HEAVE COMPENSATED OFFSHORE ACCESS SYSTEM

TECHNICAL SPECIFICATION

PROJECT:

Heave Compensated Offshore Access System

PROJECT Ref: CLIENT: PREPARED BY: DOCUMENT No:

75000-001-SPC-001-A3 (LIVE)

1.

Executive Summary The problem of transferring personnel onto fixed installations is one that has existed for a number of years within the offshore industry. Historically, this has been provided by helicopter or via boat landing stations. Offshore Solutions BV has developed and patented the Offshore Access System (OAS) to provide safe access from a support vessel to a fixed offshore structure. The standard OAS unit encompasses the following primary features.

1

•

Heave compensated walkway

•

Operational up to 2.5 metres significant wave height1

•

Maximised length to facilitate connection

•

Patented hook connection system

•

Safety features aligned with ship’s systems

A2

The operating sea state condition of Hs=2.5m is a resultant of both wind driven waves and swell.

Date: 05/11/08

Page ii

Prepared by: Steve Beales

2. 1. 2. 3. 4. 5. 6.

Table of Contents EXECUTIVE SUMMARY ...................................................................................................................II TABLE OF CONTENTS ................................................................................................................... III NOMENCLATURE .......................................................................................................................... 1 REFERENCES ............................................................................................................................... 1 INTRODUCTION............................................................................................................................. 2 WALKWAY SPECIFICATION ........................................................................................................... 3

6.1 6.2 6.2.1 6.2.2 6.2.3 6.2.4 6.3 6.4

7.

SYSTEM OVERVIEW ...................................................................................................................... 6

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

8.

General.......................................................................................................................................................6 Pedestal .....................................................................................................................................................6 Turret..........................................................................................................................................................6 Bridge.........................................................................................................................................................7 Access Platform ........................................................................................................................................7 Boom Rest & Access Platform ................................................................................................................7 Landing Station Interface.........................................................................................................................8 Vessel Foundation ....................................................................................................................................8

MOTION FUNCTIONALITY .............................................................................................................. 9

8.1 8.2 8.3 8.4 8.5 8.5.1 8.5.2 8.5.3 8.5.4 8.6 8.6.1 8.6.2 8.6.3

9. 9.1 9.2

Operating Parameters ..............................................................................................................................3 Working Parameters .................................................................................................................................3 Walkway Position .....................................................................................................................................3 Luffing.......................................................................................................................................................3 Telescope .................................................................................................................................................4 Slewing .....................................................................................................................................................5 OAS Dimensions .......................................................................................................................................5 Materials of Construction.........................................................................................................................5

Luffing ........................................................................................................................................................9 Slewing.......................................................................................................................................................9 Telescoping ...............................................................................................................................................9 Hydraulics..................................................................................................................................................9 Electrical/Control ......................................................................................................................................9 General .....................................................................................................................................................9 Control System .......................................................................................................................................10 Electrical UPS System ...........................................................................................................................11 Sensors ..................................................................................................................................................11 Audio/Visual Aids....................................................................................................................................11 Alarm System .........................................................................................................................................11 CCTV System.........................................................................................................................................11 Lighting ...................................................................................................................................................11

SAFETY ..................................................................................................................................... 12 Walkway Access .....................................................................................................................................12 Hook Release...........................................................................................................................................12

10. OPERATION ............................................................................................................................... 13 10.1 General Description ................................................................................................................................13 10.2 Manoeuvre & Connection Sequence ....................................................................................................14 10.3 Retrieval & Parking Sequence ...............................................................................................................15 Date:

Prepared by:

10.5 Process Flow Diagram ...........................................................................................................................16

11. INSTALLATION ........................................................................................................................... 17 12. MAINTENANCE ........................................................................................................................... 18 12.1 General.....................................................................................................................................................18 12.2 Redundancy.............................................................................................................................................18

3.

Nomenclature The following abbreviations are used throughout this document: CCTV DPI EC GUI MMI MPI MRU MSL NDT OAS OSbv UPS UT WCS

4.

Closed Circuit Television Dye Penetrant Inspection Eddy Current Examination Graphical User Interface Man Machine Interface Magnetic Particle Inspection Motion Reference Unit Mean Sea Level Non Destructive Testing Offshore Access System Offshore Solutions bv Uninterruptible Power Supply Ultrasonic Testing World Coordinate System

References This document should be read in conjunction with the following documents: •

Lloyd’s Register of Shipping............................. Rules for lifting appliances

•

OAS-Asset Interface Requirements ................. 75000-000-SPC-002

•

OAS-Vessel Interface Requirements................ 75000-000-SPC-004

5.

