Patent ID: 9663841
Date: 2017-05-30
CPC Classifications: B23K,C21D,H05B,Y02B

Claim:
1. A method for local heat treatment of a walled steel pipe following welding, comprising steps: (1) obtaining a heated band width, HB as a parameter for local heat treatment by carrying out the following calculation: where R in mm is the inner radius of the walled steel pipe and t in mm is the wall thickness of the walled steel pipe; (2) obtaining a gradient control band, GCB as another parameter for local heat treatment by carrying out the following calculation: (3) performing a welding process on the walled steel pipe; (4) after welding, when the temperature of the walled steel pipe is cooled down to 120-150° C., setting up a heating device and an insulation device according to the HB and GCB values calculated in step 1 and, when the temperature of the walled steel pipe is further cooled down to 80-100° C., the heating device is turned on to maintain the temperature of the wall steel pipe at 80-100° C. for 2 hours; (5) heating the walled steel pipe, at a first heating rate of 150° C. per hour, to reach a temperature of 300° C. then further heating the walled steel pipe, at a second heating rate of 80° C. per hour to reach a temperature of 765° C. and maintaining the temperature at 765° C. for 4 hours or a duration based on the following calculation, whichever is longer, where D is duration in minute and t is the wall thickness in mm; (6) lowering the temperature to 300° C. at a cooling rate of 100° C. per hour and then turning off the heating device and letting the walled steel pipe naturally cool down to room temperature before removing the heating device and insulating device and completing the local heat treatment.