ROV remotely operated vehicle SF safety factor SMYS specified minimum yield strength TDR time-domain reflectometry TVE true volumetric expansion U0 rated power-frequency voltage between
Terms and Definitions
For the purposes of this document, the following terms and definitions apply
Accidental loads refer to the forces that an umbilical may experience due to unplanned activities, which can arise from abnormal conditions, improper operation, or technical failures as specified by the purchaser.
Minimum radius to which an umbilical, at a given tension, may be bent to without infringing design criteria or suffering loss of performance
NOTE 1 The bend radius is measured to the centerline of the umbilical
NOTE 2 Allowable bend radius increases with increasing tensile load and varies depending on internal pressure and condition, i.e safety level
NOTE 3 Increasing the level of safety generally increases the allowable bend radius and decreases the allowable tensile load, i.e moves the capacity curves toward origin
NOTE 4 Increasing the internal pressure generally increases the allowable bend radius and decreases the allowable tensile load, i.e moves the capacity curves toward origin
X inverse of the normalized bend radius, MBR per radius
Y normalized allowable tensile load, tension
1 maximum tensile load, with, no bending
2 increasing pressure and/or increasing safety level
3 inverse of minimum bend radius (MBR) with no tension
Maximum tensile load that an umbilical, at a given bend radius, can be loaded to without infringing design criteria or suffering loss of performance
NOTE Allowable tensile load decreases with decreasing bend radius and varies depending on internal pressure and condition, i.e safety level
Accessory to the umbilical system that does not form part of the main functional purpose
EXAMPLES Weak link, buoyancy attachments, I-tube or J-tube seals, VIV strakes, centralizers, anchors, external clamps
Device for limiting the bend radius of the umbilical by mechanical means
NOTE 1 A bend restrictor typically is comprised of a series of interlocking metallic or molded rings, applied over the umbilical
NOTE 2 It is sometimes referred to as a bend limiter
Device for providing a localized increase in bending stiffness, preserving the minimum bend radius of the umbilical under defined bending moment conditions
NOTE The stiffener is usually a molded device, sometimes reinforced, depending on the required duty, applied over the umbilical It is sometimes referred to as a bend strain reliever (BSR)
Phenomenon whereby armor wires locally rearrange with an increase and/or decrease in pitch-circle diameter as a result of accumulated axial and radial stresses in the armor layer(s)
Laid-up functional components and associated fillers in the umbilical prior to further processing
NOTE Typical functional components in a bundle include hoses, tubes, electric cables, optical fiber cables
Curve that defines the relationship between the allowable curvature and allowable tension for an internal pressure condition
NOTE Curves can, therefore, differ for storage, testing, installation, and operation scenarios
Storage container that can be rotated by a drive about a vertical axis
A device known as a caterpillar, also referred to as an in-line cable engine, haul-off, or tensioner, serves to hold the umbilical between belts or pads while transferring axial linear motive power to the umbilical.
Data relating to a component or an umbilical giving an indication of performance but not giving specific acceptance/rejection criteria
Type of gripper used to hold the umbilical via its outer diameter, comprised of a number of spirally interwoven wires or synthetic rope attached to a built-in anchorage arrangement
Generic term used to describe an individual electrically insulated conductor
Installation deployment activity whereby the installation vessel moves sideways along, or at the end of, the installation route
Load that acts in the radial direction that might not be evenly distributed along the circumference and that is limited in length along the umbilical
NOTE A crushing load is typically induced during installation
Water depth generally ranging from 610 m (2000 ft) to 1830 m (6000 ft)
Service life multiplied by an appropriate factor that is equal to, or greater than, one
Maximum pressure at which a hose or tube is rated
Maximum tensile load multiplied by an appropriate factor that is equal to, or less than, one
Analysis of an umbilical system that will be subject to dynamic excitation during installation or operation to ensure that the system is designed, installed, and operated safely and reliably
Time-dependent excitation applied while in service
A mechanical fitting is connected to the end of an umbilical, facilitating the transfer of installation and operational loads, along with fluid and electrical services, to a corresponding assembly on either a subsea or surface facility.
Load induced by external forces caused directly or indirectly by all environmental parameters acting on the umbilical, including those induced by waves, currents, winds, and vessel motion
Series of tests carried out on the completed umbilical component or complete umbilical to demonstrate the integrity of the item under test
An item that fills the gaps between functional components serves multiple purposes, including maintaining their relative positions, preserving the cross-sectional shape, influencing the weight-to-diameter ratio, separating components to reduce wear, and providing specific radial stiffness.
Hoses, tubes, and electric/optical fiber cables included within an umbilical that are required to fulfill the operational service needs
The umbilical experiences various loads throughout its lifecycle, including those encountered during manufacturing, installation, and operation, as well as loads present in still water, excluding wind, wave, or current influences.
Document that specifies the features, characteristics, process conditions, boundaries, and exclusions defining the performance of a product or service, including quality assurance requirements
Type of thermoplastic hose that contains a feature that enables it to resist collapse at greater water depths than a thermoplastic hose of equivalent bore and pressure rating
Fixed or floating facility to which the umbilical is mechanically and functionally connected and that provides the functions and services transmitted through the umbilical
EXAMPLES Platform, buoy, floating production system
Gel material applied inside the tube (metal or polymer) holding the optical fiber to absorb hydrogen ions that prevent the fiber from “darkening” and from reducing transmission capabilities
Operation of helically assembling (SZ where appropriate) electrical cores or optical fibers into a cable , or hoses, tubes, electric cables, and optical fiber cables, into a bundle or sub-bundle
NOTE Sometimes referred to as “cabling.”
