Buckle Propagation And Its Arrest For Deep- Water Pipe-in-Pipe Systems

Offshore pipelines are the lifelines of oil and gas exploitation projects in deep waters. It is the top priority to ensure the safety of pipelines during installation and service period. Subsea pipelines are inevitably subjected to tremendous hydrostatic pressure utilized in deep and ultra-deep water applications. Due to the complicated exterior ocean environment, once the buckle initiates by the imperfection of the tube, it can propagate along the pipeline driven by hydrostatic pressure, and then destroy the whole pipe which causes catastrophic loss. Compared with the traditional single-walled steel pipe, pipe-in-pipe system can provide effective load-carrying capacity and excellent thermal insulation. This design configuration alse ensures the containment of the product while either pipe is damaged. These benefits mentioned endow PIP systems with outstanding economy, practicality and safety in deep-water oil and gas exploitation projects.The resource situation our country confronts remains severe since the foreign dependency of oil has been beyond the international alertness line for years. With the gradual exhaustion in shallow waters, it is an inevitable trend for oil and gas exploitation projects to march onto deep-water areas. Therefore, carrying out the research on the propagation of the PIP system and the performance of the integral arrestors is of significant importance to promote the design ability of deep-water pipelines and enhance the exploitation of the subsea resource.Based upon the previous research results, this essay mainly focuses on the propagation of the PIP system and the performance of the integral arrestors. The research work conducted and results obtained can be summarized into several aspects listed below.(1) The scale model experiments were carried out with the pressure cylinder to simulate deep-water environment, aiming to scrutinize the propagation of the PIP system and the performance of the integral arrestors. The collapse pressure, propagation pressure and the crossover pressure were measured and the pressure-changes in volume responses during the experiments were recorded.(2) The numerical simulation method was developed to simulate the buckle propagation of the PIP system and the process of buckle arrest within the framework of ABAQUS. The accuracy of this method was verified by comparing the results of the FEM and experiments.(3) Using the finite element method developed above, a parameter sensitivity analysis on the propagation pressure of the PIP system was conducted, which took the effect of the strain hardening modulus into account. A more effective model to simulate the constitutive curves with different material hardening property was proposed simultaneously. Compared to the results of experiments and parameter sensitivity analysis, an empirical formula was put forward aiming at calculating the propagation pressure of PIP systems. Two patterns of the buckle propagation modes were also disclosed, and the condition of the mode switch was verified with the help of finite element model.(4) The fact that integral arrestors can upgrade the capacity of the PIP system against buckle propagation notably has been validated. Two crossover modes of the arrestors, i.e. flattening mode and flipping mode, were disclosed, and the influences of the arrestor's specification on working performance were analyzed. According to the numerical and experimental results, a formula to calculate the efficiency of integral arrestors was obtained, and the corresponding design guidelines for the integral arrestors were drawn up.