For the past several years the Pipeline Research Committee of the American Gas Association has sponsored research at Battelle's Columbus Laboratories with the objective of obtaining a better understanding of the behavior of defects in pressurized pipe. This objective is being pursued by means of full-scale experiments on line pipe specimens containing both artificial and actual defects. These experiments have led to the development of semiempirical equations for predicting the ductile failure stress levels of through-wall flaws and surface flaws. Although these equations have been presented before, the supporting data and analyses are described in this paper. The through-wall flaw equation is analogous to fracture mechanics criteria for plane stress fracture; but because it has been adapted to ductile line pipe materials, it contains the Dugdale Model for plastic flow in the material and a correction for the bulging stress resulting from pressure acting on the curved pipe walls. The surface flaw equation evolved from the experimental results on surface-flawed pipe specimens. It accounts for both length along the axis of the pipe, depth through the wall, and the bulging which also takes place at surface flaws. Both equations have been shown to give reliable prediction of failure stress levels for not only steel line pipe materials but for stainless steel and aluminum pressure vessels as well. The usefulness of these equations extends over a wide range of material toughness and strength levels, because they embody both tensile strength parameters and the notch-toughness as determined from the ductile shelf energy of Charpy V-notch impact specimens. The experimental results upon which the equations are based are presented and discussed herein as are the utility and degree of reliability of the equations.

Presented is a discussion of an hypothesized analytical explanation of ductile fracture initiation, propagation, and arrest in cylindrical pressure vessels and piping. The hypothesized analytical treatment is an attempt to predict initiation and arrest conditions for ductile fractures using Charpy V-notch plateau energy as a means of determining the toughness of the material. Data from a number of full-scale experiments on gas transmission pipe, nuclear reactor piping, and other cylindrical vessels are presented and are shown to be in agreement with the hypothesis.

The program of research on line pipe under the sponsorship of the A.G.A. Pipeline Research Committee is a comprehensive effort to investigate the important properties of pipe used in gas transmission. Several different phases are involved in this project, ranging from fundamental laboratory studies to fracture-behavior experiments on large-diameter pipe. This paper discusses the full-scale experimental parts of the program in which the fracture toughness of line pipe is being studied. Some of the factors that influence full-scale fracture behavior are discussed—material properties, fracture speed, temperature, wall thickness, nominal stress level, and type of backfill. Laboratory fracture tests that are being run and correlated with full-scale behavior are also described.

No abstract

The repair procedure for removal of a girth weld defect in offshore pipelines involves arc-gouging a groove into the defective area. Since high bending stresses in the pipes exist at the repair station, the concern was whether the weld repair groove may cause failure of the pipes. An experimental research program was conducted to determine the critical length and depth of repair grooves. Experiments were conducted on 100, 150, and 762-mm-dia pipes. A plastic instability failure criteria was developed and verified to predict the failure stresses for carbon steel pipes. The failure criterion is given as a function of three nondimensional parameters. These parameters are groove depth to pipe thickness ratio, groove length to pipe circumference ratio, and longitudinal stress to flow stress ratio. Stable versus unstable (i.e., leak versus break) behavior is also predicted from the failure criteria.