Failure Estimation Method Research Articles

Failure-Aware and Delay-Predicted Multipath Virtual Queue Scheduling for Multimedia Transmission in Edge IoT

The spread of Edge Internet of Things (IoT) radically changes our lifestyle. However, the multimedia services in edge IoT are still stuck by inefficiency. The dynamic typologies perplex the transmission of massive real-time data. To solve this problem, multipath transmission control protocol (MPTCP) which has a natural advantage in transmission robustness and bandwidth aggregation is becoming a good choice. In this paper, failure-aware and delay-predicted multipath virtual queue scheduling (FD-MVQS) is proposed to optimize the MPTCP performance in edge IoT. FD-MVQS constructs a two-plane cooperative scheduling system. In the control plane, the transmission failure estimation and chaos theory-based arrival delay prediction methods are introduced to provide the foundation for prescheduling. In the data plane, the multipath virtual queue scheduling is designed to allocate segments to different subflows. Simulation results showed that the proposed FD-MVQS performed better than standard and typical multipath transmission solutions in throughput, delay, and segment disorder.

Failure bending moment of pipes containing multiple circumferential flaws with complex shape

Flaws due to stress corrosion cracking have been detected in stainless steel or nickel-based alloy dissimilar metal weld joints of piping systems in nuclear power plants. Generally, stainless steel and nickel-based alloy are ductile materials with high toughness, and the failure mode of flawed pipes made of ductile materials is expected to be net-section plastic collapse. Failure bending moment of a ductile pipe containing a circumferential flaw is predicted using the net-section stress approach according to ASME Code Section XI as a limit load criterion. However, in the current code, the failure bending moment can only be adopted for a pipe containing a single circumferential flaw with constant depth, although many flaws detected actually are multiple flaws, and the flaw shapes are generally complex. In this study, a failure estimation method for pipes containing multiple circumferential flaws with complex shapes was proposed. Furthermore, failure experiments were performed for 8-inch diameter Schedule 80 stainless steel pipes containing two circular circumferential flaws. The failure bending moments obtained from the experiments were compared with the estimated results. Based on the experimental results, it was concluded that the proposed failure estimation method satisfactorily represents the failure behavior of the pipes and can be applied in engineering application.

Failure Experiments on Pipes With Local Wall Thinning Subjected to Multi-Axial Loads

Piping lines in nuclear power plants may experience multi-axial loads including tensile force, bending, and torsion moments during operation. There is a lack of guidance for failure evaluation of locally wall-thinned pipes under the multi-axial loads including torsion moment. The ASME B&PV Code Section XI Working Group is currently developing fully plastic failure evaluation procedures for pressurized piping items containing local wall thinning subjected to multi-axial loads. A failure estimation method for locally wall-thinned pipes subjected to multi-axial loads including torsion moment has been proposed through numerical analyses. In this study, in order to investigate the failure behavior of the pipes with local wall thinning subjected to multi-axial loads including the torsion, failure experiments were performed on 20 mm diameter carbon steel pipes with a local wall thinning. Based on the experimental results, the proposed failure estimation method is confirmed to be applicable to pipes with local wall thinning.

A Failure Estimation Method of Steel Pipe Elbows under In-plane Cyclic Loading

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

Experimental Study on Failure Estimation Method for Circumferentially Cracked Pipes Subjected to Multi-Axial Loads

When a crack is detected in a piping line during in-service inspections, failure estimation method provided in ASME Boiler and Pressure Vessel Code Section XI (ASME Code Section XI) or JSME Rules on Fitness-for-Service for Nuclear Power Plants (JSME FFS Code) can be applied to evaluate the structural integrity of the cracked pipe. The failure estimation method in the current codes accounts for the bending moment and axial force due to pressure. The torsion moment is not considered. Recently, analytical investigation was carried out by the authors on the limit load of cracked pipes considering multi-axial loads including torsion. Two failure estimation methods for multi-axial loads including torsion moment with different ranges were proposed. In this study, to investigate the failure behavior of cracked pipes subjected to multi-axial loads including the torsion moment and to provide experimental support for the failure estimation methods, failure experiments were performed on 20 mm diameter stainless steel pipes with a circumferential surface crack or a through-wall crack under combined axial force, bending moment, and torsion moment. Based on the experimental results, the proposed failure estimation methods were confirmed to be applicable to cracked pipes subjected to multi-axial loads.