Angle between the axis of a spiral-wound element (e.g armor wires) and a line parallel to the longitudinal axis of the umbilical
The transfer of an umbilical system from a storage facility to an installation or shipping vessel can be accomplished through transfer spooling or by lifting the product directly from its storage reel.
Electrical cable with extruded solid insulation for rated voltages up to 1.8/3 (3.6) kV (AC) for use in subsea umbilical applications
Specification for the umbilical, the umbilical components, and their manufacture, generated by the manufacturer in compliance with requirements specified by the purchaser and this document
NOTE The specification may be comprised of a multiplicity of documents (design plan, inspection and test plan, test procedures, etc.)
Maximum axial load an umbilical, with zero curvature, can withstand without infringing the stress criterion or suffering loss of performance
Electrical cable with extruded solid insulation for rated voltages from 3.6/6 (7.2) kV up to 18/30 (36) kV (AC) for use in subsea umbilical applications
A device is installed or pre-fitted into an I-tube or J-tube to facilitate the transfer of the primary pulling device, typically a wire rope, into the tube This setup enables the effective pulling of an umbilical through the tube.
Data describing meteorological, environmental, and oceanographic conditions for a particular offshore area
NOTE At a minimum, metocean data typically include information on wind, waves, currents, tides, temperatures (air and seawater), and sea ice
Minimum radius to which an umbilical, at zero tensile load, can be bent to without infringing the stress criterion or suffering loss of performance
Separate length of an umbilical or component manufactured prior to the main production for which the intention is to perform qualification testing
A device is utilized to terminate the end of an umbilical, enabling it to be efficiently loaded or offloaded from a vessel This device also facilitates the umbilical's movement along the seabed and through I-tubes or J-tubes.
In certain designs, terminated armors serve as anchors for the umbilical at the top of I-tubes or J-tubes These armors typically consist of a streamlined cylindrical housing that encloses the terminated umbilical armoring and the ends of its functional components They are designed for quick disassembly, allowing easy access for post-pull-in tests and monitoring Additionally, a pull-in head may be utilized at the subsea end of the umbilical.
Activity undertaken to prove that a prototype umbilical component or prototype umbilical can withstand the manufacturing process and that the design requirements for the component or umbilical have been fulfilled
Device for storing, transporting, or installing umbilicals or components comprised of two flanges, separated by a barrel, with the barrel axis normally being horizontal
NOTE Reels are designed for the intended use
Specified time during which the umbilical system is capable of meeting the functional requirements
Data obtained by plotting cyclic stress level versus number of cycles to failure
To join together component lengths or sub-components to achieve the required production length
Application for which the load effect(s) due to dynamic loads (e.g wave action, induced vibrations, etc.) when installed can be neglected
NOTE Free spans, in an otherwise static umbilical, should be treated as a dynamic application
Mechanism that forms the transition between the umbilical and the subsea termination
NOTE 1 The interface is comprised typically of an umbilical armor termination and/or a mechanical anchoring device for the tubes, bend stiffener/limiter, and tube or hose-end fittings
NOTE 2 If the umbilical contains electric cables/fiber optics, penetrator(s) and/or connectors may also be incorporated
Mechanism for mechanically, electrically, optically, and/or hydraulically connecting an umbilical or jumper bundle to a subsea system
Structural layer consisting of, for example, steel wires, fiber-reinforced plastic rods, etc., that is used to sustain tensile loads in the umbilical
NOTE For some applications, the tensile armor may also have the additional function of providing added weight and/or impact protection
Cylindrical single-point mooring system geostationary with the seabed, allowing rotation of the vessel in response to environmental conditions
Load at which the weakest component of the umbilical bundle fails when the axial load is applied with the umbilical in a straight condition
Water depths exceeding 1830 m (6000 ft) that can necessitate the consideration of design and/or technology alternatives
A collection of functional components, including electric cables, optical fiber cables, hoses, and tubes, are often bundled together to deliver essential services such as hydraulics, fluid injection, power, and communication.
NOTE Other elements or armoring may be included for strength, protection, or weight considerations
Means of joining together two lengths of umbilical to effect a repair or to achieve the required production length.
Umbilical, complete with end terminations and other ancillary equipment
A non-degraded umbilical sample refers to a component that has not experienced any operational or installation loadings, stresses, elevated temperatures, or other conditions that could lead to its degradation.
EXAMPLES Electric cables, hoses, tubes, and optical fibers
Activity undertaken to document that an umbilical component or manufactured umbilical meets the specified design requirements or predicted properties
Device that is used to ensure that the umbilical parts or severs at a specified load and location.
