Collapse Pressure Research Articles

Effect of Winding Steel Wire on the Collapse Pressure of Submarine Hose

The submarine hose plays a vital role in the single-point mooring system and is a necessary channel for medium transportation. Once crushed under the load of the seawater external pressure, it will cause oil and gas leakage and major safety accidents. It is a composite hose composed of a rubber layer, cord layer and steel helix wire, of which the steel helix wire plays an important part in bearing mechanical properties. In this work, python language was used to model the submarine hose parametrically, the finite element (FE) analysis software ABAQUS was utilized to analyze the ultimate bearing capacity of the hose under uniformly distributed external pressure loads and the influence of the initial ovality of the submarine hose, the diameter and pitch of the helix wire, the yield strength of the helix wire material on the ultimate bearing capacity of the submarine hose were studied. Through a large number of FE results, the ultimate bearing capacity of the hose was obtained by fitting the prediction formula.

Wellbore Stabilization Technology of “Fluid-Solid-Chemical Coupling” in Continental Shale Oil—A Case Study of Shale Oil in Block GL

During the oil shale drilling in Group Q of Block GL, the shale is prone to hydration, deterioration, sidewall exfoliation and frequent collapse, which affects the efficient exploration and development of shale oil. In order to reveal the mechanism of wellbore instability in the shale formation, the tectonic characteristics of shale are studied by combining microscopic and macroscopic methods, which identifies three key factors of physics, chemistry and mechanics about wellbore instability. Based on the analysis of earth stress and rock mechanics parameters, the experiment has established the prediction model of “fluid-solid-chemical coupling” collapse pressure of shale formation in Group Q, and calculated the safe drilling fluid density window for the horizontal wells of shale oil in Block GL by the prediction model. The main factors of wellbore instability in shale formation, deterioration characteristics and high density of oil-based drilling fluid on the well site is combined. The targeted plugging anti-sloughing and strong wetting agent were developed by using laser particle size instruments and pressure transmission experiments. A high thixotropy and strong plugging oil-based drilling fluid system is formed. The research results have been successfully applied in 16 horizontal wells of the shale oil test platform. The excellent rheological property, reliable plugging and bearing capacity and outstanding wellbore stabilization effect provides technical support for high-quality and efficient exploration and development of shale oil in Block GL. The “fluid-solid-chemical coupling” wellbore stabilization technology of continental shale oil formed in this study can provide a reference for the exploration and development of similar types of shale oil and gas reservoirs.

Buckling pressure of imperfect spherical shell damaged by concentrated impact load

Spherical pressure shells are an important component to ensure the safety of personnel and equipment. Due to the impact of seabed reefs, marine organisms and floating objects, spherical pressure shells undergo different degrees of deformation, leading to a sharp decline in buckling pressure. Therefore, the buckling characteristics of spherical shells damaged by concentrated impact load were studied using an experiment and numerical calculation. The crater formation of spherical shells under impact was generated by striking the spherical shell with a drop hammer. The collapse pressure and the final failure mode were obtained through a hydrostatic test to verify the validity and accuracy of the numerical calculation results. Numerical calculation entailed plastic deformation model and residual stress. On this basis, the effects of the impact velocity, impact angle and residual stress on the buckling of spherical shells were studied.

Optimization of Composite Cylindrical Shell Structures for Hydrostatic Pressure Loading

Abstract Deep-sea structures will collapse/implode under hydrostatic pressure when the structure dives below an instability threshold, leading to catastrophic failure. To better understand how the layup angle of composite cylindrical shells influences this instability threshold, this work explores how composite cylinders can achieve the highest (optimum) critical collapse pressure under hydrostatic loading conditions. To perform this analysis, a closed-form analytical cylinder buckling solution developed by previous work is used in conjunction with different cylindrical geometrical configurations and composite properties for glass, carbon, and intraply hybrid composite properties for woven and unidirectional structures. The results show that a composite structure's optimum layup configuration is unique to the structure's geometry and material system. However, general trends are observed for these different systems, such as how symmetric and asymmetric constructions place the axial-resistant layers near the neutral plane of the composite system. In addition, both constructions need an increase in shear-resistance layers as the L/D ratio decreases regardless of the material system. Lastly, the analytical approach presented in this work can be used to accurately determine the optimum layup angle for thin composite cylindrical structures that are subjected to external hydrostatic pressure.

