An Analytical Structural Strain Method for Steel Umbilical in Low Cycle Fatigue

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Wei Wang ◽  
Xianjun Pei
Keyword(s):  
Plastic Deformation ◽  
Production System ◽  
Low Cycle Fatigue ◽  
Structural Stress ◽  
Cycle Fatigue ◽  
Additional Processing ◽  
Subsea Production System ◽  
Welded Pipe ◽  
Structural Strain ◽  
Strain Method

Pipes, especially risers, pipelines, and umbilicals, are extensively used in the subsea production system. Umbilical, as a controlling component of subsea production system, as well as other pipes, will resist reeling, unreeling, and additional processing before on-site installation, which might lead to yielding and plastic deformation of the pipe. This plastic deformation often results in low cycle fatigue (LCF) issue of the pipes, and how to effectively estimate the corresponding fatigue life has become a topic of practical engineering interest. In the present paper, a structural strain method is applied to determine the elastic core of the pipe and to calculate the pseudo structural stress. The pseudo structural stress concept has been applied to analyze the pipe in LCF regime. Further, the results obtained have been compared with the experimental and other available data. It can be seen that the results coincide well with the experimental data. In addition to the demonstrated effectiveness, the key advantage of this pseudo structural stress approach is the simplicity in dealing with girth-welded pipe sections, since finite element stress analysis is unnecessary.

An Analytical-Based Structural Strain Method for Low Cycle Fatigue Evaluation of Girth-Welded Pipes

2017 ◽  
Author(s):  
Xianjun Pei ◽  
Wei Wang ◽  
Pingsha Dong
Keyword(s):  
Test Data ◽  
Low Cycle Fatigue ◽  
Deformation Condition ◽  
Structural Stress ◽  
Pipe Section ◽  
Fatigue Evaluation ◽  
Welded Pipe ◽  
Structural Strain ◽  
Outer Fiber ◽  
Strain Method

As a further extension to the structural stress based master S-N curve method adopted by ASME Div 2 since 2007, this paper presents an analytical-based structural strain method for girth-welded piping components. Here, structural strain is defined as outer and inner fiber strains calculated corresponding to a deformation condition in which a pipe section plane before deformation remains as a plane after deformation. The analytical formation takes into account all possible plastic deformation conditions a pipe section subjected to a combined remote cyclic bending and axial tension. A simple numerical procedure is used for solving both outer fiber and inner fiber strains, as well as the corresponding elastic core size. For fatigue evaluation purpose, the outer fiber strain can be used to calculate the corresponding pseudo elastic structural stress range so that the structural stress based master S-N curve can be directly used. Under linear elastic deformation conditions, the structural strain definition becomes exactly the same as that calculated by the structural stress method which is the basis on the ASME Div 2 master S-N was developed. A set of a recent full scale girth-welded pipe component test data in low-cycle regime was analyzed using the structural strain method. The results showed that all these new test data fall well within the ASME Div 2 master S-N curve scatter band defined by mean+-standard deviations. In addition to its demonstrated effectiveness, the key advantage of this structural strain method is its simplicity for dealing with girth-welded pipe sections, since finite element stress analysis is no longer needed.

A Structural Strain Method for Fatigue Evaluation of Welded Components

2014 ◽  
Author(s):  
Pingsha Dong ◽  
Xianjun Pei ◽  
Shizhu Xing
Keyword(s):  
Fatigue Test ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Structural Stress ◽  
Cycle Fatigue ◽  
Equilibrium Conditions ◽  
Curve Method ◽  
Structural Stresses ◽  
Structural Strain ◽  
Strain Method

In this paper, a new structural strain method is presented to extend the early structural stress based master S-N curve method to low cycle fatigue regime in which plastic deformation can be significant while an elastic core is still present. The method is formulated by taking advantage of elastically calculated mesh-insensitive structural stresses based on nodal forces available from finite element solutions. The structural strain definition is consistent with classical plate and shell theory in which a linear through-thickness deformation field is assumed a priori in both elastic and elastic-plastic regimes. With considerations of both yield and equilibrium conditions, the resulting structural strains are analytically solved if assuming elastic and perfectly plastic material behavior. The formulation can be readily extended to strain-hardening materials for which structural strains can be numerically calculated with ease. The method is shown effective in correlating low-cycle fatigue test data of various sources documented in the literature into a single narrow scatter band which is remarkable consistent with the scatter band of the existing master S-N curve adopted ASME B&PV Code since 2007. With this new method, some of the inconsistencies of the pseudo-elastic structural stress procedure in 2007 ASME Div 2 Code can now be eliminated, such as its use of Neuber’s rule in approximating structural strain beyond yield. More importantly, both low cycle and high cycle fatigue behaviors can now be treated in a unified manner. The earlier mesh-insensitive structural stress based master S-N curve method can now be viewed as an application of the structural strain method in high cycle regime, in which structural strains are linearly related to traction-based structural stresses according to Hook’s law. In low-cycle regime, the structural strain method characterizes fatigue damage directly in terms of structural strains that satisfy linear through-thickness deformation gradient assumption, material nonlinear behavior, and equilibrium conditions. The use of a pseudo-elastic structural stress definition is not fundamental, but merely a means to put low-cycle and high-cycle fatigue test data in a conventional stress-based S-N data representation which is typically preferred in engineering practice, than a strain-based representation.

The Influence of Plastic Deformation on the Low-Cycle Fatigue During the Burnishing of Holes in Flat Specimens of D16chT Steel

2018 ◽  
Vol 50 (3) ◽  
pp. 448-452
Author(s):  
O. V. Tymoshenko ◽  
V. V. Koval’ ◽  
A. M. Babak ◽  
Quan Fam Dyk ◽  
Yu. M. Sydorenko
Keyword(s):  
Plastic Deformation ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue

A Comprehensive Structural Strain Method Incorporating Strain-Hardening Effects: From LCF to Ratcheting Evaluations

2018 ◽  
Author(s):  
Xianjun Pei ◽  
Pingsha Dong ◽  
Shaopin Song ◽  
David Osage
Keyword(s):  
Low Cycle Fatigue ◽  
Numerical Algorithms ◽  
Complex Stress ◽  
Structural Effect ◽  
Complex Stress State ◽  
Material Nonlinearity ◽  
Strain Behavior ◽  
Nonlinear Stress ◽  
Structural Strain ◽  
Strain Method

As a further extension to the structural strain method first introduced by Dong et al [1], this paper presents an enhanced structural strain method which incorporates material nonlinearity and for two typical weld structures, i.e. weldment with plate sections (e.g. gusset weld or cruciform weld etc.) and weldment with beam sections. (e.g. pipe structures). A modified Ramberg-Osgood is introduced to capture nonlinear stress strain behavior of the material. A set of numerical algorithms is used to deal with complex stress state induced by structural effect such as beam section and plane strain condition. The proposed structural strain method is then applied to analysis of fatigue data of weldment made from different materials including steel, aluminum and titanium. It is shown that the enhanced structural strain method provides a unified way to correlate fatigue life of weldment in both high cycle and low cycle fatigue regime. The method is also used to study ratcheting problem raised up by Bree. A modified Bree diagram is given by considering material nonlinearity.

Sign in / Sign up

Export Citation Format

Share Document