Large Steel Tanks: Brittle Fracture and Repair

Abstract

Steel tanks that are welded to their base plates may become vulnerable to brittle fracture if the joints between base‐plate segments are defectively welded. A case history is discussed in which one of two large welded steel tanks (used for storage of grain) developed a sevenfoot (2.13‐m) long vertical crack in January 1982, but did not collapse. The crack originated at a defectively welded base plate. Field and laboratory investigations were conducted. Although brittle fracture had taken place, and the tank might have split open, the crack did not propagate all the way to the eaves, but was arrested at a vertical butt‐welded joint. An explanation for this behavior is obtained by recognizing the contribution of the large fracture toughness of the welding at the joint, and that of vertical tube stiffeners welded to the inside surface of the shell. The repair procedure for the actual crack, and various welding defects found by ultrasonic testing in both tanks, is also discussed at length. Once repaired, both tanks were successfully returned to service.