Experimental Investigation of Failure Estimation Method for Circumferentially Cracked Pipes Subjected to Combined Bending and Torsion Moments

When a crack is detected in a nuclear piping system during in-service inspections, failure estimation method provided in codes such as ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. In the current codes, the failure estimation method for circumferentially cracked pipes is applicable for both bending moment and axial force due to pressure. Torsion moment is not considered. Recently, two failure estimation methods for circumferentially cracked pipes subjected to combined bending and torsion moments were proposed based on analytical investigations on the limit load for cracked pipes. In this study, experimental investigation was conducted to confirm the applicability of the failure estimation method for cracked pipes subjected to bending and torsion moments. Experiments were carried out on 8-in. diameter Schedule 80 stainless steel pipes containing a circumferential surface crack. Based on the experimental results, the proposed failure estimation methods were confirmed to be applicable to cracked pipes subjected to combined bending and torsion moments.

Experimental Investigation of Failure Estimation Method for Stainless Steel Pipes With a Circumferential Crack Subjected to Combined Tensile and Torsion Loads

When a crack is detected in a stainless steel pipe during in-service inspections, the failure estimation method given in codes such as the ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be applied to evaluate the structural integrity of the cracked pipe. In the current codes, the failure estimation method includes the bending moment and tensile force due to pressure. The torsion moment is assumed to be relatively small and is not considered. Recently, analytical investigations considering multiaxial loads including torsion were conducted in several previous studies by examining the limit load for pipes with a circumferential crack. A failure estimation method for the combined bending moment, torsion moment, and internal pressure was proposed. In this study, the failure behavior of pipes with a circumferential crack subjected to multiaxial loads including the torsion is investigated to provide experimental support for the failure estimation method. Experiments were carried out on small size stainless steel cylinders containing a circumferential surface or through-wall crack, subjected to the combined tensile load and torsion moment. Based on the experimental results, the proposed failure estimation method was confirmed to be applicable to cracked pipes subjected to combined tensile and torsion loads.

Prediction Method for Plastic Collapse of Circumferentially Cracked Pipes Subjected to Combined Bending and Torsion Moments

When a crack is detected in a pipe during in-service inspection, the failure estimation method given in the Codes such as the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section XI or the Japan Society of Mechanical Engineers (JSME) S NA-1-2008 can be applied to assess the integrity of the pipe. In the current edition of the ASME Code Section XI, the failure estimation method is provided for combined bending moment and pressure loads. The provision of evaluating torsion load is not made in the ASME Code Section XI. In this paper, finite element analyses are conducted for stainless steel pipes with a circumferential surface crack subjected to the combined bending and torsion moments, focusing on the entire range of torsion moments, including pure torsion. The effect of the internal pressure on failure behavior is also investigated. Based on the analysis results, a prediction method for plastic collapse under the combined loading conditions of bending and torsion is proposed for the general magnitude of torsion moments.

Prediction of Collapse Stress for Pipes With Arbitrary Multiple Circumferential Surface Flaws

When a flaw is detected in a stainless steel piping system of a nuclear power plant during in-service inspection, the limit load estimation method provided in codes such as ASME Section XI or JSME S NA-1-2008 can be applied to evaluate the integrity of the pipe. However, in the current editions of these codes, a limit load estimation method is only provided for pipes containing a single flaw. Independent multiple flaws, such as stress corrosion cracks, have actually been detected in the same plane of stainless steel piping systems. In this paper, a failure estimation method by formula is proposed for any number and arbitrary distribution of multiple independent circumferential flaws in the same plane of a pipe. Using the proposed method, numerical solutions are compared with experimental results to validate the model, and several numerical examples are provided to show its effectiveness.