Seam welding especially in a continuous mode can be a major power consumer. It can really be surprising the first time you see a drum or dishwasher water tight weld being welded. It may look and sound like the machine is welding continuously. It is not. Seem Welders never exceed 50% duty cycle. The equipment is designed for a maximum 50% duty cycle. If run higher they will fail prematurely. Therefor you may not hear it but half of the time the welder could be off as it is running. The closer the welds are together and the faster the wheels turn the more power will be consumed. A simple guide to power consumption is:
Reference: RWMA - Resistance Welding Manual 4th Edition