In late November, a 52,000-ton barge eased into this ramshackle port on the Bay of Bengal and came to rest on a wide, muddy beach. After nearly four decades crisscrossing the oceans for an American offshore engineering company, the DB-101 did not come to erect another oil rig or lay miles of undersea pipe. It came here to die. For scores of large commercial vessels that reach the end of their seagoing lives each year, the final port of call is Chittagong in southern Bangladesh, home to the world’s largest — and least regulated — ship-breaking industry.