Abbreviated Terms
DP design pressure (mathematical symbol: DP)
ID inside diameter (mathematical symbol: d)
MBR minimum bending radius at zero tensile load
OD outside diameter (mathematical symbol: D)
OTDR optical time-domain reflectometer/reflectometry
SMYS specified minimum yield strength
U 0 rated power-frequency voltage between conductor and earth or metallic screen, for which the cable is designed
U rated power-frequency voltage between conductors, for which the cable is designed
U m maximum value of the “highest system voltage” for which the equipment may be used (See IEC 60038)
WT wall thickness (mathematical symbol: t)
General Requirements
The umbilical and its components must meet several essential characteristics: they should withstand specified design loads and perform effectively throughout their design life, operate within designated temperature ranges, and be made from materials compatible with their environment, including permeating fluids, while adhering to corrosion control standards Additionally, if applicable, they must include electric cables for power and signal transmission, optical fibers for specific wavelengths, and hoses or tubes for fluid conveyance at required flow rates and pressures The system should also allow for controlled venting if permeation occurs, and be installable and recoverable according to the manufacturer's specifications For dynamic umbilicals, the dynamic section must be constructed as a single continuous length.
End Terminations and Ancillary Equipment
End terminations and ancillary equipment must meet the same functional requirements as the umbilical They should provide a structural interface with the support structure and, if applicable, with bend restrictors or stiffeners It is essential that these terminations do not compromise the umbilical's service life or system performance Additionally, cathodic protection must align with the design life requirements, and any contingency or planned recovery during installation should not affect the umbilical's longevity or performance Finally, the materials used in end terminations must be compatible with any fluids they may encounter, including considerations for potential permeation.
Project-specific Requirements
The purchaser shall specify the functional requirements for the umbilical
Manufacturers must specify functional requirements that are not explicitly required or specified by the purchaser but could influence the design, materials, manufacturing, testing, installation, and operation of the umbilical If a purchaser does not outline a requirement and its absence does not impact these activities, the manufacturer can assume that no such requirement exists.
NOTE 2 An example of a project functional specification can be found in Annex B
5 Safety, Design, and Testing Philosophy
Application
Section 5 shall apply to umbilical systems, including umbilicals, terminations, and auxiliary equipment that are built in accordance with this document.
Safety Objective
An overall safety objective shall be established, planned, and implemented, covering all phases from conceptual development until retrieval or abandonment
Companies establish policies addressing human and environmental concerns, which serve as a foundation for more specific objectives and requirements These overarching policies are essential for defining safety objectives related to particular umbilical systems.
Systematic Review
A comprehensive review will be conducted across all phases, including manufacturing, load-out, installation, and operation, to assess the impacts of individual and multiple failures in the umbilical system, enabling the implementation of essential corrective actions.
The operator shall determine the extent of risk assessments and the risk assessment methods, and it should be the operator's responsibility to perform the systematic review
NOTE The consequences include consequences of such events for people, environment, subsea system, and financial interests.
Fundamental Requirements
The fundamental requirements for materials and products include adherence to specified guidelines, ensuring adequate supervision and quality control during manufacturing, and employing skilled personnel for all operations Proper maintenance of the umbilical, including inspections, is essential, along with compliance with design and operational manuals Design reviews must involve all relevant disciplines to address potential issues, and verification processes should confirm adherence to both purchaser requirements and applicable regulations Manufacturers are required to provide an inspection and test plan detailing quality control measures and oversight of sub-supplier activities, ensuring thorough compliance throughout all phases of production.
Equipment produced under this document must adhere to a certified quality assurance program The manufacturer is required to create detailed written specifications outlining the implementation of the quality assurance program.
Design Philosophy
The umbilical system must be designed to meet specific functional and operational requirements, ensuring that unintended events do not lead to more severe accidents It should allow for easy installation, retrieval, and reinstallation while being robust in use Adequate access for maintenance and repairs is essential, and the design must consider the impacts of corrosion, aging, erosion, and wear A conservative approach should guide the design of mechanical components, with redundancy for critical elements being a consideration.
A design basis document must be created during the early stages of the design process, encompassing all essential information for the umbilical system's design This document typically includes specifications provided by the purchaser, such as functional requirements and relevant field and host data Additionally, it outlines procedures for load-effect analyses of the umbilical and its components, along with load-case matrices that address various conditions, including temporary, installation, extreme, and fatigue scenarios.
Testing
This document categorizes all tests into three types: qualification, verification, and acceptance testing The chosen testing methodology must be mutually agreed upon by the purchaser and manufacturer, considering the associated risks of the intended application and the feasibility of the testing program within the project timeline.
See B.2.9 for guidance on the responsibility of identifying the need for qualification testing Guidance on the recommended testing program is given in Annex D and Annex J
Qualification testing is essential for verifying that a prototype component or umbilical can endure the intended manufacturing processes, environmental conditions, and loads This testing ensures that the component possesses the predicted properties and is not limited to new designs The selection of a testing philosophy is influenced by the purchaser's risk profile and the manufacturer's design and testing history, indicating either high project risk or a low willingness to accept risk from the purchaser.
Qualification testing for umbilicals and components involving new technology or high risk must adhere to a structured methodology outlined in the manufacturer's specifications, DNV RP-A203, or an equivalent standard.
The manufacturer must maintain a documented history of qualification testing and assess its necessity The purchaser is responsible for approving the evaluation of existing data and the scope of qualification testing.
Qualification testing is essential when there is a lack of relevant track record or test data for the specific umbilical design, component, or environment.
When a new component is introduced that influences the overall properties of the umbilical, it is essential to conduct qualification testing on the entire umbilical system, rather than just the individual component.
Analysis is essential for comparing umbilical and component designs, as well as evaluating the significance of data from prior testing and operational experiences Any such analysis must adhere to the requirements outlined in this document (refer to Section 6).
