fabrication, and are supplied in the form of sheet, plate, forgings, and bar, as well as extrusions. With the few exceptions noted below, the designer should assume that the 7XXX alloys are non-weldable. The most common of these alloys is 7075, which should never be welded for structural applications. In addition, these alloys often suffer from poor corrosion performance in many environments.

A few of the 7XXX series defy the general rule and are weldable. These are alloys 7003 and 7005, which are often seen as extrusions, and 7039, which is most often seen as sheet or plate. Some common uses of these alloys today are bicycle frames and baseball bats, both of which are welded. These alloys are easily welded and can sometimes offer strength advantages in the as-welded condition over the 6XXX and 5XXX alloys.

There is one other exception to the general rule that 2XXX and 7XXX alloys are unweldable. There are a number of thick cast and/or wrought plate alloys designed as mold plate material for the injection molding industry. These alloys, which include Alca Plus, Alca Max, and QC-7, are all very close in chemistry to 7075 or 2618. The designer should absolutely avoid structural welds on these alloys. However, welding is often performed on these alloys to correct machining mistakes, die erosion, etc. This is acceptable because there are only low stresses on such welds and, in fact, the weld is often in compression.

This discussion has tried to make a few points:

• First, when designing a structure of any kind, don’t scroll through the nearest list of aluminum alloys and pick the strongest.
• Realize that some alloys, often the stronger ones, are non-weldable. Make sure the selected alloy is readily weldable.
• Recognize that some alloys or alloy families are more suitable for some applications than others.

One more caveat: when welding aluminum, the designer must not assume that the properties of the starting material and the properties of the weld are equivalent.

Why Isn’t the Weld as Strong as the Original Base Metal?

A designer of steel structures generally assumes that a weld is as strong as the parent material, and the welding engineer who is responsible for fabricating the structure expects to make a weld which is as strong as the steel being used. It would be tempting to assume that the situation is the same when designing and fabricating aluminum structures, but it isn’t. In most cases, a weld in an aluminum alloy is weaker, often to a significant degree, than the alloy being welded.

Non-Heat-Treatable Alloys

Figure 2

Alloys in this category (i.e., 1XXX, 3XXX, 4XXX, and 5XXX families) are produced by a cold working process: rolling, drawing, etc. After the cold working process, the alloy is given the designation of an F temper (as-fabricated). Alloys are then often given a subsequent annealing heat treatment, after which they are classified as an O temper (annealed). Many alloys are sold in this condition. Thus the correct designation for a plate of 5083 which was annealed after rolling is 5083 – O. One of the attractive properties of these alloys is that they can be significantly increased in strength if they are cold worked after annealing. Figure 2 shows what happens to several alloys with varying amounts of cold work. For example, alloy 5086 rises in yield strength from approximately 18 ksi (125 MPa) to 40 ksi (275 MPa) and is now said to be strain-hardened. A complete designation for this alloy would be 5056-H36. The H temper designation can be somewhat complicated, since it is used to designate a number of processing variables. However, the last digit designates the level of cold working in the alloy, with 9 denoting the highest.

Figure 3

A common mistake in designing welded structures using non-heat-treatable alloys is to look down a list of properties, disregard the O temper material, and choose an alloy of the highest temper because it is significantly stronger. This would seem to make sense, but it often doesn’t, because the heat of welding acts as a local annealing operation, significantly weakening the heat affected zone (HAZ) of the weld. If one plots the yield or tensile stress versus distance from the weld, a curve such as that seen in Figure 3 is obtained. If the design is based on the strain hardened properties, the allowable design stress will usually be above the actual yield point of the HAZ. Although it may seem counter-intuitive, the fact is this: No matter what temper one starts with, the properties in the HAZ will be those of the O temper annealed material due to the welding operation. Therefore, the design must be based on the annealed properties, not on the strain-hardened properties. Because of this, it usually doesn’t make sense to buy the more expensive strain hardened tempers for welded fabrications. One should design with and specify the alloy in the O temper and up-gauge as necessary.

