3 Interface Requirement
3.1 Introduction
The main interface requirements in the Deepwater installation of subsea components and structures are related to:
Storage, transportation and equipment means for the safe installation of products, e.g. flowlines, umbilical, etc.
Lifting and safe deployment (e.g. to the required water depths) of subsea structures
ROV interface engineering with all subsea equipments and products.
They are further described in the following sections.
3.2 Storage and Laying of Products
3.2.1 General
Products such as flexible or umbilical are generally stored on reel. The reel is either loaded on the vessel or product is transferred from yard to vessel (if vessel is already equipped with own reels). The storage of pipeline onboard vessel depends on the selected installation method (see section Section 4.3, “Deepwater Pipelay Method”) such as:
Reel lay: continuous rigid pipe stored on reel during loading operation at spool base (see section Section 4.4, “Spool Base Facilities”).
S-lay and J-lay: sections of rigid pipe are stored on vessel deck. The length of pipe sections are approximately 12m.depending from the installation method the pipes could be single (12.2m) or double (24.4m) or quad (48.8m) joints. For J-lay the min is typically a double joint.
The storage and subsea installation of products are to be performed in a timely and safe manner, taking into account all site limitations, typically:
Weather conditions and limitations
Seabed soil conditions and visibility (ROV intervention close to seafloor)
Site constraints and obstructions (drilling rigs, mooring lines, other subsea structures)
For this purpose, the storage and laying equipment must be designed, built and operated to suit the conditions in which they are to perform, taking account of the products properties, installation constraints and emergency situation as defined by the HAZOP/HAZID sessions, and if needed, SIMOPS dossier must be managed.
For all offshore activities or tasks, laying and installation detailed procedures must be provided and weather limitations identified (waves, winds, currents, etc) in relation to vessel heading. DP operations are to be defined in Critical Activity Mode of Operation (CAMO) and Task Appropriate Mode of Operation documents (TAMO).
Reversal of all operations (e.g. subsea equipment) must be possible and related procedures should also be provided.
3.2.2 Product Safe Handling
The products to be laid or installed are typically:
Rigid steel pipelines and risers
Flexible flowlines and risers
Control umbilical (electrical, hydraulic, steel tubes, service lines, etc) in 'static' or dynamic Riser applications
Power electric cables (e.g. subsea processing)
other types of pipelines / products such as bundle, piggy back etc.
The products must be handled, stored, sea-fastened, transported and installed in a safe manner and according to the specified requirements (e.g. product properties/load capacities) and procedures.
For each product, the installation or laying parameters (dynamic mode) and product load capacities must be calculated and analysed against the vessel and equipment performance and capabilities.
A formal FMECA study for the laying and installation equipment (e.g. including all ancillaries such as abandonment & recovery means) is to be performed.
The objectives being to demonstrate that the product will not be damaged by the installation or laying equipment during normal operation and back-up procedure exists, in case of emergency situation arising from environmental condition changes or vessel equipment failures. Oceano meteo conditions & particularly HS -Hmax battery limits must be assessed, defined and risk assessed. If possible laying and initiation should be performed during good season (less swell period)
The product bending radius and tension must be accurately controlled (i.e. the main monitoring parameters: top tension on the vessel, pipeline/product departure angle, TDP distance) during handling and laying operation; in particular during critical operations such as line initiation, over boarding of intermediate pipe fittings, lay-down of end termination, cross-hauled and pull-in operations.
3.2.3 Installation and Laying Parameters
The following installation and laying parameters must be analysed:
Nominal and maximum dynamic lay tensions for empty product in submerged conditions
Maximum hold-back tension in case of product 'wet buckle' (flooded condition)
Minimum bending radius vs. applied dynamic tension (combined with bending)
Touch down point distance from lay vessel
Product sag bend radius
Product maximum stress level
Accumulated strain and maximum residual as-laid strain
limiting squeeze pressure
The above installation and laying parameters are one of the key input data for the laying & installation procedures.
As a result of the HAZOP/HAZID sessions, emergency & contingency procedures must be provided for all identified hazardous activities, e.g. contingency procedures in case of pipelay accidental flooding.
