Actual Piping System Research Articles

Seismic fragility evaluation of the base-isolated nuclear power plant piping system using the failure criterion based on stress-strain

Abstract In the design criterion for the nuclear power plant piping system, the limit state of the piping against an earthquake is assumed to be plastic collapse. The failure of a common piping system, however, means the leakage caused by the cracks. Therefore, for the seismic fragility analysis of a nuclear power plant, a method capable of quantitatively expressing the failure of an actual piping system is required. In this study, it was conducted to propose a quantitative failure criterion for piping system, which is required for the seismic fragility analysis of nuclear power plants against critical accidents. The in-plane cyclic loading test was conducted to propose a quantitative failure criterion for steel pipe elbows in the nuclear power plant piping system. Nonlinear analysis was conducted using a finite element model, and the results were compared with the test results to verify the effectiveness of the finite element model. The collapse load point derived from the experiment and analysis results and the damage index based on the stress-strain relationship were defined as failure criteria, and seismic fragility analysis was conducted for the piping system of the BNL (Brookhaven National Laboratory) - NRC (Nuclear Regulatory Commission) benchmark model.

Noncontact Measurement Method of Vibration Stress Using Optical Displacement Sensors for Piping Systems in Nuclear Power Plants

In nuclear power plants, vibration stress of piping is frequently measured to prevent the occurrence of fatigue failure. A simpler and more efficient measurement method is desired for rapid integrity evaluation of piping. In this study, a method to measure vibration stress in a noncontact manner using optical displacement sensors is presented and validated. The proposed method estimates vibration-induced stress of small-bore piping directly using noncontact sensors based on a light-emission diode. First, the noncontact measurement method was proposed, and the measurement instrument based on the proposed method was developed for the validation. Next, vibration measurement experiments using the instrument were conducted for a mock-up piping system and an actual piping system. The measurement results were compared with the values measured by the conventional method of known accuracy using strain gauges. From this comparison, the proposed noncontact measurement method was demonstrated to be able to provide sufficient accuracy for practical use.

The Effect of the Distance From the Center of a Weld to the Fixed End on the Residual Stress and Stress Intensity Factor of a Piping Weld

The fixed conditions of butt welds between straight pipe and the valves or pump in an actual piping system are different from those of straight pipes. However, the effect of the fixed condition on the residual stress and the stress intensity factor for the evaluation of the structural integrity of cracked piping is not clear. In this study, finite element analyses were conducted by considering the differences in the distance from the center of weld to the fixed end L, to clarify the effect of the fixed condition on the residual stress and the stress intensity factor. For 600A piping, the residual stress distribution was not affected by L. Furthermore, the stress intensity factors of circumferential cracks under the residual stress field can be estimated by using an existing simplified solution for piping.

配管端部から円周溶接部までの距離が残留応力と応力拡大係数に及ぼす影響―溶接残留応力場におけるＳＣＣき裂進展評価（第１報）―

The fixed conditions of butt welds between straight pipe and valve or pump in the actual piping system are different from those of straight pipes. However, the effect of fixed condition on the residual stress and the stress intensity factor for evaluation of structural integrity of cracked piping was not clear. In this study, the finite element analyses were conducted by considering the differences in the distance from the center of weld to the fixed end L to clarify the effect of fixed condition on the residual stress and the stress intensity factor. For the 600A piping, the axial residual stress distribution was not affected by the distance L. Furthermore, the stress intensity factor of circumferential crack under the residual stress field with fixed condition could be estimated by using the existing simplified solution for piping.

To the Subject of Structural Control of Dynamic Flow Distribution

The work is suggested that represents a further extension of the methods related to the theory of hydraulic circuits of V.Ya. Hasilev and A.P. Merenkov in the direction of the substantiation, mathematical description, and statement of problems of regulation and control, which involve the nonstationary flow distribution in multiloop hydraulic circuits with lumped parameters. Consideration is given to a structural change in the diagram of a hydraulic circuit by way of a sequential exclusion of branches (edges) of the graph, which does not lead to its decomposition. The statement and description of this kind provide a model representation of the problem of structural control of actual piping systems, in particular, engineering systems of water and heat supply.

Pressure Loss Calculation Software-2002

We would like to introduce you new pressure loss calculation software for piping system, which is the renewed and updated version from one of last year and easier to use. We would like to explain to you mainly additional features from the previous one here, not the same features. The previous software calculated fluid pressure loss based upon virtual installation of valves and elbows on a fixed piping system.There had been some differences from the actual piping system with this way, which sometimes created difficulties in handling. The new software was programmed to solve this problem. You can design plane and lateral drawings automatically by selecting piping materials from the menu and calculate pressure loss by setting fluid conditions at the piping system.Thus, there is no restriction for number of piping system patterns. Users can specify as many piping system patterns as possible.Also you can check pressure losses at the specific locations by clicking mouse at any points of the piping system. You can print out the whole piping system to verify it clearly. We hope that this new software will be of great help to you.

Experimental Study of Mechanical Pipe Snubber Seismic Behavior

A series of seismic tests of mechanical snubbers on a full-scale model piping system provided a unique opportunity for detailed scrutiny of snubber seismic behavior on an actual piping system. The observed snubber behavior is a complicated pattern of braking and releasing, drag and drift, and the dynamic characteristics of the snubber, as well as the input motion, play a role in the response of the snubber. The snubbers were effective in limiting pipe displacements. Relative accelerations across the snubber were larger than expected. Snubber hysteretic behavior was irregular. Results from this testing are important in understanding snubber behavior, evaluating snubber performance, and in assessing alternatives to snubbers.

