Successful application of NDE for continued operation of pressure boundary components

摘要

Nondestructive evaluation (NDE) provides a methodology for assessing the fitness of a component or system for continued operation. NDE is used to detect flaws and characterize them as to type and size. Quantitative NDE information about flaw size and location is the initial information used in subsequent analysis to determine the continued usefulness of a component. New methods in quantitative NDE include use of computers, focused energy sources, and advanced signal processing.It is not a function of NDE to distinguish between flaws and defects. A flaw is a defect when the component can no longer function properly or safely. It is usually accepted that very small flaws will not cause failure during normal use. But, under some conditions, these small flaws can grow to larger flaws which indeed will cause failure. The structural lifetime assurance method predicts the flaw growth rate that affects the continued safe operation of pressure boundary components.Three distinct disciplines are needed to implement structural lifetime assurance. NDE detects and characterizes flaws as to size, shape, and location; structural analysis determines the stress concentrations near flaws or potential flaw locations; andmaterials science determines the flaw growth rate. Fracture mechanics embodies these technologies to measure and predict crack growth. Structural lifetime assurance or life extension methodologies are usually applied to large and expensive componentswhere the cost of failure, the loss of productivity, or the risk to life is great. Examples of quantitative NDE and structural lifetime assurance determinations for continued operation of generic pressure boundary components are discussed in this paper.