United States Nuclear Regulatory Commission - Protecting People and the Environment

Assessment of Crack Detection in Heavy-Walled Cast Stainless Steel Piping Welds Using Advanced Low-Frequency Ultrasonic Methods (NUREG/CR-6933)

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Manuscript Completed: August 2006

Publication Information


Date Published: March 2007

Prepared by:
M.T. Anderson, S.L. Crawford, S.E. Cumblidge,
K.M. Denslow, A.A. Diaz, S.R. Doctor

Pacific Northwest National Laboratory
Richland, WA 99352

D.A. Jackson and W.E. Norris, NRC Project Managers

Prepared for:
Division of Fuel, Engineering and Radiological Research
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code Y6604

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Abstract

Studies conducted at the Pacific Northwest National Laboratory in Richland, Washington, have focused on assessing the effectiveness and reliability of novel approaches to nondestructive examination (NDE) for inspecting coarse-grained, cast stainless steel reactor components. The primary objective of this work is to provide information to the U.S. Nuclear Regulatory Commission on the effectiveness and reliability of advanced NDE methods as related to the inservice inspection of safety-related components in pressurized water reactors (PWRs). This report provides progress, recent developments, and results from an assessment of low frequency ultrasonic testing (UT) for detection of inside surface-breaking cracks in cast stainless steel reactor piping weldments as applied from the outside surface of the components.

Vintage centrifugally cast stainless steel piping segments were examined to assess the capability of low-frequency UT to adequately penetrate challenging microstructures and determine acoustic propagation limitations or conditions that may interfere with reliable flaw detection. In addition, welded specimens containing mechanical and thermal fatigue cracks were examined. The specimens were fabricated using vintage centrifugally cast and statically cast stainless steel materials, which are typical of configurations installed in PWR primary coolant circuits.

Ultrasonic studies on the vintage centrifugally cast stainless steel piping segments were conducted with a 400-kHz synthetic aperture focusing technique and phased array technology applied at 500 kHz, 750 kHz, and 1.0 MHz. Flaw detection and characterization on the welded specimens was performed with the phased array method operating at the frequencies stated above. This report documents the methodologies used and provides results from laboratory studies to assess baseline material noise, crack detection, and length-sizing capability for low-frequency UT in cast stainless steel piping.

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