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PETROMAKS2-Stort program petroleum

Structural integrity of PVDF pressure liners

Alternative title: Kapasitetsevaluering av trykkbarrierer bestående av PVDF

Awarded: NOK 6.2 mill.

Project Number:

317673

Project Period:

2020 - 2023

Organisation:

Partner countries:

The purpose of this project (STIP) was to develop a methodology that enables us to predict whether the pressure liner in a flexible pipe can contain the bore fluid. The pressure liner in question was made from PVDF, which is often used in flexible pipes. Under certain load conditions, PVDF can develop porous zones that can cause leakage. These porous zones are called crazes. We developed a novel test method to recreate the conditions under which crazes occur. Using this test method, we conducted numerous experiments where the specimen was subjected to high pressures. Micromechanical imaging and advanced numerical analysis have in combination with the experiments, offered explanations to how and why crazes occur. It is now possible to directly compare materials through testing. Another option is to use numerical simulations to investigate how different loads and pipe geometries influence crazing. The knowledge and methodology that we have developed are already contributing to reduced cost and higher safety on the Norwegian continental shelf. The expertise and competence from the project can be transferred to other business sectors like offshore wind and transportation of CO2 related to carbon capture and storage (CCS).

In STIP, the project participants gained new expertise and improved methods to evaluate the state of a pressure liner and to design flexible pipes. Specifically, the increased understanding of crazing in PVDF allows engineers to evaluate structural integrity of pipes through detailed analyses. Specific outcomes: - The conditions under which crazing occurs are now known. - It is now possible to directly compare susceptibility to crazing in different materials using a new test method. - The project laid the foundation for detailed numerical analysis of not only crazing, but also the general thermo-mechanical behavior of PVDF. - The modeling approach is used by Equinor and Baker Hughes to evaluate and develop new polymer products. The outcome of this project on a societal scale can be significant. Better methodology can lead to substantial material savings in a wide range of business sectors, higher safety by reducing the risk and consequence of oil spillage, reduced cost for energy companies, and expertise that can spill over into other business sectors, for instance offshore wind and transportation of CO2 relating to Carbon capture and storage (CCS). The methodology is already being utilized in investigations regarding life extension of flexible pipes.

The goal of the project is to develop methodology to accurately evaluate the capacity of flexible pipes with a polyvinylidene difluoride (PVDF) pressure liner. The resulting methodology is transferable to a wide range of applications and will be a valuable asset for all the partners in this project. It merges novel insights from fundamental investigations on PVDF with engineering know-how of advanced numerical analysis and structural behavior of flexible pipes. Specifically, the crazing phenomenon will be investigated. A craze is a network of microvoids on the surface of the material. It is not well understood why they form and what the effects of crazing are. Consequently, we need a systematic study to establish the cause of crazing, how the craze interacts with various pressurized fluids, and if the craze will evolve into a crack. The major research challenges are partly experimental and partly numerical. Mechanical tests where crazing can be identified must be designed. Important factors will be stress state, temperature, strain level, and strain rate. With basis in the mechanical tests, fundamental investigations using both microscopic imaging and advanced simulation technology will be used to identify the driving causes of craze formation and propagation. Testing of components under realistic load conditions are challenging but can potentially be extremely useful to validate numerical models and to generate knowledge. Developing an engineering methodology that can predict the structural integrity of flexible pipes under installation and operation is of key interest. An important aspect of the engineering approach is to minimize the computational time, while still describing the real physical behavior of the material. The methods and procedures from this project make it possible to reliably assess the status of in-service pipes and can consequently reduce the break-even cost of a project by removing the need for replacement.

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Funding scheme:

PETROMAKS2-Stort program petroleum