Some Useful Notes on Marine Loading Systems 1 Emcostrasse 2-4 35274 Kirchhain, Germany Ph.: (+)49 64 22 84 - 0 Fax: (+)49 64 22 51 00 [email protected]www.emcowheaton.de Parameters for Design When designing Marine Loading Arms different parameters need to be considered Draught Change Flange Set-Back Flange Spacing High / Low Water Flange Set-Back & Flange Spacing Drift & Surge Envelope Flow-rates Loading time Manual or Hydraulic
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The final envelope is a combination of the range of movements as mentioned above:
• Tanker draught changes combined with tide levels • Tanker manifold set-back combined with drift • Tanker manifold spacing combined with surge
This sketch shows the actual volume, that can be swept by a unit extended to it's maximum reach.
This increased volume should not be taken as an enlarged envelope since stresses and manifold loads can be considerably higher in certain portions of this increased volume.
Typical marine unit combinations for a range of tanker sizes
TANKER DEAD-WEIGHT
TONNAGE (DWT TONS)
FLANGE DIA.
(INCHES)
TYPICAL TIME TO UNLOAD
SUGGESTED MARINE UNIT COMBINATIONS, NOT INCLUDING BUNKERING OF TANKER
1000 6 - 8 3 h 1 x 6'' 5000 6 - 10 6 h 2 x 8" 10000 6 – 12 9 h 2 x 8" 20000 8 – 12 12 h 3 x 8" 50000 10 – 16 12 h 4 x 10" 100000 12 – 20 18 h 4 x 12" 250000 16 – 24 18 h 4 x 16"
The table shows typical combinations of loaders related to tanker size to give a reasonable turn round time at the jetty.
The larger tankers are often dependant on high tide conditions for approaching or leaving the installation and hence a multiple of 12 hours is the ideal solution. Allowing 18 hours for loading or unloading leaves about 6-7 hours for mooring, connecting and disconnecting port formalities etc.
For small tankers the unloading is usually controlled by the available pump capacity.
Where a range of tankers is to be served, consideration must be given as to whether large diameter arms could be connected to the smallest tankers.
Where a number of products are to be handled, the prime consideration may be the need to segregate the products to prevent contamination. This can give installation up to 6 or 8 arms, but not all can be used simultaneously.
Installations can include more than one size of marine unit.
The Loading Arms offered are the Emco design which are of all steel double counterweighted construction.
The Loading Arms are designed specifically with the following criteria in mind:-
a. Strength, long life and easy operation b. Minimum maintenance c. Simplicity of maintenance (no special tools)
The following features are used in the design:-
1. To reduce wind loadings and consequent stresses in the arm, extensive use is made of circular sections as the wind coefficient is greatly reduced.
i. e. Wind coefficient Cf = 0.7 for Circular Sections Cf = 2.0 for Flat Sections
All balance weights are located at the rear of the pedestal to reduce wind loads, particularly when stowed.
2. The outboard arm is moved and balanced via a rigid pantograph link. This link is maintenance free with all linkage pins manufactured from stainless steel. The pins are mounted in non-lubricated bearings, giving life-long maintenance free operations.
Other loading arm manufacturers use wire rope for the outboard arm linkage which requires frequent inspection and maintenance, or alternatively, balance weights are located at the apex which induces high wind loads, makes swivel maintenance difficult and increases the stress in the pipe-work.
b. Wires are subject to corrosion (not easily visible)
c. Broken single strands lead to accelerated breakage of adjacent strands
d. Wire and pulleys are subject to wear
e. Wire suffers loss in cross-sectional area due to strain
f. Wire slip on pulleys causing loss of balance
g. Regular inspection and load testing required
h. Inherent slack and natural catenary lead to imperfect balance
Because of the slacking ropes the counterweight tends to move uncontrolled either to the left or the right when being in vertical position. This movement is a very impulsive one and puts a tremendous stress impact on the complete design
We know from customers who were using this design, that stress effect can destroy the ropes
a. Site adjustable double counterweights for accurate balancing of inner and outer arm.