Introduction This technical document contains the outline operating characteristics of the proposed OAS operating system. It also contains an overview of the operating procedures and maintenance regime required to maintain the operability of the system. The walkway system shall refer to the complete scope of supply which includes the access bridge, rotating turret, pedestal section, control system and hydraulic power units. The walkway measures circa. 20m in length and has a mass (exclusive of power unit, boom rest, etc) of circa. 24Te. The walkway shall be designed in accordance with the Lloyds Register rules for certification of lifting appliances. Where these rules are not specific, other relevant codes shall be utilised and specified accordingly. This technical document contains the outline operating characteristics of the proposed OAS operating system. It also contains an overview of the operating procedures and maintenance regime required to maintain the operability of the system.

6.

Walkway Specification

6.1

Operating Parameters • Significant wave height HS ............................. 2.5m • Ambient temperature..................................... -20°C → +40°C (-4°F → +113°F) • Safe Working Load........................................ 0.6Te2

6.2

Working Parameters

6.2.1 Walkway Position The final installed position of the OAS system will be decided following a review of the vessel deck plan area and intended connection regime. As a base, historically, the OAS has been installed on the port stern quarter, with the power unit running forward from the connection. 6.2.2 Luffing The following heights demonstrate the mechanical range of motion of the walkway in the vertical plane. • Min hook height3 ............................................ 5.0m above MSL • Max hook height3........................................... 9.0m above MSL • Walkway angle (green operating) .................. ±15° (±5.5m at max extension) • Walkway angle (max mechanical) ................. ±21° (±7.8m at max extension) These figures do not take into account the motion or the potential variation in the draft of the vessel. Various sensor limits and software limits are set to prevent excursions beyond the operating limits to reduce the risk of damage to the walkway or vessel.

6.2.4 Slewing The working slewing angles are wholly dependant on the position of the OAS on the vessel and the intended working angles based on vessel and platform operational procedures. • Slewing angle (max overall mechanical)........ 225° Various sensor limits and software limits are set to prevent excursions beyond the operating limits to reduce the risk of damage to the walkway or vessel. 6.3

OAS Dimensions • Overall length (retracted)............................... 17.5m • Overall width ................................................. 5.2m • Overall height (maximum) ............................. 6.1m • Clear walkway width...................................... 0.8m • Foundation diameter requirements................ 2.0m • Overall mass ................................................. 24Te5 Note that the heights of the walkway relate to the height to the top of the operator cabin from deck level. Also that the stated dimensions refer to the overall dimensions of the OAS and can also be termed shipping dimensions.

6.4

Materials of Construction • Primary steelwork.......................................... BS EN 10210 GrS355J2G3, 3.2 cert6. • Secondary steelwork ..................................... BS EN 10210 Gr270GP, 3.1 cert. • Flooring ......................................................... GRP open floor grating • Handrails....................................................... GRP modular construction • Hydraulic pipe work ....................................... Stainless steel, 3.1 certification All fabrications will be subjected to the appropriate level of NDT and using an approved method such as Radiography, MPI, EC, UT or DPI.

7.

System Overview

7.1

General The system operates essentially in three modes, the first of which is a fully manual mode, the second “active” heave compensation mode which is designed to remove the vertical movement resulting from the vessel movement and allow the walkway to be “connected” to the fixed installation. The final “passive” floating mode automatically operates when the walkway is fully connected to the fixed installation. The floating mode ensures that, once connected, the relative movements between the walkway and fixed installation are absorbed within the movement planes of the walkway. The walkway has three primary movement planes, these being; slewing, luffing and telescoping.

7.2

Pedestal The pedestal is a cylindrical rolled plate construction and essential comprises two halves. The lower half forms the supporting foundation onto the vessel and in between the two halves; a slew ring bearing is mounted to provide the rotational interface between the revolving part and the stationary part. The internally geared part of this bearing is mounted to the upper, rotating part thus allowing the slew drive units to remain stationary. The upper part of the pedestal also provides the anchor points for the two hydraulic luffing cylinders which are mounted as compression members. The upper part of the pedestal also provides the mountings for the primary hydraulic manifolds. Access hatches are provided to allow access into both upper and lower parts of the pedestal.

7.3

Turret The rotating turret assembly shall be of fabricated steel construction, whilst the flooring shall be provided by GRP open floor grating. Handrails are provided around the perimeter of the turret. The revolving turrets primary function is to provide the interface piece between the nonrotating pedestal and the bridge sections. It provides the anchor/hinge points for the suspension of the bridge sections. The turret also provides the foundation for the operator cabin (described below), and also houses the hydraulic accumulator banks that are required.

