Submarine Steel Research Articles

Dynamics of a pipeline buried in loosely deposited seabed to nonlinear wave [formula omitted] current

Submarine pipeline is a type of important infrastructure in petroleum industry, used for transporting crude oil or natural gas. Understanding of the dynamics characteristics under hydrodynamic loading is crucial for engineers when assessing the stability of offshore pipelines in their designed service period. In this study, taking the integrated numerical model FSSI-CAS 2D as the tool, the nonlinear ocean wave & current-induced dynamics of a shallowly buried submarine steel pipeline and its surrounding loosely deposited seabed soil is numerically investigated. The excellent soil model Pastor-Zienkiewicz-Mark III (PZIII) is adopted to describe the complicated mechanical behaviour of loose seabed soil under cyclic loading. Computational results indicate that the shallowly buried submarine pipeline eventually significantly float up, and extrude the seabed soil over the pipeline driven by the gradually increased buoyancy on the pipeline caused by the accumulation of pore pressure around the pipeline, making the seabed over the pipeline hunch significantly. As a result, considerable deformation occurs in the seabed soil surrounding the pipeline. Two effective stress-based criterion are proposed to judge the occurrence of soil liquefaction. Adopting the two criterion. it is found that the surrounding seabed soil around the pipeline does not become liquefied; only stiffness softening has occurred in it. However, the soil in the upper seabed with shallow depth away from the pipeline becomes liquefied with a liquefaction depth 1.2–1.5 m. Comparative analysis indicates that the pipeline transporting natural gas floats upward with a much greater displacement than that if crude oil is transported. The computational results show that the integrated mode FSSI-CAS 2D has successfully and subtly captured a series of nonlinear physical phenomena of the intensive interaction between pipeline and its surrounding seabed soil. Finally, it is indicated that the integrated model FSSI-CAS 2D has an advantage to investigate the complicated interaction between fluid-structure-seabed foundation.

Determination of the corrosion resistance of the welded steels used in underwater marine systems (including the submerged parts of wave energy converters)

Abstract The experimental investigation of the corrosion resistance of welded shipbuilding and submarine steels with the optimum weld quality which can be used in the future for the improvement of the quality of already existing underwater marine systems (including oil platforms, bridge columns and ships) and for the construction of new and unfamiliar underwater sea-structures (including the submerged parts of Wave Energy Converters and Tidal Energy Converters) in many countries like Greece is an essential parameter from a technical, qualitative and economical point of view. This study presents, justifies and discusses the outputs of the experimental investigation of the corrosion resistance of three different welded steels (HY 100 steels, 316Ti and S355J2 + N) which are currently used in shipbuilding and submarine constructions.

On-bottom stability design of submarine pipelines: the fundamentals

Pipelines are major cost of items in the oil and gas field development. Poor on-bottom stability design may lead to fatigue, lateral and propagation buckling problems. Consequently, additional cost may be incurred during pipeline design and construction due to critical problems relating to poor design. But cost related to the on-bottom stability problem can be significantly reduced by optimizing design. This paper presents comparative review of submarine pipelines on-bottom stability design methods. Comparing absolute lateral stability, generalized lateral stability and traditional force balance methods show variation in submerged weight and effect of pipe-soil interaction on submerged weight parameters. Overall, most literatures agreed that pipelines lateral stability can be increased by increasing porosity of soil, soil embedment and submerged weight. But steel wall and concrete thicknesses are the major parameters used to establish lateral stability of submarine steel pipelines. Therefore, providing an in depth understanding of on-bottom pipeline stability design is necessary to prevent pipeline movement during operation, its associated risks and optimized design.Keywords: Displacement, lateral stability, on-bottom design, pipeline, submerge weight

Seismic Dynamics of Pipeline Buried in Dense Seabed Foundation

Submarine pipeline is a type of important infrastructure in petroleum industry used for transporting crude oil or natural gas. However, submarine pipelines constructed in high seismic intensity zones are vulnerable of attacks from seismic waves. It is important and meaningful in engineering design to comprehensively understand the seismic wave-induced dynamics characteristics of submarine pipelines. In this study, taking the coupled numerical model FSSI-CAS 2D as the tool, the seismic dynamics of a submarine steel pipeline buried in dense soil is investigated. Computational results indicate that submarine pipeline buried in dense seabed soil strongly responds to seismic wave. The peak acceleration could be double of that of input seismic wave. There is no residual pore pressure in the dense seabed. Significant resonance of the pipeline is observed in horizontal direction. Comparative study shows that the lateral boundary condition which can avoid wave reflection on it, such as laminar boundary and absorbing boundary should be used for seabed foundation domain in computation. Finally, it is proven that the coupled numerical model FSSI-CAS 2D is applicable to evaluate the seismic dynamics of submarine pipeline.

Determination of optimum welding parameters for the welding execution of steels used in underwater marine systems (including the submerged parts of Wave Energy Converters)

Abstract The experimental determination of the optimum values of welding parameters and consequently the optimum weld quality of shipbuilding and submarine steels which can be used in the future for the improvement of the quality of already existing underwater marine systems (including oil platforms, bridge columns and ships) and for the construction of new and unfamiliar underwater sea-structures (including the submerged parts of Wave Energy Converters and Tidal Energy Converters) in many countries like Greece is an essential parameter from a technical, qualitative and economical point of view. The purpose of this study is the presentation, justification and discussion of the outputs of the welding experimental execution of three different steels (HY 100 steels, 316Ti and S355J2+N) which are currently used in shipbuilding and submarine constructions.

Mechanical Behavior of Submarine Pipelines under Active Strike-Slip Fault Movement

AbstractThis paper presents comprehensive results on the mechanical behavior of submarine steel pipelines subjected to various strike-slip fault displacement loads. The investigation uses strain-ba...

Crack Arrest Fracture Toughness Testing of Naval Construction Steels

Abstract A program was undertaken to apply the ASTM E 1221 test method to two submarine steels exhibiting high ratios of toughness to yield stress. The objective was to measure the capacities of these steels and representative shipyard welds to arrest fast running cracks. Although the method is not a measure of dynamic toughness, it was considered to be a procedure capable of comparing the crack arresting abilities of these steels. The work has shown that it is possible to follow ASTM E 1221 and obtain valid crack arrest fracture toughness results for materials with room temperature KJc as high as 240 MPa√m and a yield stress of 690 MPa using specimens of 50-mm thickness. The process did, however, have a high level of unreliability, necessitating a large number of tests and extensive re-testing to obtain valid results. Test temperatures below −60°C were required to obtain run-arrest events, and as such could not easily be related to material qualification procedures such as explosion bulge testing or to submarine operating temperatures.