A dynamic quantitative risk assessment method for drilling well control by integrating multi types of risk factors

Drilling well control is complex and dynamic with high uncertainty because of the complicated geological conditions and operational environments. Until now, quantitative risk assessment on drilling well control is not integrating human errors, equipment failure, and internal mechanisms together. To address the research gap, this paper presents a novel dynamic quantitative risk assessment method for drilling well control by integrating multi types of risk factors. The entire dynamic Bayesian network is composed of models of human factors, mechanical factors, and environmental factors. The presented method is demonstrated by a case of well section. The dynamic characteristics of the overall risk and individual risks caused by different types of factors are obtained. The influences of human, mechanical and environmental factors on drilling well control risk are researched. It shows that environmental factors have the highest influence on the whole drilling well control risk in Breccia formation. The parameters uncertainty analysis on collapse pressure and fracture pressure of three different rock formations are carried out. It is found out that in-situ stresses have the highest influence on the collapse and fracture pressure.

Mesoscopic modeling of vapor cavitation bubbles collapse and interaction in near-wall region with a pseudopotential lattice Boltzmann method

A multi-relaxation-time pseudopotential lattice Boltzmann (LB) model was developed to simulate multiphase flow with a large density ratio (1000) and wide viscosity ratio (15), which are highly close to the realistic cavitation phenomenon. The model is validated by Laplace law and is implemented to simulate the collapse process of single and multiple cavitation bubbles. The simulation results are in accordance with the experimental results. By comparing to other LB models and numerical methods, the stability and superiority of the present model are morphologically demonstrated. The collapse pressure and the impact jet velocity on the wall are investigated, and the jet velocity on the wall shows a typical bimodal distribution, while only one perk is observed on the pressure distribution for a single bubble collapse in near-wall region. Moreover, the results indicated that the wall–bubble distance has a greater influence on the wall pressure than the bubble–bubble distance for double bubble interactions. Finally, the simulation of the bubble cluster indicated that the inner bubble has stronger collapse intensity than the outer layer bubble, while the side bubble collapse intensity is stronger than the corner bubbles. The simulation of a series of cases proves that the proposed model is a reliable tool to investigate realistic cavitation bubble dynamics.

Analysis of the Wall Force on the Bubble Collapse of the Benzamide Based on Molecular Dynamics Simulation

The cavitation damage of the pollutant wall caused by shock wave and microjet in the process of bubble collapse has attracted widespread attention from scholars. However, many researches focus on bubble collapse from the macroscopic experimental point of view, the dynamics of which is still not clear. In this paper, it constructs bubbles with different radii, runs different models under different compressive strain rates, takes the pressure on the upper and lower walls of pollutants as the research target, and summarizes the influence of compressive strain rates, initial radius of bubbles and temperatures on the release pressure of bubble collapse on the pollutant wall. The results show that: as the initial radius of bubbles increase, the maximum pressure on the upper and lower walls of benzamide increases first and then decreases. The pressure release rate of bubble increases with the increase of the compressive strain rate. Based on the pressure on the upper and lower wall surfaces of the benzamide, the temperature and initial radius of the bubble have a large influence, and the influence of the compressive strain rate is small. Under the simulation conditions of the paper, when bubble collapse is used to release energy to treat pollutants, the recommended bubble radius is 10-15 Å. The paper not only reveals the influence of the initial radius of the bubble, the compressive strain rate and the temperature on the pressure released by the bubble collapse on the pollutant wall, but also provides theoretical guidance for the application of cavitation.

LBM study of ice nucleation induced by the collapse of cavitation bubbles

In this study, we extended the conventional lattice Boltzmann method (LBM) to numerically examine ice nucleation induced by the collapse of a cavitation bubble. Specifically, a pseudo-potential multi-relaxation-time lattice Boltzmann method (MRT-LBM) coupled with a thermal LBM and a criterion for pressure-dependent ice nucleation onset was developed to investigate the cavitation bubble dynamics including growth and collapse, and the subsequently induced ice nucleation. Using the present model, the water vapour-liquid coexistence curve was extended to temperatures lower than 42% of its critical point, excellently matching the Maxwell construction curve. Two practical application scenarios of ice nucleation were investigated: I, near a solid boundary and II, within a pressurised space. Effects of key system parameters including the stand-off distance (λ), differential pressure (Δp) and initial bubble size (R0) on the maximum collapse pressure (pmax) were examined. The results show that under the same conditions, a much higher pmax is generated in scenario II than that in scenario I, thus more readily initialises ice nucleation. After initialisation, part of the initially formed ice melts when the local temperature exceeds the ice melting temperature due to the rapid dissipation of pressure wave. To ensure the complete freezing of water, a large initial supercooling is required for scenario II.

