By: Dick Mattson and Minghao Qin
A U.S. BWR utility contracted with Structural Integrity (SI) to review their current reinspection guidance documents relative to those contained in the BWRVIP inspection guidelines, the purpose of which was two-fold:
By: Mark Jaeger and Andrew Crompton
Acoustic resonance is a phenomenon in which an acoustic system amplifies sound waves whose frequency matches one of its own natural frequencies of vibration (its resonance frequencies).
in everyday life. In the most simple at home example, blowing air over the open end of a bottle. Blow too hard, nothing. Blow too soft, nothing. When done just right, the bottle produces a sound (audible vibration). Just like that, you have acoustic resonance. Every wind instrument in a band uses acoustic cavity resonance to produce music. Take a piece of flexible hose, spin it in the air until it whistles, again, acoustic resonance. When an acoustic cavity resonance happens inside piping systems, especially those with high energy flow, those seemingly harmless vibrations we illustrated above can cause serious damage. This phenomena can occur in nearly any industry, sometimes with benign consequences and other times with catastrophic results.
By: Erica Libra-Sharkey
INDUSTRY CHALLENGE
From the US Department of Energy, Office of Nuclear Energy, “The demanding environments of an operating nuclear reactor may impact the ability of a broad range of materials to perform their intended function over extended service periods. Routine surveillance and repair/replacement activities can mitigate the impact of this degradation; however, failures still occur. With reactors being licensed to operate for periods up to 60 years, with further extensions under consideration, and power uprates being planned, many of the plant systems, structures, and components will be expected to tolerate more demanding environments for longer periods. The longer plant operating lifetimes may increase the susceptibility of different systems, structures, and components to degradation and may introduce new degradation modes.
While all components potentially can be replaced, decisions to simply replace components may not be practical or the most economically favorable option. Therefore, understanding, controlling, and mitigating materials degradation processes and establishing a sound technical basis for long-range planning of necessary replacements are key priorities for extended nuclear power plant operations and power uprate considerations. https://www.energy.gov/ne/materials-aging-and-degradation”.
By: Bill Weitze
100% of thermal stress was treated as nonlinear gradient stress and linear bending stress was about 12% of the moment stress. Structural Integrity’s (SI’s) review of the stress terms used in piping analysis show that pressure stress does create bending stress in components…
EPRI Report 3002014121 “Development of Fatigue Usage Life and Gradient Factors” has developed fatigue usage adjustment factors that account for: 1) increased cyclic life associated with the growth of potential engineering size fatigue cracks in thicker components (thickness factor, TF; also called life factor, LF), and 2) the presence of through-thickness stress gradients (gradient factor, GF). (TF is used in the issued Code Case.) These factors are applied to cumulative usage factor, U, in air.
By: Scott Chesworth, Bob Grizzi, and Dilip Dedhia
Optimizing the inspection interval for high-reliability components whose examinations have a significant outage impact.
Welds and similar components in nuclear power plants are subject to periodic examination under ASME Code, Section XI. Typically, examinations are performed during every ten-year inspection interval using volumetric examination techniques, or a combination of volumetric and surface examination techniques. Nuclear plants worldwide have performed numerous such inspections over the plant history with few service induced flaws identified. Since personnel health and safety, radiation exposure, and overall outage costs associated with these inspections can be significant, Structural Integrity (SI) was contracted by the Electric Power Research Institute (EPRI) to review the technical bases for the inspection intervals for select components. The goal was to determine whether the frequency of current inspection requirements was justified or could be optimized (i.e., reduced in order to devote more attention to higher-value inspections and thereby maximize overall plant safety). Special priority was given to components demonstrating an exceptional history of reliability and whose examinations have a significant outage impact.
By: Dave Gerber and Terry Herrmann
Environmentally-Assisted Fatigue (EAF) screening is used to systematically identify limiting locations for managing EAF effects on Class 1 reactor coolant pressure boundary components wetted by primary coolant. This article provides an overview of the methods developed and used by Structural Integrity (SI) for Class 1 components having explicit fatigue analyses performed using ANSI/ASME B31.7(1) and ASME Section III(2). A future article will discuss how this is performed for Class 1 piping designed and analyzed to ASME/ANSI B31.1(3).
By: Curt Carney
As plants enter their initial or subsequent license renewal period one of the requirements is to show that fatigue (including environmental effects) is adequately managed. For some locations in pressurized water reactors (PWRs), it can be difficult to demonstrate an environmental fatigue usage factor less than the code allowable value of 1.0. Therefore, plants are increasingly turning to flaw tolerance evaluations using the rules of the ASME Code, Section XI, Appendix L. Appendix L analytically determines an inspection interval based on the time it takes for a postulated flaw (axial or circumferential) to grow to the allowable flaw size. For surge line locations, this evaluation can be very complex, as the crack growth assessment must consider many loadings, such as: insurge/outsurge effects, thermal stratification in the horizontal section of the line, thermal expansion of the piping (including anchor movements), and internal pressure. Trying to envelope all of these loads using traditional tools can lead to excess conservatism in the evaluation, and short inspection intervals that reduce the value of an Appendix L evaluation.
By: Wendy Weiss and Terry Totemeier
Structural Integrity (SI) personnel visited a power plant construction site to examine four Grade 91 elbows (ASTM A234-WP91 20-inch OD Sch. 60) that were found to contain axially oriented surface indications. The elbows had not yet been installed. The indications were initially noticed during magnetic particle testing (MT) after one end of an elbow was field welded to a straight section and post weld heat treated (PWHT). Subsequently, three additional similarly welded elbows were inspected and indications were found at both the welded (inlet) and open (outlet) ends of three elbows. The elbow with the most significant indications was selected for SI’s on-site examinations. Figure 1 shows the inlet and outlet ends of the selected elbow.
By: Ben Ruchte and Kane Riggenbach
To provide operating flexibility, combined cycle plants are typically equipped with bypass systems (high pressure routing steam to cold reheat and hot reheat routing steam to the condenser). These bypass systems include conditioning valves designed to reduce steam pressures followed by outlet desuperheaters which inject water to reduce steam temperatures.
This service environment exposes the downstream piping to a high frequency of temperature transients making these areas one of the most prominent ‘industry issues’.
By: Cliff Lange and Matt Freeman
OEMs recommend periodic inspection of pinned finger turbine blade attachments for detection of service-induced damage as part of ongoing rotor
maintenance activity.
This article provides an example where ultrasonic inspection detected cracking in several pins of finger attachments and outlines an engineering assessment to support continued operation and identify a re-inspection interval. This approach can be applied to other pinned finger blade attachments to determine suitability for service.
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