7.4

Bridge Both the inner and outer bridge sections shall be fabricated predominantly from triangulated square hollow section steelwork. The bridge assembly comprises a number of sub-assemblies; one fixed outer bridge section, one telescoping inner bridge section and the access platform assembly. Flooring on both bridge sections is provided by the means of GRP open floor grating and handrails are provided along the entire length of the bridge sections. A linear elastomer type shock absorbing system is installed to the outer bridge section which also provides the mechanical limits of the extremities of travel. A number of hose carrier arrangements are provided on the bridge assembly; one to carry the walkway system electrical and control cables, one to carry the hydraulics, both of which are mounted in a vertical arrangement within the void between the inner and outer bridge sections.

7.5

Access Platform This is an access platform located at the end of the inner telescopic bridge section and is a multi-functional arrangement. Firstly, and simply, it provides the step interface to allow personnel to step from the inner bridge section to the fixed installation landing area. Secondly, it houses the connection arrangement (or “gripper” platform) for “connecting” the walkway to the fixed installation. In the event that no suitable connection and/or access arrangement is available on the fixed installation, then a landing platform will be required to be installed. The system is designed so that connection can be made from either port or starboard approaches.

7.6

Boom Rest & Access Platform As part of the complete OAS installation, a boom rest and access platform is required to be installed. OSBV can provide the necessary expertise and experience for designing, manufacturing and installing these items which are integral to the overall system, in accordance with the selected, specific vessel.

7.7

Landing Station Interface This section refers to the requirements of the equipment that need to be installed on the fixed installation that the walkway will be connecting to. There are no active systems that require installation on the fixed installation. The equipment will comprise of a connecting pole (diameter and length to be confirmed), a reinforced landing area and suitable handrails to allow safe access/egress to and from the walkway to the fixed installation. The detail of any landing station interface is specific to each installation to which connection is to be made. OSBV can, however, provide the necessary expertise and experience required for designing, manufacturing and installing this part of the complete OAS experience.

7.8

Vessel Foundation In addition, a foundation (lower pedestal half) is also required to provide a connection between the OAS and the vessel. This is vessel dependant and requires significant vessel details and naval architect input. OSBV can provide the necessary expertise and experience for designing and manufacturing this item, although installation should be carried out by a nominated shipyard or repair facility.

8.

Motion Functionality This section describes the motive forces behind each of the primary walkway movements. Real time monitoring of the elevation, extension and slew positions is fed into the heave compensation system.

8.1

Luffing The luffing function of the walkway is performed by two off differential hydraulic cylinders. All oscillating/rotating joints are of the plain bearing type (including spherical type as required).

8.2

Slewing The slewing drive is provided by three off drive units. Each drive unit comprises a multistage gearbox and variable displacement hydraulic motor. The output of each drive unit is fitted with a spur tooth pinion and each interface with the internally geared slew ring bearing which is mounted as described above.

8.3

Telescoping The telescopic bridge motion shall be a rack and pinion type system. Six off direct mounted hydraulic motors shall provide the motive force against two toothed racks mounted on the under side of the inner bridge section. The inner bridge section moves within the outer section with a wear pad assembly which has a computer controlled automatic greasing system installed.

8.4

Hydraulics Hydraulic power is supplied to the OAS via a stand-alone 410kW diesel-hydraulic power unit. This consists of a single 30’ ISO container. Please refer to the vessel interface section contained within Appendix A for a listing of the required hook-ups between the vessel and power unit.

8.5

Electrical/Control

8.5.1 General The diesel-hydraulic power unit also contains a 20kW generator which is used for supplying power to the OAS cabin. A separate electrical supply from the vessel to the power unit for standby power is also routed directly to the OAS cabin so that the systems can be utilised without the diesel unit being started. • Power supply requirements ........................... 230V, 16A

8.5.2 Control System At the heart of the walkway control system is a stand-alone Bachmann controller with heave compensation software. This is a “fly-by-wire” type system, i.e., the hydraulic valves are not directly controlled via the operator, but indirectly, via the controller. This controller interfaces with sensors, switches, joysticks; control valves, etc., and transfers data to and from remote operating consoles. The control system has three operational modes (as described within section 10 of this document). There are also three active compensation systems: •

The approach heave compensation system is activated automatically when the walkway is slewed outboard beyond a set position and also when the walkway is disconnected from the fixed installation. This compensation system can also be enabled or disabled by the operator. Automatic disabling of the system can also occur during certain alarm modes. During heave compensation mode, the vertical position of the connection hook is kept constant (with a stated degree of accuracy) to the World Coordinate System (WCS). The approach heave compensation system takes it’s inputs from the motion reference unit (MRU), which is positioned within the turret section of the walkway and essentially provides information regarding the acceleration of the vessel.