Unless otherwise agreed, all qualification testing shall be performed prior to manufacture of the umbilical
Qualification testing should also be considered for the end terminations, midline connectors, and ancillary equipment, if applicable
Verification tests shall include end terminations, midline connectors, and ancillary equipment
The scope of verification testing shall be specified by the purchaser based on the purchaser's risk profile and the manufacturer's design/testing statistics (see B.2.9)
NOTE Guidance on the possible testing program is given in Annex D and Annex J
Factory acceptance testing is essential to verify that the umbilical or its components align with the design values and criteria specified by the purchaser This process ensures that the tested samples accurately represent the manufactured components, as outlined in the design basis.
Factory acceptance testing involves evaluating the actual delivery component or umbilical to ensure it meets specified standards This includes tests to confirm that a welded tube string can endure the test pressure for a designated duration and to verify that an electrical or optical signal element possesses its intended characteristics Typically, these tests are conducted multiple times for each product.
Acceptance tests for common components shall be performed as specified in Annex D
Acceptance tests shall also be carried out for the end terminations, midline connectors, and ancillary equipment
General
The design of the umbilical and its components must fulfill the functional and technical specifications outlined in this document A risk evaluation will determine the necessary analysis for the umbilical, taking into account various factors, including environmental and service conditions, as well as the potential consequences of non-performance.
Fatigue analyses must account for fatigue at operating temperatures, predict load cycles, and convert these cycles into nominal stress or strain cycles Furthermore, the analysis should encompass not only operational load cycles but also those from reeling, handling, construction, installation, and unforeseen events like partial recovery and reinstallation, as outlined in the design basis.
The effect of mean stresses, internal (service), and external (environmental) plastic pre-strain, and rate of cyclic loading shall be evaluated when determining fatigue resistance
Evaluating fatigue resistance can be achieved through S-N data from representative components or through a fracture mechanics fatigue-life assessment It is crucial to consider safety factors that reflect the inherent sensitivity in predicting fatigue resistance for these designs.
Account shall be taken of the effect of the strain accumulated during manufacturing, handling, and installation on the umbilical fatigue performance
Assessment of creep in electrical cables from the effects of axial tension shall be undertaken
See Annex E for guidance on fatigue testing.
Loads
Loads shall be classified as functional, environmental (external), or accidental
Identifying the functional loads relevant to the umbilical system is crucial Key examples include: the weight and buoyancy of the umbilical and its contents; marine growth influenced by geographical location; internal pressure within hoses and tubes; thermal loads from radiant heat and adjacent hot risers; external hydrostatic pressure; testing pressures during installation and storage; soil or rock reaction forces for buried umbilicals; static loads from support structures; temporary installation loads such as tension and impact; displacements from pressure-induced rotation; clamping interaction effects; loads from pipe crossings; positioning tolerance loads during installation; and loads from inspection and maintenance tools.
Identifying the relevant environmental loads for a specific geographical location is crucial Key examples of these loads include waves, currents, wave-frequency host motions, low-frequency host motions caused by wave drift and wind-loading, vortex-induced motions from current loading, host offsets from nominal positions due to environmental factors, ice, earthquakes, wind, subsea landslides, and UV radiation.
Identifying accidental-load scenarios is crucial for the effective operation of umbilical systems Key examples of these loads include dropped objects, trawl-board impacts, anchor-line failures, and incidents involving fire or explosions Additionally, risks such as compartment damage or unintended flooding of support vessels, loss of buoyancy modules in lazy-wave configurations, and failures of thrusters or dynamic-positioning systems must be considered Other significant factors include net external and internal pressures resulting from flooding, crushing, or incorrect installation rates, as well as potential failures in turret drive systems.
The umbilical must be engineered to endure the most demanding combinations of functional, environmental, and accidental loads as determined by the purchaser's specified extreme design and fatigue conditions This selection of load combinations should encompass all pertinent loading scenarios applicable to the umbilical throughout factory acceptance testing, installation, operation, and any temporary conditions outlined by the purchaser, as detailed in Annex B.
Variation of the loads with respect to time shall be addressed
Extreme load combinations must accurately represent the most likely combined load effects over a designated design time period These combinations are categorized into three conditions: a) Normal operation, which considers permanent functional and environmental loads with a 10^{-2} annual exceedance probability (100-year return period); b) Abnormal operation, which includes functional, environmental, and accidental loads, evaluated with an annual exceedance probability between 10^{-2} and 10^{-4}; and c) Temporary conditions, relevant during installation, retrieval, pressure testing, and other interim phases before permanent operation The return periods for temporary conditions should ensure that the probability of exceedance does not exceed that of the permanent normal operational state.
Accidental loads must be assessed based on risk analyses and historical data regarding their frequency and magnitude It is essential to consider additional loads that may reasonably occur during the accidental event.
Further, accidental loads shall be determined with due account of the factors of influence
NOTE 1 Such factors may be personnel qualifications, operational procedures, the arrangement of the installation, equipment, safety systems, and control procedures
Combined design conditions with an annual exceedance probability higher than 10 2 should be considered to be normal operation
NOTE 2 Load combinations with an annual exceedance probability lower than 104 may normally be ignored
Recommended load combinations for assessment of the extreme-load effect are summarized in Table 1
Table 1—Load Combinations Load type Temporary conditions Normal operation Abnormal operation
Functional Expected, specified, or extreme Expected, specified, or extreme
Environmental Probability of exceedance according to season and duration of the temporary period
If more information is not available, the following return period values may be applied for temporary conditions:
— a 100-year return period if duration is in excess of six months;
— a 10-year return period for the actual seasonal environmental condition if duration is in excess of three days but less than six months
For temporary conditions lasting less than three days, or operations that can be completed within this timeframe, an extreme load condition may be established The startup and shutdown of these operations will rely on accurate weather forecasts.