Effect of inertial loadings on the criterion for stable growth of a crack in a piping system

In the research on the effect of circumferential cracks in piping, the International Piping Integrity Research Group (IPIRG) has shown that inertial loadings are more conducive to crack growth instability than displacement controlled loadings. In applying the results to an an actual piping system that is subjected to a seismic event, when both types of loading occur simultaneously, it was inferred that the two types of loading are likely to behave differently as regards unstable crack growth leading to a double-ended guillotine pipe break. However, it is important to appreciate that the two configurations used in experiments of separate effects are completely different; displacement-controlled loadings were simulated by displacement-controlled four-point bending, while inertial loadings were simulated by actuating a beam with masses at its free ends. This latter situation is particularly susceptible to instability and is not reproducible in a piping system that is built-in at its end points. The present paper argues that, with an actual piping system and provided the deformation at the cracked section proceeds primarily by bending, then the two types of loading can be treated in the same way, as regards their effects on the crack growth stability criterion.

Leak-before-break: estimating the leakage area associated with a through-wall circumferential crack in a steel piping system

A key element in the development of a leak-before-break case for circumferentially cracked steel piping is an estimation of the size of through-wall circumferential crack that will give a measurable leakage under normal operating conditions. This estimation is usually made by calculating the stresses at the assumed crack section via a purely elastic analysis for the piping system, but assuming that the system is in fact uncracked. However because a piping system is built-in at its ends into some large component, and because the crack's presence is associated with an effective kink (rotational discontinuity) at the cracked section, this procedure will underpredict the crack size associated with a specified leakage area, and this has the potential to jeopardise the leak-before-break case. The present paper addresses this problem, and presents a very simple analysis which suggests that, for actual piping systems, the error is very small when one uses a methodology based on the uncracked piping stress to calculate the measurable leakage crack size.

A Test and Analysis of the Multiple Support Piping Systems

Abstract One of the current topics in the seismic design of piping systems is the overall reliability of them in earthquake events. Actual piping systems are generally supported by independent structures such as vessels and steel structures. So, it is very important to clarify the behavior of actual piping systems during the seismic events. For this purpose, the analytical method of multiple excitation problems is a preferable approach to not only evaluate the actual behavior of the piping systems, but also improve the reliability of piping systems. To clarify the dynamic characteristics of the piping systems and to assess the computational methods in the linear system subjected to multiple support excitations, an experimental study using a realistic large-scale piping model has been conducted. The equations for the multiple excitation problem have been validated and the adequacy of the multiple response spectra method has been confirmed by the comparison of the test results with the analytical one. This paper reports the results focusing on the analytical methods of the multiple support piping system. It is noted that the multiple response spectrum method is efficient for the multiple excitation problems.

Impact of structural steel flexibility and restraints gaps on the dynamic behaviour of piping

The effect of gaps present in the seismic supports of nuclear piping systems and of the flexibility of the steel structure to which intermediate supports are attached, is studied in this paper. An actual piping system is used to investigate the impact of structural steel and mechanical snubber gaps on the dynamic behaviour of piping. An evaluation is thus performed of the finite element modeling techniques employed by the designers in the dynamic analysis of piping systems.

延性不安定破壊の破壊力学的検討およびその配管系の安全性評価への適用

One of the most serious accidents which might possibly occur in piping systems is the sudden severing of pipe by tearing instability. Among safety assessment methods against this kind of fracture, the tearing instability theory based on the J-integral resistance curve is believed to be the most attractive one, because it can take account of compliance which is one of the important factors for tearing instability.This paper firstly presents tearing instability experiments using center and double-edge notched specimens. Load was applied to the specimens through a pipe tab with high compliance. Tearing instability occurred in all specimens after maximum load. The instability was predicted to take place when the value of Tappl, which is related to specimen configuration, compliance and other parameters, exceeded that of Tmat, which is concerned with the slope of J-integral resistance curve. The predicted instability point for each test compared well with the experimental point.Next, the paper proposed a formula of calculating the value of Tappl for a circumferential crack which lies in piping systems. The formula had been limitted to the simplest configuration of piping system, i.e. a straight pipe subjected to bending moment at both ends, because actual piping systems have three-dimensional structures, and that made it difficult to obtain the formula which took account of the overall compliance quantitatively. The paper showed that the problem for actual three-dimensional piping systems could be reduced to the equivalent problem of a straight pipe subjected to bending, where the equivalent length of straight pipe could be calculated from conventional finite element analysis of the piping system. The proposed formula can be used for the safety assessment of piping systems against tearing instability.

Cyclic Heating Test of Main Steam Piping Materials and Welds at the Sewaren Generating Station

Abstract This paper describes a continuation of previously reported cyclic heating tests of austenitic and ferritic piping and welds, representing the main steam piping installed at Sewaren Generating Station. In the current test, a section made up of these materials was subjected to thermal cycling from room temperature to 1100 F, and from atmospheric pressure to the operating pressure of 1500 psi. The heating and cooling rates were somewhat more severe than are experienced during regular starting and shutting-down conditions in the actual piping systems. The results show that 100 cycles did not produce any cracking. It is proposed to continue the test to destruction by further cycling and the addition of external bending forces.