Steel Catenary Riser

Steel catenary risers are an enabling technology for deepwater oil and gas production. A steel catenary riser consists of a steel pipeline suspended between the vessel and the seabed forming a catenary shape. Tools to analyse and design steel catenary risers show that the point where the steel catenary riser first touches the seabed, termed the touchdown point, has the highest stress and the greatest fatigue damage. Current understanding of pipe/soil interaction is limited and consequently
there is concern within the industry regarding the conservatism of the analysis. In particular, the implications of pipe/soil interaction for maximum stress and fatigue damage at the touchdown point are significant. To address these concerns, research has been conducted into the following areas:

• Steel catenary riser trenches – using video survey data from installed steel catenary risers to determine the shape of seabed trenches. A steel catenary riser trench profile has been developed for use in finite element analysis.

• Pipe/soil suction force – i.e. the bond that forms between the riser pipe and a clay seabed. Experiments have been conducted and a pipe/soil suction model developed for use in steel catenary riser analysis.

• Pipe/soil stiffness – test data from the CARISIMA and STRIDE JIPs has been examined and a series of soil stiffness models for static penetration, small and large displacements, and cyclic loading have been developed for use in finite element analysis programs.

• Closed form and finite element models of steel catenary risers were constructed to determine the effect of the soil on stress and fatigue damage at the touchdown point.

A finite element model of a representative steel catenary riser has been created and analysed using the seabed interaction models developed. The results show that the seabed trench, pipe/soil suction and soil stiffness have little effect on extreme stress in the steel catenary riser during normal operating conditions. However, pipe/soil suction is shown to have a large effect during slow drift motions where the stress in the riser at the touchdown point could double. The results from a closed form seabed model and finite element analysis show that the fatigue life of a steel catenary riser is sensitive to soil stiffness.If the soil stiffness used to model the seabed is too high the fatigue life may be underestimated; conversely, if the soil stiffness is too low the fatigue life may be over estimated.

