Small Bore Piping System Research Articles

Seismic response of small-bore piping system with damage of multiple supports

Seismic response of small-bore piping system with damage of multiple supports

Shaking table test on small-bore piping system with damage of support structure

As a countermeasure to mitigate the catastrophic damage by an excessive seismic load beyond the design level, a concept of fracture control was proposed in the previous study. To apply this concept to the piping system, one of ideas is to cause the failure at pipe supports prior to the failure of pipe body itself, because the failure at support is minor failure compared to that at pipe body. To examine the feasibility of this fracture control concept to the piping system, a shaking table test on a small-bore piping system with supports were conducted. Through the shaking table test, it was confirmed that the response of the piping system can be suppressed by damaging the support structure prior to the damage of the piping system so as to the frequency ratio to be over 1.0. Meanwhile, it was also confirmed that the loss of the support may result in large response displacement and strain concentration at anchors. In addition, the importance of strength evaluation based on the actual material strength was also confirmed. These points should be well considered when applying the fracture control concept to the piping system.

Effect of Dynamic Vibration Absorber on Seismic Response of Piping Systems

The purpose of this study is to clarify the seismic response reduction effect of the piping system by a dynamic vibration absorber. The piping system with a dynamic vibration absorber was modeled into a two-degree-of-freedom system composed of a simple modal mass and a dynamic vibration absorber. Using this model, the floor response spectrum for the observed seismic waves was calculated. By comparing the changes in the two floor response spectra of the piping system with the dynamic vibration absorber and the piping system without the dynamic vibration absorber, the response reduction effect of the dynamic vibration absorber and the magnitude of the added damping ratio were discussed. When a dynamic vibration absorber was installed, the peak height of the floor response spectrum of the piping system decreased, and the effect was useful for the piping system with a smaller damping ratio. Dynamic vibration absorbers are suggested to be an effective method for reducing the seismic response of small-bore piping systems with a small damping ratio.

Experimental validation of non-contacting measurement method using LED-optical displacement sensors for vibration stress of small-bore piping

There have been many reports of fatigue failures of small-bore piping systems such as drain piping, vent piping and instrumentation piping in nuclear power plants that arise from vibration sources such as pumps. To prevent the failures, integrity evaluation of piping is conducted by measuring and analyzing vibration stress in the piping. But, a more efficient and economical measurement method is desirable to evaluate the vibration fatigue in small-bore piping. In this study, a non-contacting measurement method was proposed that is based on optical displacement sensors using light emission diodes (LEDs) to measure the vibration stress. The applicability of the method was discussed based on the vibration experiments using pipe elements and a mock-up piping system. From the experimental results, the proposed method was clarified to be sufficiently applicable and practically useful for the vibration measurement and stress evaluation in small-bore piping systems.

Localization and evaluation of corrosion in a small-bore piping system using a bobbin-type magnetic camera

This paper presents a nondestructive evaluation algorithm for locating, discriminating, and evaluating inner and outer diameter (ID and OD) corrosion on a small-bore pipe by means of a bobbin-type magnetic camera that uses arrayed solid-state Hall effect sensor elements for measuring alternating magnetic fields. The proposed magnetic camera system is used to experimentally measure artificial ID and OD hole-type cracks on a small-bore copper alloy pipe over a low-frequency range (2-8 kHz). The measured amplitude signal is analyzed to determine both the position and type of crack. The volumes of the cracks are estimated with standard deviation of 0.77 mm 3 to be in the range 1.00-9.01 mm 3 .

Fast simulation of alternating magnetic fields around a crack in a pipeline system using a dipole model method

This study proposes a method for the fast simulation of the distribution of alternating magnetic fields around internal cracks as well as cracks on the inner and outer diameter surfaces of a pipe. This method, which uses a bobbin-type magnetic camera to inspect cracks in small-bore piping systems, is based on a dipole model, allowing for the rapid calculation and storage of data on the distribution of alternating magnetic fields around cracks from a sensor moving inside a pipe. Copyright © 2014 John Wiley & Sons, Ltd.

