Low Cycle Fatigue Evaluation of Pipe Bends With Local Wall Thinning Considering Multi-Axial Stress State

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Yoshio Urabe ◽  
Koji Takahashi ◽  
Hisanori Abe
Keyword(s):  
Fatigue Strength ◽  
Stress State ◽  
Low Cycle Fatigue ◽  
Axial Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Pipe Bend ◽  
Wall Thinning ◽  
Damage Rule ◽  
Local Wall Thinning

Low cycle fatigue tests and finite element (FEM) analysis were conducted using 100A pipe bend specimens made of STPT410 carbon steel with and without local wall thinning local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown, and intrados. The parameters of the wall thinning were same (the wall thinning ratio = 0.5, the wall thinning angle = 180 deg, and the wall thinning length = 100 mm) in the all test cases. The pipe bend specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0–12 MPa. Also, low cycle fatigue tests using sound pipe bend specimens were carried out for comparison. According to the test results, low cycle fatigue strength of wall thinned pipe bend specimens was not so different, regardless of location of wall thinning. Low cycle fatigue strength of the pipe bend specimens was beneath the best fit fatigue curve and its reason can be explained quantitatively by a proposed cumulated damage rule introducing ductility exhaustion considering multi-axial stress state. The validity of the new proposed cumulative damage rule was also confirmed by the another sample analysis using other reference data obtained by pre-overloaded in-plane cyclic bending tests.

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

2010 ◽  
Author(s):  
Kyohei Sato ◽  
Koji Takahashi ◽  
Kanako Ogino ◽  
Yoshio Urabe ◽  
Kotoji Ando
Keyword(s):  
Fatigue Life ◽  
Low Cycle Fatigue ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Metal Loss ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Inner Pressure ◽  
Wall Thinning ◽  
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.

Detection of the Crack Initiation by Means of AE Method Under Low Cycle Fatigue of Elbow Pipe Having Local Wall Thinning

2010 ◽  
Author(s):  
Naoya Kasai ◽  
Kotoji Ando ◽  
Maki Nishio ◽  
Yoshio Urabe ◽  
Koji Takahashi
Keyword(s):  
Crack Initiation ◽  
Low Cycle Fatigue ◽  
Axial Strain ◽  
Wide Band ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Cycle Fatigue ◽  
Accelerated Corrosion ◽  
Wall Thinning ◽  
Local Wall Thinning

This paper describes the detectability of the crack initiation by means of the AE method under low cycle fatigue of the elbow pipe having local wall thinning to clarify the crack growth behavior for the pipes. Elbow specimens having local wall thinning were prepared, and local wall thinning due to flow accelerated corrosion was simulated by machined pipe wall thinning. Low cycle fatigue tests for the specimens were then carried out. AE method during low cycle fatigue tests was conducted to evaluate the crack initiation and location. In AE measurement, wide band AE sensors of 5mm in diameter were used to attach to the convex surfaces of the specimens. The circumference and axial strain of the specimens and the cross head displacement were also stored to the digital AE system signal. As a result, it is clear that the AE signals indicated the crack initiation in small circumference strain.

scholarly journals Theoretical Study on Low Cycle Fatigue Strength of Elbows with Local Wall Thinning

2013 ◽  
Vol 79 (804) ◽  
pp. 1303-1316 ◽  
Author(s):  
Yoshio URABE ◽  
Koji TAKAHASHI ◽  
Kazuya MATSUO ◽  
Kyohei SATO ◽  
Hisanori ABE
Keyword(s):  
Fatigue Strength ◽  
Theoretical Study ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Local Wall Thinning

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

2011 ◽  
Author(s):  
Koji Takahashi ◽  
Kazuya Matsuo ◽  
Kyohei Sato ◽  
Kotoji Ando ◽  
Yoshio Urabe ◽  
...  
Keyword(s):  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Three Dimensional ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Metal Loss ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Wall Thinning ◽  
Local Wall Thinning

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.