3.2.4 Product Squeeze Pressure
Required level of the top tension capacity during laying of a product is ensured through the squeeze force applied by the pipelay equipment (tensioners, hang off clamp, etc) contact pads directly onto the product. The level of the squeeze/clamping pressure shall be limited depending on:
- the product capacity (acceptance criteria) to withstand such a compression/crushing loading
- required top tension to ensure integrity of the product catenary during laying (e.g to ensure allowable stress/strain)
Such clamping pressure shall consider the effects on pressure containing elements, load bearing elements and electrical cables, e.g. umbilical components.
Tensioner track number, length and contact pad type & shape will be selected based on product size, capacity and constraints (e.g. friction coefficient between pipe layers) as well as established equipment operation procedures.
The tensioner must be fitted with a failsafe system that ensures that the caterpillar track cannot open while the product is under tension.
3.2.5 Load Matrix
The possible damage scenarios to be evaluated for the installation phase are, as follows:
Crushing
Product crushing resistance is to be checked against laying equipment characteristics during product handling, such as reeling, packing, passes through straightener, tensioner, roller, gutter, hang-off or hold-back clamps, etc.
Excessive Pull
Actual tension combined with other loads (e.g. bending, torsion) is to be compared against product axial resistance load.
Excessive Bending
Special care shall be taken to avoid excessive bending during product over-boarding with intermediate connections, FLET, PLEM, ILT, subsea splice, buoyancy modules, clamps, etc.
Tearing
Sharp edges and abrasive surfaces shall be avoided and the clamping force properly selected.
If the product passes a gutter/chute, it shall be verified that the friction (products vs. gutter) will not damage the outer sheath.
Excessive Twist
The product allowable twist (angle°/m) must be specified and excessive twist avoided during the installation phase (e.g. during Riser cross-haul to floater or fixed structures).
Collapse/Compression
The laying parameters and procedures must carefully avoid exposure of the products to local loads superior to the maximum design loads.
To ensure that the installation will be carried out in such a way that the different product design capacities are not exceeded, all relevant loads (dynamic mode) and their combinations are to be considered.
A load matrix (load cases and loads) are to be established based on the selected installation method, vessel & equipment and specified environmental conditions.
The load matrix must be used to verify if all relevant load combinations have been considered and the product design capacities are not exceeded when being handled by the installation or laying equipment.
A typical load matrix is provided in Table 3.1, “Load Matrix (typical)”:
Table 3.1 - Load Matrix (typical)
Case | Position | Load Combination | Damage Scenarios | Comments |
Laying | Tensioner or hang off clamp/table | Max. tension vs. clamping pressure at weather limits and fatigue | Crushing, Tearing | For laying this includes normal, far and close position of vessel to touch-down-point |
Ramp, Gutter, Chute, Rollers, stingers | Max. tension and bending contact at roller ramp and weather limits local point loading during transfer over supports/rollers | Crushing, Tearing, Excessive Bending and Tension | As above | |
Straightener, Aligner | Max. tension and bending contact lateral point loads | Crushing, Excessive Bending and Tension, Tearing | Accumulated strain level Fatigue life limitation on Riser application | |
Sag bend & touch-down | Min. tension at weather limit inducing compression at bending Fatigue | Excessive Bending, Twist, Compression | Further Product abandonment & recovery is to be considered | |
Pull-in | Bellmouth, J-tube | Max. tension and bending at contact radius and weather limits | Excessive Bending, Crushing, Ovalisation and Tearing | For cross-haul of Riser, twist angle is to be considered |
Docking | Riser structure & base | Min. radius & Max. tension inducing bending, compression at weather limits (induce heave) | Excessive Bending, Tearing, Compression | For laying this include normal, far and close position of vessel to touch-down-point |
Hydrotest | All applicable positions | Max. pressure & tension, Min. bending | Crushing, Tearing, Leakage, Burst, Yield in pipe/tube | Any weather limitation during Riser pressure test is to be considered |
3.2.6 Laying Accuracy, Monitoring & Control
As a minimum, the following parameters must be monitored, recorded and displayed in a suitable location (e.g. lay control room, DP bridge) during all laying operations:
Line tension and departure angle
Subsea Stinger overview and stinger exit must be monitored trough camera or diver checks
Touch-down point monitoring, e.g. using ROV
Line length paid out from vessel
Vessel position & heading and layback distance
Laying speed
water depth
Environmental conditions: sea-state (swell/wave and current), wind, etc.
