Low Cycle Fatigue Behavior and Seismic Assessment for Elbow Pipe Having 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 90 deg and 180 deg. The elbow specimens were subjected to cyclic in-plane bending under displacement control (±20 mm) without and with internal pressure of 3 MPa using a universal testing machine. Fatigue life was defined as fatigue crack penetration through the thickness and crack penetration was watched by naked eyes during the test through the protection window made of a transparent plastic plate. Obtained main conclusions are as follows: (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 for an elbow with local wall thinning at extrados. This conclusion should be confirmed using eroded elbow specimens under more high pressure. (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 Section 3 allowable seismic stress criteria.

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

ASME 2010 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2010-25612 ◽

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.

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

ASME 2010 Pressure Vessels and Piping Conference: Volume 5 ◽

10.1115/pvp2010-25571 ◽

2010 ◽

Cited By ~ 1

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.

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Low Cycle Fatigue Behavior of Elbows with Local Wall Thinning

Metals ◽

10.3390/met10020260 ◽

2020 ◽

Vol 10 (2) ◽

pp. 260

Author(s):

Muhammad Faiz Harun ◽

Roslina Mohammad ◽

Andrei Kotousov

Keyword(s):

Power Plants ◽

Low Cycle Fatigue ◽

Fatigue Behavior ◽

Safety Margin ◽

Active Regions ◽

Fatigue Loading ◽

Civil Infrastructure ◽

Cycle Fatigue ◽

Wall Thinning ◽

Local Wall Thinning

There have been a number of studies concerning the integrity of high-strength carbon steel pipe elbows weakened by local pipe wall thinning, the latter can be typically caused by flow accelerated erosion/corrosion. In particular, the focus of several recent studies was on low cycle fatigue behavior of damaged elbows, mainly, in relation to strength and integrity of piping systems of nuclear power plants subjected to extreme loading conditions, such as earthquake or shutdown. The current paper largely adopts the existing methodology, which was previously developed, and extends it to copper-nickel elbows, which are widely utilized in civil infrastructure in seismically active regions. FE (finite element) studies along with a full-scale testing program were conducted and the outcomes are summarized in this article. The overall conclusion is that the tested elbows with various severity of local wall thinning, which were artificially introduced at different locations, demonstrate a strong resistance against low cycle fatigue loading. In addition, elbows with wall thinning defects possess a significant safety margin against seismic loading. These research outcomes will contribute to the development of strength evaluation procedures and will help to develop more effective maintenance procedures for piping equipment utilized in civil infrastructure.

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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

Volume 1A: Codes and Standards ◽

10.1115/pvp2013-97836 ◽

2013 ◽

Cited By ~ 1

Author(s):

Koji Takahashi ◽

Kyohei Sato ◽

Kazuya Matsuo ◽

Kotoji Ando ◽

Yoshio Urabe ◽

...

Keyword(s):

Fatigue Crack ◽

Crack Initiation ◽

Internal Pressure ◽

Low Cycle Fatigue ◽

Fatigue Crack Initiation ◽

Local Buckling ◽

Cycle Fatigue ◽

Slope Method ◽

Wall Thinning ◽

Local Wall Thinning

Low-cycle fatigue tests and finite element analysis were conducted using 100A 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) was 0.5 and 0.8. The elbow specimens were subjected to cyclic in-plane bending under displacement control with internal pressure of 0 or 9 MPa. 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.

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

ASME 2011 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2011-57322 ◽

2011 ◽

Cited By ~ 2

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.

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Low Cycle Fatigue Behavior of Elbow Pipe With Local Wall Thinning

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2008-61427 ◽

2008 ◽

Cited By ~ 2

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.

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

Journal of Pressure Vessel Technology ◽

10.1115/1.4024444 ◽

2013 ◽

Vol 135 (4) ◽

Cited By ~ 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.

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Analysis on Low Cycle Fatigue Life and Fatigue Fracture Surface Morphology of TC25 Titanium Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.697.652 ◽

2016 ◽

Vol 697 ◽

pp. 652-657

Author(s):

Rong Guo Zhao ◽

Yi Yan ◽

Yong Zhou Jiang ◽

Xi Yan Luo ◽

Qi Bang Li ◽

...

Keyword(s):

Titanium Alloy ◽

Fatigue Crack ◽

Fatigue Life ◽

Fracture Surface ◽

Crack Growth ◽

Fatigue Fracture ◽

Low Cycle Fatigue ◽

Observation System ◽

Cycle Fatigue ◽

Stress Strain

At room temperature, the low cycle fatigue tests for smooth specimens of TC25 titanium alloy under various stress ranges are operated at a CSS280I-20w Electro Hydraulic Servo Universal Testing Machine with a microscopic observation system, and the low cycle fatigue lifetimes are measured. Based upon the analysis of stress-strain hysteresis loop of low cycle fatigue of TC25 titanium alloy, a simplified Manson-Coffin formula is derived according to both the experimental characteristics and the stress-strain constitutive model, the fatigue lifetimes are plotted against stress ranges, and a stress-fatigue life curve for TC25 titanium alloy is obtained by the linear regression analysis method. Finally, the fracture surface morphologies of TC25 specimens are investigated using a JSM-6360 Scanning Electron Microscopy, and the fatigue fracture mechanisms of low cycle fatigue are studied. It shows that the plastic deformations are mainly formed at the accelerated fracture stage, and various shear lips can be observed on the fracture surfaces, which demonstrates that the shear stress results in the final rupture of TC25 titanium alloy. During the fracture of low cycle fatigue, the cleavage nucleation leads to the formation of fatigue crack initiation region, the fatigue crack growth exhibits a mixed transgranular and intergranular crack growth mode, and in the final rupture region, the fracture surface of low cycle fatigue of TC25 titanium alloy appears as a typical semi-brittle fracture mode.

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