Abstract: A floating reference voltage is generated in response to the low frequency components of weld current and is utilized in the control of the width of travel of a welding arc back and forth across a gap to be filled with weld metal. The arc current is integrated during each traverse across the gap and this integral is compared with the floating reference so that as the wall of the gap is approached, the direction of travel of the arc will be reversed. Provision is made for avoidance of the effects of "dip transfer".

Abstract: The specification discloses a method and apparatus for assuring the integrity of outside weldings of pipelines. Pipe sections are prepared for welding by forming a beveled profile with a relatively narrow annular contact band on the ends of each pipe section. When the pipe sections are abutted end to end for welding, the leveled profiles form a relatively deep groove on the outside of the pipe between the pipe sections, with the annular contact bands abutting and spaced inwardly from the grooves. The contact band on at least one of the pipe sections is circumferentially prepared such as by knurling to provide controlled spacing between the contact bands of the pipe sections. A welding arc is applied to the bottom of the groove from the exterior of the pipe sections to weld the annular contact bands together. Welding penetration is enhanced by the circumferential preparation of the contact bands.

Abstract: An improved back-up pad apparatus for use in externally welding abutting ends of pipe comprises a plurality of arcuate back-up pads positioned to face the interior of the weld. Each arcuate pad is mounted on a support shoe for radial movement into and out of biased engagement with the interior cylindrical surfaces of the pipes. The arcuate pads are pivotally supported by the support shoes and biased about axes parallel with the centerline of the pipe to permit retraction of the pads without interference. Preferably, the pads are constructed of hard anodized aluminum material.

Abstract: An improved back-up pad apparatus for use in externally welding abutting ends of pipe is formed of hard anodized aluminum material and comprises a plurality of arcuate back-up pads for interior positioning to face the weld. Each arcuate pad is mounted on a shoe for biased engagement with the interior cylindrical surfaces of the pipes. Intermediate shoes carrying cylindrically surfaced members are provided at the rounded ends of adjacent back-up pads.

Abstract: An apparatus for welding the adjoining ends of annular work members, such as lengths of pipe, employing an arc nozzle for melting and depositing metal in the gap between said adjoining ends. A drive motor coupled to the nozzle drives the nozzle laterally back and forth across the gap while the current that flows in said arc is integrated to generate a physical representation of magnitude of the integral. Means are provided to arrest the motor each time the magnitude reaches a predetermined threshold value, and to reverse the direction of travel of the motor.