|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
Lee, Chin-Hyung (Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology) | Shin, Hyun-Seop (Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology) | Park, Ki-Tae (Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology) | Kang, Su-Tae (Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology) | Joo, Bong-Chul (Structural Engineering & Bridges Research Division, Korea Institute of Construction Technology) | Chang, Kyong-Ho (Department of Civil and Environmental Engineering, Chung-Ang University)
Understanding welding-induced residual stresses can help the pipeline industry to produce and install safer, more reliable and potentially more cost-efficient pipeline designs. The weld residual stresses are often found to be in the tensile stress state in parts of the weld which is well-known to have a destructive effect on the fatigue life and fracture properties of the pipeline. With the latest development within Computational Welding Mechanics, it is today it is possible to give accurate estimations of the residual stresses and distortions due to welding and the results can be used to optimise and determine the structural life time of the pipeline. However, it is vital that the welding simulation methods are validated against reliable measured data, so that welding-induced residual stresses distribution can be accurately predicted using computational methods. During the welding there are several factors that might affect the influence of welding residual stresses, such as the materials properties of the base and filler material, the welding process parameters, number of passes, joint groove parameters, geometry effects such as the thickness and t/D ratio. The different factors contribute all to the weld residual stress in different levels and it is therefore crucial to understand how this will influence residual stress level. This paper presents a review of the latest achievements within Computational Welding Mechanics (CWM) simulations to determine the weld residual stresses in pipeline girth welds and the influence the weld residual stress has on the pipeline integrity.
It is widely recognized that the application of different welding processes, involving different heat input, lead to different residual stresses on the weld joints. A very few experimental tests and numerical simulations have been carried out to improve the knowledge of the impact of residual stresses on typical welded joints for offshore pipeline industry. In this paper is reported the outcome of a dedicated study on the subject, in which the same pipe joint, a carbon steel grade API 5L X65, has been welded with two different welding procedures and then subjected to experimental tests to determine surface residual stresses through the hole-drilling strain gage method. The two welding procedure under testing were both representative of welding procedures typically applied during the installation of SCR in deepwater, in offshore vessel firing line or during prefabrication of multiple joints, but involving different welding processes combinations and different heat input values. A numerical simulation of the two welding procedures has been also carried out through SYSWELD®, a well-known commercial tool. Capabilities of the numerical model to provide a satisfactory prediction of the final residual stresses have been investigated. Both 2D and 3D approaches available in the numerical model are analyzed with a comparison of results between simulations and experimental measurements. Advanced numerical tools could enhance engineering leverage for fracture mechanics phenomenon comprehension, experiment design optimization and technology improvements.
In offshore Oil & Gas industry a typical example of components highly subjected to cyclic loads are Steel Catenary Risers, a common solution connecting a subsea pipeline to deepwater floating production units. SCRs are short subsea pipelines connecting other pipelines laid on the seabed with a floating or fixed production structure in a catenary shape; they are commonly subjected to fatigue loads, particularly in the touchdown zones, due to floating units movements, Vortex Induced Vibrations (VIV) due to waves and sea currents.
Mechanically Corrosion Resistant Alloy (CRA)-lined pipes have been increasingly used and the reel-lay installation method has been considered as an efficient way in installation of the CRA-lined pipe. A pipe can be subjected to multiple reeling cycles of up to 2% axial strain and a realistic treatment of welding residual stress during reel-lay is crucial for reeling engineering critical assessment (ECA). In this paper, a comprehensive testing program was conducted for measurement of the welding residual stresses at a CRA pipe girth weld. Welding residual stresses were measured during the pre-reeling and post-reeling stages and it demonstrates that the reel-lay installation relaxes the welding residual stresses. Welding numerical simulation was also performed and this provides a self-balanced residual stress profile in the girth weld and seal weld of the CRA-lined pipe. The residual stress profiles are compared between the finite element (FE) analysis and measurement. The implementation of welding residual stress distributions into the FE-based reeling ECA is described.
There is a lack of formalised standards and procedures in the pipeline industry in engineering critical assessment (ECA) for partially overmatching or under-matching girth welds particularly during reel lay installation. This paper provides a finite element based ECA methodology for assessing such girth welds during reeling. The crack driving force is derived from 3D finite element fracture models. The crack tip blunting and ductile tearing are explicitly distinguished. Tearing-fatigue is considered as the crack growth driving mechanism between multiple reeling cycles. The treatment of welding residual stress is also discussed.