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1. GENERAL
1.1 Purpose
This document is to give a technical description of the new Icarus subsea launching crane
1.2 Project Background
The background to the project is that wishes to replace an existing crane on with a new crane that provides increased reach and additional functionality for subsea
launching operations. A study was conducted by JMC Engineering (Ref. Doc. No. R80576-001) resulting in the recommendation of the following:
The crane boom must have an extended reach of at least 11m, sufficient to clear the pontoon and rig structure.
It must also be able to place the load on the deck overhang. In order to bring the boom into the main structure, it should be no longer than 4.6m when
retracted. Without making new calculations, the existing pedestal is to be used for the new crane.
Although the new crane will have larger dimensions than the existing one with respect to reach, it is necessary to have the new crane as light as possible so that the lifting moment capacity is maintained. Total weight of the existing crane is 17.2T, including the pedestal adapter that weighs 2.6T
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4. CRANE IDENTIFICATION DATA
4.1 Manufacturer’s contact data
The manufacturer/supplier of the total crane package:
16092
4.2 Icarus Crane Overview
Fig.1
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6 MAIN DATA
6.1 General
1. Construction All Welded, 3 section telescopic box boom and king. 2. Type Multipurpose 3 Axis, pedestal mounted. 3. Motive Power Self contained Electro-Hydraulic HPU 4. Capacity 15T / 8m – 11T / 11m 5. Purpose of use Platform and Subsea lifting only. (See Safety Note) 6. Total weight 14000kg (Excluding Pedestal and Main Motor weight)
The pedestal is an existing structure welded on the rig deck, to which the new crane is bolted. The pedestal also contains the main electric motor that drives the HPU.
Safety Note: This crane is not to be used for lifting loads from vessels, or lifting personnel.
6.2 Environmental data
1. Design temperature -20 C2. Max./Min. ambient temp. Max: 45 C / Min: -20 C3. Humidity 100% 4. Area classification Zone 1 (ATEX)
Accelerations on Crane Ax Ay Az WindCondition (m/s2) (°) (m/s2) (°) (m/s2) (°) (m/s) Still water – static heel (3°+3°) parallel to jib 0.074 4.24 0.00 0.0 0.0 - 0 Still water – static heel (3°+3°) normal to jib 0.00 0.0 0.074 4.24 0.0 - 0 Op. + wind – heel (4.5°+4.5°) parallel to jib 0.11 6.4 0.00 0.0 1.6 - 25 Op. + wind – heel (4.5°+4.5°) normal to jib 0.00 0.0 0.11 6.4 1.6 - 25 Survival – environmental loads parallel to jib 1.80 10.4 0.00 0.0 1.9 - 63 Survival – environmental loads normal to jib 0.00 0.0 1.80 10.4 1.9 - 63
6.3 Construction
5. Regulation PSA, HES Regulations6. Design standard NS-EN 14985 / NS-EN 14492-1 7. Construction standard DNV Lifting appliances / NS5514 8. Duty group U1 – 31500 cycles (EN 13001-1) 9. Loading Q4 – 0,25 – 0.5 (EN 13001-1)
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6.4 Parameters
6.4.1 Crane
1. Capacity 15T @ 8m – 11T @ 11m 2. Slewing angle 180° range (Limits set on installation) 3. Boom luffing angle 0° to +50° (0°=Horizontal) 4. Boom telescopic extension 6,2m 5. Max working radius 11m 6. Min working radius 3 m (Boom fully elevated, telescope fully closed) 7. Luffing time (0-50°) 50 sec (Without Load) 8. Boom extension time (0-6,2m) 55 sec (Without Load) 9. Slewing speed 1,2 rpm (Without Load)
1. Working pressure 285Bar 2. Maximum Oil flow 270 L/min 3. Oil reservoir 1000 L 4. Filtration Pressure & Return lines 5. Electrical motor 690V / 60Hz / 145kW
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6.6 Anticipated crane usage frequency
The anticipated crane usage frequency is set by the customer in the table below:
FEM 1.001Lifting appliance The crane as a whole Appliance group A2 Class of utilization U1 (nmax=32000 cycles) Load spectrum class
Q3 (kp=0.25-0.5)
Machinery Type of mechanism Hoisting Luffing Slewing Telescope
Mechanism group M5 M2 M1 M1 Class of utilization T5(T=6300 h) T1(T=400 h) T1(T=400 h) T1(T=400 h) Load spectrum class
L2 (km=0.25) L3(km=0.5) L2(km=0.25) L2(km=0.25)
Structural Structural partKing (Column) Boom
Mechanism group M2 M2 Class of utilization T0(T=200 h) T0(T=200 h) Load spectrum class
L2(km=0.25) L2(km=0.25)
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7.1.2 Crane booms
The main boom is a rectangular open box boom connected to the column with axle pin and bronze bushings. Two parallel hydraulic cylinders connected between the column and boom, provide luffing motion. The cylinders are connected to the structure via axle pins and bronze bushings. The two extension booms (telescopic booms) are of rectangular box construction and retract within the main boom. Sliding bearing pads ensure correct operation and load support. A single 2-stage telescopic ram is connected internally to drive the extension booms and is connected via axle pins and bronze bushings to the main, first and second extension booms. Access panels are provided at the back of the main boom and in the sides of the second extension boom for maintenance. The operation of the ram is such that the booms extend in sequence but retract randomly. The outer tip of the second extension boom carries two rope sheaves, the upper of which has a load cell axle for payload monitoring and overload protection.
7.1.3 Hydraulic Cylinders The 2 luffing cylinders are double acting single stroke, with fixed bronze bushings in the end connections. The cylinder tubes are metalized carbon steel and the cylinder rods are of nicrom alloy.
The single 2 stage telescopic cylinder is double acting and constructed from metalized carbon steel outer cylinder with nicrom alloy rod and duplex stainless first extension tube. The cylinder has fixed bronze bushings to the end attachments and bronze bushed trunnion mountings to the first extension cylinder body. The cylinder assembly also carries a drag chain arrangement for the handling of services to the boom tip.
7.1.4 Winch The winch is mounted directly onto the top of the main boom. It is a 2 speed hydraulically driven unit with integrated motor, gearbox and negative (fail safe) disc brake. The winch is a single line, multi-layer unit with spooling gear and rope counter assembly attached. It has a total rope capacity of 470m x Ø28mm, with a ‘3 turn remaining’ sensor to stop the winch at maximum rope out limit. It is rated at 15T SWL.
7.1.5 Service platform A service platform is fitted on the crane. It is an all welded Aluminum Alloy (6082 T6) construction and provides personnel access to: emergency / service operation panel, main hydraulic filter, electrical services cabinet and centralised lubrication system.