•

The constant torque system of the control system is operated when the walkway is in contact with the connection pole. This mode automatically keeps the walkway against the connection pole, allowing the operator to retract the inner bridge section against the connection point.

•

The constant tension system is activated before the hook is fully engaged with the connection pole. At this point, the telescope and slew functions of the walkway are effectively disabled and the operator can now lower the walkway to contact with the landing platform.

The front end (GUI) of the walkway control system is a Man Machine Interface (MMI) and is used for system visualisation, display of system status and parameter values, and for displaying and logging alarms.

8.5.3 Electrical UPS System A “no-break” electrical system or uninterruptible power supply is installed in two locations. One, primary UPS system is installed within the main power unit and will ensure that the walkway lighting, control and alarm system is maintained for 30 minutes in the event of mains incomer failure. A secondary system is installed along with the vessel bridge mounted equipment. 8.5.4 Sensors The walkway system uses a large number of various types of sensors located at various points. The primary movements of the walkway and lifting system are fitted with real time positional measurement sensors which interface with the heave compensation system. The location of the sensors is designed to be as robust as possible to reduce the risk of damage to the sensor system. Not every sensor has executive actions – some are for positional display purposes only. An extensive cause and effects diagram will be supplied within the operation and maintenance manual for the unit. 8.6

Audio/Visual Aids

8.6.1 Alarm System An extensive audio/visual alarm system will be provided local to the walkway and at the operators’ position. This system will consist of locally mounted flashing lights and horns/sirens. These alarms are repeated at the DP operators’ position on the vessel bridge. 8.6.2 CCTV System A CCTV system is installed to provide the operator with close-up visibility of the bridge and hook arrangement to provide assistance in connecting to the landing station on the installation. 8.6.3 Lighting The walkway shall be fitted with a lighting system with the bridge sections will be illuminated by strip lights.

9.

Safety

9.1

Walkway Access A traffic light system will be installed on the walkway and all access/waiting areas to control access onto the walkway. On the walkway, this consists of a set of lights (visible from both directions) mounted onto the walkway handrail. Within the vessel, a single set of lights will be installed at a suitable location, such as the maintenance crew waiting area or at the exit from the accommodation module.

9.2

Hook Release The walkway “gripper” hook arrangement is fitted with a fail-safe mechanism which allows automatic release from the landing station’s connection pole. This system allows an emergency vessel sail-away to be performed without the need for operator intervention. In the event of this emergency situation, the walkway automatically activates the heave compensation system, thereby maintaining the height of the walkway preventing collision with the landing station. Also refer to section 10.4 for a description of this system.

10.

Operation

10.1

General Description The full and final operating procedure will be integrated into both the ship’s and platform’s procedures. The walkway is connected to the fixed installation as per the basic connecting operation described below. The control system eliminates one motion plane of the walkway at various stages of the procedure, until such point that final connection can be made onto the landing platform. This methodology means that the operator has to control only one function at a time, thereby significantly reducing the complexity of the operation. The walkway has three main operational modes, these being: • Parked • Approach • Connected The control system has three active compensation systems: • Heave compensation • Constant torque • Constant tension The control system consists of the following elements: • Luffing control • Slewing control • Telescope control • Hook and platform control • Traffic light control When parked, the walkway has various braking systems applied to ensure that the unit remains stationary during transit and other non-operational states. When in operational approach to an installation, the walkway has two primary control functions, one being active heave compensation, and the other being manual control. Once the connection procedure has been carried out, the walkway will be joined to the fixed installation in connected mode. This is a passive system and the walkway is allowed to move freely.

It should be noted that the following text outlines the operation procedure whilst the walkway is under full “manual” control. A number of the operation sequences have automated functions reduce the tasks of the operator. 10.2