An obvious question is whether anything can be done to restore material properties after welding a strain-hardened material. Unfortunately, the answer is almost always no. The only way to harden these materials is through mechanical deformation, and this is almost never practical for welded structures.

Heat-Treatable Alloys

Figure 4

The situation is somewhat different when welding the heat-treatable alloys. Alloys are heat-treated by initially heating the material to approximately 1000°F (540°C), holding the temperature for a short time, and then quenching it in water. This operation is intended to dissolve all the alloying additions in solution and hold them there at room temperature. Alloys in this condition are said to be in the T4 temper and have significantly higher strengths than the same alloy in the O temper. Depending on the alloy, "natural aging" at room temperature can lead to further strength increases over time. This takes place over a matter of days or, at most, a few weeks. After that, the properties will remain stable over decades. If one buys T4 material, it is stable and the properties will not change over the course of a lifetime.

However, most alloys are given an additional heat treatment to obtain the highest mechanical properties. This heat treatment consists of holding the material at approximately 400°F (205°C) for a few hours. During this time, the alloying additions that were dissolved in the prior heat treatment precipitate in a controlled manner, which strengthens the alloy. Material in this condition is designated as T6 (artificially aged) temper, the most common heat-treated alloy temper.

Again, the complete temper designation system is actually much more complex than this, but understanding the T4 and T6 tempers will help to overcome some of the most common mistakes made when designing aluminum weldments. It is important to note that heat treatable alloys can also be strain-hardened after heat treatment, and this can further complicate the temper designation.

Remember that the aging treatment is performed at approximately 400°F (205°C). Any arc welding process gets the HAZ much hotter than this. Therefore, welding constitutes an additional heat treatment for the HAZ. Some alloys experience an additional solution heat treatment, while other alloys become overaged in the HAZ. This results in degradation of material properties, especially if the as-welded properties are compared to T6 properties. For example, the minimum specified tensile strength in ASTM B209 for 6061 – T6 is 40 ksi (275 MPa). Most fabrication codes require a minimum as-welded tensile strength of 24 ksi (165 MPa), which is a significant degradation.

As when designing for the non-heat-treatable alloys, the designer must not use the parent material properties in design. Realistic as-welded properties must be used. It is difficult to generalize what these properties are. They change from alloy to alloy and depend strongly on the starting temper of the alloy. Most design codes contain as-welded properties for aluminum alloys and these should be used.

With heat-treatable alloys, however, there are some ways to recover some of the material properties of the parent. Figure 4 shows a plot of tensile stress versus distance from the weld for 6061, revealing curves for both T4 and T6 material in both the as-welded (AW) and post-weld-aged (PWA) conditions. The PWA condition represents a weld that is subsequently aged for one hour at approximately 400°F (205°C). Post weld aging improves the mechanical properties for both T4 and T6 starting materials. In fact, often times it is better to weld in the T4 condition and post weld age after the welding process.

There is one final alternative to discuss. If after welding, the structure is given a complete heat treatment (i.e., solution treat at 1000°F [540°C], quench, age at 400°F [205°C]), all of the material properties (even in the weld) will be recovered and T6 properties will be obtained. This practice is frequently followed on small structures such as bicycle frames, but it is impractical for larger structures. Furthermore, the quenching usually causes enough distortion of the structure that a straightening operation is necessary before aging.

Conclusions

In the design of welded aluminum structures, too often the differences between steel and aluminum are not taken into account. To recap, common mistakes include:

• Not all aluminum alloys are weldable. In general, the least weldable alloys are also the strongest alloys.
• The weld will rarely be as strong as the parent material.
• The HAZ will have O temper annealed properties for non-heat-treatable alloys regardless of the initial material temper.
• For the heat treatable alloys, the as-welded properties will be significantly lower than the properties of the T6 alloy temper.
• Post-weld heat treatment can help to restore the mechanical properties of welds in heat treatable alloys.