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7.2 Hydraulic system
7.2.1 General
The description of the hydraulic system refers to the hydraulic flow diagrams: Hydraulic Flow Diagram – Crane S6-HP-LBF-1000-001 Hydraulic Flow Diagram – HPU S6-HP-LBF-1000-002
The HPU is a load sense (LS) type with variable displacement pump, delivering full working pressure, but operational flow only on demand. This provides a fast, but energy-saving system. Hydraulic function operation is via a valve manifold (distributor) with electro and manual lever actuation.
The hydraulic system has the following features: Internal oil reservoir, integral with crane column. Main electrical motor housed within crane pedestal. Flexible coupling between motor and pump. Main hydraulic pump within crane pedestal. Strainer on pump inlet side. Check valve on pressure side. NO butterfly valve between tank and pump. Pressure relief valve integral with main pump valve block. Start-Up relief valve integral with main pump valve block. Pressure filter with indicator. Return filter with indicator. Breather filter. Electrical level sensor and visual level indicator. Temperature sensor. Electrical heater in oil reservoir. Oil cooler with electrically driven fan. Rear hatch on column for inspection/cleaning of oil reservoir. Ball valve inside pedestal for drainage of oil.
The main hydraulic unit has the following specification: Working pressure 285Bar Oil flow 270 L/min Oil reservoir 1000 L Filter pressure indication return and drain Electrical motor 690V / 60Hz / 145kW
The crane is also equipped with a pneumatically driven back-up pump located on the rear side of the column. In case of power loss, the backup HPU is be connected to the rig air supply. In this case all movements of the crane are operated by the manual control levers, with limited speed. The speed is regulated by the air flow. The backup HPU has the following features:
Pneumatic motor flanged to column. Flexible coupling between motor and pump. Hydraulic pump inside the oil tank (column). Check valve on pressure line. Column mounted air supply FRL unit. Recommended air supply 3900 NL/min @7barg.
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7.2.2 Parts description - Crane
Referring to the crane hydraulic diagram – S6-HP-LBF-1000-001
Item Part Description 1. Hydraulic distributor Standard Sauer-Danfoss PVG 120/32, 5 sections, with electrical
activation for remote operation and manual levers for emergency / maintenance operation. Two valves operate in parallel to provide the required flow rate for the winch at maximum speed. Integrated main pressure relief valve for system protection if the HPU supply pressure rises above a pre-set value. Individually adjustable pressure control valves for each crane movement. A pressure signal (LS) is delivered to the hydraulic pump when any of the valves are actuated.
2. Slewing motor Including planetary gearbox with brake and pinion. There are 2 off slewing motors installed on the crane, to the left side of the column. Both act on the internally geared slewing ring.
3. Overcenter valve Double overcenter valve with brake outlet per slewing motor. This controls the pressure to the brake and also provides smooth operation of slewing. The valve for each slewing gear is flanged directly to the motor and has an emergency release line for controlled recovery operation.
4. Slewing limitationvalve
An NC centre off valve is connected to the slewing motor supply lines. When the crane is slewed to either end limit, the valve is mechanically actuated to divert the flow to tank, thus stopping further rotation in the demanded direction. The crane is still allowed to slew away from the end point. Upon moving away from the end point the valve returns to centre NC condition.
5. Main boom liftingcylinder
Double acting cylinder for the luffing movement of main boom. There are 2 off parallel cylinders for the crane.
6. Overcenter valve A single acting overcenter valve is built in to each main boom lifting cylinder. The valve keeps the load in position and also provides smooth operation of the boom. There is piping between the cylinder ports and an emergency release line for controlled lowering the boom.
7. Winch 1 off single pull, multi layer winch with spooling gear, positioned on the main boom. The winch also includes a gearbox, negative disc brake and a hydraulic motor. Limitation of movement (up/down) is handled by electrical switches: Hoisting: Stop on boom tip. Lowering: Three turn limit on winch drum. Rope deployed length measured by sensor on spooling gear.
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Item Part Description 8. Winch motor Dual displacement, radial piston motor to give selectable high and low
speed operation of the winch. The speed is controlled by an integral pilot operated valve and an external NC solenoid valve. In the ‘Normal Lifting’ mode the motor operates at the highest speed. In ‘Heavy Lifting’ mode the motor operates at the lowest speed. In ‘Backup’ mode, with HPU stopped, the motor is set to operate at the lowest speed that ensures maximum lifting effort.
9. Overcenter valve Double overcenter valve with brake outlet for the winch motor. This controls the pressure to the brake, and also provides smooth operation of the winch. The valve is directly mounted to the motor valve block.
10. Winch EmergencyLowering Valves
A pilot operated NC valve (LE) in line with a needle valve (NV) permits the emergency lowering of payload in conjunction with the hand pump and manual emergency function valve. The Needle valve is pre-set to limit the winch motor speed for safe lowering of the payload. This valve arrangement is directly mounted to the motor valve block.
11. ‘Sea-Lift’ controlvalves
Pilot operated relief valve, shuttle valve, counter balance and check valves. This assembly is directly mounted to the winch motor valve block and provides enhanced control of the winch motor during ‘Sea-Lift’ mode only. See sections 10 & 11.2 for detailed operational description.
12. ‘Sea-Lift’ operatingvalves
A pilot operated, adjustable pressure, counterbalance valve in combination with a normally closed (NC) solenoid valve permits the activation of the ‘Sea-Lift’ control valve when the crane is selected to be used in ‘Sea-Lift’ mode. An NC solenoid valve is also activated to hold the winch brake off during ‘Sea-Lift’ mode. See sections 10 & 11.2 for detailed operational description.
13. Accumulator The accumulator stores hydraulic fluid at pressure in order to provide an independent source of fluid for emergency winch brake release only.
14. Pressure gauge(Accumulator)
High pressure gauge giving visual indication of accumulator content pressure.
15. Manual Ball Valve 3-Way ‘L’ port, manual ball valve, locked in the NC position.Used only in emergency, to allow fluid from the accumulator to release the winch brake. This then permits lowering of the load using the emergency manual hydraulic circuit in conjunction with the hand pump.
16. Check valve(Accumulator)
Permits the accumulator to be automatically charged during normal system running.
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Item Part Description 17. Pressure gauge
(System)High pressure gauge connected to the main pressure line allowing visual inspection of system pressure. The same gauge may also be connected to the LS port (quick connection) in order to check LS pressure from each function valve during trouble shooting.
18. Pressure gauge(Return)
Low pressure gauge connected to the return line enabling visual inspection of return line pressure.
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7.2.3 Parts description - HPU
Referring to the HPU hydraulic diagram – S6-HP-LBF-1000-002
Item Part Description 1. Main Electric motor Located inside the existing pedestal and connected to the hydraulic
pump via a flexible coupling. (Note, the initial motor to be used is the existing one, as fitted to the previous crane.)
2. Main hydraulicpump
Variable pump operated by LS line from hydraulic distributor, bolted to the underside of the column, inside the pedestal.