The tension applied to the pipeline / product must be continuously controlled, monitored and recorded in order to avoid sudden changes in line tension, and to ensure line integrity and routing within the specified laying tolerances, e.g. pipe out-of-straightness.
A protocol & control system between the vessel DP and the laying equipment will allow the continuous and safe product laying within a pre-determined track with or without turning points.
At completion of installation or laying operations the line end shall be lowered onto the seabed under controlled conditions and abandoned in its target area within a specified heading and roll angle (FLET vertical angle).
For specific installation tolerances, see[27] (Section 9).
3.3 Lifting & Installation of Structures
3.3.1 General
Lifting and installation of topside process modules, or subsea structures must be performed in a timely and safe manner, taking into account all site limitations (see section Section 3.2.1, “General”).
For this purpose the dedicated lifting and installation equipment (i.e. cranes, winches) must be designed, built and operated to suit the conditions in which they are to perform. More specifically taking account of the structures installation criteria and constraints, as specified by the designer/manufacturers and national codes/certifying authority rules (e.g. Det Norske Veritas (DnV), American Petroleum Institute (API), Lloyds Register of Shipping (LRS)) and Total General Specification ref.[30].
For all offshore activities or tasks, lifting and installation detailed procedures must be provided and weather limitations identified (waves, winds, currents, etc) in relation to vessel heading.
DP operations are to be defined in Critical Activity Mode of Operation (CAMO) and Task Appropriate Mode of Operation (TAMO) documents.
3.3.2 Subsea Structures Safe Handling
The subsea components and structures to be lifted and installed are typically:
Mooring lines and anchors
Foundation bases (e.g. suction piles, gravity bases)
Manifold structure, guide and support bases
Manifolds / templates
X-mas trees
Pipes
Production Well Jumper, Injection Well Jumper
Manifold ancillary components (e.g. pigging loop, module control pods,)
Closing spool pieces
Protective structures
The subsea structures must be handled, stored, sea-fastened, transported, offshore lifted and installed in a safe manner all in accordance with the specified requirements (e.g. SPS's manufacturer) and procedures.
For each structure, the lifting and installation parameters (dynamic mode) must be calculated and analysed through a lifting analysis study against the vessel and equipment performance and capabilities and validated by the TOTAL' s CPLO. Reversal of the installation operations must be possible.
The deck handling system and the lifting devices must be designed to control and prevent the pendulum movements of the subsea structures between leaving the deck storage area, passing through the splash zone and safely landing on the seabed.
The landing criteria (speed, energy) must be defined through the SPS manufacturer interface activities. The following landing criteria are to be considered as typical for Deepwater installation:
Maximum heave amplitude : 1 m
Maximum landing speed : 0,2 m/s (manifold), 0,5 m/s (manifold base structure)
landing criterion : 1 kJ
The objectives being to demonstrate that the subsea structures will not be damaged during normal operation and back-up procedure exists, in case of emergency situation arising from environmental condition changes or vessel equipment failures.
3.3.3 Typical Package Weight and Size
The following Table presents typical package Weight and Size:
Table 3.2 - Typical Package Weight and Size
Package Family | Package Type | Weight (t) | Dimensions (m) | ||
|---|---|---|---|---|---|
Length | Width | Height | |||
Suction/Anchor Piles | Suction Caisson | 160 | 8m diameter | 15 / 20 | |
Anchor Pile | 50-70 | 2m diameter | 100 | ||
Manifolds | 4-6 Slots Manifold | 120 / 250 | 10 | 9 | 7 |
Riser Base Manifold | 70 / 200 | 20 | 10 | 10 | |
Pipeline Subsea Structures | Pipeline End Manifold (PLEM) | Up to 100 | 10/15 | 6 | 4/5 |
In-Line Tee (ILT) | Up to 75 | 10/15 | 6 | 4/5 | |
X-mas Trees | X-mas Tree | Up to 50 | 2.1 | 3.4 | 4.1 |
Templates | Template with Mudmat | 300 / 350 | 29 | 16 | 6.5 |
Template with Spud Anchor Support | 600 | 12 | 12 | 20 | |
Subsea Processing Unit | See Document (See Ref.[34]) | ||||
Spools | Spool Pieces, Well Jumper | Up to 100 | 70 | 20 | 5 |
Buoyancy Can | FSHR Buoyancy Can | 200 / 300 | 6 / 8m diameter | 35 / 45 | |
3.3.4 Installation Accuracy, Monitoring & Control
The subsea structure installation accuracy must be performed in accordance with the pipeline/product design requirements and SPS manufacturer requirement.