b. Movable elbows fitted at pedestal head and apex swivels for ease of seal changing without dismantling the arm.
c. The small included angle between inner and outer arms, when the loading arm is stowed, minimises the space required on the jetty and the possibility of clashing between adjacent arms.
d. The offset weight design prevents any possibility of counterweights fouling adjacent arms.
e. The most important feature of a loading arm is the swivel joint. These joints are required to be capable of resisting high bending and axial load combinations due to wind and arm attitude while retaining low torque characteristics and simple maintenance.
f. The rigid pantograph link used to move and balance the outer arm is maintenance free, with all linkage pins being manufactured in stainless steel. The pins are mounted in non-lubricated bearings, giving life-long maintenance free operation, and ensuring constant perfect balance. This system obviates the need for wire-lines which are subject to stretching (causing an out of balance situation and corrosion with possibility of wire-line failure).
g. Due to the self-carrying product piping the pressure drop within the Emco Marine Loading Arm is always lower than the corresponding Marine Arm of the competition.
h. Hydraulic cylinder pistons for inner and outer arms and slew motion are made of stainless steel. Pistons are inside the body in Marine Loading Arm parking position.
i. The control system can be designed to utilise sets of control valves which allows the arm to be in a controlled (locked) condition at any position.
Movement and balance of outboard arm is achieved by means of a rigid pantograph link. Adjustable double counterweights are used for accurate balancing of inner and outer arm. Both of the above increase the reliability and safety of a Marine Loading Arm as they ensure a stable structure, that imposes minimum loads to the ship's flange, and can withstand high pressures caused by severe winds.
Due to the fact, that no cables / wheels are used for balancing maintenance cost are kept to a minimum.
The customer does not need:
- Craneage for seal replacement work - Permanent tightening of cables - Permanent greasing of cables - Scaffolding for cable maintenance
Breaking or slippage of cables exposing personnel to dangerous situations can not occur.
As opposed to the design of most of our competitors, who use snap in ball raceways the raceways of Emco Wheaton swivel joints are direct incorporated and flame hardened up to 600 BHN (~ 57 HR C) having a hardness depth of 3 mm. This ensures, that the swivel joints have an extremely long, trouble free lifetime / operation, requiring lubrication on a regular basis only. All swivels of the Emco Wheaton design have integral flanges allowing easy replacement of seals, even triple swivels. These features also ensure the safety of a Marine Loading Arm as a leakage of a swivel joint can impose harm to environment and man. Also flame hardened raceways are capable of withstanding high bending and axial load combinations due to heavy winds. We are frequently refurbishing Marine Arms which have been in service for about 20 years, and most swivels are in excellent condition and can be put back into service without refurbishment. Our experience and information from operators who use arms with replaceable raceways is not good, as over the years the groove that holds the snap in raceway can suffer from corrosion or distortion eventually requiring the replacement of complete body and sleeve.
* Excludes melting/removal of ice around bolting clamps etc.
** No de-icing required.
Comments:
A. The hydraulic QC/DC is operated via the main electric/hydraulic control system of the loading arm. The pendant control will have separate connect/disconnect buttons that are operated by the jetty operator at the appropriate time.
The time to connect or disconnect the QC/DC will be approximately 5 to 10 seconds depending on the flow rate of hydraulic oil from the control system. When nuts/bolts are utilised it takes considerably more time, especially during the disconnection phase as it would be necessary to melt the ice, before unbolting operations could commence.
B. With a QC/DC fitted to the loading arm the operator can stand away from the tanker manifold during the connection/disconnection operation. This would prevent any possible injury to the operator due to adverse movement of the vessel/loading arm caused by wind/wave action during the connection/disconnection phase.