Controlling Welding Fume, A Total Systems Approach

Controlling Welding Fume, A Total Systems Approach

Introduction
Operators are exposed to fume and gases when welding, and exposures vary depending upon the process and specific working conditions. Fabricators are under continual pressure to reduce worker exposure to potentially harmful substances in the workplace, including welding fume. This article will address the following:

• How welding fume is generated
• Coordinating factors that affect fume generation and exposure to fume such as welding design, process, equipment, consumables, gases, work management and ventilation
• Highlights of fume extraction technology
• The current U.S. regulatory climate with regard to welding fume
• Current published exposure limits for typical components of fume

What Is Welding Fume?
Although many people think of gases and vapors from gasoline or other chemicals as "fume," technically, fume is comprised of very small, solid particles. Since Arc welding usually produces only small concentrations of gases, exposure to gases is seldom a concern except in confined areas. Therefore, the issue of secondary gas production will not be specifically discussed here.

Arc welding creates fume as some of the metal boils from the tip of the electrode and from the surface of molten droplets as they cross the arc. This metal vapor combines with oxygen in the air and solidifies to form tiny fume particles. These particles are visible because of their quantity, but each particle is only between 0.2 and 1.0 micron in size. Since fume primarily comes from the electrode, it consists of oxides of its metals, alloys and flux compounds. In steel welding, therefore, fume is primarily iron oxide and oxides of alloys such as manganese and chromium. With plated or coated metals, some of the fume comes from the weld pool as well. This adds oxides of metals from the base material into the fume such as zinc oxide from welding galvanized steels.

A Total Systems Approach
There are many ways to reduce exposure to welding fume. Each solution addresses part of the welding system. Each solution, however, has its advantages and disadvantages, and should be considered in the context of the total system. Likewise, a solution cannot work without proper implementation. The most successful solutions rely on a coordinated effort between managers, engineers, welding supervisors, vendors and especially welders themselves.

Although "fume extraction" may be the first solution that comes to mind, other options should be considered as well. Approaches to controlling welding fume actually fall into two broad categories:

• Reducing fume generation
• Limiting operator exposure to fume

Fume extraction is simply a subset of the second category.

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Increasing Productivity with a FCAW Wire Optimized for Your Application

Increasing Productivity with a FCAW Wire Optimized for Your Application
Ken Lee, Application Engineer, The Lincoln Electric Company

If welding with a solid wire is satisfactory, why use a higher priced flux-cored wire? A flux-cored wire is optimized to obtain performance not possible with a solid wire. For many welding applications like vertical-up welding, flat welding, welding over galvanized, or welding hard-to-weld steels, a flux-cored wire can do it better and faster.

Although gas metal arc welding (GMAW) with a solid mild steel wire is popular, easy-to-use, and effective for many applications, it does have limitations and drawbacks. For example, GMAW is slow for out-of-position welding. It is either limited to short-circuit transfer, which is restricted by many welding codes due to the tendency for lack-of-fusion, or pulse transfer, requiring a special welding power source. It also requires very clean steel.

The ability to add a variety of materials to the core of the welding wire allows many performance enhancements to be made. Slag formers are added to shield the weld pool and shape and support the weld. Iron powder is used to increase deposition rates. Powdered alloys are added to produce low-alloy deposits or improving the mechanical properties. Scavengers and fluxing agents are used to refine the weld metal.

Flux-cored arc welding gas-shielded (FCAW-G) wires were introduced to the market around 1957. The flux-cored arc welding self-shielded (FCAW-S) wires were introduced to the market later, around 1961.

The core ingredients for FCAW-G wires have been formulated to obtain performance impossible to achieve with a solid GMAW wire. As all of shielding is provided by the shielding gas, the core materials may be carefully selected to maximize a certain area of welding performance, such as obtaining smooth spray-type transfer with 100% carbon dioxide shielding gas and welding speeds twice as fast in the vertical position.

