Typically, a roof is not the focal point of a building, but that is not the case with the new David L. Lawrence Convention Center in Pittsburgh, Pennsylvania. This architecturally unique building has a grand, sloping roof system composed of stainless steel. The roof has been designed to complement the city's skyline and has an innovative suspended truss system that imitates the look of nearby suspension bridges.
Because of the high visibility of the roofing system, Penn Perry Inc., the local Pittsburgh contractor charged with installing the sloping roof has many challenges in completing the job. First, the roof's aesthetics dictate high quality finished welds. Second, because stainless steel material is being utilized - and in some cases thin, 24-gauge stainless - the problem of distortion is very real. Third, the working conditions on the job site are less than ideal with welders having to work on the top of the roof, even through the winter months. Fourth, the time constraints on the job dictate high productivity with only a year to complete the entire roof, consisting of more than 260,000 square feet of roofing area and 6,000 linear feet of weld metal.
To help meet those challenges, Penn Perry has turned to a package of welding and cutting equipment from The Lincoln Electric Company. Each of four machines completes different aspects of the job - MIG, TIG, plasma cutting and even an engine-driven unit to power the other equipment. This package includes the SP-175 Plus (MIG), V205-T AC/DC (TIG), Pro-Cut® 55 (plasma cutter) and Ranger® 250 (engine drive).
Why was new welding equipment needed? This is the first job that Penn Perry has undertaken that requires TIG so it was imperative to buy a machine. And although the company has used MIG on previous jobs, the magnitude of this project and the sloping angle of the roof necessitated portability and a departure from Penn Perry's previous, large MIG machine that had been used for flat roofing surfaces.
About Penn Perry
Penn Perry beat out six other competing companies to win the roofing job for the David L. Lawrence Convention Center. When completed, the new, state-of-the-art convention center will be three times larger than the previous facility.
Penn Perry, a union company founded in 1957, completes all types of customized, high-end architectural projects utilizing materials such as copper, stainless, turn-coated stainless, clay tile and slate. Some of the notable projects Penn Perry has on its resume include the Allegheny County Courthouse, the Richmond Train Station, the Harrisburg Capitol Building, a Performing Arts Center in Charleston and the H.J. Heinz History Center. These jobs have included installations of domes, barrel vaults, standing and batten seam roofs as well as restoration of slate, metal and tile work on historic landmarks.
TIG: A New Application For Penn Perry
The sloping roof of the convention center calls the welding of 24-gauge stainless steel flashings that compose the coping (the roof's top cap) and the fascia (the vertical piece that runs down the building's outside wall). Because of the thin material and the high aesthetics required, the job dictated the use of TIG.
Although company representatives first had their eye on a competitive machine, a demonstration of the capabilities of the Lincoln Invertec® V205-T quickly changed their minds. "Our steel supplier recommended a machine to us, but when we compared that machine and the Invertec side by side, we noticed that Lincoln's was more than 50 lbs. lighter, more versatile and offered excellent quality," said Richard J. Esswein, Vice President of Sales for Penn Perry, Inc. "We felt the value for quality was far ahead.
The Invertec V205-T excels in this particular application because it is able to produce high quality welds without distortion. "The Invertec welds at low amperages with high quality so we are able to turn it down to a lower setting to get a cooler weld with no discoloration or distortion." explained Esswein. "We also take advantage of the 4-step trigger mechanism which provides low amperage at the start, the ability to ramp up quickly and then ramp down to finish the weld." Penn Perry uses .040" diameter filler and a helium shielding gas to complete the TIG welds.
Esswein notes that although they are not using the pulse TIG and AC capabilities of the Invertec V205-T on the current job, the contractor hopes to take advantage of these features for future jobs, such as when welding heavy gauge aluminum.
MIG Portion of the Roofing Job
While TIG is used on the detailed finish work, the majority of the welding performed at the convention center job is MIG in the two gutter systems. One large trough gutter is located at the base of the main rafter and a second, smaller gutter rests at the end of a 30 foot bay. These systems are being lined with 18-gauge stainless steel for long-term durability. With approximately 260,000 square feet of roofing area draining into these gutters, having something that is watertight and able to stand up to the snow and ice build-up is a necessity.
Lincoln's SP-175 Plus is being used to make a continuous weld 8 inches out of the bottom of the 4 foot deep by 4 foot wide gutter running down both sides of the building. In addition, this portable machine also creates butt welds every 10 feet to weld the pieces of stainless together. The gutters themselves can range from 50 to 80 feet in length.
"The SP is the workhorse on the site - we use it five to six hours a day, five days a week and we have had no downtime," said Esswein. "The machine is very dependable and functions extremely well, especially under our unique working conditions. Its portability is what sold us on the machine, we can take it up on the roof very easily."
The SP-175 Plus can also operate at lower amperages to reduce distortion and the potential of gutter puckering. Because the welds are of such high quality, no grinding is necessary. Operators just finish the weld with a stainless wire wheel to get off any remaining residue.
Penn Perry representatives are using .030" diameter 308L Stainless wire on the job site with 90% He/7.5% Ar/2.5% CO2 shielding gas.
Rounding Out the Package
To power all the equipment on the job site, Penn Perry turns to Lincoln's Ranger™ 250 engine drive which produces 8,000 watts of auxiliary power. According to Esswein, the company is very happy with the operation of the Ranger - the company has experienced no problems even though the machine runs almost continuously. For future jobs, Penn Perry hopes to be able to use its stick capabilities.
The fourth piece of Lincoln equipment in the package is the Pro-Cut® 55 plasma cutting machine, which is used to fit and cut the gutters. "Because of the architecture, this building does not have square ends," noted Esswein. "Everything needs to be cut on an angle. With the Pro-Cut we are able to make clean cuts that are ready to weld without additional prep work. We can make the cut and then immediately fit it into place to weld which is a real time saver."
To make the switch to the new machines, Penn Perry's job superintendent spent one day training with Lincoln at the local sales office. Lincoln representative Dave Daugherty also spends quite a bit of time on the job site to make sure things are running smoothly. All the machines were purchased through distributor Vince's Gas & Welding Supply.
"We originally came to Lincoln to just look at one machine but purchased all four because they proved to us they could provide a better value with more functionality," claimed Esswein. "Lincoln has backed up their claims by providing us with excellent support. I am very satisfied with the company and its products. I would highly recommend both."