3. High pressure filter Main filter for hydraulic oil, positioned between the main pump andhydraulic distributor. Includes an electrical switch giving the operator a signal via the PLC, when filter element requires replacing. However the oil must be at normal working temperature as cold oil can temporarily clog the filter giving a false reading.
4. Return line filter Tank mounted return line filter for cleaning of return oil from the system. Includes electrical switch giving the operator a signal when filter element should be replaced. However the oil must be at normal working temperature as cold oil can temporarily clog the filter giving a false reading.
5. Main suctionstrainer
Internally, tank mounted suction strainer for protection of the main pump feed line.
6. Butterfly valve Butterfly valve (NO) situated in the main pump feed line from the oil tank.
7. Oil cooler An air cooled matrix oil cooler is fitted to help maintain the hydraulic oil temperature within specified limits. The cooler is situated in the return line prior to the oil tank. It has an internal bypass valve rated at 2 Bar. The cooler assembly is bolted under the service platform for ease of access.
8. Oil cooler motor The oil cooler fan is driven by an electric motor. The motor is controlled electronically and starts automatically when the temperature exceeds a specified limit.
9. Oil Heater An electric heater is positioned inside oil tank in order to help maintain the hydraulic oil temperature within specified limits. The heater is controlled electronically and cuts in when the temperature is below the lower specified limit and cuts out above the upper specified limit.
10. Temperaturesensor
The PT100 electrical temperature sensor is integral with the heater assembly.The temperature sensor monitors the oil in the tank in order to control the oil cooler and oil heater as required.
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Item Part Description 11. Breathing filter Tank mounted breathing filter to maintain ambient pressure within the
oil tank at all times. The breathing filter is also the filling point for the hydraulic oil reservoir.
12. Level sensor Electrical pressure transmitter to measure the oil level in tank. The pressure transmitter monitors the oil level in order to generate an alarm signal in case of low oil level.
13. Level gauge Tank mounted level gauge, including thermometer, for visual inspection of oil level and temperature.
14. Back-up pump A fixed displacement, gear pump is mounted inside the oil tank. The pump is connected directly to the main pressure line, allowing all crane movements when running. Check valves are situated in the pressure line to prevent back pressure in the back-up pump during operation of main pump and vice verse.
15. Suction strainer A suction strainer is connected directly to the inlet of the back-up pump to protect against contamination.
16. Pneumatic motor An externally mounted pneumatic motor drives the back-up pump via a flexible coupling. The motor is driven by the rig air supply during emergency operation.
17. Silencer A silencer connected to the exhaust port of the pneumatic motor reduces noise levels during running.
18. FRL Unit The FRL unit connected up-stream of the pneumatic motor provides filtration, pressure regulation and lubrication of the air supply to the motor.
19. Ball valve Ball valve (NC) underneath the tank for draining out hydraulic oil.
20. Ball valve Ball valve (NO) for isolation of emergency hand pump feed line.
21. Hand pump Manual hydraulic hand pump, used in emergency only to provide pressure to the manual emergency function valve. The hand pump includes integral check valves and NC pressure release valve. Any return line pressure is vented back to tank via a check valve.
22. Manual emergencyfunction valve
A monoblock, two station, manual lever, NC ‘Hold-To-Run’ valve. Used only in emergency, in conjunction with the manual hand pump, to selectively release the slewing motor brakes, luffing cylinder overcentre valves and winch motor emergency load lowering valve.
23. Start-up relief valve An NC solenoid valve is mounted in the main pump control circuit tomomentarily ‘off-load’ the pump during the main electric motor start sequence. Once the motor has run up the valve is closed. Approximate time valve open = 5s (This value is engineer adjustable to suit the motor characteristics and will be set during commissioning).
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7.3.4 Hydraulic control cabinet
The crane will be normally operated by the portable radio remote control unit, but for emergency / service operation it is driven via the manual levers on the hydraulic distributor, situated in the hydraulic control cabinet. This cabinet is accessed from the service platform. Inside this cabinet there is:
A selector switch to change from ‘remote’ to ‘manual’ operation. When the switch is set to ‘manual’ it disables the crane functions being operated from the radio remote control, including the remote emergency stop button, but still permits all information and warnings to be displayed on the radio remote control.
An emergency stop button.
Note: Operation from this panel is only for emergency / service movements of the crane.
7.3.5 Radio remote control
The crane will normally be operated by the radio remote control unit. This unit is portable, giving the operator a better view of the crane and load during operation.
The radio remote control system consists of the following: 4 each 1-axis joysticks for proportional operation of all crane movements. Display showing suspended load, length of wire and operating radius. It will also show
various error messages/codes. (see 7.3.5.1 to 7.3.5.3) 7 each LED indicators for warning/information. Buttons for operation modes. Emergency stop button. Button for start and stop of HPU. Connector for cable operation in the event of radio signal failure. (20m cable supplied)
Function DescriptionSystem av/på PÅ (switch I) Enables the crane system.
AV (switch O) Switches off the HPU motor. Start Starts the HPU main electrical motor. Status Green light indicating that crane is ready for use.
(Note: The crane always starts up in ‘Normal’ mode) Lampetest Checks that all LED indicators, alarm-sounder and flash beacon on crane are
working. It is also the fault reset.Sjøløft 5 sec push on the button enables the crane for subsea lifting. (only if certain
parameters are met, see section 11.2.1) The yellow LED is lit. By pressing the button 5 sec again, the crane returns to ‘normal’ platform lifting mode and the LED turns off.
Tungløft 5 sec push on the button enables the crane for heavy lifting (0-15T). The yellow LED is lit. By pressing the button 5 sec again, the crane goes back (if permitted) to normal lifting (0-5T) and LED turns off.
Wirelengde Pushing the button for 5 sec switches the wire length indicator display from ‘absolute’, total deployed length to ‘incremental’, local length and sets the local length to zero. Momentary operation of the button toggles between ‘absolute’ and ‘local’ length values on the display. By pressing the button for 5 sec again resets the local length display to zero.
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7.3.5.2 Warning messages (10 characters) Message Description OBS 90%SWL 90% of SWL is exceeded. Justr sving Crane not in center position during sea lifting. Juster bom Crane not at full extension during travel past pontoon or not horizontal.
7.3.5.3 Error Messages Error messages are displayed on the radio remote control LCD display in Norwegian text for all faults.
7.3.6 Antenna
For maximum operating range the antennas should be mounted so that a clear “line of sight” between the antennas and remote-control units exists during crane operation. Antennas should not be mounted inside metal enclosures, and must be mounted vertically, pointing upwards. The operating range will be degraded if two or more antennas are mounted in close proximity.
7.3.7 Crane instrumentation and feedback
The crane has one ‘Load Cell’ device to measure the Load in metric tonnes (T) and encoders for rotary position, boom extension, boom elevation and winch wire length.
