Riser Weight Research Articles

Local tailored design of deep water composite risers subjected to burst, collapse and tension loads

There is an increasing demand for more sustainable and adaptable technologies in the offshore industry. Thus, composite structures are more frequently used in the industry. Secondly, the shift in offshore exploration from shallow to deep waters has necessitated advancements on more lightweight composite structures to minimise platform loads, ease fluid transport, and service, using conduit pipes like composite production risers (CPR). The properties of composites are harnessed to improve riser weight and strength performance as Composite risers. In this research, the local tailored design of deep water composite risers was subjected to burst, collapse, tension and combined loads. Three design methodologies are considered-conventional, local, and tailored designs for different configurations. The structure is made up of configurations having 17 layers, 18 layers, 19 layers, 20 layers and 21 layers. The numerical technique for the CPR model with 3 m section considered five loadings. The model was developed utilising ANSYS ACP to conduct the numerical stress analysis with parametric studies. From the design, it is recommended to consider liners like PA12 and include environmental loads from global design. This study presents the CPR behaviour. Since CPR structures are response-sensitive and fatigue-sensitive, the global dynamic analysis of full-length composite riser is recommended.

Behavior of unbonded flexible riser with composite armor layers under coupling loads

Unbonded flexible risers are widely applied in the field of ocean engineering due to their unique mechanical properties and composite materials have been introduced to reduce riser's weight. In this paper, the behavior of a typical 2.5-inch 8-layer unbonded flexible riser model with composite armor layers under coupling axisymmetric loads and bending moment is studied by theoretical and numerical methods. Firstly, considered the material and geometric properties, the bending model of composite armor layers is present according to its slipping stages; and a mathematical model that explains the effect of axisymmetric loads on the bending characteristics of unbonded flexible riser is proposed. Then, a numerical model with detailed geometric properties of unbonded flexible riser is established within ABAQUS software. After verified through experimental results by Witz (1996), the bending behavior and hysteresis phenomenon of the unbonded flexible riser with composite armor layers is conducted. Furthermore, several characteristics related to the bending properties, including external and internal pressures, axial tension, friction coefficient are discussed, and the axial and radial stress of composite tendon at different angle location is also present. The comparison results show that the effective tension would enhance the ability of unbonded flexible risers to resist bending moment.

Static Optimization of a Compliant Vertical Access Riser

The compliant vertical access riser (CVAR) is a new riser concept with good compliance; it can significantly reduce operating costs by eliminating the need for additional machines to operate wells directly on the platform. In this study, we determined the optimal riser parameters in terms of the stress and riser weight by optimizing the CVAR, and we compared the optimization results. A two-dimensional nonlinear static CVAR model was deduced according to the principles of virtual work and variation, and the model was verified using MATLAB. Design of experiments and Kriging method were used to reduce the number of sample calculations and improve the modeling accuracy. An appropriate selection of the multi-objective optimization problem (MOP) and the non-dominated sorting genetic algorithm helped to optimize the CVAR design. The non-dominated sorting genetic algorithm II was used to solve the Pareto frontier of the optimization model in order to provide decision makers with more choices for the optimization results. After optimizing the riser parameters, the geometry of the riser was smoother, and the stress and stress differences were greatly reduced; the maximum equivalent stresses at the top and bottom were reduced by 36.6% and 44%, respectively. In addition, the stress difference in the buoyancy block area was reduced by 20.9%, and the weight of the riser was increased significantly by 28.1%.

Increase of Liquid Metal Utilization during Production of Bearing Circle Castings for Cement Furnaces

In manufacture of super heavy castings for cement furnaces a saving of liquid metal has been achieved by lowering the riser weight. By solidification modelling with the aid of the Niyama criterion a zone in the riser was designated where the occurrence of foundry defects (shrinkage porosity) can be expected. A plate of the material of dimensions ca 700*800*250 mm was taken from the riser. After thermal treatment the samples for making the bars for the static tensile test were taken from it. Based on done tests it has been found out that mechanical characteristics obtained from the static tensile test correlate, besides contraction, in the chosen level of statistical importance of p = 0.01 with carbon content. Neither in the zone of probable occurrence of defects designated by the Niyama criterion during solidification modelling the drop of strength characteristics was observed. Carbon content in a decisive extent influenced the strength characteristics. In case of ductility and contraction the convenient correlations with carbon content were observed from the riser height of 200 mm only. In the height of 400 mm there was already considerable variation of values and some values were lower ones than is demanded by standards.

