Results of Seawater Crack Propagation Tests, of Zinc Dissolution Experiments, and Data Analysis

摘要

Results of seawater crack propagation tests, of zinc dissolution experiments, and data analysis are presented. Tests were performed on specimens of rectangular cross sections containing partial thickness starter cracks. The specimens were submerged in seawater and subjected to fluctuating loads. Specimens were tested at a constant mean stress but at several alternating stresses. In general, the effect of alternating stress level on crack propagation is the same for the seawater tests as for the air tests. That is, as the alternating stress is increased, the crack growth rate increases at a given crack length. It is clear that environment has no influence on the crack length at fracture. All these failures are of the plane stress-ductile type since the net section stress at fracture is greater than either yield or ultimate strength. The fracture surfaces further demonstrate this point, and fractographs will be presented in the final report. Both the room temperature and 200 F studies of the zinc dissolution rate in the new fresh-water mud have been completed. The results of these experiments indicate that a zinc coating will provide adequate protection to the drill string in the fresh-water drilling mud. On the other hand, the data suggest that more rapid dissolution of the zinc may occur in areas where the mud clings to the pipe surface. (Author)