Qualification of Polymer Materials for Dynamic Riser Service

Polymer liners have been used extensively in water injection flowlines for several years, however, have only recently gained traction as a corrosion protection solution for Steel Catenary Risers and other similar rigid pipe risers as the industry moves to more novel systems. In order to qualify a system for a dynamic service environment such as a riser, it is important to understand the system's fatigue response and characteristics to ensure that all potential failure modes are addressed. This is typically accomplished for rigid pipes via full scale resonance fatigue testing whereby a test specimen is subjected to a representative fatigue environment and point of failure determined. Rigid pipe specimens with polymer liner installed have been trialed and reported previously. In this programme, the full-scale test strings demonstrated that all the lined system components can withstand the standard fatigue performance test curves. However, it did not confirm the boundary conditions for failure of the polymer liner, as failure of the metallic host pipe always occurred first. A similar method can be used to test the polymer material in isolation, however given the strain levels involved and the material's inherent fatigue resistance, it was expected that the duration of testing would be impractical. It was therefore necessary to implement a test method that allowed for identification of the polymer boundary conditions within a reasonable time frame, whilst also allowing for comparison with existing fatigue testing. In order to achieve this, a small-scale fatigue testing programme was setup in line with ISO 18489, whereby pre-notched dumbbell samples would be prepared and tested, firstly at 23°C but also at 0°C and 60°C to not only allow comparison with existing full-scale data, but also allow determination of suitability across the full temperature range expected in service. Testing results have demonstrated that the polymer's fatigue resistance far exceeds that of the steel pipe, even with the inclusion of pre-initiated cracking in the samples. The testing was able to provide key data on parameters and their influence on the material's fatigue life such as temperature, stress and strain. Further to this, an additional test programme was setup to evaluate the influence that the vertical orientation of the riser has on the polymer liner system. In this test programme, the interaction force between the steel pipe and polymer liner was assessed to establish the necessary design criteria to ensure that the interaction force always exceeds the vertical self-weight of the liner. Testing results demonstrated that the steel pipe/liner interaction force exceeded the equivalent self-weight of the liner eliminating potential failure modes associated with creep. As a result, the vertical orientation of the riser does not present a risk to the integrity of the liner system.

Numerical Analysis of Filament Wound Cylindrical Composite Pressure Vessels Accounting for Variable Dome Contour

In this work, the stress distribution along cylindrical composite pressure vessels with different dome geometries is investigated. The dome contours are generated through an integral method based on shell stresses. Here, the influence of each dome contour on the stress distribution at the interface of the dome-cylinder is evaluated. At first, the integral formulation for dome curve generation is presented and solved for the different dome contours. An analytical approach for the calculation of the secondary stresses in a cylindrical pressure vessel is introduced. For the analysis, three different cases were investigated: (i) a polymer liner; (ii) a single layer of carbon-epoxy composite wrapped on a polymer liner; and (iii) multilayer carbon-epoxy pressure vessel. Accounting for nonlinear geometry is seen to have an effect on the stress distribution on the pressure vessel, also on the isotropic liner. Significant secondary stresses were observed at the dome-cylinder interface and they reach a maximum at a specific distance from the interface. A discussion on the trend in these stresses is presented. The numerical results are compared with the experimental results of the multilayer pressure vessel. It is observed that the secondary stresses present in the vicinity of the dome-cylinder interface has a significant effect on the failure mechanism, especially for thick walled cylindrical composite pressure vessel. It is critical that these secondary stresses are directly accounted for in the initial design phase.

Permeation Damage of Polymer Liner in Oil and Gas Pipelines: A Review

Non-metallic pipe (NMP) materials are used as an internal lining and standalone pipes in the oil and gas industry, constituting an emerging corrosion strategy. The NMP materials are inherently susceptible to gradual damage due to creep, fatigue, permeation, processing defects, and installation blunder. In the presence of acid gases (CO2, H2S), and hydrocarbons under high pressure and temperature, the main damage is due to permeation. The monitoring of possible damage due to permeation is not well defined, which leads to uncertainty in asset integrity management. Assessment of permeation damage is currently performed through mechanical, thermal, chemical, and structural properties, employing Tensile Test, Differential Scanning Calorimetry (DSC), Fourier-transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM)/Transmission Electron Microscopy (TEM), to evaluate the change in tensile strength, elongation, weight loss or gain, crystallinity, chemical properties, and molecular structure. Coupons are commonly used to analyze the degradation of polymers. They are point sensors and did not give real-time information. Polymers are dielectric materials, and this dielectric property can be studied using Impedance Analyzer and Dielectric Spectroscopy. This review presents a brief status report on the failure of polymer liners in pipelines due to the exposure of acid gases, hydrocarbons, and other contaminants. Permeation, liner failures, the importance of monitoring, and new exclusive (dielectric) property are briefly discussed. An inclusive perspective is provided, showing the challenges associated with the monitoring of the polymer liner material in the pipeline as it relates to the life-time prediction requirement.

