NR198704 Crack Initiation and Growth Modeling and Definition of Crack Growth Behavior in Line Pipe Steels

The objective of the Crack Growth Modeling effort is to develop an understanding of the factors that control stress-corrosion crack growth. This effort has two main tasks: initiation and growth modeling; and definition of crack growth behavior. The model is used to predict crack growth based on determining when conditions are conducive to crack growth. Since the model deals with early crack growth, the properties of the metal nearest the surface must be considered. The second task, definition of crack growth behavior, deals with the growth of large cracks up to the point of failure. Of particular interest is the crack length-to-depth ratio because a crack with a small ratio gives a greater chance of leaking before breaking into a larger ratio. Also there is less chance of small crack linkage to form larger cracks when the lengthwise crack velocity is reduced. Thus a good understanding of the factors that control crack shape is essential for formulating a predictive model for long term crack growth.