Weidong Ruan

Buckling of reinforced thermoplastic pipe (RTP) under combined bending and tension

Nowadays composite pipelines are being widely used in the offshore oil and gas industry. However, composite pipelines are often subjected to combined bending and tension during the reeling process and offshore installations, which may lead to elliptical buckling due to the Brazier effect and material failure. The mechanical behaviour of reinforced thermoplastic pipe (RTP) under combined bending and tension is hence a significant parameter for the design of composite pipelines, and it was thoroughly investigated in this paper. Based on the nonlinear ring theory, mechanical behaviour of RTP under combined bending and tension was analysed. The formulations are based on the principle of virtual work and are solved by a numerical solution. To verify the accuracy of the theoretical formulations, an ABAQUS model was employed to simulate the buckling response of RTP under combined bending and tension. The results obtained by the theoretical method and ABAQUS simulation show excellent consistency. Furthermore, a series of sensitivity analyses were presented to highlight the influencing parameters under combined bending and tension. The proposed method will be helpful for RTPs engineering applications.

Behaviour of reinforced thermoplastic pipe (RTP) under combined external pressure and tension

The problem of reinforced thermoplastic pipe (RTP) buckling or collapse as a result of combined tension and external pressure is investigated in this paper. Based on the theory initially proposed by Kyriakides and his co-workers, a two-dimensional (2D) theoretical model, which takes into account transverse shear deformation, the mean radius change, the wall thickness change and pre-buckling deformation, is developed. By means of numerical calculation, pressure–ovalisation and pressure–axial strain curve are presented for T→P loading. Two failure modes were investigated during the loading path. A three-dimensional (3D) finite element model was further established in ABAQUS to confirm the accuracy of the theoretical model, and the results were found to be in good agreement in the small strain stage. Finally, additional parametric studies were conducted, including the effects of initial ovality, tension, pressure, loading path and pressure-to-tension ratio. Predicted T→P and P→T collapse interaction envelopes are presented and useful conclusions are drawn for RTPs marine engineering application.

3D mechanical analysis of subsea manifold installation by drill pipe in deep water

Taking the vessels RAO (response amplitude operator), wave and lowering velocity into consideration, a 3D mechanical analysis of a manifold installation by a drill pipe in deep water is presented in this paper. On the basis of the small-deformation bending theory, the theoretical formulas of displacements, axial tension, bending moment and inclination along the drill pipe are derived by finite-element discretisation. The key results obtained from the proposed method are compared with the ones achieved from the finite-element model using OrcaFlex and the results are in good consistency. A series of sensitivity analyses are also presented to highlight the most influencing parameters in the installation. The proposed method is useful for the feasibility study of the manifold installation.

On-bottom stability of subsea lightweight pipeline (LWP) on sand soil surface

This paper discusses the on-bottom stability of subsea lightweight pipeline (LWP) on sand soil seabed subjected to a combined load of wave and current. Hydrodynamic loads were applied on an LWP to test the on-bottom stability of the pipe. The tests of LWP were carried out with different pipe outer diameter (OD) and different pipe submerged weight. The lateral movement of pipe experiences three characteristic periods based on the lateral displacement of pipe: (1) slightly shaking with sand scour; (2) crossover sand breakouts; (3) laterally moving within a displacement of 2.0 × OD or the pipe will continue to lateral movement after the lateral displacement of 2.0 × OD. A lateral displacement of 2.0 × OD is selected as the displacement criteria for the on-bottom stability of LWP because the pipe will be continuously laterally moving in case the lateral displacement of pipe is larger than 2.0 × OD for LWP, which is different from the on-bottom stability of a rigid steel pipe. Based on the test results, an empirical correlation was established to describe pipelines lateral on-bottom stability. Three-dimensional ABAQUS dynamic finite element simulations of an LWP on flat seabed are carried out. In accordance with the experimental observations, a modified correlation suggested in DNV-RP-F109 code is used for simulating the lateral resistance of LWP on sand soil surface. The effects of lift force on the pipe when the pipe contacts the seabed were considered. A MathCAD worksheet based on the generalised lateral stability method in DNV-RP-F109 was used to assess the pipeline on-bottom stability. The comparison results of MathCAD and finite element analysis (FEA) showed that the FEA simulation gives a good agreement with test results when the lateral pipe displacement is less than 2.0 × OD. The modified FEA model can be used for the on-bottom stability analysis of LWP to reduce conservatism.

Behaviour of steel wire-reinforced thermoplastic pipe under combined bending and internal pressure

ABSTRACT Plastic pipe reinforced by steel wires (PSP) is a new kind of composite pipe, which has the advantages of corrosion-resistant, light weight and low cost. Generally, the middle layer of PSP includes helically wound high-strength steel wires as enhanced body and high-density PE as a matrix. In the engineering practice, this kind of composite pipe endures combined bending and internal pressure. Thus, it is of great importance to investigate the burst pressure of PSP under this load condition. In this paper, a full-scale laboratorial test of PSP under combined bending and internal pressure was carried out. A finite-element model (FEM) was established to study the mechanical behaviour and failure mode. In addition, we deduced a simple but effective formula for calculating the burst pressure of PSP under combined bending and internal pressure. The results obtained from the three methods show a good agreement.

A New Leak Detection Method for Subsea Pipelines

ABSTRACT Subsea pipelines are being installed in the Arctic or deeper water. There is an increased interest in improving leak detection system capabilities throughout the pipeline industry. In this paper, a leak detection system with leak detection module and leak location module is developed. Sequential probability ratio test, negative pressure wave method and pressure gradient method are used in this software. Also, a pattern recognition system is embedded in this software to minimise false alarms. The simulation results are well compared with OLGA and PIPESIM results. Based on the test results and the comparisons, it can be demonstrated that the leak detection system proposed in this paper has been proved with a good sensitivity and accuracy. This study can provide a reference for further studies of leak detection.

Behavior of Flexible Pipe Subjected to Internal Pressure

The increasing use of flexible pipes in subsea with high pressure/high temperature brings about much more challenges. Although there has been a simple prediction method for burst pressure, a more comprehensive prediction of the ultimate strength of flexible pipe subjected to internal pressure is essential for the safe use of flexible pipe under complex environments in terms of different failure modes. In this paper, based on the principle of virtual work, a theoretical model for stresses and deformations of the pipe under the short-term internal pressure have been developed and the obtained results have been compared with the ones from the FEM which is used to simulate the pipe under increasing internal pressure using ABAQUS. And the mechanical properties of two kinds of armor layers have been studied comprehensively considering different boundary conditions. The results and FEA models can be useful for the design of flexible pipes. Finally, the failure prediction of a complete model is discussed.Copyright

Three-Dimensional Mechanical Analysis of Flexible Jumper Installation

This paper presents a simple method to study the installation process of a flexible jumper lowered into deep water by use of cables in a 3D space. Based on the catenary theory, the initial configuration of the installation system can be obtained easily. Then an iterative procedure, which uses force equilibrium and compatibility requirements as convergence criteria, is adopted to establish the final configuration considering the environmental loads. The internal force, bend radius and displacement of the flexible jumper are also obtained by finite-element discretization. The acquired results are compared with those derived from OrcaFlex finite-element model, in order to verify the accuracy and reliability of the proposed method. The influence on the minimum bend radius and maximum axial tension of the flexible jumper due to the difference between the lowering cable lengths, is also studied. The approach presented throughout this paper can offer some suggestions in regards to the installation of a flexible jumper in practical engineering.Copyright