The Effects of Surface Condition on an Ultrasonic Inspection: Engineering Studies Using Validated Computer Model (NUREG/CR-6589)
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Manuscript Completed: October 1997
Date Published: April 1998
Pacific Northwest National Laboratory
Richland, WA 99352
D. Jackson, NRC Project Manager
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code B2289 and W6275
This report documents work performed at Pacific Northwest National Laboratory (PNNL) on the effects of surface roughness on the reliability of an ultrasonic inservice inspection. The primary objective of this research is to develop ASME Code recommendations in order to limit the adverse effects of a rough surface and thereby increase the reliability of ultrasonic inservice inspections. In order to achieve this objective engineering studies were conducted that included experimental validation of computer codes, developed at the Center for Nondestructive Evaluation (CNDE) at Iowa State University as a result of a cooperative effort between the Electric Power Research Institute (EPRI) and the Nuclear Regulatory Commission.
The basic problem associated with a rough surface in an inservice inspection is that, as the transducer rotates slightly to accommodate the rough surface, the beam direction in the metal changes and the time-of-flight of the echo changes as well. One problem is the excessive weld crown, where weld material protrudes above the adjoining surfaces. In this research this condition is modeled by considering a step discontinuity on the top surface. CNDE developed several models of increasing complexity in order to model an inservice inspection. This report describes the validation of four computer codes.
These codes were used to mimic an inservice inspection in order to understand effects associated with rotation of the transdu-cer as it traverses a step discontinuity. Systematic engineering studies were conducted using these computer codes and as a result ASME Section XI Code recommendations were developed. Briefly, Recommendation I is that the wedge be tilted by no more than 5°. A 5° tilt of the transducer wedge results in the angle of the ultrasonic beam in steel changing from 45° to 60°. Recommendation II is that the angle of inclination of the transducer wedge on a wavy or blended surface be limited to 14°. This means that, for a 45° beam in steel, the angle can range from 31° up to 59°. Recommendation III is that the excessive weld crown should be reduced uniformly until flush with the adjacent surface or until the 5° limit stated in Recom-mendation I can be maintained. Also, for new welds and repair welds the method of contour grinding should not be used.