Fatigue reliability assessment of tubular joints of existing offshore structures

2001 ◽  
Vol 28 (4) ◽  
pp. 691-698 ◽  
Author(s):  
A A Aghakouchak ◽  
S F Stiemer
Keyword(s):  
Decision Making ◽  
Reliability Assessment ◽  
Offshore Structures ◽  
Fatigue Reliability ◽  
Inspection Planning ◽  
Additional Information ◽  
Linear Elastic ◽  
Tubular Joints ◽  
Elastic Fracture ◽  
Tubular Joint

Tubular joints of offshore structures are prone to fatigue damage. Because of uncertainties involved in quantifying the fatigue process in this type of structure, a reliability approach may be adopted to assess the risks of failure. In-service inspections of structures produce additional information, which may be taken into consideration in order to update the reliability. The paper reviews the methods for carrying out such reliability analyses based on principles of linear elastic fracture mechanics and applies them to a sample tubular joint. The results of this type of analyses may be used for inspection, planning, and (or) decision making regarding repairs or modification of the service life of a structure.Key words: fatigue, reliability, tubular joints, offshore structures, condition assessment.

scholarly journals Fatigue Strength Curve for Tubular Joints of Offshore Structures under Dynamic Loading

Dynamics ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 125-133
Author(s):  
Sudath C. Siriwardane ◽  
Nirosha D. Adasooriya ◽  
Dimitrios Pavlou
Keyword(s):  
Fatigue Strength ◽  
Hot Spot ◽  
Offshore Structures ◽  
Hot Spot Stress ◽  
Tubular Joints ◽  
Jacket Structures ◽  
Strength Curve ◽  
Tubular Joint ◽  
Stress Concentration Factors

Offshore structures are subjected to dynamic environmental loads (wave and wind loads). A stress-life fatigue strength curve is proposed for tubular joints which are in the splash zone area of offshore jacket structures. The Det Norske Veritas (DNV) offshore structures standards given design T-curve in the air is modified with the environment-dependent parameters to obtain this fatigue strength curve. Validity of the curve is done by comparing fatigue lives given by the proposed curve with experimental fatigue lives of tubular joints tested in seawater under different loading conditions. The fatigue assessment of a case study tubular joint is performed using the proposed curve. Nominal stress ranges of the members, which are connected to the joint, are obtained by dynamic analysis of the jacket structure. Stress concentration factors are utilized with the nominal stresses to obtain the hot spot stress ranges. Fatigue lives are calculated and compared with the conventional approach. Hence the applicability and significance of the proposed fatigue strength curve are discussed.

Numerical Investigation of Static Strength for Tubular Joints Reinforced by Inner Plate

2013 ◽  
Vol 470 ◽  
pp. 547-552 ◽  
Author(s):  
Dong Ping Yang ◽  
Yong Bo Shao ◽  
Feng Le Long ◽  
Geng Qi Niu ◽  
Lu Zhang ◽  
...  
Keyword(s):  
Axial Direction ◽  
Offshore Structures ◽  
Static Strength ◽  
Joint Models ◽  
Element Analysis ◽  
Tubular Joints ◽  
Long Span ◽  
Weld Toe ◽  
Ring Reinforcement ◽  
Tubular Joint

Welded tubular joints are widely used in long-span, space and offshore structures. In a welded tubular joint, the chord is generally subjected to loads in radius direction which are transmitted from the brace members in axial direction. As the strength of the chord in radius direction is generally much weaker than that of the brace in axial direction, failure occurs easily at the weld toe on the chord surface. To improve the bearing capacity of the joint structure, reinforcement is necessary. Several reinforcing methods were reported in the literature, such as doubler or collar plate reinforcement, internal stiffened ring reinforcement and bracket reinforcement etc. This paper presents the strengthening method by inner plate. From finite element analysis of many inner plated reinforced tubular joint models, the efficiency of reinforcement by inner plate is analyzed by comparing the static strength of reinforced models with that of unreinforced models. Based on a parametric study of the static strength of tubular joints reinforced by inner plate, the design considerations on inner plate strengthening tubular joints are also proposed.