Experimental and numerical studies on collapse of subsea pipelines with interacting corrosion defects

The pipeline is prone to collapse under the combined external pressure and multiple corrosion defects. Experiments of the full-scale pipelines with longitudinally, circumferentially and diagonally dual defects are conducted, respectively. Finite element models are established to simulate the experimental process, and achieved good consistency. Then the influences of corrosion defect dimensions on the interaction are analyzed, and the corresponding critical spacing is determined. Moreover, the collapse modes of the pipeline under different defect forms are studied. The collapse mode of the pipeline with two external corrosion defects changes from U-shaped to ∞-shaped mode. However, the collapse modes for the pipeline with internal and external corrosion defects or two internal corrosion defects are irregular and the deformation is mainly concentrated on the region of corrosion defects. In addition, the critical pressure of the pipeline is sensitive to the defect distribution type (distributed axially, circumferentially, or diagonally along the pipeline, etc.). Finally, a formula for estimating the collapse pressure of the pipeline with dual corrosion defects is proposed. The comparison between the proposed formula and finite element results proves that this formula can be used for the collapse pressure of the pipeline with multiple corrosion defects in a slightly conservative manner.

Effect of Ester Moiety on Structural Properties of Binary Mixed Monolayers of Alpha-Tocopherol Derivatives with DPPC.

Phospholipid membranes are ubiquitous components of cells involved in physiological processes; thus, knowledge regarding their interactions with other molecules, including tocopherol ester derivatives, is of great importance. The surface pressure–area isotherms of pure α-tocopherol (Toc) and its derivatives (oxalate (OT), malonate (MT), succinate (ST), and carbo analog (CT)) were studied in Langmuir monolayers in order to evaluate phase formation, compressibility, packing, and ordering. The isotherms and compressibility results indicate that, under pressure, the ester derivatives and CT are able to form two-dimensional liquid-condensed (LC) ordered structures with collapse pressures ranging from 27 mN/m for CT to 44 mN/m for OT. Next, the effect of length of ester moiety on the surface behavior of DPPC/Toc derivatives’ binary monolayers at air–water interface was investigated. The average molecular area, elastic modulus, compressibility, and miscibility were calculated as a function of molar fraction of derivatives. Increasing the presence of Toc derivatives in DPPC monolayer induces expansion of isotherms, increased monolayer elasticity, interrupted packing, and lowered ordering in monolayer, leading to its fluidization. Decreasing collapse pressure with increasing molar ratio of derivatives indicates on the miscibility of Toc esters in DPPC monolayer. The interactions between components were analyzed using additivity rule and thermodynamic calculations of excess and total Gibbs energy of mixing. Calculated excess area and Gibbs energy indicated repulsion between components, confirming their partial mixing. In summary, the mechanism of the observed phenomena is mainly connected with interactions of ionized carboxyl groups of ester moieties with DPPC headgroup moieties where formed conformations perturb alignment of acyl chains, resulting in increasing mean area per molecule, leading to disordering and fluidization of mixed monolayer.

Study on Wellbore Stability Evaluation Method of New Drilled Well in Old Reservoir

The borehole wall stability of depleted reservoirs is a key problem that restricts the deeper potential exploitation of old oilfields. Based on these, according to the seepage and elastic mechanics theory of porous media, combined with laboratory rock mechanics experiments, the dynamic evaluation model of geomechanical parameters of the old reservoir is established, and on this basis, the evaluation method of wellbore stability of new wells in the old reservoir is established, and the changing laws and influencing factors of the wellbore stability of the old reservoir are quantitatively evaluated. The research shows that reservoir pressure, reservoir porosity, effective stress coefficient, strength, in situ magnitude, and direction were all changed due to long-term exploitation; both collapse and fracture pressure decreased, the loss risk of drilling fluid was increased, and safe drilling azimuth was changed. The results can guide reasonable choices such as well position, track and mud density, and strengthening sealing while drilling in order to ensure wellbore stability effectively.

