Stress Concentration Factor for some DTK Joints Based on Finite Element

2011 ◽  
Vol 58-60 ◽  
pp. 1482-1486
Author(s):  
Long Guo ◽  
Xiu Feng Zhang
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Axial Load ◽  
Thin Shell ◽  
Nonlinear Least Squares ◽  
Shell Element ◽  
Offshore Structures ◽  
Empirical Formulas ◽  
Tubular Joints ◽  
The Difference

By research of simple tubular joints, thin-shell element analyses have been conducted for thousands of DTK joints frequently used in offshore structures in this paper. These joints are subjected to axial load, by use of nonlinear least squares fitter, the above results are derived a new set of parametric equations, in terms of several non-dimensional geometric ratios γ, ξ, β, τ and θ with the Origin software. Separate analyses have been conducted for the difference of SCFs in DTK joints and SCFs for TK joint from empirical formulas. The SCF results of these joints could act as a good reference for both further academic studies on SCF of other complex joints and engineering designing works.

Formulas for Variation of Stress Concentration Around Intersection in Tubular Joints

1988 ◽  
Vol 110 (4) ◽  
pp. 237-245 ◽  
Author(s):  
R. Sundaravadivelu ◽  
M. Hariharan ◽  
C. Ganapathy
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Current Practice ◽  
Saddle Points ◽  
Offshore Structures ◽  
Exploration And Exploitation ◽  
Empirical Formulas ◽  
Tubular Joints ◽  
Fatigue Design ◽  
Semi Empirical

Many of the offshore structures used for oil exploration and exploitation are built of tubular members. The repeated damages in tubular joints have clearly shown that the safety of these structures depends on the safe fatigue design of the joints. The fatigue life of the joint depends very much on the Stress Concentration Factor, SCF. The current practice is to use semi-empirical formulas proposed by various investigators to determine SCF. While some of the formulas give the maximum SCF, others give the SCFs at both the crown and saddle points. The design of fatigue life using the value of maximum SCF is conservative, while using SCFs at crown and saddle is unsafe. The main aim of this paper is to propose a set of formulas for T and Y-joints, which gives not only the magnitude of maximum SCF as in the presently available formulas, but also the variation of SCF around intersection.

Stress Concentration Factors in T and K-T Tubular Joints Using Finite Element Analysis

1988 ◽  
Vol 110 (4) ◽  
pp. 246-254 ◽  
Author(s):  
O. D. Dijkstra ◽  
R. S. Puthli ◽  
H. H. Snijder
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Axial Load ◽  
Bending Moment ◽  
The Finite Element Method ◽  
Element Analysis ◽  
Tubular Joints ◽  
Tubular Joint ◽  
Concentration Factors ◽  
Stress Concentration Factors

Stress concentration factors (SCFs) in a T and a K-T tubular joint have been determined using the finite element method (FEM). The SCFs are determined for basic load cases (axial load or bending moment) in one of the braces or in the chord. The results of the FEM are compared with available experimental data and with parametric formulas. The T-joint results for brace loadings agree reasonably with the parametric formulas. The K-T joint results for in-plane bending agree reasonably with the parametric formulas.

Stress Concentration Factors Calculation: Analytical and Numerical Approaches for Welded Tubular Joints

2020 ◽  
Author(s):  
Nathalia Paruolo ◽  
Thalita Mello ◽  
Paula Teixeira ◽  
Marco Pérez
Keyword(s):  
Stress Concentration ◽  
Oil And Gas ◽  
Hot Spot ◽  
Experimental Tests ◽  
Oil And Gas Industry ◽  
Offshore Structures ◽  
Gas Industry ◽  
Tubular Joints ◽  
Concentration Factors ◽  
Stress Concentration Factors

Abstract In the oil and gas industry, fixed platforms are commonly applied in shallow water production. In-place environmental conditions generates cyclic loads on the structure that might lead to structural degradation due to fatigue damage. Fatigue is one of the most common failure modes of offshore structures and is typically estimated when dimensioning of the structure during design phase. However, in times when life extension of existing offshore structures is being a topic in high demand by industry, mature fields may represent an interesting investment, especially for small companies. Concerning fixed platforms, composed mainly by welded tubular joints, the assessment of hot spot stresses is considered to predict structure fatigue. The estimation of welded joint hot spot stresses is based on the stress concentration factors (SCFs), which are given by parametric formulae, finite element analysis (FEA) or experimental tests. Parametric formulae may be defined as a fast and low-cost method, meanwhile finite elements analysis may be time consuming and experimental tests associated with higher costs. Given these different characteristics, each method is applied according to the study case, which will rely on the joint geometry and associated loads. Considering simple joint geometries several sets of parametric equations found in the literature may be applied. On the other hand, the SCFs calculation of non-studied yet complex joints consider known formulae adapted according to the under load joint behavior and geometry. Previous analysis shows that this adaptation may furnish different results compared to those obtained by FEA. Furthermore, it is observed that even for simple joints the results derived from the different methods may differ. Given their importance for the oil and gas industry, since they are the basis for the assessment of the fatigue life of welded tubular joints which may impact on additional costs related to maintenance and inspection campaigns, the estimation of SCFs must be the most accurate as possible. Therefore, this paper intends to investigate the differences between results derived from parametric formulae and different FEA studies.