Rheological Properties of Composite Polymer Liner Based on Hydroxyl‐Terminated Polybutadiene

An experimental study to determine the dependence of the viscosity and shear stress of hydroxyl-terminated polybutadiene (HTPB) and dimeryl diisocyanate (DII) liner on curing time is presented. Viscosity and shear-stress were measured by HAAKE RheoStress 600 rheometer with parallel disks configuration at a constant temperature of 65 °C. The viscosity and shear-stress change were monitored for 8 h. Analysis of data showed that the liner viscosity and shear-stress dependency on time matched to pseudoplastic fluid model. For low shear-rates, the viscosity build-up is highest, with the logarithm of the viscosity being practically linear with time and the viscosity increases by more than two orders of magnitude for these cases. When the shear rates increase, the viscosity build-up slows down considerably with time and the viscosity is increased only by one order of magnitude.

Effect of Pad and Liner Material Properties on the Static Load Performance of a Tilting Pad Thrust Bearing

Tilting pad thrust bearings (TPTBs) control rotor axial placement in rotating machinery, and their main advantages include low drag power loss, simple installation, and low-cost maintenance. The paper details a novel thermo-elasto-hydrodynamic (TEHD) analysis predictive tool for TPTBs that considers a three-dimensional (3D) thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation. The predicted pressure field and temperature rise are employed in a finite element (FE) structural model to produce 3D elastic deformation fields in the bearing pads. Solutions of the governing equations delivers the operating film thickness, required flowrate, and shear drag power loss, and the pad and lubricant temperature rises as a function of an applied load and shaft speed. To verify the model, predictions of pad subsurface temperature are benchmarked against published test data for a centrally pivoted eight-pad TPTB with 267 mm in outer diameter (OD) operating at 4–13 krpm (maximum surface speed = 175 m/s) and under a specific load ranging from 0.69 to 3.44 MPa. The current TEHD temperature predictions match well the test data with a maximum difference of 4 °C and 11 °C (<10%) at laminar and turbulent flow conditions, receptively. Next, the TEHD predictive tool is used to study the influence of both pad and liner material properties on the performance of a TPTB. The analysis takes a whole steel pad (without a liner or babbitt), a steel pad with a 2-mm-thick babbitt layer (common usage), a steel pad with a 2-mm-thick hard-polymer (polyether ether ketone, e.g., PEEK®) liner, and a pad entirely made of hard-polymer material, whose elastic modulus is just 12.5 GPa, only 6% that of steel. The bare steel pad reveals the poorest performance among all the pads as it produces the smallest fluid film thickness and consumes the largest drag power loss. For laminar flow operations (Reynolds number Re < 580), the babbitted-steel pad operates with the thickest fluid film and the lowest film temperature rise. For turbulent flow conditions Re > 800, the solid hard-polymer pad, however, shows a 23% thicker film than that in the babbitted pad and produces up to 25% lesser drag power loss. In general, the solid hard-polymer TPTB is found to be a good fit for operation at a turbulent flow condition as it shows a lower drag power loss and a larger film thickness; however, its demand for a too large supply flowrate is significant. Predictions for steel pads with various hard-polymer liner and babbitt thicknesses demonstrate that using a hard-polymer liner, instead of white metal, isolates the pad from the fluid film and results in an up to 30 °C (50%) lower temperature rise in the pads than that for a babbitted-steel pad. For operations under a heavy specific load (>3.0 MPa), however, a thick hard-polymer liner extensively deforms and results in a small film thickness.

Damage characteristics of polymer expansive jet based on the crater growth enhanced effect

In this study, a polymer liner is applied to a shaped charge warhead, and the formed expansive jet exhibits a crater growth enhancement effect that can effectively damage the armored vehicle target. To examine the damage characteristics of polymer expansive jet, three polymer materials with different properties were selected, namely polytetrafluoroethylene (PTFE), nylon (PA), and polycarbonate (PC). The penetration results of light aluminum target and heavy steel target are analyzed via the SPH method and AUTODYN finite element software and verified via experiments. The results indicate that for light aluminum targets, the enlarged hole diameter of polymer expansive jet exceeds that of metal jets, and the penetration depth is lower than that of a metal jet. The results also suggest that the crater growth enhanced effect is more evident when the stand-off is small. With respect to high strength steel targets, the penetration ability of polymer expansive jet is limited. However, for low strength aluminum targets, the crater growth enhancement of the polymer expansive jet is reflected.