Annual exceedance probability of 10 2 to 10 4
If combined with accidental loads, the environmental load may be established so that the combined annual exceedance probability is
Accidental As appropriate to the actual temporary condition
Fatigue damage in umbilicals must be assessed by accounting for all cyclic loading throughout their design life, including fabrication and temporary conditions such as installation and in-place operation It is essential to consider the long-term probabilistic nature of fatigue loading Key sources of fatigue damage include: a) wave-frequency response from direct wave loading and first-order host motions; b) slow drift host motions, which involve changes in mean position; c) vortex-induced vibration (VIV) response under steady current conditions; d) potential vortex-induced motion (VIM) of the host hull, particularly in spar platforms; e) cyclic loading during fabrication and installation, such as reeling and unreeling; and f) operational cyclic loading, which encompasses variations in temperature and pressure.
The critical locations for fatigue loading on dynamic umbilicals operated from a floating host are typically the interfaces with supporting rigid structures The fatigue performance of these umbilicals is primarily influenced by the bend limiting devices, such as bend stiffeners or bellmouths, installed at the rigid supports.
When evaluating the long-term performance of the host or station-keeping system, it is essential to consider factors such as variations in loading conditions, changes in mooring pretension, and adjustments in restoring forces due to additional riser tie-ins or relocation Additionally, the operational mode—whether connected or disconnected—of loading systems must be taken into account In the absence of precise information, conservative assumptions should be applied to ensure safety and reliability.
Average values may be applied for functional loading unless more precise information is available regarding the long-term variation of functional loading
Calculation of fatigue stresses shall address wear/corrosion
For accurate fatigue stress calculations, it is essential to use nominal component dimensions reduced by half of the corrosion or wear allowance, unless more specific data is provided In environments with uniform thickness degradation, this approach reflects the average wall thickness throughout the service life of the umbilical.
Fatigue calculations must utilize material properties that account for the effects of high operating temperatures and thermal aging, which can occur due to the operation of medium voltage (MV) power conductors within the umbilical or from other nearby heat sources.
Load Effect Analysis
The manufacturer is responsible for designing the umbilical to meet the specified loads and environmental conditions The analysis results will confirm that the umbilical is appropriate for installation and operational use throughout its intended design life.
The analysis results will be validated through qualification or verification testing Instead of conducting physical tests on the components or umbilical, manufacturers may provide representative historical data to support the models or calculations utilized, as outlined in Section 5.
All load-effect analyses must adhere to established physical and numerical principles for modeling umbilical responses under various static and dynamic loading conditions The software tools employed for both global and local umbilical analysis should be verified against closed-form analytical solutions, validated through multiple simulations or by an independent verification agent to ensure internal consistency and flawlessness, and calibrated with full-scale tests by adjusting independent variables to align observed and simulated distributions of dependent variables.
The validity range of the calibration shall be documented
The accuracy/validity range of the software should be specified based on a correlation to observed values from the physical testing (full scale/model tests)
The manufacturer must provide the purchaser with verification, validation, and confirmation documentation for all analysis tools, both global and local, utilized in the umbilical analysis and design, including any in-house developed tools.
The main types of load-effect analyses in Table 2 may be required, depending on the actual concept
Type of analysis Description Main application
Global analysis Static- and dynamic-load effect analysis due to static and dynamic environmental loading (current, waves, and host offset/motions)
Extreme-load analyses of umbilicals in dynamic service Fatigue-load analyses of umbilicals in dynamic service Analyses of installation scenarios to establish limiting criteria for the operations
Analyses to assess the displacement of on- bottom umbilicals exposed to functional and environmental loading
Stability analysis of umbilicals in static service Stability analysis of laying operations
Stability analysis of on-bottom part of umbilicals in dynamic service
VIV analyses Analysis of VIV in steady current Fatigue analyses of umbilicals in dynamic service
Fatigue analyses of umbilicals during installation operations
The assessment of the need for VIV suppression devices involves evaluating their impact on drag coefficients, which is essential for conducting global and interference analyses where accuracy is crucial.
Analysis to determine minimum distance or contact loads/forces between adjacent structures exposed to static and dynamic environmental loading
Assessment of minimum distance to neighboring risers, umbilicals, and mooring lines; applies to in-place analyses of umbilicals in dynamic service, as well as installation scenarios
Analysis of VIV of free spans in steady current and to establish product curvature
Fatigue analyses of free spans of umbilicals in static service
Pull-in analyses Analysis of pull-in installation operations Analysis of I/J tube pull-in operations of umbilicals in dynamic/static service
Analyses to establish the lay limits of installation operations and to assess and compare the variables for all planned and contingency operations
The assessment of permissible environmental criteria encompasses various stages, including first-end initiation, initial lay, normal lay, curve lay, second-end approach, and second-end installation Each end may involve a subsea termination, an I/J tube pull-in operation, or a landfall approach.
The assessment ensures that the planned handling routes and loads adhere to the manufacturer's recommendations, considering factors such as bend radius, contact force, tension, squeeze load from the caterpillar, and internal pressure Additionally, it involves analyzing the installation scenario and comparing it with the assumptions utilized in calculating fatigue damage.
