Search Results for crack sizes

This appendix presents an analytical model that estimates damage rates for both crack initiation and propagation mechanisms. The model provides a nonarbitrary definition of fatigue crack initiation length, which serves as an analytical link between initiation and propagation analyses and appears to have considerable merit in estimating the total fatigue life of notched and cracked structures.

This chapter describes how ultrasonic testing came to be a viable method for evaluating intergranular stress-corrosion cracking (SCC) in large-diameter stainless steel pipe welds in boiling water reactor service. Intergranular SCC can be difficult to detect using nondestructive evaluation (NDE) techniques because of its treelike branching pattern and its location in the heat-affected zone within the weld. As the chapter explains, by optimizing excitation and reflected waveforms, switching to dual-element sensing, properly orienting the scanning path, and using crack-tip diffraction and amplitude-drop techniques, the height, length, and location of intergranular cracks can be accurately determined anywhere along the walls of the pipe as well as in weld areas.

Fracture control can be defined as a concerted effort to maintain operating safety without catastrophic failure by fracture. It requires an understanding of how cracks affect structural integrity and strength and the time that a crack can grow before it exceeds permissible size. The chapter describes some of methods used to determine maximum permissible crack size and predict growth rates. It explains how the information can then be used to control fractures through periodic inspection, fail-safe features, mandated retirement, and proof testing. It presents a number of fracture control plans optimized for different circumstances, examines the damage tolerance requirements used by different industries, and discusses various approaches for fatigue design.

This chapter discusses the practices and procedures used to reveal and record macrostructural features such as hardening depth, weld thickness, crack size, porosity, hot folds, and machining and tooling marks. It provides information on sectioning, sample location, orientation, surface grinding, and etching. It describes macrographic etchants and the features they reveal along with common etching problems and how to avoid them. It explains how to evaluate etching results and how they can be improved using remedial processes such as light grinding. It also discusses photographic reproduction, lighting, and image enhancement techniques.