Sensitivity of Fatigue Assessment to the Use of Different Reference S-N Curves

2003 ◽  
Author(s):  
Xiaozhi Wang ◽  
Zhan Cheng
Keyword(s):  
Loading Condition ◽  
Offshore Structures ◽  
Constant Amplitude ◽  
Fatigue Assessment ◽  
Tubular Joints ◽  
Environment Effects ◽  
Assessment Approach ◽  
The Difference ◽  
Offshore Industry ◽  
Number Of Cycles

The S-N curve based fatigue assessment approach is the most widely used one in both ship and offshore industry, in contrast with a fracture mechanics approach. The S-N approach, implemented by either simplified or spectral method, has to apply S-N curves to calculate fatigue strength. The S-N curve, which represents the number of cycles (N) of a constant amplitude stress range (S) that will cause a fatigue failure, is normally developed based on experimental data. Which S-N curve should be applied to a particular detail depends very much on the geometry of the detail, welding information as well as loading condition. There are various S-N curves published by different institutions, e.g., S-N curves published by UK HSE, IIW, AWS etc. The newly developed ABS “Guidance on Fatigue Assessment of Offshore Structures”, [1], proposes the ABS S-N curves, in which two categories of joints, tubular and non-tubular, are included, and both size and environment effects are taken into account. However, the application in Gulf of Mexico is also influenced by API recommendations. In API RP 2A, AWS S-N curves are referred, which in US practice is accepted for fixed (buoyant and non-buoyant) platform deck structures. The objective of this paper is to address the difference between different S-N curves and to present the detailed results of fatigue assessment by using different S-N curves for non-tubular joints. Conclusions made based on the study provide more background on the S-N curve application in fatigue assessment.

Distortion Simulation of Unsymmetrical Composite Laminates Using the Finite Element Analysis Method

2007 ◽  
Vol 546-549 ◽  
pp. 1563-1566
Author(s):  
Min Li ◽  
Bao Yan Zhang ◽  
Xiang Bao Chen
Keyword(s):  
Experimental Data ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Composite Laminates ◽  
Shell Element ◽  
Element Analysis ◽  
Unsymmetric Laminates ◽  
The Finite Element Analysis ◽  
Simulation Results ◽  
The Difference

Unsymmetric composite laminates were benefit to reducing the structure weight of some aircrafts. However, the cured unsymmetric laminates showed distortion at room temperature. Therefore, predicting the deformation before using the unsymmetrical composite is very important. In this study an attempt was made to predict the shapes of some unsymmetric cross-ply laminates using the finite element analysis (FEA). The bilinear shell-element was adopted in the process. Then the simulation results were compared with the experimental data. The studies we had performed showed that the theoretical calculation agreed well with the experimental results, the predicted shapes were similar to the real laminates, and the difference between the calculated maximum deflections and the experimental data were less than 5%. Hence the FEA method was suitable for predicting the warpage of unsymmetric laminates. The error analysis showed that the simulation results were very sensitive to the lamina thickness, 2 α and (T.

Experimental studies to determine strain concentration factors for space tubular joints

1987 ◽  
Vol 22 (4) ◽  
pp. 237-245 ◽  
Author(s):  
R Sundaravadivelu ◽  
C G Nandakumar ◽  
S K Srivastava ◽  
C Ganapathy
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Experimental Studies ◽  
Offshore Structures ◽  
Strain Concentration ◽  
Tubular Joints ◽  
Orthogonal Plane ◽  
Concentration Factors ◽  
Semi Empirical

This paper presents studies carried out on grouted and ungrouted space tubular joints, with K in one plane and T in the orthogonal plane. Three models have been tested for different load cases adopting T, K, and both T and K (STK) configurations. The tubular joints used in offshore structures, especially in jacket platforms, are multiplanar and some are grouted and hence their study is essential. The stress concentration factor, SCF, as determined using the semi-empirical formulae which are applicable for planar joints are not appropriate for space, grouted joints. The results of the present study indicates that the SCF as determined by formulae for simple joints is unsafe in the plane of K and conservative in the plane of T for the space joint. The effect of the grout is to reduce the stress concentration.

