In Moscow Bauman State Technical University new method and system for computer control of dual arc seam welding of duplex stainless steel pipes developed. The method is based on using original thermodynamical models of formation of seam weld and undercuts in it, which are adapted to the conditions of real welding. This adaptation is made on the base of measurements of seam width on the face side and special point temperature in HAZ after the main arc. This measurements allow to take into consideration deviations of gap width between pipe edges, thickness and chemical composition along the strip, welding speed and the main arc parameters, and with help of models to choose optimal heat input in the main arc, which produces seam weld of desired shape and size with minimizing amount and size of undercuts. It allows to adjust heat input of the second arc at lower level. The choosing of this level is produced with help of neural network model, which also evaluates the probability of hot cracks appearance in the welds and decreasing of HAZ toughness using measurements of special points temperature in HAZ in place of the second arc acting. Computer system, with program built on this method, controls all welding equipment for dual arc TIG welding of duplex stainless steel pipes.