7.3.7.1 Load cell The load cell is an axle mounted device in the upper rope sheave at the boom tip that measures the suspended load.
7.3.7.2 Encoders Slew Encoder is a pulse generator signal, which is converted to angular position in the PLC. The Encoder Data is referenced by the ‘Slew Zero’ position switch, which is also used as the ‘Sea-Lift’ position. (i.e. with the boom 90° to the rig side). The absolute maximum slew movements are limited hydraulically.
Lift Axis is an Inclinometer, and provides data that is computed in the PLC to produce 0 to 60 degrees feedback. This data is critical, as it is used for ‘Load Calculations’. The encoder feedback is monitored by the PLC, if a ‘movement’ demand is executed, and no encoder feedback is received in time t, then a ‘critical fault’ is recorded, and all load increasing movement (lowering of the boom) is prohibited.
Telescopic/Boom Axis encoder is a Quadrature Pulse type; two separate pulse signals are computed by the PLC to produce distance and direction. A Limit Switch references the axis when the booms are fully closed. The total Boom lengths are shown below. This Telescope/Boom data is critical, as it is used for ‘Load Calculations’. The encoder feedback is monitored by the PLC, if a ‘movement’ demand is executed, and no encoder feedback is received in time t, then a ‘critical fault’ is recorded, and all load increasing movement (extending the boom) is prohibited.
Extension of Boom 1: 0 to 3.2m Extension of Boom2: 3.2 to 6.0m Booms fully closed radius: 4.8m (From Slew Axis to Rope Centre) Booms fully extended radius: 11.0m (From Slew Axis to Rope Centre)
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Winch wire deployed length encoder, mounted on the outside of the winch spooling unit, is a pulse generator signal which is converted to deployed length in the PLC. The encoder is zero referenced by the hook upper limit switch on the boom tip. The maximum paid out rope length is also limited by an independent ‘3 turns remaining’ switch on the winch drum. (Ref. Block diagram S6-HP-EBL-1000 B10)
7.3.8 Visual / audible alarms The following alarms are available.
Flash beacon Yellow (Ref. Block diagram S6-HP-EBL-1000 C3) Alarm horn 118dB (Ref. Block diagram S6-HP-EBL-1000 D3) LEDs on remote control
The flash beacon is on as long as the main motor is running and consequently hydraulic pressure is supplied to the crane.
In an overload condition, the alarm horn will sound. The horn can be tested via the lamp test function on the radio control terminal.
LEDs on the radio control terminal will indicate overload conditions, 90% load conditions and sensor/system errors. The LEDs can be tested via the lamp test function on the radio control terminal.
The electrical panel will also show sensor / system errors by a red lamp H4 on the cabinet door (Ref. circuit diagram S6-HP-EBI-1005-004).
7.3.9 Oil Heater
The oil heater, placed inside the hydraulic oil tank to control the oil temperature, has the following electrical data:
230VAC single phase 1kW / 4A Lower Set Point (ON): <30°C Upper Set Point (OFF): 40°C (Hardware adjustable) Upper Set Point High (STOP) 90°C (Hardware fixed cutout)
During crane operations the heater control (ON/OFF) is provided by the PLC and depends on the built in PT100 temperature information. Additionally, the heater contains 1 independent safety thermostat with the upper set-point as above. Serial connection of the thermostats and the heating elements with the 230VAC supply ensures the circuit to be operated when the trigger temperatures are reached. The electrical cabinet contains the heater contactor and over-current protection (ref. circuit diagram S6-HP-EBI-1005-001). The heater has an independent Standby mode indicated by lamp H4 on the electrical cabinet showing the 2 states:
‘Standby ON’: Heater on in automatic operation with main motor stopped. ‘Standby OFF’: Heater off when the crane is shut down.
In either standby state, when the crane system is started the heater system is activated and controlled by the PLC. If the radio remote control is switched to manual or a ‘time-out’ situation occurs, the heater will remain active to maintain oil temperature. If an emergency stop or fault stop occurs, the heater is switched off. The heater is produced by NORSKE BACKER A/S and designed for operations in hazardous areas (Ex).
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7.3.10 Oil Cooler
The oil cooler, located under the work platform, used to control the oil temperature, has the following electrical data:
230VAC single phase 1kW / 4A Upper Set Point (ON) 65°C Lower Set Point (OFF) 50°C
Cooler control (ON/OFF) is provided by the PLC and depends on the built in PT100 temperature sensor information from the oil heater. In a high temperature condition, the fan is switched on by the PLC, simultaneously cutting the power to the heater contactor (ref. circuit diagram S6-HP-EBI-1005-002 C11) to prevent the heater to be on at the same time. The hardwired power cut-off works in parallel to the software based heater shut-down function. The cooler is produced by ASA and designed for operations in hazardous areas (Ex).
7.4 Control system
7.4.1 PLC system The control system utilizes a SIEMENS S7-300 PLC system with the following components:
PLC Control, General Overview The PLS Control program is designed in modular format Note: SI units only, are used on this Crane Siemens PLC Hardware Description, Reference Electrical Drawings SX-HP-EBI-1005-xxx
Rack (0), Slot 1 Short description: PS 307 5A Order no.: 6ES7 307-1EA00-0AA0 Designation: PS 307 5A Width: 1 Rack (0), Slot 2 Short description: CPU 315-2 PN/DP Firmware version: V2.6 Order no.: 6ES7 315-2EH13-0AB0 Designation: CPU 315-2 PN/DP Width: 1 Rack (0), Slot 2, Interface X1 Short description: MPI/DP Order no.: - - - Designation: MPI/DP Width: 1 PROFIBUS address: 2 Highest PROFIBUS address: 126 Baud rate: 1.5 Mbps Rack (0), Slot 2 Interface X2 Short description: PN-IO Order no.: Device name: PN-IO IP address: 192.168.1.1 Diagnostic addresses Interface: 2046
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Rack 0, Slot 2, Interface X2 P1 Device name Port 1 Local port: SIMATIC 300\PN-IO (CPU 315-2 PN/DP)\Port 1 (X2 P1) Partner port: Any partner Rack (0), Slot 4 Short description: DO8xRelay Order no.: 6ES7 322-1HF10-0AA0 Designation: DO8xRelay Digital channels: 8 Outputs Width: 1 Addresses OutputsStart: 0 End: 0 Rack (0), Slot 5 Short description: DO16xDC24V/0.5A Order no.: 6ES7 322-1BH01-0AA0 Designation: DO16xDC24V/0.5A Digital channels: 16 Outputs Width: 1 Addresses OutputsStart: 4 End: 5 Rack (0), Slot 6 Short description: DI32xDC24V Order no.: 6ES7 321-1BL00-0AA0 Designation: DI32xDC24V Digital channels: 32 Inputs Width: 1 Addresses InputsStart: 8 End: 11 Rack (0), Slot 7 Short description: AO8x12Bit Order no.: 6ES7 332-5HF00-0AB0 Designation: AO8x12Bit Analog channels: 8 Outputs Width: 1 Addresses OutputsStart: 300 End: 315 Rack (0), Slot 8 Short description: AI8x16Bit Order no.: 6ES7 331-7NF10-0AB0 Designation: AI8x16Bit Analog channels: 8 Inputs Width: 1 Addresses InputsStart: 300 End: 315
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DP master system: Assigned master: Short description MPI/DP Designation MPI/DP LocationStation SIMATIC 300 Rack 0 Slot 2 Receptacle for interface Module 1 PROFIBUS address 2 Group: 1 Slave : MC-LINK-DP PROFIBUS address: 3 Slave (3) MC-LINK-DP Family: CAVOTEC BASE UNIT (Remote Control for Crane) DP slave type: MC-LINK-DP Manufacturer: Micro-control as GSD file name: MCLINKDP.GSD GSD revision: 1 Identification number: 0x1002 Revision of the DP slave: Rev. 2.4 Hardware release: Rev. 2 Software revision level: Rev. 1.2 PROFIBUS address : 3 Diagnostic address: 2044 SYNC: Yes FREEZE: Yes Watchdog: Turned on
7.4.2 Crane Safety
The PLC will ‘MIRROR’ the hardware for Emergency Stops & Manual Mode. The Emergency Stop Condition will remain until the Emergency Stop Button is depressed, and the RESET Push-Button has been activated.
