New Assessment Approach For ECA of Clad And Lined Pipes Based On Shell And Line-spring Finite Elements

Olsø, Erlend (SINTEF Materials and Chemistry) | Nyhus, Bård (SINTEF Materials and Chemistry) | Østby, Erling (SINTEF Materials and Chemistry) | Berg, Espen (FMC Technologies) | Thaulow, Christian (Norwegian University of Science and Technology)

OnePetro 

ABSTRACT:

Utilization of clad and lined pipes, where a thin layer of corrosion resistant alloy (CRA) provides corrosion resistance inside a conventional carbon steel pipe, is with increasing frequency considered an economically viable alternative for corrosion management in many new oil and gas developments that are facing problems with highly corrosive products. In order to ensure that integrity is maintained in the presence of challenging loading conditions during installation and service, however, consistent integrity assessment methods suitable for such pipes must be made available. Today’s analytical equations that are the basis for most engineering critical assessments (ECA) are currently not able to account for the effect of internal pressure, and the industry does not have a common recognized procedure for assessing the integrity of clad or lined pipes subjected to plastic strains. This paper describes the development of a new finite element approach for assessing the integrity of clad pipes through implementation of a bimetallic shell element combined with line-spring elements. Comparisons with Abaqus analyses have been included and results for fracture under internal pressure and local buckling are shown. A proposed new procedure for accounting for weld material mismatch in clad pipes as well as conventional carbon steel pipes has also been included. Finally, potential limitations and needs for additional work for the new approach have been discussed.



INTRODUCTION

Pipelines may be subjected to high longitudinal strains during installation and service. Offshore pipelines are typically subjected to the highest strains during pipe laying, but strains well into the plastic regime may be experienced for offshore and onshore pipelines in service due to lateral or upheaval buckling from high temperature/high pressure or due to i.e. impact from trawl equipment, ice scour, frost heave etc. Pipeline integrity during service may also be affected by the installation history.