The following installation tolerances for FLET and ILT are to be considered as typical:
Radial position within +/- 2.5 m while lateral position within +/-2.5m from its nominal position
Heading of structure within +/- 2.5°
Maximum vertical inclination within +/- 1.5°
As a minimum, the following installation parameters must be monitored, recorded and displayed in a suitable location (e.g. installation control room, DP bridge) during the lifting and installation operations:
Load tension monitoring
Lift line paid out from vessel
Vessel position & heading
Subsea structure depth monitoring
Environmental conditions: water depth, sea state, wind, etc
Touch-down monitoring e.g. using ROV
The tension applied to the line must be continuously controlled in order to avoid sudden changes in line tension (snatch loads).
3.4 Remotely Operated Vehicles
Remotely Operated Vehicles (ROVs) are required for all subsea operations and assistance activities, such as:
Route survey, debris removal
Observation & touch down point monitoring during product lay
Monitoring and landing of product ILT and PLEM, in pre-determined target area
Subsea structures observation, guiding, monitoring, landing, levelling & locking
Spool piece and well jumper metrology and tie-ins
Flying lead tie-ins between ILT, manifolds and trees
Valve operations as primary or override functions
Control or choke modules change over
Video monitoring, during tool manoeuvring and positioning
Hot stab for hydraulic primary and secondary tool operations
Torque operations on subsea valves/panels/clamp connectors
Water jetting and dredging
Connection of lifting gear
Post survey (as built)
Primary support for tie ins tools
Deployment of subsea Hydro acoustic positioning transponders
etc
The ROV system must be depth rated to project max water depth, e.g. sufficient cables to reach and work at the required depth.
For most ROV-dependent tasks, there is no substituted solution. If the ROV fails or is unavailable when required for such an activity, the vessel-based subsea operations will be suspended. So ROV Reliability and equipment back-up philosophy are critical considerations to ensure ‘24 hrs availability’ during subsea interventions.
For Deepwater operations, special attention shall be paid to the ROV umbilical and tether management system in terms of design and operating procedures.
For construction and installation tasks, it is advised to have 2 ROV in water. For connection (WJ for instance) 2 ROVs at depth is a must
Due to the ROV water depth descent & ascent times and system Redundancy requirement, the following Table 3.3, “ROVrequirements (typical)” sets the basic and typical number & type of ROV spreads:
Table 3.3 - ROVrequirements (typical)
Note: Refer to document ([39]) for more details on ROV Operations and Crew.
The proposed ROV number & type for each dedicated vessel shall be analysed and documented on above basis.
The ROV vehicle will be launched using the over-the-side method or through the moonpool and will require a dedicated Launch & Recovery System to control the pendulum movements on deck and through the splash-zone. Such handling system shall be designed, built and operated to suit the conditions in which they are to perform. A particularly attention must be required for the latch and unlatch between ROV and TMS, launch & recovery of ROV system (Splash zone, Umbilical management, pendulum movements)
On a DP vessel the position for the safe launching and recovery of ROV vehicles shall be evaluated, based on vessel motions and thruster positions.
As a minimum, the ROV deck equipment will include:
Electro-hydraulic umbilical winch (fast winch for more efficiency) complete with drum, cables and umbilical capable of operating in required water depths. A LARS load test must be performed during mobilization or ROV integration and on a regular base. Wire termination must be regularly inspected & certified
ROV control cabin fully equipped (i.e. monitor recorder with hard copy print out off the screen), with air conditioned
Direct communication and telephone links between the ROV control cabin and the laying & installation room and DP control room facilities
Workshop cabin(s)
All required spare parts for above ROV vehicle, LARS and other deck equipment
Please refer to the document “Deepwater ROV and TOOLS” (Ref.[39] ) of Offshore Reference Book, for further details on ROV technology, capabilities and specific requirements.
