Subsea Pipeline Lateral Buckling Design—Strain Concentration or Strain Capacity Reduction Factors

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Safety Margin ◽  
Local Buckling ◽  
Cycle Fatigue ◽  
Lateral Buckling ◽  
Strain Concentration ◽  
Strain Capacity ◽  
Global Strain ◽  
Capacity Reduction

A strain concentration factor is typically incorporated in the higher-pressure and high-temperature (HPHT) pipeline lateral buckling assessment to account for nonuniform stiffness or plastic bending moment. Increased strain concentration can compromise pipeline low cycle fatigue and lateral buckling capacity, leading to an early onset of local buckling failure. In this paper, the philosophy of local buckling mitigation using the strain concentration factor is examined. The local buckling behavior is evaluated. Global strain reduction and evolution against buckling are analyzed with respect to varying joint mismatch level. The concept of a strain reduction factor (SNRF) due to joint mismatch is developed based on the global strain capacity reduction with reference to the uniform configuration. It is demonstrated that the SNRF in terms of strain capacity reduction is a unique characteristic parameter. As opposed to strain concentration, it is an invariant insensitive to evaluation methods and design strain demand level, hence more representative as a limiting design metric to maintain the safety margin. The rationale for its introduction as an alternative to the strain concentration factor is outlined and its benefits are established. The method for obtaining the SNRF and its application is developed. The discernible difference and scenarios for application of either factor are discussed, including low and high cycle fatigue, linearity and stress concentration, engineering criticality assessment (ECA), and lateral buckling. Additional causal factors giving rise to mismatch such as pipe schedule transition and buckler arrestor are also discussed. Iterations of finite element (FE) analyses are performed for a pipe-in-pipe (PIP) configuration in a case study.

Subsea Pipeline Lateral Buckling Design: Strain Concentration or Strain Reduction Factors

2017 ◽  
Author(s):  
M. Liu
Keyword(s):  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Safety Margin ◽  
Local Buckling ◽  
Reduction Factor ◽  
Material Strength ◽  
Cycle Fatigue ◽  
Lateral Buckling ◽  
Strain Concentration ◽  
Global Strain

Strain based design is normally applied for HPHT pipelines when the conventional stress based method becomes impractical. In addition to a design safety factor, a strain concentration factor is typically incorporated in the lateral buckling assessment to account for non-uniform stiffness or plastic bending moment due to geometry and material strength mismatch between adjacent pipe joints. Increased strain concentration can compromise pipeline low cycle fatigue and lateral buckling capacity, leading to an early onset of local buckling failure. In this paper, the philosophy of local buckling mitigation using the strain concentration factor is examined. The local buckling behaviour is evaluated in relation to strain concentration. Global strain reduction and evolution against buckling is analysed with respect to varying joint mismatch level derived according to a structural reliability analysis. The concept of a strain reduction factor due to mismatch is developed and proposed based on the global strain capacity reduction with reference to the uniform configuration. It is demonstrated that the strain reduction factor is a unique characteristic parameter. As opposed to strain concentrations it is an invariant insensitive to evaluation methods and the design strain demand level, hence more representative as a limiting design metric to maintain the safety margin. The use of the strain reduction factor is thus put forward in strain based lateral buckling design as an alternative to using the strain concentration factor. The method for obtaining the strain reduction factor and its application is developed. The rationale for its introduction is outlined and some of its benefits are established. The discernible difference and scenarios for application of either factors are discussed, including low and high cycle fatigue, linearity and stress concentration (SNCF from SCF for welds), ECA and lateral buckling. Additional causal factors giving rise to mismatch such as pipe schedule transition and buckler arrestor are also discussed. Iterations of FE analyses are performed for a pipe-in-pipe configuration in a case study.

Failure Analysis of Thinned Wall Elbows Under Excessive Seismic Loading

2002 ◽  
Author(s):  
Masaki Shiratori ◽  
Yoji Ochi ◽  
Izumi Nakamura ◽  
Akihito Otani
Keyword(s):  
Finite Element ◽  
Fatigue Damage ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Local Buckling ◽  
Seismic Loading ◽  
Cycle Fatigue ◽  
Finite Element Analyses ◽  
Residual Thickness ◽  
Limited Period

A series of finite element analyses has been carried out in order to investigate the failure behaviors of degraded bent pipes with local thinning against seismic loading. The sensitivity of such parameters as the residual thickness, locations and width of the local thinning to the failure modes such as ovaling and local buckling and to the low cycle fatigue damage has been studied. It has been found that this approach is useful to make a reasonable experimental plan, which has to be carried out under the condition of limited cost and limited period.

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.

Effect of Reinforcement on the Strength of Junctions Between Cylindrical and Conical Shells

1995 ◽  
Vol 117 (2) ◽  
pp. 135-141 ◽  
Author(s):  
A. Kalnins ◽  
D. P. Updike
Keyword(s):  
Failure Criterion ◽  
Failure Modes ◽  
Low Cycle Fatigue ◽  
Safety Margin ◽  
External Pressure ◽  
Cycle Fatigue ◽  
Conical Shells ◽  
Section Viii ◽  
Cyclic Service ◽  
Reinforcement Distribution