Establish loads and/or load sharing between the components of the umbilical cross- section
To ensure comprehensive global capacity checks, it is essential to establish the combined tension and curvature capacity of the umbilical cross-section Additionally, determining the stress and strain in individual components for specific tension and curvature combinations is crucial for conducting fatigue analyses Establishing the cross-sectional stiffness—encompassing bending, axial, and torsional stiffness—is necessary for global analyses Furthermore, analyzing installation scenarios will help define limiting criteria for operations, such as evaluating load effects from crushing loads caused by caterpillars.
Global load-effect analysis aims to characterize the overall static and dynamic response of the umbilical system through established principles of analysis, utilizing discrete modeling, material strength, environmental loading, and soil mechanics This analysis should employ numerical simulations, such as finite element (FE) methods, ensuring the global response model encompasses the entire umbilical system with precise modeling of stiffness, mass, damping, and hydrodynamic effects, while also considering boundary conditions Validation of regular-wave approaches with irregular-wave analyses is essential, alongside the application of appropriate drag and inertia coefficients, including the effects of marine growth and potential drag magnification due to vortex-induced vibrations (VIV) The cross-sectional properties must accurately reflect the umbilical's stiffness and damping characteristics, and the model should consist of a sufficient number of elements to capture environmental loading and structural responses in critical areas, with verified time and frequency discretization for accuracy Sensitivity studies are crucial to assess the impact of uncertain parameters, supporting conservative assumptions and identifying areas needing further investigation Lastly, any simplified modeling techniques must be validated against more advanced analyses for critical load cases.
For further details, see Annex C
The umbilical must be designed for stability on the seabed to comply with Section 4 requirements If necessary, an assessment of additional ballast and its effects on other installation activities will be conducted.
DNV RP-F109 is an example of a standard suitable for assessing the lateral stability of umbilicals exposed to current and wave loading
Routing static service umbilicals on the seabed often necessitates a predefined curved configuration It is essential to conduct pull-out analyses to ensure that the geometry of the curved sections remains stable under maximum apparent effective tension Documentation must confirm that the axial and sideways soil resistance adequately supports the tension in this configuration Static analyses should utilize analytical expressions for the holding capacity of both straight and curved umbilical sections as outlined in DNV RP-F109 Additionally, sensitivity studies are required to validate conservative assumptions regarding key parameters, such as soil friction coefficients and submerged weight.
Pull-out analyses will evaluate the seabed's capacity to withstand the bottom tension produced by the dynamic service umbilical system Additionally, these analyses will assess the stability of curved sections during installation processes.
The impact of vortex-induced vibration (VIV) will be assessed for all umbilicals subjected to currents and waves In situations where VIV poses a potential design challenge, a detailed evaluation based on the methods specified in this section is necessary Additionally, the need for qualification testing will be determined in line with section 5.6.
This assessment primarily aims to determine if the fatigue capacity is adequate A simplified conservative VIV analysis is sufficient when the resulting fatigue damage remains within acceptable limits However, if this analysis reveals inadequate fatigue capacity, more advanced methods must be employed, tailored to the specific case being examined.
Key factors influencing Vortex-Induced Vibration (VIV) response include cross-sectional diameter, mass, damping, bending stiffness, and effective tension Additionally, the mass ratio, reduced damping, and the number of natural frequencies within the vortex shedding frequency bandwidth play a crucial role in determining lock-in behavior and VIV amplitude.
Electrical System Analysis
The electrical analysis aims to verify that the specified medium voltage (MV) power conductors are appropriate for safe operation under the defined power transfer requirements It also ensures that their configuration within the umbilical cross-section delivers acceptable electrical system performance across the necessary operating voltages and frequencies, considering various environmental conditions throughout the design life.
The analysis will determine the conductor cross-sectional area or confirm the size specified by the purchaser, establish the minimum insulation thickness needed for the system's operating voltages, and assess the key electrical parameters of the medium voltage (MV) conductors within the umbilical, including resistance, inductance, capacitance, and series impedance Additionally, it will evaluate the anticipated voltage drop in the MV power conductors.
The analysis will assess the electrical characteristics and performance of medium voltage (MV) conductors in the umbilical, focusing on the induced voltage levels between various MV power circuits, as well as between MV circuits and low voltage (LV) power/signal cables, along with other electrically conductive materials present in the umbilical.
In the analysis, it is essential to consider the operating conditions both in the absence of ground faults and during single-phase faults Additionally, the selection of materials must account for factors such as corrosion of metallic components, cathodic attack, and delamination of bonded elements The performance of electrical circuits should be evaluated across a spectrum of operating voltages, including maximum voltage, nominal transmission voltage, and megavolt amps (MVA) power transmission, as well as varying frequencies Furthermore, the analysis must encompass the full range of operating temperatures that could affect conductor resistance.
The electrical analysis should be based on analytical or numerical (FE) methods that are validated by physical testing.
Thermal Analysis
Thermal analysis is required for umbilicals exposed to high temperatures, whether from internal or external sources, as specified by the purchaser This analysis must assess the steady-state temperature distribution across the umbilical's cross-section.
The manufacturer shall demonstrate that temperatures in the umbilical are within all materials limits at the specified environmental and loading conditions
The analysis may lead to decreased material strength, fatigue performance, chemical compatibility, or corrosion resistance, all of which must be considered in the umbilical design Key factors to consider include the environmental operating conditions that impose the greatest thermal input on the umbilical system.