o The hardware is the MASTER, therefore, the Hardware will remove POWER fromthe Crane, with the PLC as a back-up/Diagnostics.
The Crane axis Valves are enabled/disabled by the PLC during normal operation. o In Emergency Stop Condition, the Hardware is the Master. Therefore, 24VDC
Supply will be removed from the Axis Valves.o The PLC will compute the LOAD and the WARNING and OVERLOAD Limits. If the
LOAD Value is equal to, or Greater than 90% of the Computed Maximum LOAD, aWARNING is displayed.
o If the LOAD Value is equal to, or Greater than 110% of the Computed MaximumLOAD, an OVERLOAD condition will exist. All forward movement is inhibited, that is,only movement that can safely bring the LOAD to ground will be allowed. Viz:LOWER LIFT axis, RETRACT Telescope Axis, LOWER Winch.
CAVOTEC RC Unit o If the RC Unit not communicating, then an Emergency Stop is invoked.
Crane selected MANUAL Datum Axes / encoders Prevent Axes from Overtravel Hydraulic Failure
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7.4.3 Remote control communication The PLC communicates with the CAVOTEC crane control system using a Profibus (Process Field Bus) communications cable (distributed peripherals, remote I/O) frm the Siemens CPU, to the Comms port on the CAVOTEC base unit, mounted in the main electrical cabinet. A GSD (generic station) file provided by CAVOTEC is loaded to the PLC hardware configuration: This creates the interface between the PLC and the CAVOTEC remote I/O base station unit for data transmit / receive.
7.4.4 Software structure The software has been written using LAD ladder logic under Siemens Simatic S7 V5.4 SP5 programming environment.
Software functionality in processing order:
Upload data from CAVOTEC ‘Radio Control’ crane unit. All data is in digital format. o Monitor received data from CAVOTEC ‘Radio Control’ crane Unito Movement request for each axis. This data is received via a ‘joystick’ on the RC
control unit, one joystick for each axis. This data is computed to +ve and –vevalues, then processed and moved to the ‘analog output data area’ for each axisproportional valve.
o Start/Stop control: Start/Stop main motoro Reset: reset faultso Audible alarm / horn
Scale input data o Industry standard 4-20mA data to the analog input card. The analog input card
converts the analog data to digital, before being processed by the PLC. The digital data is converted / scaled to engineering units (SI units). All scale data is provided by the instrument manufacturer.
o Winch wire load cell (Tones)o Winch wire length (meters)o Boom Raise Axis 1 angular position (degrees)o Boom Extension length (meters)o Slew Rotation angular position (degrees)o HPU Oil temperature (degrees Celsius)o HPU Oil level (mBar)
Alarms / safety control: o Circuit breaker monitor.o Emergency stops.o Equipment status.o LOAD status.o Hydraulic Oil temperature status.o Oil level status
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Main power control o Hydraulic motoro Motor fan controlo Oil heater control
Axis control o Slew / rotate crane controlo Boom Lift raise crane controlo Telescopic / extend axis crane controlo Winch crane control
Crane load control. Hardware Limits prevent Boom Lift and Telescope OVERTRAVEL movement, and provide a reference point to Datum Telescope Axis.
o Compute actual crane load from ‘LOAD CELL’ datao Compute maximum allowed LOAD dependant on LIFT axis angle, and telescope
extension dimensiono Compute WARNING at 90% of allowed loado Compute OVERLOAD at 110% of allowed loado Compute SEA-LIFT permission dependant on lift axis ANGLE. Telescope
o Fault analysis, and display order of faults / alarms. Note: Only one message can bedisplayed at any one time, therefore, diagnostic data must be displayed in fault priority order
o Compute text in ASCII for CAVOTEC displayo Text display data for winch actual Loado Text display data for winch cable lengtho Text display data for telescope actual lengtho Text display data for slew rotation angleo CAVOTEC RC unit LED display
Output control o Down load diagnostic / display & LED status data to CAVOTEC ‘RC Control’ unito SCALE data for analog output control. Viz. proportional valves for axis movement
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8 SAFETY SYSTEM
There are a number of installed safety features on the crane in order to avoid dangerous situations during operation. They cover mechanical situations, system failures and errors and explosion protection.
The system has the following safety features: Overcentre valves. Negative disc brakes. Emergency stops. Control system monitoring. Safety interlock system. Overload protection. Manual release of winch brake. Oil temperature regulation. Thermistor protection for main electrical motor.
8.1 Overcentre valves
All hydraulic cylinders and motors are fitted with overcentre valves. These valves, in conjunction with the negative disc brakes, prevent the load from falling in case of power loss or emergency stop condition.
8.2 Negative disc brakes
All hydraulic motors have fail-safe brakes which activate (on) to prevent the load from falling or the crane slewing, in the event of power loss. During subsea lifting only, the winch brakes are held off to ensure that the wire is pulled out in case of overload. In this condition only, the load is then held by the hydraulic motor. Brakes are immediately active at emergency stop condition, power failure, fault conditions and when all manoeuvre handles are released.
8.3 Emergency stop buttons
The emergency stop buttons immediately halt all crane operations when activated. There are 3 emergency stop buttons at the following locations:
On the radio remote control. On the rig wall adjacent to the crane. Inside the hydraulic control cabinet. Available only when the crane is being used in manual
service / emergency operation.
Additionally there is also an E-Stop button on the existing motor start-stop panel on the rig.