Two failure modes are addressed for cylinder-cone junctions under internal or external pressure: axisymmetric yielding and low-cycle fatigue. If the junction fails to meet the failure criterion of any one of the two modes, then it must be strengthened by reinforcement. It is shown in the paper that the degree to which a junction is strengthened depends on the distribution of the reinforcement. A placement of reinforcement on the cylinder alone, leaving the actual connection between the cylinder and cone unreinforced, adds strength with regard to axisymmetric yielding, but may not strengthen the junction sufficiently with regard to low-cycle fatigue. This means that the junction may appear reinforced, but is not strengthened. It is pointed out that the design rules of Section VIII, Div. 1 of the ASME B & PV Code (1992) set the need for reinforcement according to the failure criterion of low-cycle fatigue, while the distribution of the reinforcement is guided by the criterion of axisymmetric yielding. There is no assurance that the reinforced junction will meet the failure criterion of low-cycle fatigue. This means that the safety margin on the number of allowed cycles is less than that which is expected and that the junction may be unfit for cyclic service. It is also shown in the paper that a reinforcement distribution that requires minimum thicknesses for sections of both the cylinder and cone near the junction can satisfy criteria for both failure modes. This approach is already used in Code Case 2150 of Section VIII, Div. 1, for half-apex cone angles from 30 to 60 deg, and required in Div. 2 for cone angles from 0 to 30 deg. Its extension to angles from 0 to 60 deg for both internal and external pressure is recommended.

Prediction of the fracture life of a wrinkled steel pipe subject to low cycle fatigue load

2007 ◽  
Vol 34 (9) ◽  
pp. 1131-1139 ◽  
Author(s):  
Sreekanta Das ◽  
J J. Roger Cheng ◽  
David W Murray
Keyword(s):  
Plastic Strain ◽  
Oil And Gas ◽  
Pipe Wall ◽  
Low Cycle Fatigue ◽  
Local Buckling ◽  
Petroleum Products ◽  
Assessment Model ◽  
Life Assessment ◽  
Cycle Fatigue ◽  
Fatigue Load

The economy of Canada depends largely on the performance of the hydrocarbon-based energy industry (oil and gas), which in turn is dependent on the performance of steel pipelines that are used for transporting crude oil, natural gas, and petroleum products. Field observations of buried pipelines indicate that it is not uncommon for geotechnical movements to impose large displacements on the pipelines, resulting in localized curvature, deformations, and strain in the pipe wall. Often these local deformations result in local buckling (wrinkling) in the pipe wall, and in the post-buckling range of response such wrinkles develop rapidly. Subsequent cyclic load histories may produce cyclic plastic strain reversals leading to the formation of fractures in the wrinkle region. This paper presents the development and application of a simple fracture-life assessment model that can be used successfully by the pipeline industries to assess the remaining life before fracture of wrinkled pipelines subject to strain reversals due to low cycle fatigue loadings.Key words: wrinkled pipeline, low cycle fatigue load, plastic strain reversal, fracture, hysteresis loop energy, fracture-life assessment model.

Surface integrity generated with peripheral milling and the effect on low-cycle fatigue performance of aeronautic titanium alloy Ti-6Al-4V

2017 ◽  
Vol 122 (1248) ◽  
pp. 316-332 ◽  
Author(s):  
D. Yang ◽  
Z. Liu
Keyword(s):  
Residual Stress ◽  
Titanium Alloy ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Surface Integrity ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Micro Hardness

ABSTRACTMachining-induced surface integrity has an important effect on reliability and service life of the components used in the aerospace industry where titanium alloy Ti-6Al-4V is widely applied. Characterisation of machining-induced surface integrity and revealing its effect on fatigue life are conducive to structural fatigue life optimisation design. In the present study, surface topography, residual stress, microstructure and micro-hardness were first characterised in peripheral milling of titanium alloy Ti-6Al-4V. Then, low-cycle fatigue performances of machined specimens were investigated on the basis of the tension-tension tests. Finally, the effects of surface integrity factors (stress concentration factor, residual stress and micro-hardness) on fatigue performances were discussed. Results show that stress concentration can reduce the fatigue life while increasing the residual compressive stress, and micro-hardness is beneficial to prolonging the fatigue life, but when the surface material of the specimen is subjected to plastic deformation due to yield, the residual stress on the surface is relaxed, and the effect on the fatigue performance is disappeared. Under the condition of residual stress relaxation, the stress concentration factor is the main factor to determine the low-cycle fatigue life of titanium alloy Ti-6Al-4V. While for the specimens with no residual stress relaxation, micro-hardness was the key factor to affect the fatigue life, followed by residual stress and stress concentration factor, respectively.

A Kt-Based Method for Calculating LCF Life of Notched Specimens

1994 ◽  
Vol 116 (4) ◽  
pp. 403-408 ◽  
Author(s):  
N. Merah ◽  
T. Bui-Quoc ◽  
M. Bernard
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cycle Fatigue ◽  
Unnotched Specimen ◽  
Stress Raisers

Under cyclic loading, the effect of stress raisers on the fatigue life depends upon several parameters, the most important being the stress concentration factor, the stress level, and the material notch sensitivity. In particular, in the low-cycle fatigue region, a number of procedures are currently used, but additional developments are required for improvement of the life prediction capabilities. In this paper, a method is proposed for calculating notched specimen low-cycle fatigue life from unnotched specimen data using as the main parameter the stress concentration factor combined with the applied stress level and the cyclic-hardening properties of the material. The proposed method is then applied to several materials with a variety of notch geometries to obtain the predicted lives. The correlation between the calculated lives and the experimental data is discussed in connection with the predictions obtained from Neuber’s and Zwicky’s relations.

scholarly journals Low Cycle Fatigue Behavior of Elbows with Local Wall Thinning

Metals ◽  
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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