A WELDING METHOD TO MINIMIZE WELDING INDUCED DISTORTION IN FABRICATION OF AIR DUCT ASSEMBLY OF WIND-BOX IN ONCE-THROUGH SUPERCRITICAL BOILERS

摘要

The invention relates to a welding method to minimize welding induced distortion in fabrication of air duct assembly of wind-box in once-Through supercritical boilers, the fabrication of the air-duct assembly consisting of laying multiple welds at different locations along the entire length of the assembly which constitutes a box-type welded structure, the method comprising the steps of selecting and locating a base plate of decided length; placing a cord plate over the base plate and tack-welding the plates; placing a plurality of web plates at right angle to the base plate and tack welded to form a T-joint; locating a side cover plate on a first edge of the base plate at right angle with the base plate including the web plate and tack welding the side cover plate; positioning a rear cover plate over all the web plates with the base plate at right angle to the rear cover plate and the web plates tack-welding multiple plates with the protruding edges of the web plates to form box type sections; tack-welding a plurality of longitudinal members with the sub-assembly formed through the preceding steps to complete fit-up and tack welding of the air-duct assembly; carrying-out shielded metal arc welding (SMAW) or gas metal arc welding (GMAW) to complete the final welding of each step, wherein a welding sequence starting from a centre of component proceeding slowly toward both the ends of the component, and wherein a single or twin operators can be deployed.