All emergency stop buttons cut off the power to the main electrical motor. All brakes will activate, and no crane movements will be allowed.
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8.4 Control System. Monitoring
The control system has a continuous self-monitoring function that alerts the user to malfunctions, or in severe circumstances, stops crane movements. The following are covered:
Radio communication between the remote and the base. Analog transmitters signal shall be between 4 and 20mA. Switches shall be normally closed (NC) i.e. fail safe.
8.5 Safety Interlock system
A total crane stop will be triggered by certain system conditions resulting in a safety interlock. These conditions are:
Oil Level low low. Oil temperature high high. Oil temperature sensor burn-out. Radio control fault. (Including ‘Out-of-Range) Main Motor Over Temperature
The oil temperature is monitored for ATEX reasons and is monitored both in the barrier of the sensor and the PLC. The barrier U2 has two switch outputs energizing / de-energizing the relays d9 (high temperature) and d10 (burn out). The outputs are programmable with the barrier. (Ref. Circuit diagram S6-HP-EBI-1005-009 C8) In parallel the PLC is doing the same monitoring within its software. If one of the conditions is triggered, the relays d1 and d1A are de-energized (PLC output NC), (ref Circuit diagram S6-HP-EBI-1005-004 E7), opening the 230VAC supply line to the main contactors K1, K2 and K3 with the same result as an E-Stop situation. (Ref. Circuit diagram S6-HP-EBI-1005-002 C10/11)
A radio control fault is monitored via U12 of the radio control base station U11 and the radio control fault relay d12 (Ref. Circuit diagram S6-HP-EBI-1005-011 E3). This fault, in series with the oil temperature monitoring, also triggers the safety interlock system. However, a radio control fault can be bypassed by the manual operation switch via the manual control relay d15. The radio control unit has a normal operational range of 100 meters, but can operate at up to 1000 meters if conditions are optimal. If the radio control unit moves out of radio range, an emergency stop condition will exist. When the radio control unit is moved back into radio range, a reset must be executed to allow crane operation to resume. The radio control unit has a “time-out” function. If it is not used within the “time-out” period, it will automatically switch off. The “time-out” period is 30 minutes. (Default value).
8.5.1 Proportional valve output As well as the power cut-off to the crane’s main components due to an emergency stop or a safety interlock condition, the power to all actuators of the proportional valves is cut. The valves then spring return to the centre off position. The power cut-off takes place via the safety relay K0.
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8.5.2 Resetting Emergency stop and safety interlock The release of an E-Stop switch or the end of a safety interlock condition will not cause the system to automatically re-start again.
The system has to be manually reset by switching the radio terminal off then on again and then pressing the ‘lamp test’ button on the radio control for 1 second. After that, the START button on the radio control will start the main HPU motor again.
Safety Note: Even when the main motor has been stopped, there will be hydraulic pressure contained within the system. On no account should work be performed on any part of the system until it has been safely bled down.
8.6 Overload protection
8.6.1 Platform lift mode
Overload is limited by load cell output and crane positional feedback. The crane does not have a varying load spectrum at varying angles of luffing, only at varying boom lengths. (Ref. Load Diagram S6-HP-AVM-002) External dynamic forces are not a concern in this mode of use.
8.6.2 Sea-Lift mode
The ‘Sea-Lift’ mode of operation is only available for deploying and recovery of loads into and out of the sea through the splash zone. (See sections 10 and 11.2 for further details). During Sea-Lift operation, the brakes on the winch are held off by pilot pressure from a solenoid valve and the rope tension is controlled by the PLC within set limits either side of the known payload given by the load-cell. In the case of excess load on the winch rope due to wave motion or hydrodynamic drag, a pilot operated relief valve opens to slow or reverse the winch motor in order to reduce the load in the rope until it is within the operating limits. If the designed crane load limits are approached the system will automatically warn when these limits have been reached and stop the crane operation, where appropriate, in the normal manner.
Note:For Sea-Lift use, the external forces due to buoyancy, drag, added mass & slamming must be calculated for each item to be lifted, and compared to the load diagram for Sea-Lift mode. (Ref. Load Diagram S6-HP-AVM-004). Operations must be planned to take into account the wire weight that the proposed operating depth will add to the load, although the system will automatically account for this value as the rope is paid out. The wire weight is typically 360kg/100m with a total length of 470m.
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8.7 Manual release of winch brake
In the event of power failure, emergency stop actuation or fault condition stop, the load on the winch can be lowered manually. This is achieved by the following sequence:
Operating the Manual Brake Release Valve, (Normally locked closed).The valve is located under the crane’s access platform and is reached from deck level.
The accumulator, pre-charged during normal operation, then discharges to the winch brake, release circuit, thus holding the brake off.
The load will then be held by the overcentre valve. The load can then be lowered manually by using the hand operated oil pump in conjunction
with the manual emergency ‘Hold-to-Run’ valve. (See section 9.6 below).
8.8 Oil temperature regulation
The heater is controlled by thermostats to regulate temperature in the oil tank and also prevent temperatures that could lead to internal fires or ignition of the hydraulic oil. A PT100 temperature element provides the output data to operate the thermostats, trigger any alarm signals or cut the power to the heater. An independent hardware internal cut-out also switches the heater off in the event of excess temperature.
8.9 Main motor thermistor protection
The main motor has embedded thermistor protection against overheating of the windings. These are monitored by the control system as part of the safety interlock system.
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9 FUNCTIONALITY ENHANCEMENT SYSTEMS
The following features / systems are provided to give additional functionality to the operation of the crane. Load, load radius and rope length indication. Limit switch for wire up/down. Warning lamps. Alarm sounder. Load and utilization recording system. Emergency lowering system. Emergency operation. Centralised lubrication system. Overview CCTV Camera.
9.1 Load, load radius and rope length indication
The display on the radio remote control will indicate actual load in rope (rope tension), actual load radius and actual wire length.
The rope length is measured by an encoder on the winch spooling gear. The rope length indication on the radio remote display can be toggled between ‘Absolute’ and ‘’Incremental’ (local) values by the “Wirelengde” button on the remote control panel. The ‘Absolute’ rope length is recorded by the PLC and used for operational calculations. The ‘Incremental’ value is used for assisting with local fine adjustment of relative load positions and is zeroed by holding in the “Wirelengde” button on the remote control panel for 5 sec. This function does not alter the ‘Absolute’ length value recorded by the PLC. The ‘zero’ point of rope length is taken by the system when the Hook up-stop switch is actuated.
The load in the rope is measured by a load-cell axle pin on the upper wire sheave at the boom tip. This automatically takes into account the payload, deployed rope weight in air and any changes when in the water.
The load radius is calculated by the PLC from data from the cable pull encoder inside the telescopic boom and the inclinometer on the main boom.