Assessment of Fatigue Reliability for Jacket-Type Offshore Platforms Considering Dynamic Behavior

2013 ◽  
Author(s):  
Mohammad Reza Khedmati ◽  
Philippe Rigo ◽  
Amirouche Amrane ◽  
Masoud Nazari
Keyword(s):  
Fatigue Life ◽  
Reaction Force ◽  
Offshore Structures ◽  
Oil Field ◽  
Wave Forces ◽  
Offshore Platforms ◽  
Limited Information ◽  
Fatigue Reliability ◽  
Marine Structures ◽  
Linear Elastic

In order to traditionally investigate the strength of marine structures, the structure is subjected to a maximum static load. However, the marine structures are usually suffering environmental forces varying with time. Wave forces are the most important time dependent loading that causes fatigue in structural elements and joints. In this paper different methods base on S-N curve and linear elastic failure mechanics are presented. The governing equations and theories that are used in each method are expressed and the application of each method will be discussed. The two main methods of deterministic analyses are: stress-based approach (S-N curve approach) and linear elastic fracture mechanics (LEFM) approaches. These approaches are applicable to different analyzing strategies, ie the first approach is used for cases in which general form of fatigue is dominant, but the latter involves the calculations of reliability as functions of crack geometry and its boundary conditions. The SPD12C jacket platform in South Pars Oil Field is also modeled as a case study and the results of fatigue reliability analysis are presented. In this paper a comprehensive method is presented to accurately predict the reliability of offshore platforms. This method is based on S-N curve and the results are compared with the fatigue life of joints. Due to nonlinear interaction of soil and piles and the other affecting parameters such as flexibility of joints, non Gaussian procedure of loading, and nonlinearity of reaction force, the precise analyzing of stress levels will be impossible and a complex numerical analysis could only give limited information about the statistical properties of stress. In order to perform the fatigue analysis and predicting the cycles of stress SACS was used which is known as a powerful software in designing and analyzing offshore structures [1]. In this paper the whole structure was modeled subjected to different forces such as wave and sea currents. The effects of parameters such as marine growth and interaction of soil and piles are also included. The latter is shown to have a significant effect on determination of fatigue life of the platform.

Investigation of a Simplified Fatigue Reliability Model for Optimising the Design of Tubular Joints

2002 ◽  
Author(s):  
G. K. Cole ◽  
R. Pinna ◽  
B. F. Ronalds ◽  
P. Romagnolo
Keyword(s):  
Fatigue Failure ◽  
Research Effort ◽  
Fatigue Reliability ◽  
Inspection Planning ◽  
Construction Costs ◽  
Planning Techniques ◽  
Tubular Joints ◽  
Considerable Research ◽  
Target Probability ◽  
Probabilistic Technique

While there has been considerable research effort over the last decade aimed at refining risk based fatigue inspection planning techniques, there has been relatively less effort aimed at using the same techniques to optimise the design of welded joints. This paper discusses the use of a simplified, semi-probabilistic technique for optimising the design of tubular joints on the basis of their total through-life costs. A model is developed which combines the probability of fatigue failure with initial construction costs, inspection costs, and repair and failure costs. An example study of a critical joint in a minimum structure is provided. In this example, where costs associated with joint failure were assumed to be purely financial, an optimum target probability of failure (threshold for inspection) was found to be 10−4 to 10−3. Provided the target probability of fatigue failure used in inspection planning is kept below this level, design in accordance with API RP2A appears to provide a reasonably optimised joint. The sensitivity of the total cost to this target failure probability, and a range of other important cost variables, was also investigated.

Damage Tolerance Evaluation of Cracked Tubular Joints Subjected to Fatigue Loading

2010 ◽  
Vol 452-453 ◽  
pp. 653-656
Author(s):  
A. Rama Chandra Murthy ◽  
G.S. Palani ◽  
Nagesh R. Iyer
Keyword(s):  
Crack Growth ◽  
Life Prediction ◽  
Damage Tolerance ◽  
Fatigue Loading ◽  
Analytical Prediction ◽  
Remaining Life ◽  
Linear Elastic ◽  
Tubular Joints ◽  
Elastic Fracture ◽  
Experimental Values

This paper presents methodologies for damage tolerance evaluation of tubular T- and Y-joints by using linear elastic fracture mechanics (LEFM) principles. The damage tolerance evaluation is in terms of crack growth analysis and remaining life prediction of tubular joints. Stress intensity factor (SIF) for T-butt plates which can be used for computation of SIF for tubular joints has been evaluated as per BS: 7910. It is observed from the literature that the expressions given in BS: 7910 for computation of SIF have not been used for remaining life prediction of tubular joints. In this paper, these expressions have been used for analytical prediction of remaining life of tubular T- and Y- joints subjected to constant amplitude loading (CAL) and variable amplitude loading (VAL). Wheeler residual stress model has been employed to represent the retardation effects due to tensile overloads. It is observed that remaining life predicted for T- and Y-joints under CAL are found to be in good agreement with those of experimental values reported in the literature. In the case of VAL, it is observed that crack growth retardation increases with increase of OLR resulting in higher predicted remaining life. It has also been observed that the predicted remaining life is influenced by the number of OLs and occurrence of OL. Early occurrence of OL causes the higher remaining life compared to later OLs.

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