Parametric Study of the Coupling Power Factor for the Statistical Energy Analysis of Piping Acoustic Vibration

Energy-based finite element model is utilized for the evaluation of the Statistical Energy Analysis (SEA) coupling factor and the dependence of the coupling factor on the different system parameters is studied. Previous research has shown that the coupling factor is largely dependent on the modal densities of the fluid and pipe subsystems, which depend on the pipe dimensional parameters. The coupling factor depends also on the spectrum of the acoustic power generated, which in turn depends on the mass flow rate, the pressure reduction ratio and the characteristics of the pressure-reducing device. This study is concerned with the piping system parameters, downstream of the pressure-reducing valve. The system parameters selected for consideration are the pipe diameter to thickness ratio D/T and the pipe length to diameter ratio L/D. The study presents the effect of the variation in these two dimensionless parameters on the coupling factor. The results of the analysis can be used directly in the formulation of SEA power flow equations for large piping systems with multiple sources of acoustic energy as part of the fatigue life evaluation in critical services.

Development of Inverse Analysis of Heat Conduction and Thermal Stress for Elbow: Part I

Thermal fatigue may develop in piping elbow with high temperature stratified flow. To prevent the fatigue damage by stratified flow, it is important to know the distribution of thermal stress and temperature history in a pipe. In this study, heat conduction inverse analysis method for piping elbow was developed to estimate the temperature history and thermal stress distribution on the inner surface from the outer surface temperature history. In the inverse analysis method, the inner surface temperature was estimated by using the transfer function database which interrelates the inner surface temperature with the outer surface temperature. Transfer function database was calculated by FE analysis in advance. For some patterns of the temperature history, inverse analysis simulations were made. It was found that the inner surface temperature history was estimated with high accuracy.

Comparison of the Limit Loads Between Defected Pressure Pipes With an Internal Pit and an External Pit at High Temperature

High temperature pressure pipes are widely used in power stations, nuclear power plants, and petroleum refinery, which always bear combined effects of high temperature, high pressure, and corrosive media, so the local pits are the most common volume defects in pressure pipe. Due to various reasons, the defects usually appear on the internal or external wall of pipe. In this paper, the dimensions of a defect were characterized as three dimensionless factors: relative depth, relative gradient and relative length. The main objects of study were the pipe with an internal pit and pipe with an external pit. Orthogonal array testing of three factors at four different levels was applied to analyze the sequence of the influence of three parameters. In present study, when the maximum principal strain nearby the location of the defects reaches 2%, the corresponding load is defined as the limit load, which is classified as two kinds of load type: limit pressure and limit bending moment. According to this strain criterion and isochronous stress strain data of P91 steel, the limit load of high temperature pipe with a local pit was determined by using ABAQUS. And in the same load condition of the pipe with the same dimensionless factors, the limit load of the internal defected pipe was compared with that of the external defected pipe. The results of this study can provide a reference for safety assessment and structural integrity analysis of high temperature creep pressure pipe with pit defects.

Brittle Fracture Analysis of a Dissimilar Metal Weld

One important part of the integrity demonstration of large ferritic components is based on the demonstration that they could never undergo brittle fracture. Connections between a ferritic component and an austenitic piping (Dissimilar Metal Weld — DMW) have to respect these rules, in particular the Heat Affected Zone (HAZ) created by the welding process and which encounters a brittle-to-ductile transition. Within that frame, the case considered in this article is a Ni base alloy narrow gap weld joint between a ferritic pipe (A533 steel) and an austenitic pipe (316L stainless steel). The aim of the present study is to show that in the same loading conditions, the weld joint is less sensitive to the brittle fracture than the surrounding ferritic part of the component. That is to say that the demonstration should be focused on the ferritic base metal which is the weakest material. The bases of this study rely on a stress-based criterion developed by Chapuliot et al., using a threshold stress (σth) below which the cleavage cannot occur. This threshold stress can be used to define the brittle crack occurrence probability, which means it is possible to determine the highest loading conditions without any brittle fracture risk.

ASME Section III Stress Analysis of a Heat Exchanger Tubesheet With a Misdrilled Hole and Irregular or Thin Ligaments

A stress analysis is described for a nuclear steam generator tubesheet with a thin or irregular ligament associated with a mis-drilled hole using the rules of ASME B&PV Section III and Non-Mandatory Appendix A, Article A-8000 for Stresses in Perforated Flat Plates. The analysis demonstrates the proper application of the NB-3200 rules for this special application with discussion of the differences between an actual tube hole deviation from what is assumed in ASME Appendix A. This is a companion paper to “Technical Justification Supporting Operation with a Tube Installed in a Mis-Drilled Hole of a Steam Generator Tubesheet”.

