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Electric utility speeds heat exchanger repair
At a power utility's generating station, two high pressure feedwater heaters were decommissioned because of poor condition. Instead of removing the heaters and reconfiguring the plant, they were left in place allowing the flow to pass through, thus saving downtime and expenses. This project entailed taking the units for out of service, removing the torus ring, blanking off the inside tubes, and finally welding the torus ring back on. To get the equipment the utility turned to the Electric Power Research Institute (EPRI), Charlotte, NC, for recommendations for ways to improve welding results. In accordance with the utility and EPRI it was decided to use the Lincoln Electric's patented Surface Tension Transfer (STT) process. The STT process is a modified MIG (GMAW) short arc welding process that uses high frequency inverter technology with advanced waveform control to produce quality welds while reducing smoke and spatter. Unlike the standard short arc MIG process, STT technololy has the ability to control current independent of wire feed speed. By doing this, an optimal level of energy is delivered to the weld pool (puddle). By ensuring enough energy is added, lack of fusion can be minimized. Conversely, by avoiding excessive energy, the tendency of metal to 'suck back' is overcome. For the utility's repair project, the open root procedure called for 0.045 inch SuperArc L-56 solid electrode (AWS ER70S-6) with 100 % CO2 shielding gas, welding vertically down. The hot pass and subsequent passes were made with Lincoln's Outershield 71 Elite gas-shielded flux-cored electrode (AWS E71T-1) with a shielding gas blend of 75% Ar-25% CO2. The material being welded was an FA 350 LF2 carbon steel.
Electric utility speeds heat exchanger repair
At a power utility's generating station, two high pressure feedwater heaters were decommissioned because of poor condition. Instead of removing the heaters and reconfiguring the plant, they were left in place allowing the flow to pass through, thus saving downtime and expenses. This project entailed taking the units for out of service, removing the torus ring, blanking off the inside tubes, and finally welding the torus ring back on. To get the equipment the utility turned to the Electric Power Research Institute (EPRI), Charlotte, NC, for recommendations for ways to improve welding results. In accordance with the utility and EPRI it was decided to use the Lincoln Electric's patented Surface Tension Transfer (STT) process. The STT process is a modified MIG (GMAW) short arc welding process that uses high frequency inverter technology with advanced waveform control to produce quality welds while reducing smoke and spatter. Unlike the standard short arc MIG process, STT technololy has the ability to control current independent of wire feed speed. By doing this, an optimal level of energy is delivered to the weld pool (puddle). By ensuring enough energy is added, lack of fusion can be minimized. Conversely, by avoiding excessive energy, the tendency of metal to 'suck back' is overcome. For the utility's repair project, the open root procedure called for 0.045 inch SuperArc L-56 solid electrode (AWS ER70S-6) with 100 % CO2 shielding gas, welding vertically down. The hot pass and subsequent passes were made with Lincoln's Outershield 71 Elite gas-shielded flux-cored electrode (AWS E71T-1) with a shielding gas blend of 75% Ar-25% CO2. The material being welded was an FA 350 LF2 carbon steel.
Electric utility speeds heat exchanger repair
Stava, E.K. (author)
Welding Design and Fabrication ; 30-32
2003
3 Seiten, 4 Bilder
Article (Journal)
English
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