A finite element study of stress fields and stress intensity factors in tubular joints

1995 ◽  
Vol 30 (2) ◽  
pp. 135-142 ◽  
Author(s):  
D Bowness ◽  
M M K Lee
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Stress Concentration ◽  
Stress Intensity Factors ◽  
Numerical Models ◽  
Three Dimensional ◽  
Intensity Factors ◽  
Numerical Work ◽  
Tubular Joints ◽  
Jacket Structures

This paper reports a study on the determination of stress intensity factors in tubular joints in offshore jacket structures. Using finite elements, information on stress concentration factors and through-thickness stress distributions was first obtained from uncracked geometries. This was correlated with the stress intensity factors in joints containing semi-elliptical cracks which were modelled with line-spring elements. The validity of the numerical models was established, using a simple T-joint, by comparing the results with existing experimental data and results from three-dimensional finite element analyses. Various modelling assumptions used in previous numerical work were critically examined. The multi-planar effects in tubular joints were simulated by subjecting the out-of-plane braces to various loadings and restraints. It was found that a relationship exists between the stress concentration factor, the degree of bending and the stress intensity factor for the various loading and restraint cases considered, and that the stress intensity factors in multi-planar tubular joints can be estimated by suitably modifying an existing empirical equation for surface cracks in plain plates.

Stress Resultant Analysis of Steel Penstocks Using a Flat Shell Element

2012 ◽  
Vol 170-173 ◽  
pp. 1887-1892
Author(s):  
Jing Min Liu ◽  
Lu Feng Yang ◽  
Jin Zhang ◽  
Wei Zhang
Keyword(s):  
Finite Element ◽  
Structural Analysis ◽  
Thin Shell ◽  
Shell Element ◽  
Shell Structures ◽  
Stress Resultant ◽  
Flat Shell ◽  
Flat Shell Element ◽  
Finite Element Procedure ◽  
Internal Forces

A finite element procedure of a four-node rectangular flat shell element (FSE) is programmed for structural analysis of steel penstocks. The influence of axial constraint and support settlement on the internal forces of the steel penstocks is investigated. It can be concluded that the FSE is suitable for thin shell structures of steel penstocks and can achieve satisfying accuracy. The axial constraint caused by rest piers would remarkably increase the axial internal forces along pipeline, while the influence of support settlement on the internal forces of the steel penstock is limited, and so is the increment.

scholarly journals Stress Concentration Factor of A Two-Planar Double KT Tubular Joint due to In-Plane Bending Loading in Steel Offshore Structures

2018 ◽  
Vol 177 ◽  
pp. 01006
Author(s):  
Prastianto Rudi Walujo ◽  
Hadiwidodo Yoyok Setyo ◽  
Fuadi Ibnu Fasyin
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Element Model ◽  
Offshore Structures ◽  
Geometrical Parameters ◽  
Offshore Structure ◽  
Wide Range ◽  
Tubular Joint

The purpose of this study is to investigate the proper Stress Concentration Factor (SCF) of a 60° two-planar DKT tubular joint of a tripod wellhead offshore structure. So far, calculation of SCF for a multi-plane tubular joint was based on the formulation for the simple/uniplanar tubular joints that yield in over/under prediction of the SCF of the joint. This situation in turn decreasing the accuracy of fatigue life prediction of the structures. The SCF is one of the most important parameters in the tubular joint fatigue analysis. The tubular joint is modelled as finite element models with bending loads acting on the braces that cover a wide range of dimensionless geometrical parameters (β, τ, γ). The effect of such parameters on the SCF distribution along the weld toe of braces and chord on the joint are investigated. Validation of the finite element model has shown good agreement to the global structural analysis results. The results of parametric studies show that the peak SCF mostly occurs at around crown 2 point of the outer central brace. The increase of the β leads to decrease the SCF. While the increase of the τ and γ leads to increase the SCF. The effect of parameter β and γ on the SCF are greater than the effect of parameter τ.

Load Distribution Between Threads in Threaded Connections

1997 ◽  
Vol 119 (1) ◽  
pp. 91-95 ◽  
Author(s):  
A. S. Grewal ◽  
M. Sabbaghian
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Pressure Vessel ◽  
Load Distribution ◽  
Axial Load ◽  
Three Dimensional ◽  
Nonlinear Finite Element ◽  
Finite Element Code ◽  
Finite Element Analyses ◽  
Threaded Connections

Threaded connections are commonly employed in axial load-bearing equipment and pressure vessel components. There are a number of parameters that affect the load distribution between the threads and the stress concentration at the thread roots. These include the thread form, the thickness of walls supporting the threads, the pitch of threads, number of threads engaged, and the boundary conditions. In this paper, the influence of these parameters on the load distribution between threads is reported. Load distribution analyses in threaded connections is performed by analytical and by finite element methods. Square and buttress-type threads have been considered. Three-dimensional nonlinear finite element analyses on threaded connections have been performed using MSC/NASTRAN finite element code. The effect of clearance between the nonmating faces of threads as well as the presence of a flexible media between the mating faces of threads are investigated.

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