Simple Models for Predicting Stress Intensity Factors for Tubular Joints

Abstract

Offshore structures are subjected to onerous environmental conditions. These conditions can cause cracking at tubular joints in these jacket structures and increasingly fracture mechanics is being applied to assess the cracks.There are a variety of fracture mechanics approaches to assessing cracks in tubular joints, all of which predict similar trends but give a wide variation of stress intensity factors. This variation is caused by the different models and inconsistent input parameters used.This paper presents a finite element study of a cracked tubular joint using several different structural models and consistent input parameters. The analysis includes both simple representations of a tubular joint, e.g. a plate model, and a full-scale analysis on the joint. A comparison of the full-scale analysis and the simple representations allow conclusions to be drawn on the applicability of simplifications to the problem and also allows errors to be quantified. NOMENCLATURE u = crack depth c = half crack length d = brace diameter D = chord diameter E = Young's modulus F = chord length J = J-integral K = stress intensity factor (SIF) L = plate length Q = shape factor for semi-elliptical defect t =brace wall thickness T = chord wall thickness or plate wall thickness W =plate width u = 2 L / D f l = d / D y = D / 2 T 5 = 2 / T D = stress u = Poisson's ratio Subscripts HS = hot spot TUB = tubular TOT = total.

Junctions in shell structures: A review

“…The analytical results obtained by the computer were compared to those obtained previously experimentally. Applying the FE numerical analysis, Haswell [327] presented a study of a cracked tubular joint using several different structural models and consistent input parameters. A comparison of the full-scale analysis and the simple representations allowed conclusions to be drawn on the applicability of simplifications to the problem and also allowed errors to be quantified.…”

A Simple Reliability Model for the Fatigue Failure of Repairable Offshore Structures

“…From equation (4) the probability density of initial defect sizes can be obtained by applying equation (3) to calculate a j . The probability of failure after N , cycles is related to the distribution of initial defect sizes through In order words, equation (5) says that the probability of failure before N,, cycles is equal to the probability that the initial defect size is greater than a,, where a,, is the initial defect size that will cause failure in N,, cycles. This relationship is illustrated in Fig.…”

Fatigue life estimation of tubular joints – a comparative study

“…The accurate geometry is beneficial for the fatigue assessment of offshore tubular joints . Complex joint and geometry for such case are solved by finite element (FE) employed software as stress intensity factors from three dimensional finite element analysis (FEA) of a tubular joint are in reasonable agreement with semi‐empirical data in previous studies . This enables an engineer to solve the problem in more sufficient manner with the benefit of a visual modelling in combination with numerical analysis.…”

“…2 Complex joint and geometry for such case are solved by finite element (FE) employed software as stress intensity factors from three dimensional finite element analysis (FEA) of a tubular joint are in reasonable agreement with semiempirical data in previous studies. 3,4 This enables an engineer to solve the problem in more sufficient manner with the benefit of a visual modelling in combination with numerical analysis. Even though this is not a demanded method for fatigue analysis for simple tubular joint cases, the reliability on the analysis of fatigue worked through guidelines equations is awakening some questions around the accuracy of fatigue analysis of tubular joints.…”