The ornamental design for a pivot joint for expandableframe, as shown and described.
FIG. 1 is a pivot joint for expandable frame in a perspective view;
FIG. 2 is a front view thereof, with the rear view being identical;
FIG. 3 is a right side view thereof, with the left side view being identical;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a perspective view showing the pivot joint for expandable frame positioned on a frame.
The broken lines are included for the purpose of illustrating portions of the pivot joint for expandable frame that form no part of the claimed design.