If nuts and bolts are utilised the operators could suffer injury to hands/fingers etc. due to this adverse movement. It is important to understand that at a particular moment in time ‘one bolt only’ will connect the loading arm to the tanker flange. This bolt could be highly stressed or act as a pivot point so as to create a guillotine action between the two flanges.
There are certain periods of time when, with the tanker moored to the jetty and one or more of the loading arms connected, it is not possible or safe/practical to activate the ERS, for example, during initial connection and final disconnection of the loading arms. There is always the chance that during this critical period the tanker could breakout or it becomes absolutely essential to move the tanker quickly from the jetty e.g., a fire in the onshore facilities or on the tanker. The hydraulic QC/DC provides the means of remotely disconnection of the loading arm from the tanker manifold in seconds. This is also possible when the manifold is severely iced.
Again, if a situation occurs onshore or on the tanker that may develop into something more serious (small fire is an obvious reason) the incorporation of a hydraulic QC/DC gives the added operational flexibility to allow preparation for disconnection(i.e. stopping of loading pumps and draining of the loading arm) to take place with the option of either disconnecting in a controlled manner via the QC/DC or activating the ERS with the consequential down time for reconnection.
As well as giving operational advantages, the hydraulic QC/DC provides an added back-up method of rapid disconnection of the loading arms from the tanker in the event of unforeseen circumstances.
C. The QC/DC is designed to disconnect from a minimum of 25mm of solid ice formed at the coupler/tanker interface.
6. Maintenance No maintenance. *New seal required for each vessel connection
Few periodical maintenance is required
Monthly condition monitoring and annual maintenance is required
* If nuts/bolts were utilised, then a new seal would be recommended for every connection.
Loose nuts and bolts are easily lost. Movement of the loading arms during the connected phase could result in over stressing of some of the bolts. Therefore to ensure safety of operations a new set of bolts would be required on a frequent basis.
** With a hydraulic QC/DC fitted to the loading arm the interface seals between the tanker flange and the loading arm are contained within the face plate of the QC/DC. These seals can be utilised for many connection/disconnection operations without replacement.
7. Supply Record. Many Many In-service since
1972, now being increasing used at new terminals
The Quick Connect/Disconnect Coupler System shall include the following features:-
• Lubrication of all moving parts is possible without dismantling the coupler.
• The coupler clamps are guaranteed to operate simultaneously by means of a single double acting hydraulic cylinder.
• The coupler mechanism ensures that evenly distributed forces are applied to the ships manifold flange during the connection and disconnection operation, thus avoiding overstressing of any part of the flange. This is achieved by means of spring struts on each hook assembly.
• The coupler will connect to 16” dia ANSI 150 pressure rated tanker flanges.
• The coupler design incorporates an overcentre mechanical lock.
• The moving parts of the coupler (i.e. rotating collar, hydraulic cylinder and clamp assembly) are insulated from the product carrying body to avoid icing of these components.
• The coupler is capable of releasing from the ships manifold flange under maximum unbalanced loads induced by the loading arm and when the clamp tips are covered with 25mm of solid ice.
• The coupler is equipped with a non pressure containing blanking plate complete with an ½” drain connection.
• The coupler design incorporates external centring guides which align on the outside diameter of the ships manifold flange.
• It is possible to manually disconnect the coupler, in the event of any electric or hydraulic power failure, by means of a portable hand pump.
• The strength of the coupler is based on the requirements of the OCIMF, i.e.:
• The coupler is designed to ensure that the interface connection is leak free during cool-down of the loading arm and during full cargo transfer.
• The coupler is equipped with snap connectors which will automatically disconnect the hydraulic lines to the coupler in the event of an emergency release. There will be no leakage of hydraulic oil on release.
Para. “Remarks on hydraulic Quick couplers / De-couplers (QC/DC) for LNG Tankers” taken with kind permission of MIB International Limited, Sun Alliance House, Little Park Street, Coventry CV1 2JZ, England