Engineered Products

Bending Stiffeners

BENDING STIFFENERSAPPLICATIONS

Dynamic flexible risers, power cables, flow lines, and umbilicals maybe connected to a rigid structure such as a subsea riser base or the turret exit of a floating production vessel.The existence of environmental loads will ultimately cause the 'riser' to flex about this fixed location.The flexing, in combination with large axial loads, may damage the riser structure due to excess bending and fatigue.To prevent structure damage due to excess bending, the riser end fitting may be supplied with an integral Bend Stiffener.This device, or BS as it is more commonly known, has a conical external profile with acentral hollow cylindrical section to allow it to slide over the end of the riser.Conically shaped stiffener add local stiffness to the 'riser' adjacent to a rigid connection to limit the bending stresses and curvature to acceptable levels.Each Stiffener is designed to protect the riser minimum bend radius (MBR) under the defined tension and angle combinations.Plastiprene designs each stiffener individually to meet the load cases of each particular application.Stiffeners can be specified as either static or dynamic, depending on their intended use.Static Stiffeners are designed primarily for protection during installation and overboarding.Dynamic Stiffeners are fully engineered solutions to protect umbilical or flexible pipelines in demanding applications where a long service life is required.

ANALYSIS

The preliminary and detailed design of the Bend Stiffener is completed using Plastiprene's proprietary finite element packages - STIFFENER and ORCABEND. These programs have been developed and customized by MCS and Orcina specifically for Plastiprene, based on their FLEXCOM 3-D and ORCAFLEX software packages, all recognized as market leading dynamic analysis software products throughout the offshore industry.These software packages generate a 2-D Finite Element Model of a Bend Stiffener to suit a particular set of design conditions, using a given set of properties for the Stiffener body material. The software predicts the performance of the Bend Stiffener when subject to a range of loadcase, temperatures etc., and also calculates the stress and strain within the stiffener. Another important output from the program is the bending moments and shear loads generated within the stiffener that need to be transferred into the rigid interfacing structure.A second software package known as SPOST.R is used to address the design of the metalic load transfer structure and any other interface structure required to connect the Stiffener The satisfactory performance of all the computer software packages used by Plastiprene has been verified by the use of the following:3-D Finite element analysis Static bend tests Dynamic bending testing

TESTINGTesting of Bend Stiffener can be divided into three main categories:Material Testing - to check if the properties of the polyurethane materials used in manufacturing match those used to model the Bend Stiffener in the designsoftware.Static Bend Testing - to verify that the actual Bend Stiffener deflects to the same shape predicted by the design software, under a given tension/angle loadcase.Dynamic Testing - to verify the performance of the Bend Stiffener in simulated in-service conditions, and

demonstrate fatigue life, etc.Over the last 5 years, Plastiprene has invested significantly into Research and Development and subsequent testing of a range of different polyurethane materials to suit a range of applications. Particular emphasis has been placed on behavior of materials at different temperatures, in seawater, in sunlight and under fatigue conditions.Plastiprene has an extensive track record for supplying large dynamic Bend Stiffener and conducting full-scale dynamic test programs to demonstrate their fatigue performance.Details of these test programs are as follows:

INTERFACE STRUTUCTUREPlastiprene has the in-house capability to design and manufacture a wide range of steel interface structures, to enable the Bend Stiffener to be connected to the adjacent rigid connection.These items often require complex interface engineering with riser suppliers, platform designers and installation contractors, all wishing to have an input into the design process to ensure ease of construction and installation and integrity in service.Plastiprene has expertise in designing and building such structures from simple adaptor plates to highly complex diverless pull-in connectors, and has the ability to generate detailed structural design and fatigue analyses of the complete Bend Stiffener system.

DESIGN AND ENGINEERINGPlastiprene has gathered a design and engineering team with significant technical know-how and experience gained over many

years in the offshore and oceanographic industries designing and installing flexible pipes, cables and umbilicals.This expertise is essential when working in close co-operation with clients to understand in detail the functional requirements of the Bend Stiffener, covering items such as:Operating conditionsInstallation constraintsInterface requirementsIn particular, defining operating conditions correctly is required before starting detailed engineering.The pertinent pieces of information required for the design of a Bend Stiffener include the following:Pipe diameterPipe MBRLoadcases (tension vs angle)Pipe stiffnessObtaining loadcase information can be very complex and require careful liaison with the pipe supplier and with system designers to ensure that the true worst case conditions are used in the design.After capturing all the design data required, it is then necessary to analyze the data, interpret the results, and consider any particular mechanical interfacing requirements in order to produce Bend Stiffener designed to suit the client's specification in the most cost effective way.

The stiffener body is made of molded polyurethane elastomer specifically developed, qualified and tested over many years.Plastiprene has a range of materials to suit different applications, all of which are extremely tough, durable and suitable for extended service in very arduous subsea and marine applications.The choice of polyurethane elastomer is based upon its low modulus and high elongation at break. A comparison between the stress vs. strain properties of steel and a typical polyurethane elastomer is illustrated in the graph below.Plastiprene has invested significantly in the development of new materials and qualification programs to demonstrate their suitability for use in such an application.The properties of polyurethane can be affected by a variety of both short-term and long-term factors and Plastiprene has conducted qualification testing to ascertain all of their effects, such as:Fatigue resistanceCreep resistanceTensile strengthTear resistanceTemperature dependencyAgeing in air and seawaterUV resistancePlastiprene is undoubtedly the world leader in the design and qualification of this type of polyurethane elastomer material.In order to transfer loads out of the polyurethane section of the Bend Stiffener, a steel interface structure is molded into the base of the conical section. This component is usually made of high strength structural grade carbon steel if an adjacent cathodic protection system is present, or alternatively from more exotic corrosion resistant materials.

MATERIALS

MANUFACTUREPlastiprene has over 20 years of experience in the manufacture of polyurethane products for the oil, gas and marine markets, and has harnessed this wealth of knowledge to ensure our place at the forefront of Bend Stiffener manufacture.The manufacturing process for Bend Stiffeners can be broken down into a number of key stages, as follows:Build a mold toolBuild a steel insert componentAssemble mold tool and insertPre-heat toolingInject polyurethane into moldCure cycleDemold and finishThis apparently simple process, however, includes a number of complex and demanding requirements.For example the mould tools must be heated prior to injection of polyurethane, requiring construction of an oven of large dimensions (up to 12m long) to house the assembled tool.

PLASTIPRENE PLÁSTICOS E ELASTÔMEROS INDUSTRIAIS LTDA

Alameda Itahim, 715 - Joapiranga Valinhos / SP - Brasil

Cep: 13278-510vendas@plastipreneoffshore.com

Phone: 55 (19) 3829-9999

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