Steel connections:1. CONNECTIONS IN STEEL STRUCTURES
2.  Connections are structural elements used for joining different members of a structural steel frame work.  Steel Structure is an assemblage of different member such as “BEAMS,COLUMNS” which are connected to one other, usually at member ends fastners,so that it shows a single composite unit.3.  Bolts  Weld ,4.  Connecting Plates  Connecting Angles, 5.  On the Basis of Connecting Medium.  According to the type of internal forces.  According to the type of structural Elements  According to the type of members joining, 6.  Riveted Connections  Bolted Connections, 7.  Welded Connections  Bolted-Welded Connections, 8.  Used for very long time.  Made up of: Round Ductile steel bar called shank. A head at one end The length of the rivet should sufficient to form the second head.  Design - very similar to bearing type of bolted connection.
9.  Heating of the rivet  Inserting it to an oversize hole pressure to the head.  Squeezing the plain End by Pneumatic driver Round head.  On Cooling Reduces in Length–Clamping Force
10.  The introduction of high strength structural bolts.  The labour costs associated with large riveting crews  The cost involved in careful inspection and removal of poorly installed rivets.  The high level of noise associated with driving rivets., 11.  Fastened Together primarily by Bolts.  Bolts may be loaded in: Tension Shear Both Tension & Shear  Threads of bolts under shear force: Excluded - Increased strength Included - Decreased stregth.
12.  Bearing type bolts  High strength friction grip bolts (HSFG) , 13.  The most common type is bearing bolts in clearance holes, often referred to as 1. Black Bolts  Ordinary, unfinished, rough, or common bolts.  Least Expensive  Primarily - Light structures under static load such as small trusses, purlins etc, 14. 2. Turned Bolts  Similar to unfinished bolts.  Shanks - Hexagonal Rods  Primarily - Light structures under static load such as small trusses, purlins etc  Expensive – Limited use – Structures with no Slippage Connections, 15. 3. Ribbed Bolts • Round head similar to Rivets. • Raised ribs parallel to the shank. • Actual Diameter - slightly Larger than the hole • Tightly fit into the hole. • Popular - Economical in Material & Installation, 16.  Uses when bearing type bolts slips under shear  High strength bolts (8G or 10K grade) Pre-tensioned against the plates to be bolted together so that contact pressure developed between the plates being joined  Prevents relative slip when extra shear is applied  Higher Shear Resistance., 17. Advantages 1. The bolting operation is very silent 2. Bolting is a cold process hence there is no risk of fire 3. Bolting operation is more quicker than riveting. 4. Less man power is required in making the connections. Disadvantages 1. If subjected to vibratory loads, results in reduction in strength get loosened. 2. Unfinished bolts have lesser strength because of non uniform diameter
18.  whose components are joined together primarily by welds. Welding Notations were developed by American Welding Society (AWS)., 19. • Groove ( More reliable than others)  Fillet (Mostly used, Weaker than groove and others)  Plug (expensive – poor transmission of tensile forces)  Slot (expensive - poor transmission of tensile forces)  Plug and Slot welds – stitch different parts of members together.
20.  Horizontal  Vertical  Overhead  Flat
21.  Economical – Cost of materials and labors.  Efficiency is 100% as compared to rivets (75- 90%)  Fabrication of Complex Structures – Easy – like Circular Steel pipes.  Provides Rigid Joints – Modern Practice is of Rigid Joints.,22.  No provision for expansion or contraction therefore greater chances of cracking.  Uneven heating and cooling - member may distort - may result in additional stresses.  Inspection is difficult and more costlier than rivets
23.  Most connections are Shop Welded and Field Bolted types.  More Cost Effective  Better Strength & Ductility characteristics –Fully welded.
24.  Shear (semi rigid, simple) connections  Moment (rigid) connections
25.  Allows the beam end to rotate without a significant restraint.  Transfers shear out of beam  Most Common Types: Double clip Shear End Plate Fin Plate
26.  Designed to resist both Moment and Shear.  Often referred - rigid or fully restrained connections • Provide full continuity between the connected members • Designed to carry the full factored moments.  Principal Reason - buildings has to resist the effect of lateral forces such as wind and earthquake.
27. Bolted splice Moment Connection Field Bolted Moment Connection, 28.  Single plate angle Connections  Double web angle connections  Top and seated angle connections  Seated beam connections
29. Two Step Process  A plate is welded to secondary section (beam)  An Angle is welded to Primary Section (column or Beam)  single shear plate welded to secondary beam and bolted to Primary beam or column.
30.  Two angles welded or shop bolted to the web of a secondary beam.  After erection the angles are bolted or site welded to the primary member (beam or column).
31.  Generally used in case of moment connections.  Two angles are provided at top and bottom of the beam to resist moment.  Generally used for lesser moments where heavy loads are not acting
32.  Generally used in case of shear connections.  A seating angle - at bottom of secondary beam - shop welded to the primary member.  Seating angle resists vertical shear coming from the beam.
33.  Beam to beam connections  Column to column connections (column splices)  Beam to Column Connections  Column Base Plate Connections
34. Two Types  Primary Beam to Secondary Beam Connection  Beam Splice
35.  Connects column to column.  Column splice comes under this category.  Used to connect column sections of different sizes.  Splices - designed for both moment and shear unless intended to utilize the splices as internal hinges.
36.  Connects Beam to column.  Very Common  A wide range of different types are used Fin Plates End Plates Web or Flange Cleats Hunched Connections
37.  Beams are normally attached using two or more bolts through the web. End plate connections  single plate welded to the end of the beams  Bolted to the column flange or web - two or bolts pair. Fin plate connections  Single Plate welded to the Column.  Beams are normally attached using two or more bolts through the web.
38.  Steel plates placed at the bottom of Columns.  Function - to transmit column loads to the concrete pedestal.  The design of a column base plate: determining the size of the plate. determining the thickness of the plate
39.  A layer of grout should be placed between the base plate and its support for the purpose of leveling.  Anchor bolts should be provided to stabilize the column during erection or to prevent uplift.
40.  R Usually cost of fabrication and erection constitute as high as 50% of the total cost of steel structures, per tones of material used
41. BY NAVEEN ANKUR SWARNAKAR & AJEET SHARMA