Meta-modelling the climate of dry tide-locked rocky planets

Context. Rocky planets hosted by close-in extrasolar systems are likely to be tidally locked in 1:1 spin-orbit resonance, a configuration where they exhibit a permanent dayside and nightside. Because of the resulting day-night temperature gradient, the climate and large-scale circulation of these planets are strongly determined by their atmospheric stability against collapse, which designates the runaway condensation of greenhouse gases on the nightside. Aims. To better constrain the surface conditions and climatic regime of rocky extrasolar planets located in the habitable zone of their host star, it is therefore crucial to elucidate the mechanisms that govern the day-night heat redistribution. Methods. As a first attempt to bridge the gap between multiple modelling approaches ranging from simplified analytical greenhouse models to sophisticated 3D general circulation models (GCMs), we developed a general circulation meta-model (GCMM) able to reproduce the closed-form solutions obtained in earlier studies, the numerical solutions obtained from GCM simulations, and solutions provided by intermediate models, assuming the slow rotator approximation. We used this approach to characterise the atmospheric stability of Earth-sized rocky planets with dry atmospheres containing CO2, and we benchmarked it against 3D GCM simulations using the THOR GCM. Results. We observe that the collapse pressure below which collapse occurs can vary by ~40% around the value predicted by analytical scaling laws depending on the mechanisms taken into account among radiative transfer, atmospheric dynamics, and turbulent diffusion. Particularly, we find (i) that the turbulent diffusion taking place in the dayside planetary boundary layer (PBL) globally tends to warm up the nightside surface hemisphere except in the transition zone between optically thin and optically thick regimes, (ii) that the PBL also significantly affects the day-night advection timescale, and (iii) that the slow rotator approximation holds from the moment that the normalised equatorial Rossby deformation radius is greater than 2.

Investigations on the role of ionic liquid on the physicochemical characteristics and toxicological consequences of liposomes

Effect of 1-butyl-3-methylimidazolium chloride ionic liquid ([bmim]Cl, IL) on the monolayer/bilayer of either soy-phosphatidylcholine (SPC) or hydrogenated soy-phosphatidylcholine (HSPC), in combination with 30 ​mol% cholesterol (Chol), were investigated. Impact of IL on monolayers were explored by measuring the surface pressure (π)-area (A) isotherm with a Langmuir-surface balance. Lift-off area (A0) of the monomolecular films gradually increased [A0(HSPC+IL) ​> ​A0(SPC+IL)], collapse pressures (πc) decreased and passed through minima [πc(HSPC+IL) ​> ​πc(SPC+IL)] with increasing IL concentration ([IL]). Minimum molecular area (Amin) increased monotonously and compression moduli (Cs−1) followed the sequence (HSPC+IL) ​> ​(SPC+IL) at a particular π with respect to [IL]. Dynamic light scattering studies were carried out to determine the hydrodynamic diameter (dh), zeta potential (Z.P.) and polydispersity index (PDI) values while fluorescence anisotropy studies, using 7-hydroxycoumarin and 1,6-diphenyl-1,3,5-hexatriene, could reveal the micro-viscosity of liposomes. Increased size and rigidity, induced by IL, suggest the formation of leak-proof, condensed liposomes. Disruption of vesicles induced by IL were observed from transmission electron microscopic (TEM) studies. IL induced disintegration of liposome and kinetics of subsequent formation of adsorbed monolayer were accomplished by surface pressure-time isotherms. IL-induced liposomes were substantially less toxic as revealed by MTT assay. These liposomes are considered to be safely used as effective and controlled drug delivery systems.

Geological Considerations Related to Casing setting depth selection and design of Iraqi oil wells (case study)

