Kinematic Performance Analysis of a Controllable Mechanism Welding Robot with Joint Clearance

Because the motor and reducer of the conventional tandem welding robot are installed at the revolute joint, the robot has large rotational inertia and long residual vibration time. However, due to the limitation of workspace and other reasons, the current parallel robot is not suitable for all series welding robots. Therefore, based on the concept of "multi-degree-of-freedom controllable mechanism", a new controllable mechanism welding robot is proposed in this paper. The driving motor and reducer, which have great influence on the main and branch chain of the welding robot, are installed on the frame. The advantage of this design is that the inertia of the robot mechanism is significantly reduced, and its dynamic performance is improved. The position errors of the end members of the welding robot moving along the circle, as well as the angle errors of each joints under the circle movements are analysed.

Corrosion Behavior of Twin-Wire Metal Inert Gas Arc Welds in 7A52 Al Alloy Plate

7A52 aluminum alloy plate was welded using twin-wire metal inert gas arc welding (TANDEM welding). Corrosion behavior of the welded joint was investigated by immersion in 3.5% NaCl solution. Scanning electron microscopy (SEM) and electrochemical inspections, specifically, polarization curves and electrochemical impedance spectroscopy (EIS), were conducted to understand corrosion behavior of the TANDEM welding joint of 7A52 aluminum alloy. It was found that the heat affected zone (HAZ) exhibited higher corrosion susceptibility than the weld beam (WB), fusion zone (FZ) and base metal (BM). The electrochemical results showed that the WB with higher corrosion potential and larger impedance had highest corrosion resistance. Variations in the composition and grain size might have led to the differences in corrosion resistance because the welding process influenced microstructures of the TANDEM welding joint of 7A52 aluminum.

Further Large-Scale Implementation of Advanced Pipeline Technologies

TransCanada PipeLines Limited (TransCanada) has continued its leading effort in developing and implementing pipeline technologies. With a well structured and large-scale technology implementation program and collaboration of many partners over a period of three years, TransCanada has successfully implemented a number of technologies in a 38 km long NPS 42 pipeline construction project. The technology implementation program included installation of 7.3 km Grade 690 (X100) pipe supplied by two manufacturers, deployment of tandem welding system, field trial of a phased array automated ultrasonic testing (AUT) system, the application of high performance composite coating (HPCC) and Alternative Integrity Validation (AIV) process that led to first ever construction hydrostatic test waiver from National Energy Board. The paper provides an overview of the technology implementation program and the experience gained in applying a wide range of advanced pipeline technologies.