Use a stud finder to locate and mark three wall studs. Screw flanges into the studs using long screws. Use a square or straight board in between screwing in each flange to ensure they are properly aligned (Image 1).
Tighten pipes into the flanges (Image 2).
Cut 2 pieces of 3/4" plywood into equal triangles to create each gusset.
Cut a 2" x 4" to fit between the plywood triangles. When cutting the corner, make sure the board is oriented in the same direction as the triangles.
Clamp the three pieces together (Image 1), then drill holes through all three.
Insert 1/4" carriage bolts. Use a washer with the nut (Image 2).
To mount the rack, use a right-angle drill to drill between studs. Use a carriage bolt to attach the gusset to the stud (Image 3).