Well integrity is a vital feature that should be upheld into the lifespan of the well, and one constituent of which casing, necessity to be capable to endure all the interior and outside loads. The casing, through its two basic essentials: casing design and casing depth adjustment, are fundamental to a unique wellbore that plays an important role in well integrity. Casing set depths are determined based on fracturing pressure and pore pressure in the well and can usually be obtained from well-specific information. Based on the analyzes using the improved techniques in this study, the following special proposition can be projected: The selection of the first class and materials must be done correctly and accurately in accordance with the depth of casing preparation and the strategy in the considered field that must be taken into account definitely in the drilling and completion period, nevertheless correspondingly in production and upkeep, conversion to an injection well or the opposite, the plug in addition to the closing stage. Features that control the depth of the casing seat have been studied, which consist of fracture gradient, pore pressure with other issues are the surviving lithology's of rocks. Subsequently defining the casing seat can be sustained with an investigation of the determination of the suitable drilling fluid. According to the consequences of the fracture pressure and pore pressure investigation and the findings of casing setting depth by means of the bottom-up technique, the consequences are gotten to each casing for the 4 studied wells. reference point designed from the rotating table RT. For well A, the conductor casing depth is 47m, the casing surface depth is 533m, the intermediate casing setting depth is 1882 m. Finally, for the production casing depth is 3441 m. Compared to the collapse pressure method, it was found that the bottom-up method gave results that are close and similar to the real results. The results of other wells are included in the search consequences

Study on Rock Mechanics and Wellbore Stability of Igneous Formation in the Shunbei Area.

While drilling into the igneous rock formations of the Shunbei area, problems such as loss of well circulation and borehole collapse occur frequently, seriously hindering the efficient development of oil and gas resources. Aiming to solve this problem, the physicochemical and mechanical properties of igneous rocks are studied through a series of laboratory tests to determine the main factors influencing formation collapse and instability. In addition to the laboratory results, the weak plane effect of fracture mechanics, the seepage effect of drilling fluid, and the hydration effect of the drilling fluid on the borehole wall stability of igneous rock formations are evaluated and analyzed by establishing a mathematical model. The results show that the microfractures in the igneous rock are relatively developed and can be divided into unfilled fractures and calcite-filled fractures. The mechanical strength of the matrix igneous rock is higher than that of the rock samples with microfractures. The compressive strength of calcite-filled and unfilled fracture samples is 1/3–1/4 that of matrix igneous rocks, and immersion in the drilling fluid has little influence on the mechanical strength of igneous rocks. The fracture weak plane effect has the greatest influence on wellbore stability. With the increase of the number of fractures at different angles, the collapse pressure equivalent density of the formation subject to the mechanical weak plane effect increases by 21% compared with that of the homogeneous formation without fractures. The seepage effect of the drilling fluid on borehole stability is secondary, and the equivalent density of the formation collapse pressure increases by 11%. Because of the low content of clay minerals, the hydration effect of the drilling fluid on borehole stability was minimal and the equivalent density of collapse pressure increased by only 2%. During the drilling process, considering the weak plane effect of the microfractures and the seepage effect of the drilling fluid, the drilling fluid density should be controlled at about 1.82 g/cm3. The effective plugging ability and rheological properties of the drilling fluid should be improved for the formation with microfractures. The research results can provide a theoretical basis for the safe and efficient development of igneous reservoirs.

Collapse of medium-thick-walled pipes with multi-oval defects under external pressure

For exploring the effect of axial factors of oval defect on pipes collapse, the FE model verified by experimental results is used to research the collapse response of medium-thick-walled pipes with multi-oval defects. The ultimate collapse mode of pipes is “dogbone” shape, whether the pipes with single or multi-oval defects in the axial direction or uniform oval pipes. The “dogbone” mode occurs in each maximum oval defect when oval defect spacing larger than 5 times the pipe diameter, while flip-flop mode when the defect deviation angle equals to 90°. Collapse pressure decreases as the oval defect or transition length increases; first increases and then decreases as the defect spacing increases; decreases as the difference of unequal ovality increases. The deviation angle between double oval defects can improve the anti-collapse pressure of pipes while increasing the number of oval defects has an almost negligible effect on collapse pressure. Improved collapse pressure formulas consider ovality and axial factors based on DNV specification formula are proposed to predict collapse pressure of pipes with single or multi-oval defects. The improved formulas show a correlate well with numerical and experimental results.

