Wall Thinning at the Vertex of an Angle Piece for Bending in a Tool Die

Piping items in power plants may experience combined bending and torsion moments during operation. Currently, there is a lack of guidance in the ASME B&PV Code Section XI for combined loading modes including pressure, torsion and bending. Finite element analyses were conducted for 24-inch diameter Schedule 80 pipes with local wall thinning subjected to tensile and compressive stresses. Plastic collapse bending moments were calculated under constant torsion moments. From the calculation results, it can be seen that collapse bending moment for pipes with local thinning subjected to tensile stress is smaller than that subjected to compressive stress. In addition, equivalent moment is defined as the root the sum of the squares of the torsion and bending moments. It is found that the equivalent moments can be approximated with the pure bending moments, when the wall thinning length is equal or less than 7.73R·t for the wall thinning depth of 75% of the nominal thickness, where R is the mean radius and t is the wall thickness of the pipe.

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Comparison of Failure Modes of Piping Systems With Wall Thinning Subjected to In-Plane, Out-of-Plane, and Mixed Mode Bending Under Seismic Load: An Experimental Approach

Journal of Pressure Vessel Technology ◽

10.1115/1.4001517 ◽

2010 ◽

Vol 132 (3) ◽

Cited By ~ 12

Author(s):

Izumi Nakamura ◽

Akihito Otani ◽

Masaki Shiratori

Keyword(s):

Dynamic Behavior ◽

Failure Modes ◽

Seismic Load ◽

Piping System ◽

Shake Table ◽

Shake Table Tests ◽

Wall Thinning ◽

Piping Systems ◽

Out Of Plane ◽

Plane Bending

Pressurized piping systems used for an extended period may develop degradations such as wall thinning or cracks due to aging. It is important to estimate the effects of degradation on the dynamic behavior and to ascertain the failure modes and remaining strength of the piping systems with degradation through experiments and analyses to ensure the seismic safety of degraded piping systems under destructive seismic events. In order to investigate the influence of degradation on the dynamic behavior and failure modes of piping systems with local wall thinning, shake table tests using 3D piping system models were conducted. About 50% full circumferential wall thinning at elbows was considered in the test. Three types of models were used in the shake table tests. The difference of the models was the applied bending direction to the thinned-wall elbow. The bending direction considered in the tests was either of the in-plane bending, out-of-plane bending, or mixed bending of the in-plane and out-of-plane. These models were excited under the same input acceleration until failure occurred. Through these tests, the vibration characteristic and failure modes of the piping models with wall thinning under seismic load were obtained. The test results showed that the out-of-plane bending is not significant for a sound elbow, but should be considered for a thinned-wall elbow, because the life of the piping models with wall thinning subjected to out-of-plane bending may reduce significantly.

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Bayesian Inference Method for Failure Probability of Wall Thinning Pipe in Corrosion Rate Fluctuation Model

Volume 1: Codes and Standards ◽

10.1115/pvp2008-61457 ◽

2008 ◽

Author(s):

Satoshi Okajima ◽

Satoshi Izumi ◽

Shinsuke Sakai

Keyword(s):

Corrosion Rate ◽

Failure Probability ◽

Error Term ◽

Correction Term ◽

Operational Environment ◽

Bayes Method ◽

Wall Thinning ◽

Rate Fluctuation ◽

The One ◽

Linear Bayes

To rationalize the inspection interval for the wall-thinning piping element, the linear-Bayes method was proposed in the previous paper. To derive the simple formula, the linear-Bayes method ignores the corrosion rate change against time. However, this change may be caused by the one of the operational environment. Therefore, without the sufficient monitoring of the environment, the linear-Bayes method may underestimate the failure probability. In this paper, the linear-Bayes method is extended for the wall-thinning model with the corrosion rate fluctuation, which imitates the unexpected change of the corrosion rate. The extension is carried out through following two approaches: the “correction-term” and the “error-term” approaches. The correction-term approach can evaluate the change of corrosion rate, however, it requires sufficient number of inspections. The error-term approach evaluates the failure probability conservatively.

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Theoretical and Experimental Investigation of Pipe Wall Thinning Detection Using Guided Waves

Volume 5: High Pressure Technology; Nondestructive Evaluation Division; Student Paper Competition ◽

10.1115/pvp2008-61655 ◽

2008 ◽

Author(s):

Isoharu Nishiguchi ◽

Fumitoshi Sakata ◽

Seiichi Hamada

Keyword(s):

Experimental Data ◽

Power Generation ◽

Experimental Investigation ◽

Reflection Coefficient ◽

Guided Waves ◽

Pipe Wall ◽

Thermal Power ◽

Wall Thinning ◽

Torsional Waves ◽

Simplified Method

A method to investigate pipe wall thinning using guided waves has been developed for pipes in thermal power generation facilities. In this paper, the reflection coefficient and the transmission coefficient are derived for the torsional waves which propagate along a pipe and a simplified method to predict the waveform is proposed. The predictions of the waveforms by the FEM and a simplified method based on the reflection of torsional waves are also examined by comparing with experimental data.

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