Abstract This paper presents the results of experimental research conducted during the past three years with the objective of understanding ductile fracture propagation in the offshore environment. Experiments have been conducted to examine decompression phenomenon inside the carrier pipe when the exhausting gas is into a simulated deep water environment. Ductile fracture experiments of 12 inch pipe in a simulated deep offshore environment have also been examined. The most current research is designed to examine the pressure waves in the water surrounding the pipeline that are caused by the sudden release of gas from a rupture and the resulting lower differential pressure across the pipe wall thickness. The research to date suggests that long running ductile fracture propagation in an offshore pipeline is less probable than in an onshore pipeline. Future research is planned with a full-scale experiment in a water filled quarry and in the real offshore environment. Introduction The objective of this research program has been to obtain an understanding of ductile fracture propagation in the offshore environment. The approach toward this objective has been to examine individually, the various factors that are known to affect ductile fracture of pipes in general. The more important of these factors are backfill effects(1), gas decompression effects(1), and external pipe pressure (2). Previous research has examined backfill effects and found that bare pipe in shallow water had ductile fracture characteristics similar to sand backfilled pipe. Other research examined gas exhausting from a pressured pipe into pressured water and found that the decompression was identical to decompression into the air for all pressure levels above the surrounding water pressure level. The effects of external pipe pressure were examined as relating to fracture initiation and in a limited way to fracture propagation and found to corroborate logic in that the effective stress is determined by the differential pressure across the pipe wall thickness. Research was begun in 1980, and is continuing today to further examine the combined effects described above on long ductile fracture propagation in stimulated deep offshore environments. These experiments were conducted on small diameter pipe pressured with air and surrounded by pressured water inside a large diameter pressure vessel. This more recent research and the conclusions are discussed below. Summary A series of fracture propagation experiments on 12.75 inch × 0.220 inch 5LX65 pipe were conducted using air as the pressuring medium. These 12-inch diameter experiments were conducted inside a 48inch diameter pressure vessel that was half filled with water and the remaining volume was pressured with air to simulate a water pressure corresponding to various water depths. The experiments were designed based on earlier knowledge (1,2) obtained on differential pressure, decompression into pressured water and effects of water backfill. Experiments on land with sand backfill and the same or lower differential pressures readily propagated a ductile fracture in this lot of pipes. Five experiments were conducted under water and in no instance was a long running ductile fracture obtained.