Helen Boyd

Reeling Pipeline Material Characterization: Testing, Material Modeling and Offshore Measurement Validation

It is a fact that when a pipeline is installed by the reeling method, it will undergo cyclic plastic straining and the pipe will plastically deform. Due to the applied plastic bending moment, the residual deformation in terms of residual pipe ovality after reeling is difficult to predict by Finite Element Analyses (FEA) without a thorough understanding of the material characterization and changes under cyclic plastic straining.The paper describes how the material behavior of seamless pipe under plastic strain reeling cycle has been characterized by a comprehensive material testing program including Bauschinger tests and perpendicular loading pre-straining tests. It turns out that for seamless pipe, by looking at the yield stress locus of the material after plastic straining, the reeled pipe material which initially shows isotropic behavior in the un-strained condition will change and evolve to show anisotropic behavior. The material in the hoop direction of the pipe will become more hardened than the material in the longitudinal direction of the pipe. The cross hardening characteristics of material under cyclic plastic deformation have been modeled using the “distortional plasticity” principle and implemented in a user subroutine of an FEA software package.This paper includes the validation of the ovality prediction by FEA model using the developed material model against the ovality measurement from full scale bend tests at Heriot-Watt University as well as ovality measurements taken during the spooling test and trial of 16″OD pipeline at Carlyss spool base in 2013. The material testing of a sample cut out from Spoolbase test and trial, undergoes spool and un-spool 5 cycles, has been performed to confirm the distortional plasticity hardening behavior obtained from the small scale Bauschinger and perpendicular loading tests.Copyright

Development on Aegir Reeling Pipeline Analyses by Test Validation

Heerema Marine Contractors (HMC) is entering a new era of laying pipelines using the reel-lay method in order to be more cost effective for deep and shallow water pipeline installation projects. The new Deep water Construction Vessel (DCV) Aegir is designed to be able to reel/J-lay pipelines for a range of pipe dimension and water depth combinations. The paper describes how the full reeling cycles Finite Element Analysis (FEA) of the Aegir have been developed step by step from the development of the bend rig test, spooling-on to spooling-off FE models which is validated by the bend rig test program. The required material test program is performed to characterize the correct material behavior under plastic cyclic straining.The know-how from the validation of the FEA of bend rig tests by performing the bend tests program is used to setup the full-reeling cycles simulation of spooling-on pipeline on the yard and spooling-off pipeline on board of the Aegir. A series of bend rig tests have been performed at Heriot-Watt University. Ovality measurements from the tests are compared with the predicted results from the bend rig FEA simulation model. Based on small scale specimen tests which are performed to describe the proper material behavior under plastic cyclic straining, a new material model has been proposed and discussed to provide a correct prediction of ovalization against the number of bend cycles. Comparison between the bend rig test measurements and the Aegir full reeling cycles simulation results is made by comparing the deformation of the pipe (ovalization) against a number of bend cycles. Discussion is given to justify the difference in the outcomes as well as the representation of the bend tests program for the qualification test program for reeling with the Aegir.Copyright

Material Property Testing for Finite Element Modelling of Coatings

In 2012 and 2013 Heerema Marine Contractors (HMC) performed full installation testing (bend, roller, tensioner and friction clamp) on pipes with different types of coating ranging from three layer polypropylene to thick insulation coating. The material property data as supplied by the coaters and/or the material suppliers appeared to have insufficient details for HMC to develop a model for the coated pipes. In order to obtain the missing details, HMC undertook a program of material finger printing for all coating materials used in the recent full scale testing in order to establish our own baseline for material properties. The reasons for doing so were; i) the data sheets from different suppliers of similar products were based on different test procedures and the results were not directly comparable, ii) initial testing indicated that the results quoted on the data sheets could not always be achieved by HMC and iii) the data as provided by the suppliers appeared to be not sufficient to be used for material models for finite element analysis. The focus to date has been on polyurethane based insulation materials, both for line pipe coating and for field joint coating, although the plan is to continue with polypropylene based insulation materials. The purpose of this paper is to discuss the setup of the full scale level winder and bend tests, the measurements and observations from the tests, the preliminary finite element analyses of the coating and the findings from the finger printing testing to date.Copyright

Cool-Down Time Estimation Through Numerical Analysis for Partially Insulated Offshore Pipe-in-Pipe Field Joints

Offshore pipe-in-pipe systems require high performance thermal insulation to maintain high fluid temperature at arrival and to avoid hydrate formation during the cool-down process that follows a pipeline shut-down. At field joints, it might be difficult to achieve the design insulation performance due to installation challenges. In these cases, the insulation layer partially fills the gap between the inner and outer pipes and thus “cold spots” could potentially arise at field joints during the pipeline operation and cool-down. In this paper the impact on the thermal performance of partially insulated pipe-in-pipe field joints is evaluated through Computational Fluid Dynamics (CFD). Thermal convection is included in the fluid model for the pipe content and the air gap between the inner and outer pipes. Comparison is also made between the numerical analysis and simplified lumped-parameter models. Results from numerical simulations show that for the case considered no cold spot arises due to a lack of field joint insulation and length-averaged Overall Heat Transfer Coefficient (OHTC) can be used to predict the pipeline cool-down time. Numerical predictions have been compared to simulated service test results, which confirm the length-averaging effect on the OHTC. Further studies are recommended to assess potential cost savings that could be achieved for uninsulated field joints.Copyright

Extend Reel-Ability of HMC New Aegir Reeling Vessel Based on Reliability Based Assessment and Bending Tests Program

Heerema Marine Contractors (HMC) is entering a new era of pipe laying using the reel-lay method for deep and shallow water pipeline installation projects. The new Deep water Construction Vessel (DCV) Aegir is designed to be able to reel/J-lay pipelines for a range of pipe dimension and water depth combinations which on the one side is governed by the equipment limitations (reel drum size, top tension capacity) and on the other side is limited by the code (DNV, API) acceptance criteria for reel/J-lay installation. The paper describes how the code standard acceptance criteria, which have been used to estimate the reel-ability of DCV Aegir and are generally known as conservative approach, can be relaxed in a reliable manner in order to safely extend the DCV Aegir reeling capability. This approach will permit a reduction of minimum reelable pipe wall thickness and result in a wider envelope of water depth applications for reeling from the DCV Aegir. The methodology of relaxation for local buckling and residual ovality criteria has been developed with and approved by DNV specifically for the spooling-on with the DCV Aegir configuration. A series of bend rig tests have been performed at Heriot-Watt University to confirm and validate the new proposed minimum reelable pipe wall thickness. In line with the development of the extended reeling capability, the required tighter specifications for seamless pipe purchased for reeling has been discussed.Copyright