9.2 Limit switches for hook up/down
An electrical proximity switch is installed at the crane tip in order to limit the hook up travel. If activated, it will stop the hook a safe distance from the sheave block. If the switch is faulty, a warning code and the fault lamp will show on the radio control. There is also a programmed slowing down of the winch for the last 3m to avoid hard collisions between the hook weight and the crane tip. In the extreme event of the hook not being stopped by this system, the hook would be stopped by the wire sheave. This would result in the load indicator registering an overload condition and would stop the crane.
An electrical limit switch is installed on the winch in order to limit the hook down travel. If activated, it will stop further spooling out of the wire, ensuring that 3 turns remain on the winch drum. Any fault with this switch results in a warning code and fault lamp displayed on the radio control.
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9.3 Warning lamps
The LED indicators on the radio remote panel will warn the operator of the different errors that can occur during operation. These are supported by text messages in the screen.
In addition, there is a flashing yellow beacon, to alert personnel in the area of crane operations. It starts and stops with the main HPU and is situated in the immediate crane area.
9.4 Alarm sounder
There is an alarm sounder (horn) mounted on the crane in order to give an audible warning signal, >110dBA, in the following situations:
Signal when the operator pushes “Horn” button. Signal when crane is overloaded. Signal when the oil temperature is too high (>70°C) or oil level too low.
9.5 Load and utilization recording system
The system records loading and utilization of the crane in order to determinate life cycle.
Each full cycle is recorded; from zero load through load to zero load. Every overload event is recorded with loading and date & time. Every alarm (not warning) condition is recorded with date & time.
Based on this information it will be possible to review the need for inspection and maintenance. The information can be reviewed in an Excel spread sheet, and requires no special tools for interpretation. Extraction from the crane system is by Ethernet export. This does not affect the crane’s PLC program or operation.
9.6 Emergency lowering system
In case of power loss and back-up unavailability, a hydraulic hand pump, positioned on the access platform, is used for the following:
Activate overcentre release valves on luffing cylinders in order to lower the boom. To open a pilot operated LE relief valve across the winch motor in order to lower the
payload. A pre-set needle valve regulates the flow across the motor ports to control the descent rate to a maximum of 25mm per second (1.5m/min) at full load This action is performed in combination with the winch brake emergency release valve and the accumulator.
Brake Release on the slewing gear in order to allow the crane to be slewed with a chain hoist or equivalent. This overcomes the relief valve in the overcentre valve to permit motion.
The 3 functions are operated by using the Manual Emergency Control valve. Each function is controlled by a ‘Hold-To-Run’ lever and when released, the pressure delivered by the hand pump is drained back to tank.
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9.7 Back-up operation
In case of power loss or main HPU failure, an air driven back-up hydraulic pump is provided. This is connected to the rig air supply via an FRL unit located on the crane column.
Utility air is connected to the air inlet coupling located on the side of the FRL cabinet. Recommended air flow rate = 3900 NL/min at 7barg to achieve satisfactory pump performance. It is filtered, regulated and lubricated in the FRL unit and feeds directly to the air motor. This drives the back-up hydraulic pump via a flexible coupling. The pump is submerged inside the tank. Oil is drawn directly into the pump through a suction strainer and fed out to the main pressure line of the HPU. A check valve ensures pressure from the back-up pump is only delivered to the crane and not back into the main hydraulic pump. A check valve in the back-up delivery line also prevents main pump pressure feeding back to the back-up pump.
Operation of all crane movements is available via the manual levers on the hydraulic distributor within the hydraulic control cabinet. The speed of function operation will be slower due to the reduced flow rate available from the backup pump. The delivery from the pump will also depend on the air flow rate and pressure available from the rig supply.
Safety Note: This system must only be used for ‘recovery and park’ operations and not for continuous use. If the 230V power supply is available, the remote control lamps and display will continue to give warnings and alarms. They do not, however, stop or interfere with the crane’s movements. The operator is wholly responsible for the safe control and movement of the crane.
9.8 Centralised lubrication system
A centralised lubrication system is provided for ease of applying grease lubrication to the crane joints not readily accessible.
9.9 Overview CCTV system
A CCTV camera is positioned in the crane working area to provide an overview of crane operations and in particular visual indication of winch drum rotation. The control and visual output of this system is located in the ROV Control Room.
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10 SEA-LIFT SYSTEM
This is a system functionality enhancement, specifically intended to reduce the dynamic effects encountered during lowering and lifting through the splash zone and when operating sub-sea. The system, (Sjøløft), is an operator selected function via the radio remote control panel and it engages the rope tensioning system (RTS). This reduces the dynamic effects on the winch rope at each end of the loading spectrum by:
Avoiding ‘slack rope’ conditions during lowering through the splash zone and sub-sea and is controlled by the RTS such that it slows, or reels in rope automatically, to maintain the correct load in the winch rope.
Avoiding rope ‘over tension’ during lifting through the splash zone and sub-sea and is controlled by the RTS such that it slows or pays out rope automatically to maintain the correct load in the winch rope and prevent overload.
During Sea-Lift operations, the winch rope load is constantly monitored by the PLC via the load cell and enables the winch to automatically pay out rope if the load is higher than a set point, and rewind rope if the load is below a set point. The rope length is also monitored by the PLC.
Once the payload is lowered through the splash zone the boom extend is enabled to allow the boom to be moved out to full extent (providing the crane load limitations are not exceeded) so the payload has additional clearance for passing the rig pontoon. When the payload is below the pontoon the boom may be retracted back to the minimum radius for the rope to clear the deck edge and pontoon. The slew and boom luffing functions remain disabled throughout Sea-Lift operations. (See section 11.2.1 for the required conditions for engaging the ‘Sea-Lift’ Mode). In Sea-Lift mode, the operator still has to move the joystick lever to demand movement of the payload. When there is no demand from the operator for movement, the load is held by the winch motor overcenter valves.
Refer to “Sea-Lift” Mode lifting diagram S6-HP-AVM-1004.
Use of this mode does not affect any of the fundamental crane safety systems.
Note: This system is a pilot project only, and the effectiveness has not been tested. For each subsea lifting operation, external forces due to buoyancy, drag, added mass & slamming must be calculated for each item to be lifted, and compared to the “Sea-Lift” Mode load diagram S6-HP-AVM-1004A dynamic load factor of 1.5 is applied to the payload and its value must lie within the SWL of “Seal-Lift” load diagram to ensure the fundamental crane SWL is not exceeded. The system is intended to provide a greater functional operating envelope within the parameters of sea-state and payload geometry, while remaining within the SWL envelope of the crane. In order to assess the benefit of the system, a log should be kept to form a record that can show it provides improved functionality and/or increase operating envelope.
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11 CRANE OPERATION MODES
The crane has the following 2 main operation modes: Platform Lift: Used for lifting loads above deck level. ‘Sea-Lift’: Used for handling loads below deck through the splash zone and sub-sea.