Global Static Instability of Risers

Global instability of risers depends on riser weight, internal and external fluid static pressure forces, tension exerted at the top of the riser, and boundary conditions. The purpose of this work is to study the effects of these factors on the stability boundaries of risers and specifically.(i) compare buckling loads for various boundary conditions; (ii) find the long-riser instability behavior from the asymptotics of the stability boundaries; (iii) find the short-riser instability behavior; (iv) analyze the relative effects of boundary conditions, weight, internal pressure, and bending rigidity on stability; (v) show the variation of the stability boundary shape with the order of the buckling mode; and (vi) compare the critical length at which risers in tension over their entire length may buckle due to internal pressure, for various boundary conditions.

アルミニウム合金鋳物の凝固過程図を用いたひけ欠陥の対策手法

Solidification state diagrams showing the movement of solidification fronts were constructed from multipoints temperature measurements in a casting to predict the anticipated locations of shrinkage together with the specific gravity distribution diagram. The prediction well agrees with the location of shrinkage porosities in practical castings. The solidification state diagrams of AC2B plate castings at solid fractions 0.75 and 1.0 are different from those at 0.25 and 0.5. The area in which coarse shrinkage porosities are formed corresponds to the area surrounded by a closesloop isochronic line in the solidification state diagram at the solid fraction 0.5. Enlargement of the riser neck is succesfully applicable to open the closed-loop line and to prevent the shrinkage porosities without changing the riser weight.

An Effective Tool for Monitoring Marine Risers

This acoustic ball-joint angle and azimuth indicator has proved, in deep water and in severe weather, that it can monitor reliably and directly the structural integrity of the riser. The knowledge it provides of the ball-joint angle can give the operator the confidence to delay or avoid disconnecting the riser without fear of adverse consequences. Introduction The two prime objectives of the riser are to provide a return path for drilling fluids and to guide tool assemblies in and out of the wellhead. Because of its important role in maintaining well control and its high initial cost, strong efforts are made to prevent overstress, excessive fatigue, and excessive internal wear. In the brief 16-year history of floating drilling, risers of various types have been used, with the most common and successful being the single-wall tensioned riser. Through improvements in design, construction, and operating technique, the single-wall tensioned riser system has been used successfully and with confidence in water depths up to 1,500 ft. In general, the riser system (Fig. 1) is composed of a hydraulic riser connector that fastens the riser to the blowout preventers (BOP's), a lower pivot point (ball joint) next to the riser hydraulic connector, a number of joints made of pipe with end connectors, a slip joint that allows vertical motion between the drilling vessel and the riser, a gimballed connection of the inner barrel of the slip joint and the vessel, and a means of applying tension to the riser. In deep water the addition of a ball joint below the slip joint can reduce riser stress and fatigue. There are a number of excellent papers on the prediction of the behavior of risers and on criteria prediction of the behavior of risers and on criteria for successful riser design. These papers all show that the forces resulting from wave action, current action, riser weight, drilling fluid density, horizontal offset of the fluid density, and horizontal offset of the top of the riser from the wellhead tend to increase riser stress and to deform the riser. These forces are resisted by tension applied at the upper end of the riser and in some cases by the addition of buoyant material to the riser. In general, available methods are used to calculate the tension that should be used with a given set of assumed maximum conditions. If the actual conditions are less stringent than the assumed conditions, the resulting tension causes unnecessary wear and reduces the life of the tensioning system. If actual conditions are more stringent than assumed conditions and the tension is not increased accordingly, overstress, excessive fatigue, or excessive internal wear may result. Riser operations are particularly vulnerable to unfavorable changes in ocean particularly vulnerable to unfavorable changes in ocean current profiles, which are difficult to measure, especially during critical times. Studies based on the calculational methods described by Tidwell and Ilfrey showed that the angle of the riser with the vertical at the lower ball joint is directly related to the maximum stress in the riser. In essence, the angle of the ball joint shows the net effect of all the forces acting on the riser. For a given riser operating under a given set of conditions the angle of the lower ball joint is related to vessel offset and applied tension. Therefore, if that angle and its azimuth could be continuously monitored, the angle could be controlled by manipulating vessel offset and applied riser tension so as to minimize riser stress, fatigue, and internal wear. JPT P. 337