Fatigue Design Recommendations for Conical Connections in Tubular Structures

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Oil And Gas ◽  
Gas Production ◽  
Tubular Structures ◽  
Stress Concentrations ◽  
Design Standards ◽  
Oil And Gas Production ◽  
Fatigue Design ◽  
Jacket Structures ◽  
Fabrication Tolerances ◽  
Stress Concentration Factors

Conical connections are important structural members for the integrity of most types of welded tubular structures. They are for example used in traditional jacket structures for oil and gas production and in monopiles for support of wind turbines where an optimal design is aimed for. From contact with the industry, it is noted that there is uncertainty about the basis for the stress concentration factors (SCF) for conical connections in design standards for fatigue assessment. This is related to how fabrication tolerances are accounted for and how a transition in thickness from the cone to the tubular or the cylinder should be made to minimize stresses due to thickness transitions and fabrication tolerances. Analytical expressions for stress concentrations at conical transitions are outlined in this paper to get a better understanding of the effect of thickness of the cone and the cylinder. By a proper basis for fatigue design, it is possible to control additional stresses from thickness transitions and fabrication tolerances at these connections.

Fatigue Design Recommendations for Conical Connections in Tubular Structures

2017 ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Oil And Gas ◽  
Gas Production ◽  
Tubular Structures ◽  
Stress Concentrations ◽  
Design Standards ◽  
Oil And Gas Production ◽  
Fatigue Design ◽  
Jacket Structures ◽  
Fabrication Tolerances ◽  
Stress Concentration Factors

Conical connections are important structural members for the integrity of most types of welded tubular structures. They are for example used in traditional jacket structures for oil and gas production and in monopiles for support of wind turbines where an optimal design is aimed for. From contact with the industry it is noted that there is uncertainty about the basis for the stress concentration factors for conical connections in design standards for fatigue assessment. This is related to how fabrication tolerances are accounted for and how a transition in thickness from the cone to the tubular or the cylinder should be made to minimise stresses due to thickness transitions and fabrication tolerances. Analytical expressions for stress concentrations at conical transitions are outlined in this paper to get a better understanding of the thickness of the cone and the cylinder. By a proper basis for fatigue design it is possible to control additional stresses from thickness transitions and fabrication tolerances at these connections.

Design Load Measures for Vapor Cloud Explosion on Complex Systems: Review and Recommendations

2017 ◽  
Author(s):  
Maryam Mortazavi ◽  
YeongAe Heo ◽  
Yue Li
Keyword(s):  
Structural Design ◽  
Oil And Gas ◽  
Free Field ◽  
Economic Loss ◽  
Gas Production ◽  
Combustion Mechanism ◽  
Design Standards ◽  
Oil And Gas Production ◽  
Design Load ◽  
Vapor Cloud

A hydrocarbon Vapor Cloud Explosion (VCE) is one of critical hazardous events in offshore installations. Once VCE occurs in the ocean, it results in tremendous economic loss, casualties, and environmental impact. The combustion mechanism of VCE differs from HE in particular in complex geometries (e.g. offshore oil and gas production facilities) as there exist many objects which can trigger severe turbulences. Although many research efforts have been made to develop design provisions for blast resistant structures, most of those provisions are based on high-order explosives (HE) such as TNT (TriNiTrotoluene) in a free field. Therefore, typical blast resistant structural design standards were examined to address the weaknesses of standards in this study. Existing blast wave models which provide key design load parameters were also reviewed to address limitations of each approach. Finally, essential recommendations are discussed in this paper for future studies to improve blast resistant structural design provisions with the ultimate aim of protecting our lives, assets and environment from VCE in the ocean.

Stress Concentration Factors at Welded Connections Between Tubular Sections and a Transverse Plate

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Inge Lotsberg
Keyword(s):  
Stress Concentration ◽  
Wind Turbines ◽  
Oil And Gas ◽  
Superposition Principle ◽  
Gas Production ◽  
Oil And Gas Production ◽  
Weld Toe ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Weld Root

Abstract Welded connections between tubulars and transverse plates are used to build together part structures such as support of flare towers and wind turbines and deck structures on foundation structures. They are used in traditional jacket structures for oil and gas production and in support structures for wind turbines. These welded connections are typically made from the outside resulting in a weld root on the inside and a weld toe on the outside. Different S–N curves apply to these positions; therefore, stresses both on the inside and the outside are needed for fatigue assessment. From the actual design, it is noted that the thicknesses of the tubulars being connected can be different. Also, the diameters of the tubulars can be different. In addition, the fabrication is associated with some fabrication tolerances that provide local eccentricity moments to be transferred through these connections. In this paper, analytical expressions for stress concentration factors for these connections are presented based on classical shell theory. The stress concentration is dependent on the radial restraint from the transverse plate and the eccentricity of the neutral axes in the tubular thickness of one tubular relative to the other tubular. The superposition principle is used to derive resulting stress concentration factors for the inside weld root and the outside weld toe.

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