Kyohei Sato

Low Cycle Fatigue Behaviors of Elbow With Local Wall Thinning Under Combined Bending and Internal Pressure

Low-cycle fatigue tests were conducted using elbow specimens with local wall thinning in order to investigate the influences of position of local wall thinning on the low-cycle fatigue behaviors of elbows. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss from erosion corrosion. The local wall thinning was located in three different areas. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. In addition, three-dimensional elastic-plastic analyses were also carried out using the finite element method. As a result, the crack penetration area and the crack growth direction were successfully predicted by the analyses.Copyright

Low Cycle Fatigue Behavior and Seismic Assessment for Pipe Bend Having Local Wall Thinning-Influence of Internal Pressure

One of the concerned technical issues in the nuclear piping under operation is pipe wall thinning caused by flow accelerated corrosion. This paper focuses on influence of internal pressure on low cycle fatigue life of pipe bends with local wall thinning and evaluation of safety margin against seismic loading in order to apply the obtained knowledge to the nuclear piping. In-plane bending fatigue tests under several constant internal pressure magnitudes were carried out using carbon steel pipe bends with local wall thinning at the extrados. Also finite element analysis, code-based seismic evaluation and fatigue analysis based on calculated strain range were carried out. Obtained main conclusions are as follows: (1) the tested pipe bends with local wall thinning at the extrados have a strong resistance against fatigue failure based on nuclear seismic piping design in Japan at least up to 12 MPa. That is, the tested pipe bends with severe local wall thinning (eroded ratio = 0.5 and eroded angle = 180 deg) at the extrados have margins against fatigue failure, even though the wall thickness is less than the code-required minimum value based on the nuclear piping seismic design in Japan. (2) Combination of the conventional B2 index and the Ke factor provided in the JSME Design and Construction Code, which is referred by JEAC 4601-2008 overestimates fictitious stress amplitude, when sum of the primary and secondary stress is much greater than 3 Sm.

Effect of Local Wall Thinning on Low Cycle Fatigue Behaviors of Elbow with Internal Pressure : Estimation of Fatigue Life based on Revised Universal Slope Method

Low−cycle fatigue tests and finite element analysis were conducted using100A elbow specimens made of STPT410 with local wall thinning in order to investigate the influences of local wall thinning on the low−cycle fatigue behaviors of elbows with internal pressure.Local wall thinning was machined on the inside of the elbow in order to simulate metal loss by flow−accelerated corrosion. The local wall thinning located in three different areas,called extrados,crown and intrados.Eroded ratio(eroded depth/wall thickness)was0.5 and0.8.The elbow specimens were subjected to cyclic in−plane bending under displacement control with internal pressure of0 or9MPa.Fatigue failure was classified into two types.The one is the type of fatigue crack initiation and another is the type of crack initiation after local buckling.In the type of fatigue crack initiation,fatigue crack initiated at crown and propagates to the axial direction.In the type of crack initiation after local buckling, at first local buckling occurs and secondary,crack initiates at the same place and propagates to the circumferential direction.The low−cycle fatigue lives of elbows were predicted conservatively by the revised universal slope method.

Influences of Cyclic Pre-Overload on Low Cycle Fatigue Behaviours of Elbow Pipe

Low cycle fatigue tests were conducted using sound elbows made of carbon steel (STPT410). The elbows were subjected to cyclic in-plane bending under displacement control with internal pressure of 9 MPa. The preliminary fatigue tests were conducted under constant cyclic displacements. Then, two test conditions were adopted to investigate the influence of cyclic pre-overload on low cycle behavior of elbow on the basis of the preliminary test results. The fatigue test results were evaluated by using the total usage factor UFTotal (= UFpre +UFpost ), where the UFpre and UFpost correspond to usage factor for δpre and δpost , respectively. The fatigue lives of overloaded elbow pipes were estimated based on the cumulative fatigue damage rule basically from UFpre = 0.2 to UFpre = 0.6. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.Copyright

Influences of Inner Pressure and Overload on Low Cycle Fatigue Behaviors of Elbow Pipes With Local Wall Thinning

Low cycle fatigue tests were conducted using 100A elbow pipe specimens with or without local wall thinning. Local wall thinning of 50% of the nominal pipe wall thickness was machined on the inside of the test elbows to simulate metal loss due to flow-accelerated corrosion. The local wall thinning area was machined at the extrados, which has been reported to be the section most likely to suffer local wall thinning. Low cycle fatigue tests were carried out under displacement control using pipe with local wall thinning at the extrados to investigate the influences of an inner pressure of 0∼12 MPa. To simulate seismic events, low cycle fatigue tests were also carried out on pipe with or without wall thinning to investigate the influences of cyclic overloads. No differences in fatigue life were caused by an inner pressure of 3 MPa. However, degradation of fatigue life was caused as inner pressure increased from 6 MPa to 12 MPa. The fatigue lives of overloaded pipes were similar to those of non-overloaded pipes. In addition, three-dimensional elastic-plastic analyses were carried out using the finite element method. The crack penetration area and the crack growth direction were successfully predicted by the analyses.Copyright