Special Session: Advances in Flexible Riser Technology: Flexible Pipe Curved Collapse Behavior Assessment for Ultra Deep Water Developments for the Brazilian Pre-salt Area

Abstract

The collapse strength of flexible pipes is a well known property and predicted by means of numerical or analytical modelling. However, recent oil field discoveries in the Brazilian pre-salt area, in water depths up to 2500m, are pushing the industry to evaluate the effects of flexible pipe curvature on its collapse resistance when the pipe is subjected to extreme levels of hydrostatic pressure such as that expected in the Brazilian pre-salt area. As part of Wellstream's R&D programme, a numerical model was specifically developed to predict flexible pipe collapse resistance when subjected to curvature to assess and quantify the effects of curvature on the flexible pipe collapse resistance. This paper summarizes the numerical modelling process and experimental calibration performed using five different pipe structures specifically designed for the pre-salt cluster. A total of 45 calibration tests were performed using samples taken from the same production run in order to eliminate variance in production machine setup and raw material batches. Regular production equipment, setups and quality control procedures were used to manufacture the test samples so that the collapse resistance of the pipes could be evaluated against conditions identical to commercial manufacturing. Of the five different pipe structures evaluated in this test programme, one of the pipe structures supplied for the TUPI EWT project development is already installed and operating at a water depth of 2140m. The test programme allowed the experimental assessment of the curvature effects on flexible pipe collapse behaviour, demonstrated the suitability of flexible pipe structures and model to predict the effects of curvature on collapse resistance.

Prediction of the critical collapse pressure of ultra-deep water flexible risers-a: Literature review

“…Determining the critical pressure through the collapse tests ( Figure 4) of flexible risers is always the most reliable way for the anti-collapse analyses [10], [15], [16]. However, such hydrostatic tests require specialized hyperbaric chambers, which are very limited worldwide [17].…”

“…During deep/ ultra-deep water installation and operation, flexible risers experience bending within the touchdown zone (TDZ). The bending configuration may change the ovality and gap of the pipe curved regions, leading to a reduced collapse resistance [15]. The complexity of curvature effect poses barriers to analytical approach and limits most curved collapse studies to finite element methods.…”

“…Interlocked layers in this model were modelled as helical strips (like a spring ring). The prediction accuracy of this model was later examined in [15], which indicated that the predictive model provided the flexible pipe products a more than adequate anti-collapse capacity compared with the anticipated design values. Since that simplified model did not offer the engineers a physically intuitive observation and trustworthy prediction on the curvature effect, a 3D full FE model was constructed by Neto et al [45] to visualize the curvature effects in the flexible pipes.…”

Buckling collapse study for the carcass layer of flexible pipes using a strain energy equivalence method

“…A similar equivalence method was also applied to study the mechanical behaviors of a pipe under axial loads (Wang and Chen, 2011;Yue et al, 2012). After an equivalent model is created, further studies on wet collapse (Pesce et al, 2010) or collapse with curvature (Paumier et al, 2009, Clevelario et al, 2010 can easily be conducted either analytically or with the finite element method.…”

Finite Element Studies for Assessment of Collapse Modelling Methodologies for Unbonded Flexible Pipes

“…In recent years, studies have been carried out investigating the influence of special factors that may affect the collapse pressure, such as including the influence of pressure armour in models [7] and studying the influence of pipe curvature [4,10].…”