Howell and Ballard characterize common practice for moving pipe spools from engineering through off-site fabrication to erection. "When engineering falls behind schedule, fabrication will be delayed, thereby also delaying installation work." "The order in which drawings are provided to the fabricator and the sequencing in which spools are output by the fabrication process may bear little relationship to site needs, therefore requiring re-sequencing for site delivery provided that priority information be available." "Time delays and out-of-sequence work make the supply of materials to the job site unpredictable. This leads to inefficiencies because work cannot be adequately planned and executed, and thus results in low productivity.