Manoeuvre & Connection Sequence The following sequence assumes that all pre-system checks and routine maintenance has been carried out and the entire walkway system is in a fit condition. It also assumes that the walkway operator, DP operator and ship’s Captain are all comfortable to proceed given the sea conditions and ship’s DP system before the walkway is lifted from its rest position (which depending on operational readiness may or may not have sea fastenings attached). In the parked position, the walkway system is started via a key switch. The approach sequence can be initiated following integral system checks and confirmation that all systems are healthy, The walkway can now be lifted from the rest position and slewed outboard. Once the walkway is outboard of the vessel, the heave compensation system will be activated. The heave compensation system maintains the vertical position of the hook end of the walkway independent of the vessel movements. The vertical position of the hook is now fixed relative to the connecting pole on the installation. The operator’s objective is to make contact with the pole within the length of the last third of the inner bridge section by telescoping out the walkway. On contact with the connection pole or slightly before, the operator engages the constant torque mode system to ensure that the walkway remains in contact with the pole during the remaining connecting operation. The operator now retracts the walkway so that the connection hook is automatically engaged around the connection pole. When this is completed then the constant tension system is engaged which ensures that the hook remains in longitudinal contact with the pole. At this point, the walkways heave compensation, constant torque and constant tension systems are all active. The connection hook is now locked and the slewing and telescopic motions can then be de-activated and allowed to float in association with the vessel movements. The walkway can now be lowered to make contact with the landing platform. Once the walkway senses the landing platform, it enters full “free floating” status. A passive

weight reduction system is also employed to reduce the load induced on the fixed installation from the walkway. At this point, approval may be given for an OAS operator to proceed along the walkway to manually lower the access step and to carry out a visual inspection of the connection. The traffic light will change to green once the operator confirms that the walkway and the connection is safe to allow personnel to cross. It should be noted that both manual and automatic docking procedures exist within the control, both activated by the operator. Throughout the docking procedure, the three stage monitoring system on the operators console is utilised to ensure that final connection is made with the walkway in the correct position. 10.3

Retrieval & Parking Sequence The retrieval or undocking procedure is effectively the reverse of the above connection procedure. Before carrying out the operation, the operator shall make reference to the monitoring system on the operators console to verify suitable position of the walkway for disconnection. Firstly, the operator raises the access platform which automatically activates the heave compensation system. The walkway connection hook is now then opened and the walkway retracted directly away from the pole. The walkway is now in full approach mode with the heave compensation automatically activated. The walkway is then slewed to a preset slew position when the heave compensation system is deactivated and the walkway is under manual control. The walkway is further slewed until the correct is reached whereupon the walkway is automatically stopped for lowering into the boom rest.

10.4

Emergency Mode The walkway may be disconnected quickly in an emergency. Sensors ensure that should the vessel lose power and sail away, then the walkway will automatically activate the compensation system and disconnect. Control would then be passed to the operator to avoid damage to either the landing platform or the walkway system. However, the end of the walkway will be maintained at a constant height as the heave compensation system is automatically activated once contact with the pole is lost.

11.

Installation This section of the document provides a brief description of the typical OAS installation programme. The walkway will be shipped in two units; OAS walkway unit and hydraulic power unit. The necessary foundations will have been previously installed onboard the vessel. It will also be necessary to reassemble certain components which have been removed to facilitate safe transportation. Firstly, after QA/QC/dimensional verification of the installation of foundation details, the OAS walkway will be installed onto the pedestal. The hydraulic power unit is also installed and the system hook-ups between the OAS and the power unit will be made together with connections to the mimic panel located at the DP operator position in the ship’s bridge. Any transit restraints will then be removed.

12.

Maintenance

12.1

General This section outlines the maintenance strategy that will be required to ensure the smooth and continual operation of the walkway system. The maintenance regime shall be carried out as per the recommended maintenance document, and shall be logged and checked to record compliance. Pre-start up checks will be conducted prior to the walkway system being started, and part of these checks will be the verification that the maintenance regime is being adhered to. Following walkway start up, confirmation of system status through the indication screens will also be reviewed prior to any operation. Weekly maintenance includes the lubrication of the various bearings and open gear systems which do not have an automatic greasing system installed. The automatic greasing system will also be checked to confirm grease quantities are adequate before the next scheduled maintenance. Monthly checks of the batteries within the UPS units will also be carried out to verify that each system is healthy and charging correctly. All gearboxes and motors require verification of lubrication oil levels during each month. Should the oil fall below the recommended level, this will be topped up during this review. All gearboxes and motors require a full and complete oil change based on working hours or a minimum of once a year. The condition of the hydraulic oil from the power unit reservoir will be monitored on a monthly basis. Should the oil fall below the required standard (NAS 1638 Class 6), further checks will be carried out to identify action. Oil replacement will necessitate the flushing and cleaning of the entire system to eliminate sources of contamination. The primary structural elements of the walkway will undergo NDT every four years (tbc). This shall be carried out by the use of an approved NDT method such as MPI, EC, UT or DPI.

12.2

Redundancy System redundancy will be assessed and be based on client requirements for operational availability. The system currently includes a minimum redundancy which extends to the control system I/O boards ensuring that the failure of one board does not precipitate failure of the entire control system. A recommended spare parts list will be included as part of the documentation package.