Backing welding process curve based on narrow-gap U-groove and its application and product

A method of using a backing welding process curve for a narrow-gap U-groove, comprising:

• designing a groove of a pipe to be welded as the narrow-gap U-groove;
• and
• welding the narrow-gap U-groove by using the backing welding process curve,
• wherein
• in the narrow-gap U-groove, a root face thickness b is 1.45±0.1 mm, a single-side groove angle α is 3±0.5°, and a distance a between a transition arc top and a root face is 2.95±0.1 mm,
• the backing welding process curve is obtained by adjusting a Cold Metal Transfer (CMT) reference curve,
• in the CMT reference curve, a peak current is 270 A, a cycle time is 5.5 ms, a current rise rate is 220 A/ms, and a current fall rate is 130 A/ms, and
• in the backing welding process curve, the peak current increases by 30%-50% and the cycle time extends by 300%-500% to enhance a welding heat input, the current rise rate reduces by 30%-50% and the current fall rate reduces by 20%-40% to prolong a peak current action time, and two current pulses before and after a short-circuit phase are introduced in the narrow-gap U-groove respectively to increase a root weld width of the narrow-gap U-groove and to avoid a root concavity of the narrow-gap U-groove, wherein a duration of an introduced single current pulse is 5.5 ms to 7.5 ms, and a pulse peak current is 220 A to 300 A.