Transient analysis methods may be proposed to account for short-term conditions in the umbilical system It is essential to evaluate various locations to identify the highest operating temperatures Additionally, the maximum electrical loading must be determined through electrical system analysis, considering induced voltages and currents in low-voltage cables and non-current-carrying conductive components Finally, the expected range of operating frequencies should also be assessed.
The thermal analysis of umbilical materials should account for axial heat transfer along the umbilical, as well as convective heat transfer both within the umbilical and in the surrounding environment This analysis can be conducted using either analytical or numerical (finite element) methods.
Installation Analysis
All transport, load transfer, lifting, and subsea operations shall be performed according to company requirements, DNV Rules for Planning and Execution of Marine Operations, or other equivalent standard
The installation analysis must ensure the use of appropriate equipment, such as tensioners, pads, and chutes, to install the umbilical safely and without damage Key factors to evaluate include load transfer, friction among umbilical components, crushing resistance, and the friction between the umbilical and pads.
A recovery analysis will be conducted to identify the conditions necessary for recovery, following the same methodology as the installation analysis The utilization factors used will be consistent with those applied in the installation case.
Fatigue Life
The umbilical shall be designed with fatigue life that is equal to or greater than 10 times the service life
NOTE 1 The service life is determined on a project-specific basis
Qualification or verification testing is essential to ensure that the manufacturer's design methodology, analysis techniques, and software tools are reliable and precise in predicting fatigue damage and fatigue life.
7 Component Design, Manufacture, and Test
General
The umbilical components shall be designed and manufactured to meet the umbilical functional and technical requirements Conformance shall be demonstrated by verification and acceptance testing
For new component designs that closely resemble previously validated designs, design verification tests can be incorporated into some or all of the component Factory Acceptance Tests (FATs), provided that their performance can be predicted with a high degree of confidence.
If the component design closely resembles a previously validated design and the umbilical is installed under comparable environmental and service conditions, it is possible to substitute design verification with historical design verification data.
The performance of the end terminations, midline connectors, and ancillary equipment shall be verified by testing, if applicable
Verification and acceptance tests that shall be performed during and on completion of component manufacture specified in this section are summarized in Annex D
Before production begins, manufacturers must create a comprehensive quality plan that outlines how specified properties will be achieved and verified through the manufacturing process This plan should cover all factors affecting production quality and reliability, detailing each main manufacturing step from raw material control to finished product shipment, including all examinations and checkpoints It must reference established procedures for executing these steps and require approval from the purchaser At a minimum, the quality plan should include a process flow description, a project-specific quality plan, details of the manufacturing process, information on manufacturers of functional components and their quality plans, as well as handling, loading, and shipping procedures.
When selecting materials, it is essential to consider the installed environment, the specific duties they will perform, their compatibility with the manufacturing process, the potential for in-service repairs, and their resistance to degradation from seawater and service fluids.
NOTE EEMUA Publication 194 includes guidance on materials selection for umbilicals and subsea equipment.
Electric Cables
Electric cables shall be capable of continuous operation, with the insulated conductors operating in a fully flooded seawater environment
The design of the electric cables shall recognize that the cables may be terminated in some form of water- blocking arrangement(s), which shall function throughout the design life
NOTE The use of the terms “signal” or “power,” with respect to cable descriptions, are customer-specific and relate only to how they are used in service
The operating voltages shall be defined using U 0, U, and U m
Cables included in this standard shall be defined as low voltage (LV) or medium voltage (MV)
Low voltage cables shall follow the basic design requirements of IEC 60502-1, which covers the 0.6/1 (1.2) kV and 1.8/3 (3.6) kV
NOTE 1 Other voltage combinations for LV cable may be used, provided they fall within this range
NOTE 2 Most low-voltage cables likely take the form of multicore cables, such as pairs, triads, or quads
Medium-voltage cables shall follow the basic design requirements of IEC 60502-2, which covers 3.6/6 (7.2) kV; 6/10 (12) kV; 8.7/15 (17.5) kV; 12/20 (24) kV; and 18/30 (36) kV, with additional consideration for submarine applications
Other voltage combinations for medium voltage (MV) cables are permissible as long as they remain within the specified range Besides IEC 60502-2, various industry standards, including those established by ICEA and IEEE, also regulate power cable design.
Medium-voltage cables usually shall be supplied as individual cores, or as a unit containing three cores
Various cable constructions are acceptable for use in a subsea umbilical; however, the chosen design shall be verified according to requirements defined in Section 4
Cables shall be manufactured in accordance with the manufacturer's written specification
NOTE Some cables may include screening and/or armoring, depending on intended service or for other reasons
Electric cores and cables should be manufactured as continuous lengths
Splices must be performed by qualified personnel following the manufacturer's written specifications to meet final length requirements Additionally, these splices are required to adhere to the same qualification and acceptance criteria as the insulated conductors and cables.
In a multicore cable, the design must allow for easy separation of the cores during termination, ensuring they do not stick to the sheath, fillers, binder tape, or neighboring cores.
Cable cores are often sealed using boot-seal methods, requiring the insulation surface to be round, smooth, and devoid of any marks, indentations, or defects that could compromise the sealing process.
When designing for deepwater service, it is crucial to account for conductor-strain relief to mitigate the effects of compressive and tensile forces, as well as to prevent potential damage from crushing forces in the laid-up components.