Resumen— En este artículo, se presenta un modelo para caracterizar la fuerza de reacción no lineal de un riser marino, basado en polinomios dependientes y afines a su posición y velocidad. La propuesta de este modelo está relacionada con la física del sistema, pero también con la factibilidad de obtener una representación del sistema específica para el diseño de un observador de estados, con miras a identificar los parámetros estructurales de un riser. La representación requerida es una forma conocida como afín a los estados, que aquí se propone obtener via la transformada de Liénard. Se presenta además, un análisis de observabilidad e identificabilidad, en el que se considera que para llevar a cabo la identificación sólo las mediciones de posición están disponibles. En resumen, en este trabajo se propone: (1) un modelo no lineal de parámetros distribuidos que puede utilizarse para fines de monitoreo, (2) la discretización espacial de tal modelo utilizando el Método de Diferencias Finitas, (3) la transformación del modelo finito a un sistema Liénard, (4) la representación—aproximación— de la fuerza de reacción no lineal, con polinomios en función de la posición y velocidad del riser, y (5) un análisis de observabilidad e identificabilidad previo a la concepción de un observador de estados.

With oil and gas reserves moving into deeper waters, Floating Production Units (FPUs) have been widely used for production purposes. Selection of a FPU for deepwater field development is mainly governed by factors such as water depth, location of field, environmental conditions, deck space requirements, storage requirements and offloading requirements etc. Amongst all the available FPU alternatives, ship shaped FPSO has dominated the concept selection and is generally used in marginal and remote fields lacking pipeline infrastructure. Selecting riser concept for FPSO stationed in deepwater has posed challenges due to high hydrostatic pressure and large vessel payload. The most common riser concepts for the aforementioned are free hanging flexible riser, Steel Catenary Riser (SCR) and Hybrid Riser Tower (HRT). The condition is worsened if besides deepwater, FPSO is also stationed in harsh environmental conditions. This is due to large offsets and dynamics of FPSO which are directly transferred to the riser's base. To cope up with this situation offshore industry has focused on concepts like Steel Lazy Wave Riser (SLWR), Single Hybrid Riser (SHR) and Buoyancy Supported Riser (BSR).

Cast-iron girders were used in many nineteenth century structures, especially in fireproof flooring systems (such as jack arches). Many such structures are still in use today and it is important that they fulfil the current requirements on fire resistance when there is a change of use. Cast iron has limited ductility so it is not possible for cast-iron beams to achieve total plasticity as for modern steel beams. Furthermore, cast iron has different mechanical properties in tension and compression and there is often a severe non-uniform temperature distribution in cast-iron beam sections. This paper presents the development of a simplified method to calculate the bending moment capacity of cast-iron beams in a jack arched system exposed to a standard ISO 834 fire. The method is based on an assumed strain distribution in the cross-section. A comparison of the results calculated using the simplified method with those using the fibre method, validated by Abaqus simulation results, indicates that the proposed simplified method is sufficiently accurate as the basis of a design method.

This work deals with the development of a systematic iterative approach to the analysis and design of LWR with the application of catenary theory. This could be useful in preliminary screening stage of selecting the best LWR configurations. To carry out the analysis and design, PTC Mathcad was used to develop the codes used to determine and plot the LWR configurations and perform parametric investigation of several key parameters (the effect of pipe size or diameter, effect of lengths (Si, Sj, Sk); effect of arch and/ or bend height; effect of internal fluid, effect of hang-off angle;    effect of water depth; effect of effective mass ratio, effect of platform offset etc. Two design input options are considered with respect to fig.1 OPTION 1: The hang-off catenary length (Si), the buoyancy catenary length (Sj), the touchdown catenary length (Sk) are specified whereas the hang-off angle (θ) is obtained iteratively by the developed codes using the water depth as a check criteria. OPTION 2: The sag bend height (Ys) and arch bend height (Ya) are specified whereas Si, Sj, and Sk are unknown. The hang-off angle (θ) is obtained iteratively by the developed codes using the horizontal span of the riser (H) as a check criteria. In both options, the water depth (WD) is specified a priori.