Erratum: “On the Influence of Back Pressure and Size on the Performance of Safety Valves” [ASME 2002 Pressure Vessels and Piping Conference, Piping and Component Analysis and Diagnosis, Vancouver, BC, Canada, August 5–9, 2002, Conference Sponsors: Pressure Vessels and Piping Division, ISBN: 0-7918-4658-X, Copyright © 2002 by ASME. Paper No. PVP2002-1514, pp. 35-41; 7 pages; doi:10.1115/PVP2002-1514]

This erratum corrects errors that appeared in the paper “On the Influence of Back Pressure and Size on the Performance of Safety Valves” which was published in Proceedings of the ASME 2002 Pressure Vessels and Piping Conference, Piping and Component Analysis and Diagnosis, pp. 35–41, August 2002, PVP2002-1514, doi: 10.1115/PVP2002-1514.

Elastic Shakedown in Pressure Vessel Components Under Non-Proportional Loading

Bounding techniques for calculating shakedown loads are of great importance in design since this eliminates the need for performing full elasto-plastic cyclic loading analyses. The classical Melan’s lower bound theorem is widely used for calculating shakedown loads of pressure vessel components under proportional loading. Polizzotto extended the Melan’s theorem to the case of non-proportional loading acting on a structure. This paper presents a finite element method, based on Polizzotto’s theorem, to estimate the elastic shakedown load for a structure subjected to a combination of steady and cyclic mechanical loads. This method, called non-linear superposition, is then applied to investigate the shakedown behaviour of a pressure vessel component — a nozzle/cylinder intersection and that of a biaxially loaded square plate with a central hole. Results obtained for both problems are compared with those available in the literature and are verified by means of cyclic elasto-plastic finite element analysis.

Analysis of Rotating Blade Forced Vibration Due to Torsional Excitation Using the Method of Harmonic Balance

This paper presents an analysis of the forced vibration of rotating blade due to torsional excitation. The model analyzed is a multi-modal forced second order ordinary differential equation with multiple harmonically varying coefficients. The method of Harmonic Balance (HB) is employed to find approximate solutions for each of the blade modes in the form of truncated Fourier series. The solutions have shown multi resonance response for the first blade vibration mode. The examination of the determinant of the harmonic balance solution coefficient matrix for stability purposes has shown that the region between the two resonance points is an unstable vibration region. Numerical integration of the equations is conducted at different frequency ratio points and the results are discussed. This solution provides a very critical operation and design guidance for rotating blade with torsional vibration excitation.

Cross Property Correlations for Metals Subjected to Fatigue Damage Accumulation

A new method of evaluation of elastic property deterioration due to accumulated damage is suggested and experimentally verified. It is based on the explicit correlations between two groups of anisotropic properties – conductivity and elasticity, recently established for porous/microcracked materials with anisotropic microstructures. An experimental study of fatigue has been done to verify the theoretical predictions. The electrical resistance and Young’s modulus are measured as functions of the number of loading cycles in the standard fatigue tests. The agreement between the theoretical predictions and the direct experimental data is better than 10% in all cases. The results allow one to use the measurement of electric resistance to estimate the damage accumulated in metal structures and decrease in the elastic modulus.

Utilization of Micro-Electronic-Machine Systems (MEMS) to Possible Future Use in the Enhanced Analysis of Safety in Nuclear Power Plants

The focal point of this paper is to go in-depth in to the potential utilization of MEMS to further enhance safety measures within nuclear power plants. Robots, which are being researched and developed in Sandia National Laboratories, sometimes built as small as the size of a pollen grain, can be utilized to constantly monitor the stress analysis within all aspects of running a Nuclear Power Plant. From cooling towers to detecting miniscule cracks within pipes, MEMS can be utilized to constantly detect and even possibly repair minor faults within the overall structure of a nuclear power plant. MEMS technologies provide the ability to reliably produce micro actuators and sensors to meet these mission requirements. MEMS technologies are also attracting an increasing interest from the commercial sector for various applications. Currently, Sandia National Laboratories has been developing MEMS technologies to support its core missions of weapon surety, stockpile maintenance, and national security interests. Already, the project has been responsible for numerous electromechanical systems in nuclear weapons, which ensure nuclear safety and provide reliable arming, fusing and firing. With these factors in consideration, the main idea of this paper is to present ideas for producing sensors and robots on a micro scale, which could be programmed to communicate and work within each other to have enhanced safety and efficiency within a nuclear power plant.

Determination of the Regional Function of the Heart

Unlike many other engineering designs, the heart, a pressure vessel, shows variations within its chambers and surface in terms of mechanical function. This necessitates a whole field technique with high spatial resolution. Computer aided speckle interferometry (CASI), a nondestructive examination technique, is herein developed for this purpose. A speckle pattern was created on the surface of isolated rabbit hearts. Images of the beating hearts werc acquired with a charge-couple device (CCD) camera for one second at a rate of 50 frames per second. CASI was used to determine the 2-D displacement vectors over regions of approximately 4 × 6 mm. Regional area stroke work (the integral of the left ventricular pressure with respect to area), the first invariant of the 2-D strain tensor, and the principle strains were used to determine the regional function. After occluding the blood supply to a region of the heart, significant changes were detected in all the previously mentioned parameters. Commonly used techniques cannot determine 2-D strain and lack the high spatial resolution of CASI. Determination of the 2-D strain can provide useful data on the functionality of the heart.