Assembler Qualification and General Revisions for ASME PCC-1-2013

The purpose of this paper is to outline the final approved requirements for assembler qualification that will be published in ASME PCC-1-2013 Appendix A. A brief overview of the requirements and a more detailed look at the intended method of implementation of the requirements by industry are examined. In addition, a series of more general updates and corrections were made to the body of PCC-1, which will be included in the 2013 version. These changes are also briefly outlined within this paper, for the information of the user of ASME PCC-1.

The Brittle Strength Assessment of WWER-1000 Reactor Pressure Vessel Nozzle With Cladding

Brittle strength calculation of RPV nozzle is the central point of the integrity assessment of the reactor pressure vessel when extending its life. The important part of this calculation is a determination of the stress intensity factor, SIF, for the postulated crack of partly elliptical form in a nozzle under inner pressure, bending moments (from the main circulating pipe) and difference of temperatures. In this paper we use method of influence functions as the most convenient one for solution of similar tasks. Eight basic laws of the crack surface loading are introduced which account for real stress distribution in the depth and length direction of a crack including the jump of stress between cladding and main metal due to the difference in the thermal expansion factors. To determine the dimensionless SIF under chosen laws of loading were developed the FEM models of nozzle with crack of different ratios of axes. For all possible modes (regimes) of operation were carried the detailed calculations of the temperature field in the nozzle, which were used later for determining the stress state at each time point. The stress field defined in 120 discrete points of the crack surface was treated by the method of least squares for the presention as a linear combination of eight basic load laws with defined coefficients. The procedure for determination of the temperature brittle strength margin which employs the presentation of critical values of SIF (fracture toughness) in the exponential function form is described.

Working Bolts Near to Yield: Theory, Experience and Recommended Practice

For many years 50% yield was a favored generic level for bolted flanged joints, however in pursuit of leak free performance this is no longer the case. In line with the guidance given in modern documents such as Appendix O of ASME PCC-1-2010 Guidelines for Pressure Boundary Bolted Flange Assembly [1] and with the increasing number of joints requiring corrosion resistant alloys often it is necessary and desirable to take bolts to values closer to their yield point or more accurately their 0.2% proof stress. The paper will examine the issues associated with tightening bolts to values well in excess of 50% of their 0.2% proof stress and analyze the effects on the during tightening and subsequent re-tightening. The analysis will include results of actual testing of bolts tightened to high stresses and give recommendations on a sound engineering approach to this practice which considers the risks and benefits. Analysis will also include a statistical evaluation of the effects of torque and tension scatter at high levels of target bolt stress.

The Role of Computational Weld Mechanics in the Weld Repair of Canada’s NRU Nuclear Reactor

The NRU reactor at Chalk River Laboratories is one of the largest and oldest research reactors in the world. It has been the world’s largest producer of medical isotopes, which are used in cancer treatments, nuclear medicine and other diagnostic procedures. The NRU reactor was shut down in May 2009 when a heavy water leak was detected in the reactor building. Subsequent inspections indicated that the reactors aluminum vessel corroded at various locations resulting in heavy water seeping through the reactor vessel. The extent of the damage required a complex pattern of internally applied weld overlays in numerous areas. Weld repair was further complicated by concerns over the effect of radiation hardening of the aluminum and compositional changes (irradiation induced transmutation of aluminum to silicon). Considering the deformation and stress associated with welding aluminum plate (Figure 1) and the aggressive return to service schedule, Atomic Energy of Canada (AECL) commissioned an extensive Computational Weld Mechanics (CWM) campaign to guide the repair design and optimize structural integrity. This paper describes the technical issues encountered in the design of the weld repair processes and how CWM was used in selecting welding strategies. Traditionally, welding pattern, progression and sequence are determined through a combination of trial and error on mock ups along with welders experience and analyzed by computer after the fact. To the authors knowledge, this is the first weld repair that used CWM to assess proposed designs of welds.

Design Curve Construction Based on Monte Carlo Simulation

Good durability/reliability performance of products can be achieved by properly constructing and implementing design curves, which are usually obtained by analyzing test data, such as fatigue S-N data. A good design curve construction approach should consider sample size, failure probability and confidence level, and these features are especially critical when test sample size is small. The authors have developed a design S-N curve construction method based on the tolerance limit concept. However, recent studies have shown that the analytical solutions based on the tolerance limit approach may not be accurate for very small sample size because of the assumptions and approximations introduced to the analytical approach. In this paper a Monte Carlo simulation approach is used to construct design curves for test data with an assumed underlining normal (or lognormal) distribution. The difference of factor K, which measures the confidence level of the test data, between the analytical solution and the Monte Carlo simulation solutions is compared. Finally, the design curves constructed based on these methods are demonstrated and compared using fatigue S-N data with small sample size.