Prediction of Collapse Pressure of Submarine Pipelines in A Wide Range of Diameter-Thickness Ratio

Submarine pipelines play an important role in offshore oil and gas development. A touchy issue in pipeline design and application is how to avoid the local collapse of pipelines under external pressure. The pipe diameter-thickness ratio D/t is one of the key factors that determine the local critical collapse pressure of the submarine pipelines. Based on the pipeline collapse experiment and finite element simulation, this paper explores the pressure-bearing capacity of the pipeline under external pressure in a wide range of diameter-thickness ratio D/t. Some interesting and important phenomena have been observed and discussed. In the range of 16<D/t<80, both DNV specification and finite element simulation can predict the collapse pressure of pipeline quite well; in the range of 10<D/t<16, the DNV specification is conservative compared with the experimental results, while the finite element simulation results are slightly larger than the experimental results. Further parameter analysis shows that compared with thin-walled pipes, improving the material grade of thick-walled pipes has higher benefits, and for thin-walled pipes, the ovality f0 should be controlled even more. In addition, combining the results of finite element simulation and model experiment, an empirical formula of critical collapse pressure for thick-walled pipelines is proposed, which is used to correct the error of DNV specification in the range of 10<D/t<16.

Study of Wellbore Instability and Collapse Mechanism for a Layered Continental Shale Oil Horizontal Well

The shale oil horizontal wells in the Songliao Basin are affected by a lack of mature theories, technologies and experiences in the direction of wellbore stability. Wellbore collapse may occur, and in severe cases, the wellbore may be scrapped, resulting in huge economic losses. Therefore, aiming at addressing the above problems, rock mechanics experiments were carried out. Based on the theories of elasticity and rock mechanics, this paper considers not only the influence of the bedding plane, but also the influence of hydration on the strength weakening of the shale body and the bedding plane. The analysis shows that no matter under which in situ stress mechanism, the wellbore in the vertical well section is the most stable, and when the inclination angle is approximately 45°, the wellbore is most likely to be unstable. Changes in water content do not affect the most stable or unstable regions. Under the same conditions, the equivalent density of collapse pressure increases with the increase in water content. In addition, field examples are also analyzed to verify the accuracy of this model, which can provide a theoretical and technical basis for the safe construction of continental shale oil horizontal wells.

Study on the mechanism of anisotropic wellbore instability in continental shale in Songliao Basin

Wellbore instability is frequently encountered in the process of shale oil drilling. Due to the anisotropic strength characteristics of shale, most conventional models are not suitable for wellbore stability analysis in layered formation. In this paper, taking the continental shale in the north of Songliao Basin as the research object, the anisotropic elasticity and strength parameters of shale are measured experimentally. Based on pore elastic mechanics, an anisotropic wellbore stability model of layered shale is established, and the variation of collapse pressure under different formation conditions is analyzed. The results show that considering the elastic and strength anisotropy, the collapse pressure is the largest, and the influence of strength anisotropy is significantly greater than that of elastic anisotropy. The stability of horizontal wells drilled along the horizontal maximum principal stress is the optimal, followed by vertical wells and small angle directional wells. The actual drilling conditions of G101 well are basically consistent with the prediction results, which confirms the accuracy of the model. According to the traditional wellbore stability model, the equivalent density of collapse pressure in horizontal well section is 1.58 ~ 1.76 g/cm3. It is much lower than the collapse density of 1.86 g/cm3 calculated by the anisotropic model in this study. The findings of this study can help for better understanding of the mechanism of wellbore instability in horizontal wells in shale formations. The model can be used to guide the drilling engineering design of shale oil horizontal wells and reduce the losses caused by the instability of the wellbore.

The effect of eccentricity on the collapse behaviour of sandwich pipes

Sandwich pipes (SPs) with adequate strength performance and thermal insulation capacity have become an attractive choice for oil and gas transportation in deep water. The SP has a more complex structural configuration than the traditional single wall pipe. The fabrication process can induce eccentric behaviours of the pipe layers, influencing the external pressure resistance capacity. In this paper, a two-dimensional numerical model of eccentrical sandwich pipes under external pressure is developed using the finite element software ABAQUS. Experimental results are employed to calibrate the numerical models. The verified numerical model combined with a Python scripting program is employed to develop the parametric analysis models. The effects of geometric parameters, material properties, and interlayer friction coefficients with different eccentricities on the SP collapse behavior are investigated. The results show that eccentricity has a significant effect on the collapse of SPs. With the increase of eccentricity, the collapse pressure of SP decreases significantly. Based on the numerical simulations, the optimized design under different geometric parameters, material properties, and interlayer friction coefficients is proposed, reducing the eccentricity effect while optimizing the collapse strength of the sandwich pipe. The present results will support the design and engineering application of deepwater sandwich pipe structures.