Reliability, Availability and Maintainability Analysis of Steam Turbines Used in an Oil Refinery

Weibull reliability and maintainability analysis have been used to analyze the time between failures and time to repair data of a group of steam turbines being used in a large oil refinery. Failure history of a set of steam turbines was obtained from the Computerized Maintenance Management System of the plant. Out of 50 steam turbines in operation, 13 are identified as bad actors which have experienced ≥3 failures in five years. The Pareto analysis performed on this set of turbines further narrowed down the 10 most critical (worst performing) turbines. This group of most critical turbines is the primary target for this Weibull reliability and maintainability analysis. The Weibull reliability and maintainability analysis provides an indication of the equipment reliability and maintainability characteristics including their failure rates and repair rates. In addition to the failure and repair data, the associated maintenance cost for this group of turbines was also collected over a period of five years, and the trends in cost increase with respect to time are plotted.

On the Influence of Back Pressure and Size on the Performance of Safety Valves

The paper presents the results of an extensive experimental research programme performed on safety valves in order to clarify the effects of back pressure and valve size on the flow capacity of a valve. As well known, back pressure strongly influences valve operating characteristics and can also reduce the discharge coefficient. This flow rate reduction can be related to the occurrence of a subsonic flow regime along the flow path and to insufficient disc lift. Last mentioned features can play a different role on different valve sizes because of the non exact geometrical scaling within the same valve size range. This happens because the requirements of typical application design standards, such as the API Standard 526, are such that the valve inlet, valve outlet and face to face dimension are not exactly scaled with respect to the orifice diameter. Moreover, face to face dimension can limit the body bowl volume leading to different device performances the same operational conditions. In order to clarify and evaluate the influence of the above mentioned parameters on the flow capacity of safety valves, many tests were carried on a single valve for different pressure ratios, disc lifts and for different valve outlet areas and body volumes representing different sizes derived from API Standard 526. Test results show significant differences on the flow capacity of safety valves under back pressure regime. This would suggest testing every valve size of the considered valve size range at different expansion ratios to confirm performance. Since this procedure leads to an excessive number of experimental tests, a sensitivity analysis on the influence of the most important geometrical parameters has been carried out. In order to minimize the number of experimental tests required for characterizing the flowing capacity of the whole valve size range, the paper proposes an experimental correlation for the prediction of the above mentioned non similarity effects.

In-Situ Measurement of Thermowell Vibration During Production Train Pressurization

Fatigue failure of intrusive fittings such as erosion probes, sample quills and thermowells, has occurred in Woodside’s offshore and onshore operations. The mechanism of failure is generally thought to be resonant vibration caused by vortex shedding. The consequence of these failures can be severe, in particular for thermowells, as they form part of the pressure envelope, and hydrocarbon release can result. Thermowells on the Goodwyn Alpha platform flow lines were designed to withstand the maximum normal operating flow velocities. During production train pressurisation, however, the thermowells can experience velocities higher than the design limit, albeit for a limited time. These start up flow velocities are likely to cause vortex shedding frequencies exceeding flowline thermowell resonant frequencies. If a vortex shedding frequency occurs that is close to a thermowell natural frequency, a vortex “lock on” resonance can occur, resulting in large amplitude thermowell vibration transverse to the flow direction. In order to determine if thermowell replacement was warranted, a study was undertaken to measure the thermowells in situ. The specific aims were: to determine if vortex “lock on” was occurring; and to determine what cyclic stresses are present. To do this, a novel vibration measurement probe was developed and commissioned. The probe is capable of measuring bidirectional acceleration in thermowells without the need for the thermowell to be taken offline. This paper presents the development of the probe and the results of the measurements during flowline pressurisation.

Integrated Leak Rate Testing of Containments: A Regulatory Perspective

Appendix J of 10 CFR 50, “Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors,” sets the testing requirements for preoperational and periodic verification of the leak-tight integrity of the primary reactor containment, including systems and components which penetrate containment of light water-cooled power reactors, and establishes the acceptance criteria for such tests. The purposes of the tests are to assure that leakage through the primary reactor containment and systems and components penetrating primary containment would not exceed allowable leakage rate values as specified in the plants’ technical specifications. The current Appendix J requirements provide two options for performing the tests. Option A (fully deterministic) requires that after the preoperational leakage rate tests, a set of three integrated leak rate tests (ILRT — termed as Type A tests) shall be performed, at approximately equal intervals during each 10-year service period. Option B does not provide a quantitative requirement for scheduling the periodic Type A tests. However, NEI 94-01, “Industry Guideline for Implementing Performance-Based Option of 10 CFR Part 50, Appendix J,” and NRC Regulatory Guide (RG). The containment is a vital engineering safety feature of a nuclear power plant. It encloses the entire reactor and reactor coolant system and serves as a final barrier against the release of radioactive fission products to the environment under various accident conditions. Containment design is based on pressure and temperature loadings associated with a loss-of-coolant-accident resulting from a double-ended rupture of the largest pipe in the reactor coolant system. Recently, it has been reported that in certain 1.163, “Performance-Based Containment Leak Test Program,” provide guidelines for determining the frequencies of preoperational and periodic leak rate tests using a performance based approach. The Option B requirements and NEI 94-01 guidance are based on NUREG-1493, “Performance Based Containment Leak-Test Program.” Based on the information provided by the operating data and their risk significance, the study calculated the change in risk (in person-rem) to public for the 15 alternatives considered in the study. However, recognizing the non-sensitivity of risk to change in Type A leak rate testing frequencies, as depicted in NUREG-1493, a number of licensees are proposing changes to their Type A test frequencies using NRC risk-informed guidance in RG 1.174, “An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis.” The paper discusses certain key deterministic aspects of the risk-informed decision for the plant-specific changes in the ILRT frequencies.