Design Of Automatic Vertical Seam Welding System Of 9% Ni Steel For LNG Storage Tanks

With the sustained growth of the consumption of global LNG(Liquefied natural gas,called LNG),especially low temperature toughness of 9% Ni steel has become the main material of LNG cryogenic storage tank.LNG storage tank wall standing vertical seam welding of 9% Ni steel has become the main procedure of storage tank construction.At present,we mainly adopt manual welding which has low efficiency,poor working condition,high strength and no guarantee for the welding quality.So developing convenient and simple,fast and efficient,high-quality LNG storage tank with 9% Ni steel standing vertical seam automatic welding system has become a priority.Firstly,according to the design requirements of automatic seam vertical welding,we have analyzed the 9% Ni steel welding performance,put forward the reasonable welding process and method,and design base and peak current adjustable pulse welding;Wig-wag has realized the control mode of welding torch swing control and argon arc pulse the same frequency,phase,and pulse width;By hot wire control model,PID control algorithm realizes the control to hot filament current input value.According to the relationship between arc voltage and arc length,Arc length variable gain PID tracking control algorithm is realized.Through PI algorithm,wire motor can achieve stable wire feeding and other control strategies.According to the requirements of welding policy,we can design the mechanical structure of welding equipments.Then,in accordance with the controlling requirements of the welding process,the electric circuit of the hardware is chosen with a view to designing a full set of automatic seam welding controlling system based on Siemens S7-1200 PLC controller.In terms of software,the welding process and pulse welding,oscillator swaying,input index of hot-wire electric current,arc voltage rising aswell as stable wire-transporting,among other things,are designed.The controlling table top of the system can perform the outside information-collecting and the exchange between human and machine.In the meanwhile,it can set parameters and show the welding order,motion state.On the basis of PAC's Indu Soft software,the welding online monitoring system can be developed in an effort to conduct the communication between PAC and S7-1200 PL and achieve the management in welding cost,date,equipment,personnel and quality.In the end it has been proved that the resistance-proof capacity of the hardware of the PLC control system is much better and its maintenance is easier and reliability is improved through the field tests and clients demonstrated.The software of the PLC can meet the controlling requirements of the welding process and the welding cracks have been qualified.The whole system materializes the mechanization and automation of the welding process in which the LNG storing tub utilizes 9%Ni steel automatic seam welding system.