The modes are selected via the radio remote control panel to suit the required lifting task using the ‘Sjøløft’ button. The button is held in for 5 seconds to engage or disengage the sea-lift system. When the ‘Sjøløft’ mode is operational the warning lamp is lit on the radio remote control panel. This light remains lit as long as the subsea lifting mode is engaged.
The crane also has the following 2 selectable lifting capacities: Normal lifting (Normalløft): 0-5T Lifting speed: 90m/min Heavy lifting (Tungløft): 0-15T Lifting speed: 30m/min
The lifting capacity is selected by pressing the “Tungløft” button for 5 seconds. The capacity selected will remain in both Platform and Sea-Lift modes.
In Platform mode it is not permitted to change from Heavy to Normal and Normal to Heavy lifting mode unless the payload has been removed from the hook. This protects against potential overload situations.
In Sea-Lift mode it is permitted to change from Normal to Heavy Lifting and from Heavy Lifting to Normal Lifting only if the payload is less than 5T. These changes can only be effected when all crane movements are stopped. The system accounts for the weight of wire rope deployed in or out of water and also ‘soft starts’ the winch motor irrespective of operator demand or lifting speed selected.
Safety Note: This crane is not to be used for lifting loads from vessels, or lifting personnel.
11.1 Platform lifting Mode
During platform lifting, the crane has normal safety and control systems. In case of overload, all load / moment increasing movements are prohibited. Overload is limited by the maximum relief pressure setting of each function section of the hydraulic distributor control valve and the limits set by comparing the boom telescope length linear encoder with the load on the rope sheave load cell. The crane is designed to carry 11T at all positions and 15T up to a maximum radius of 8m. Reference Load Diagram S6-HP-AVM-1002 (The loads can be interpolated between the points)
11.2 ‘Sea-Lift’ Mode
During ‘Sea-Lift’ mode use, the control system varies for the following operations: Operation through splash zone. (Between B and C on diagram) Operation when passing the pontoon. (Between C and D on diagram) Operation between pontoon and seabed. (Between D and E on diagram)
When operating through the splash zone and sub-sea, the external forces due to buoyancy, drag, added mass and slamming must be calculated for each item to be lifted, and compared to the load diagram for Sea-Lift mode. Referring to Load Diagram S6-HP-AVM-004: Level ‘A’ Cellar Deck EL 542500 – Datum Level for all crane operations.
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Level ‘B’ Upper Limit of ‘Splash-Zone’ - Allowing for payload suspended from hook with clearance above maximum wave crest at maximum tide height.
Level ‘C’ Lower Limit of ‘Splash-Zone’ – Allowing for full immersion of payload below minimum wave trough at minimum tide height. Level C is also the position at which the boom is permitted to extend to give greater clearance for lowering the payload past the pontoon.
Level ‘D Lower limit of the Pontoon Clearance Zone. The boom permitted to be retracted to allow the payload closer in if required.
The above Levels are set to agreed positions during commissioning of the crane, but may be amended by an engineer if deemed necessary to suit operations.
11.2.1 Conditions for engaging ‘Sea-Lift’ (Sjøløft’) mode
At level ‘B’ on diagram. For ‘Sjøløft’ to operate, the crane has to be in the following configuration:
Warning lights will show if these conditions are not met and the system will prevent the load from being lowered.
11.2.2 Operation through splash zone
Between ‘B and C’ on diagram. When the ‘Sjøløft’ mode is engaged the system will:
Activate the RTS program in the PLC. Permit the ‘sea lift’ solenoid valve to operate from load cell ‘over-limit’ signal. Hold off the winch brake via the ‘sea-lift’ brake release solenoid valve. Allow pilot operated relief valve, component ‘RVIS’ of Winch Valve Block, to operate.
The aim of the “RTS program” is to reduce buffeting effects of the waves on the suspended payload as it passes through the splash zone. This is achieved by applying measurements of winch rope tension, through a control algorithm, to the winch hydraulic control. The steady state control of the winch, lowering or raising a load through the splash zone, is to be unaffected and under operator control at all times. The purpose of the algorithm is to act as a “shock absorber”, responding to impulse effects only and not the natural changes in weight resulting from the load as it is immersed into, or lifted out of, the water.
The method is as follows: o The analogue input from the rope load cell is programmed with zero offset, range
span and digital filtering, all engineer adjustable, so that the best 'clean' and accurate signal is obtained.
o The resultant signal is sampled at continuous regular intervals. The interval isengineer adjustable with a starting value of 0.1 second. The values are stored in arolling stack archive of 100 values, such that on the arrival of each new value, thestack is shifted down one place and the oldest value dropped. At 0.1 secondintervals for example, that yields a 10 second history of rope tension values.
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o The 100 values in the history stack will be averaged as each new sample arrives so that a rolling average level is obtained. This value will represent the steady-state load and will not change abruptly. As the load is raised or lowered, through the splash zone, it will gently ramp to the new weight value.
o By comparing the immediate load cell analogue input to the rolling average value, any surges above or below the mean will be detected. This would be done by a simple arithmetic subtraction:
Surge = {Immediate Load - Average Load}
o The significance of any surge (in terms of winch correction) is related to percentage tension change rather than absolute change. This is due to tension correction being effected by paying out or winding in the rope. Hence, the surge values are divided by the rolling average to obtain 'normalised' values of the disturbances.
o This value is expected to lie in the range -1.00 to +1.00 (extremes) and only has a non-zero value for the duration of the surge. It is therefore a derivative term, reflecting changes in load only. In steady state conditions, the value remains at zero so it does not interfere with varying effective weights experienced due to immersion or viscous drag during splash zone transition.
o The normalised surge signal is now multiplied by a 'gain' value (x5.0, engineer adjustable) and then subjected to maximum/minimum clamp values (+/-5% also engineer defined). The final value obtained will be applied as a 'trim' to the winch hydraulic proportional valve.
o A rising tension surge caused by wave drag or hydro-dynamic drag will slow the winch or pay out in order to compensate for the increased load giving the impulse.
o A falling tension surge due to wave impact or hydro-dynamic drag will cause the winch to slow or reel in to compensate for the decreased load that gives the impulse.
11.2.3 Operation when passing the pontoon
Between ‘C and D’ on diagram. When operating the crane from below the splash zone past the pontoon, the crane operator may increase the boom radius to 11m, providing the payload being lowered does not exceed the SWL of the crane at that position. This gives additional clearance between the payload and the pontoon.
During this operation, the slew remains at 0º (Boom 90º to rig side) and the boom at 0º elevation (Horizontal).
11.2.4 Operation between pontoon and seabed
Between ‘D and E’ on diagram. The boom may be retracted as far in as the rope passing over the rig side and past the pontoon permits. This is an operator controlled function and must be fully assessed before execution. The RTS function remains active when operating in this zone.
