Rotary internal pipe clamp apparatus

Welding back up assembly for disposition interiorly of the abutment between two pipes disposed end to end for welding, comprising a plurality of first arcuate strips disposed circularly spaced about said abutment, the same plurality of second arcuate strips disposed circularly spaced about said abutment and adapted to substantially fill said spaces between said first arcuate strips whereby said first and second arcuate strips together form a substantially continuous welding back up strip around said abutment, said first arcuate strips being radially movable between first positions clamped against said abutment and second positions spaced radially inward of said abutment, said second arcuate strips also being radially movable between first positions clamped against said abutment and second positions spaced radially inward of said abutment and spaced inwardly of said first arcuate strips, means for moving said first arcuate strips between their said first and second positions, means for moving said second arcuate strips between their said first and second positions, said second positions of said second arcuate strips being spaced radially inward of said second positions of said first arcuate strips, said first and second arcuate strips being spaced by open spaces therebetween when disposed away from their respective said first positions toward their respective said second positions whereby mechanical interference between said first and second arcuate strips does not occur when said first and second arcuate strips are moved between their respective said first positions and their respective said second positions, said means for moving said first arcuate strips comprising first radially slidable elements carrying said first arcuate strips at their outer ends and pivotally connected to the outer ends of first toggle elements at their inner ends, said first toggle elements being pivotally connected at their inner ends to central rotatable means which when rotated in one direction cause outward movements of said first arcuate strips toward their said first positions and which when rotated in the opposite direction cause inward movements of said first arcuate strips toward their said second positions, said means for moving said second arcuate strips comprising second radially slidable elements carrying said second arcuate strips at their outer ends and pivotally connected to the outer ends of second toggle elements at their inner ends, said second toggle elements being pivotally connected at their inner ends to central rotatable means which when rotated in said one direction cause outward movements of said second arcuate strips toward their said first positions and which when rotated in said opposite direction cause inward movements of said second arcuate strips toward their said second positions, said second toggle element pivotal connections to said central rotatable means being outward of said first toggle element pivotal connections thereto, whereby said second arcuate strips are moved farther radially than are said first arcuate strips upon rotation of said central rotatable means in either direction.