Quantitative Evaluation of Corrosion in a Thin Small-Bore Piping System Using Bobbin-Type Magnetic Camera

Nondestructive testing (NDT) methods have been developed to ensure the integrity of heat exchanger pipes. NDT systems can be used to not only locate cracks on the pipes but also evaluate the size and position of the cracks. A bobbin-type magnetic camera (BMC), an electromagnetic NDT system, was developed to inspect both the inner and outer diameters (ID and OD, respectively) for stress corrosion cracking on a small-bore piping system with a high spatial resolution at high speeds. In this paper, an algorithm that discriminates the ID cracks from the OD cracks and estimates the crack volume is proposed. Artificial ID and OD hole-type cracks which have diameter of 1–4.5 mm and depth of 0.3–27 mm were used to imitate the corrosions on a 1.27 mm thickness and 16.56 mm inner diameter copper alloy pipe to verify the proposed algorithm. The inspection results of the BMC with respect to excited frequencies from 1–9 kHz are presented. 100 % of the ID and OD cracks were discriminated, and their volumes were estimated with a standard deviation of 1.132 mm3 for volume from 1.00–9.01 mm3.

Bobbin-Type Solid-State Hall Sensor Array With High Spatial Resolution for Cracks Inspection in Small-Bore Piping Systems

Bobbin coil and bobbin-type Hall sensor arrays are proposed as an alternative for crack inspection inside a small-bore piping system. The cracks can be imaged at high speed without using a scanner since the electromagnetic (EM) field is distorted by the cracks. An array of 32 × 32 Hall sensors with 0.78 mm spatial resolution was set in a cylinder with diameter of 15 mm and length of 24.96 mm. A bobbin coil operating at 5 kHz of alternating current was positioned inside of a piping system and the sensor array outside the cylinder. Distorted EM fields around outside diameter stress corrosion cracking was imaged at 1 frame/s.

3111 金属の振動疲労における非線形変形に伴う高調波の発生(OS.10 故障診断・予知・メンテナンス・安全性)

The resonant vibration tests were carried out on type 304 stainless steel to develop the non-destructive method for evaluating fatigue damage. The authors have studied the critical strain amplitude of fatigue above which dislocation multiplication begins to occur. The critical strain amplitude was determined from the stain amplitude dependence of internal friction which is due to dislocation motion of breakaway from pinning points and multiplication. Such dislocation motion gives the nonlinear stress-strain relationship of resonant vibration. The non-linear stress-strain relationship yields higher harmonics on vibration. In this study, the dynamic displacement of resonant vibration was measured using a non-contact laser displacement meter. The 3rd harmonics was strongly dependent on the strain amplitude over the region above the critical strain amplitude, though hardly be identified below that strain. As a consequence, detecting higher harmonics could be used to determining the critical amplitude of vibrating structures such as small bore piping systems with branch joints.

High Level Dynamic Testing and Analytical Correlations for a Small Bore Piping System

High-level dynamic testing of a prototypic insulated small bore diameter pipe system is described. The pipe system was supported by a minimum number of supports, with several combinations of supports and support locations tested. Load input consisted of a dynamic multifrequency time history and sinusoidal loading at increasing acceleration levels until gross deformation of the system occurred. Very high level pipe damping was exhibited when plastic response occurred. Post-test analyses were performed to assess the structural loading and response of the pipe system under the dynamic load input. Several elastic and elasto-plastic analysis failure prediction methods were used, along with simplified inelastic analysis.

Seismic Damping Factors of Small Bore Piping as Influenced by Insulation and Support Elements

Seismic damping tests of a prototypical Liquid Metal Fast Breeder Reactor (LMFBR) small bore piping system is described, and measured transient responses to pulse excitations are reported. The test specimen was representative of a typical LMFBR insulated small bore piping system, and it was supported from a rigid test frame by prototypic dead weight supports, mechanical snubbers, and pipe clamps. Various support configurations were tested to assess the response sensitivity to insulation and other nonlinear support characteristics. Damping factors increased significantly due to the insulation and use of mechanical snubbers. Factors much higher than the magnitudes currently allowed in design by the USNRC Regulatory Guide 1.61, were found. This verified the design values, and it also pointed out the possibility of undue conservatism and costly overdesign resulting from use of the present design values.