The FCAW-S wires on the other hand, the core materials must provide all of the shielding. The core materials generate its own shielding gases, slag formers, and compounds to refine the weld pool. The benefits of self-shielded flux-cored wires lie in its simplicity. They may be used outdoors in heavy winds without tenting and the additional equipment required for gas shielding.

Now, we're going to discuss several popular types of flux-cored wires and how they can increase welding productivity.

For semi-automatic out-of-position welding, E71T-1 wires offer unsurpassed performance. Its fast freezing rutile slag provides the highest deposition rates in the vertical-up position, up to 7 pounds per hour, unmatched by any other semi-automatic arc welding process. In addition, the E71T-1 wires also offer an exceptionally smooth welding arc and minimal spatter, even with 100% carbon dioxide shielding gas. Argon/carbon dioxide blends are used for the smoothest arc and best out-of-position performance. These are reasons why E71T-1 is the world's most popular flux-cored wire. It is a top choice for shipbuilding, structural steel, and general steel fabrication applications.

For semi-automatic out-of-position welding without shielding gas, E71T-8 wires offer the highest deposition rates. Lincoln Electric's NR®-232 can deposit 4.5 lbs./hr. in the vertical-up position, 50% faster than other E71T-8 wires. Since this wire is self-shielded, it is widely used outdoors and in field erection of structural steel.

For semi-automatic welding in the flat position, the fastest way to join thick steel plate is with an E70T-4. It offers the highest semi-automatic deposition rates, up to 40 pounds per hour. This wire is widely used to join thick steels where there is no Charpy impact toughness requirement. This wire is also self-shielded, allowing it to be easily used outdoors.

The highest deposition rate gas-shielded flux-cored wire is E70T-1. Compared to E70T-4, they offer slightly lower deposition rates of up to 30 pounds per hour, but they offer a smoother welding arc and Charpy impact toughness properties. It offers higher deposition rates than GMAW, handles dirtier plates, and uses lower cost 100% carbon dioxide shielding gas. E70T-1s are widely used in structural steel fabrication shops.

For welding coated and galvanized sheet steels, E71T-14 is the wire of choice. The self-shielded E71T-14 wire has core materials which explode in the arc, volatizing the steel coating, minimizing cracking and porosity. The result is higher quality welds and fast welding speeds. E71T-14 wires are widely used in the automotive industry for fabricating galvanized steels.

What is the fastest way to weld hard-to-weld steels? E70T-5 gas shielded wire offer excellent crack resistance on hard-to-weld steels, such as T-1 quench and tempered steels, abrasion resistant steels, and free machining steels. E70T-5 has a basic slag system, similar to 7018 stick electrode, which removes phosphorus and sulfur from the weld metal, which can cause cracking, porosity, and poor toughness. E70T-5s have lowest diffusible hydrogen levels among the flux-cored wires, resulting in excellent resistance to delayed hydrogen cracking, as. In addition, they offer exceptional Charpy impact toughness properties.

Flux-cored wires offer higher productivity for many mild steel semi-automatic welding applications:

E71T-1 (FCAW-G): Highest deposition rates out-of-position.
E71T-8 (FCAW-S): Highest deposition rates out-of-position without a shielding gas.
E70T-4 (FCAW-S): Highest deposition rates in the flat position.
E70T-1 (FCAW-G): Highest deposition rates in the flat position with Charpy properties.
E71T-14 (FCAW-S): Fastest travel speed on galvanized and coated steels.
E70T-5 (FCAW-G): Fastest way to weld hard-to-weld steels.

Why be limited by a solid wire when a flux-cored wire can do it better and faster? Select the flux-cored wire optimized for your welding application. Use it and increase your productivity and lower your welding costs.

For more on Lincoln Flux-Cored Self-Shielded Electrodes, Click Here
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