Low Cycle Fatigue Behavior of Elbow Pipe With Local Wall Thinning

2008 ◽  
Author(s):  
Koji Takahashi ◽  
Satoshi Tsunoi ◽  
Takumi Hara ◽  
Sota Watanabe ◽  
Akira Mikami ◽  
...  
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Three Dimensional ◽  
Growth Direction ◽  
Fatigue Tests ◽  
Metal Loss ◽  
Cycle Fatigue ◽  
Crack Penetration ◽  
Wall Thinning ◽  
Local Wall Thinning

Low cycle fatigue tests were conducted using 100A elbow specimens with local wall thinning. Local wall thinning of 50% of the nominal pipe wall thickness was machined on the inside of elbow in order to simulate erosion/corrosion metal loss. The local wall thinning areas are located at three different areas, called extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. When the local wall thinning was located at intrados, fatigue life was the shortest. 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. The fatigue lives estimated by the analyses were close to those obtained by the experiments.

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

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Yoshio Urabe ◽  
Koji Takahashi ◽  
Kyohei Sato ◽  
Kotoji Ando
Keyword(s):  
Internal Pressure ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Safety Margin ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Pipe Bend ◽  
Wall Thinning ◽  
Local Wall Thinning

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.

J101014 Influences of Local Wall Thinning on Low Cycle Fatigue Behaviors of Elbow Pipe

2011 ◽  
Vol 2011 (0) ◽  
pp. _J101014-1-_J101014-5
Author(s):  
Kyohei SATO ◽  
Koji TAKAHASHI ◽  
Kazuya MATSUO ◽  
Kotoji ANDO ◽  
Yoshio URABE
Keyword(s):  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Local Wall Thinning

1251 Effects of local wall thinning on low-cycle fatigue behavior of tee pipes

2008 ◽  
Vol 2008.1 (0) ◽  
pp. 177-178
Author(s):  
Kanako OGINO ◽  
Sota WATANABE ◽  
Koji TAKAHASHI ◽  
Kotoji ANDO
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Local Wall Thinning

Low Cycle Fatigue Behavior and Seismic Assessment for Elbow Pipe Having Local Wall Thinning

2010 ◽  
Author(s):  
Yoshio Urabe ◽  
Koji Takahashi ◽  
Kotoji Ando
Keyword(s):  
Fatigue Crack ◽  
Pipe Wall ◽  
Low Cycle Fatigue ◽  
Safety Margin ◽  
Seismic Loading ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Erosion Corrosion ◽  
Technical Issues ◽  
Local Wall Thinning

One of the concerned technical issues in the nuclear piping under operation is pipe wall thinning caused by flow accelerated corrosion. Recently it has been reported that the elbow section is more suspicious on pipe wall thinning by erosion-corrosion. Some researchers including authors have been studied static and fatigue strength of elbows with local wall thinning. However, still more experiment and analysis data are needed to clarify the technical issues. Accordingly, further experiments and their evaluations were carried out by the authors. This paper presents the influences of size and location on fatigue life. Also as one of the application of the test results, safety margin of elbows with wall thinning against seismic loading is discussed. Low cycle fatigue tests were conducted using elbow specimens made of STPT410 steel with local wall thinning. The local wall thinning was machined on the inside of elbow specimens in order to simulate erosion/corrosion metal loss. The local wall thinning areas were located at three different areas, called extrados, crown and intrados. Eroded ratio (eroded depth/wall thickness) is 0.5 and 0.8 and eroded angle is 90deg. and 180deg..The elbow specimens were subjected to cyclic in-plane bending under displacement control (±20mm) without and with internal pressure of 3MPa. Obtained main conclusions are shown bellow. (1) Existence of local wall thinning in extrados does not have an important effect on fatigue life. Especially, fatigue crack does not initiate at the extrados where the extreme local wall thinning exists (eroded ratio = 0.8 and eroded angle = 180 deg.). (2) Regardless of existence of internal pressure, fatigue crack initiates at the crown where local wall thinning does not exist. (3) Even if the eroded ratio and the eroded angle reached up to 0.8 and 180 deg., the elbows with local wall thinning have high safety margin against seismic loading, comparing to ASME Boiler and Pressure Vessel Code Sec. III allowable seismic stress criteria.

scholarly journals Influences of Overload on Low Cycle Fatigue Behaviors of Elbow Pipe with Local Wall Thinning

2011 ◽  
Vol 77 (777) ◽  
pp. 698-702
Author(s):  
Kyohei SATO ◽  
Koji TAKAHASHI ◽  
Kanako OGINO ◽  
Kotoji ANDO ◽  
Yoshio URABE
Keyword(s):  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Wall Thinning ◽  
Local Wall Thinning
Sign in / Sign up

Export Citation Format

Share Document