Where necessary, the designs shall take into consideration the effects and mitigation of gas and liquid migration in electric cables
Electric cable construction materials, including insulation, fillers, and sheathing, must be resistant to oil and dielectric fluids This resistance is crucial to prevent the deterioration of their electrical and physical properties, especially when using pressure-compensated terminations or connectors that typically utilize electrical or hydraulic oil as an equalizing fluid.
The conductor shall comply with the relevant conductivity and material requirements of IEC 60228, Class 2
The minimum nominal cross-sectional area shall be 2.5 mm 2 (0.004 in 2 ); however, the conductor sizing shall be suitable for both the operating conditions and testing requirements
The nominal cross-sectional area for the conductor shall meet the functional requirements of Section 4 The relationship between conductor size, strand count, and stiffness should be considered
When selecting conductor size, consideration should be given to the minimum recommended size based on the insulation thickness
NOTE Where conductors are used in MV cables, a semiconducting screen may be present on top of the conductor This would be simultaneously applied as part of the insulation extrusion
The insulation material shall be suitable for immersion in seawater
The chosen insulation material shall be of virgin stock applied as a continuous, seamless, circular single/multiple extrusion, and shall meet the requirements of IEC 60502-1
Thermoplastic polyethylene and different grades of ethylene propylene rubber are effective materials that maintain their insulating properties throughout their service life These materials have been demonstrated to retain the necessary mechanical properties under actual temperature and pressure conditions.
When polyethylene is used as insulation material, the minimum thickness for EPR defined in IEC 60502-1 shall be used
During the material selection process, consideration shall be given to the operating temperature
The minimum allowable insulation thickness shall be as specified in IEC 60502-1 (or alternatively, as stated in the manufacturer's written specification)
Depending on voltage rating, insulation material, and thickness, nonmetallic conductor and insulation screening may be required, as specified in IEC 60502-1
Insulated conductors must be identified using either colors or numbers, with numerical markings printed at intervals not exceeding 100 mm (4.0 in.) along each core's length The specific colors and/or numbers used should be detailed in the manufacturer's written specifications.
Coding shall be stable under heat aging, and shall not cause a failure to satisfy the requirements of Section 4 Embossed printing shall not be permitted
The insulation material shall be suitable for immersion in seawater
The chosen insulation material shall be of virgin stock applied as a continuous, seamless, circular single/multiple extrusion, and shall meet the requirements of IEC 60502-2
During the material selection process, consideration shall be given to the operating temperature and maximum continuous temperature of the conductor
The minimum allowable insulation thickness shall be as stated in IEC 60502-2 for the chosen material
Most medium voltage (MV) cables necessitate the simultaneous extrusion of a semiconducting layer for both conductor and insulation screening An exception to this requirement is the 3.6/6 (7.2) kV cable, which follows the material selection and thickness specifications outlined in IEC 60502-2.
The process of twisting individual cores shall be qualified for the specific application
If an alternative lay-up technique is used, then it shall be qualified for the service
For an intermediate lay-up operation, the cabled cores may be bound with a helically applied overlapping tape to ensure bundle stability and a circular cross-section
The lay-up operation shall minimize compressive forces between the cores to minimize the extent of deformation of the insulation
In multicore cables, fillers or extruded materials are used to fill the gaps, ensuring a circular and consolidated structure Additionally, viscous filling compounds are incorporated to decrease internal voids and prevent water ingress.
Filler and binder tape materials must be compatible with other cable components, particularly regarding their impact on electrical insulation These materials should adhere to the specifications provided by the manufacturer The application of binder tape can be done either longitudinally or helically, depending on the presence of a screen.
For optimal performance, cables must be equipped with appropriate screening, which can be achieved using a metallic tape or a two-component tape featuring a thin metallic film adhered to a polymer substrate The manufacturer's specifications will dictate the required thickness and number of layers It is essential that the screen maintains electrical continuity along the entire length of the cable, ensuring that this continuity remains intact throughout the cable's design life.
Plain metal tape screens for electric cables or individual power cores must ensure complete coverage of the enclosed electrical cores These screens should be applied in a helical manner with an overlap, and care must be taken not to place the screen directly over the twisted cores without considering the underlying cores.
A drain wire, when included, must consist of at least three strands with a minimum total cross-sectional area of 0.35 mm² (0.0005 in²) It should be installed to ensure continuous contact with the metallic part of the screen.
All MV cables (with the exception of 3.6/6 (7.2) kV cables referenced in 7.2.5.5) shall contain a screen, either individually or collectively, comprising of a metallic layer in combination with the semiconducting insulation screening
The construction of the screen shall be as described in IEC 60502-2 In addition to these requirements, other nonmetallic or semiconducting tapes may be present to inhibit longitudinal water penetration
The area of metallic screen, combined with any grounding wires, shall be capable of withstanding the required short-circuit current rating
The screen shall be electrically continuous throughout the cable length, and should be applied in such a manner that its electrical continuity shall not be broken throughout its design life
The electric cable sheath must be made of a polymeric material that offers protection against UV radiation and oxidation, as specified by the manufacturer This material should be continuously and concentrically extruded over the laid-up cores to ensure a uniform cross-section Additionally, it must be compatible with seawater and specified service fluids during manufacture, installation, and service, without degrading the quality of other materials it contacts in the lay-up.