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Design Codes - Jetties

This Technical Measures Document covers the design, operation and maintenance of jetty systems. Reference is made to relevant codes of practice and standards.

The relevant Level 2 Criteria are:

Related Technical Measures documents are:

Introduction

A jetty is defined as "a pier projecting out into the waterway and with facilities for mooring ships at its head or along its flank".

Jetties are normally used at major hazard plant for the loading and/or offloading of hazardous substances in bulk quantities between ship and land based storage facilities. Incidents which occur at the jetty and involve hazardous substances have the potential to result in a major accident.

For the majority of jetty installations there are five main events which individually or jointly have the potential to cause significant harm or damage:

Common causes of such events are:

Many of these are common to other activities and are considered elsewhere. See Technical Measures Documents for – Site Security etc.

This Technical Measures Document considers only issues that are specific to jetty design and to equipment used for ship to shore transfers.

General principles

Jetties should be designed to meet the requirements of the appropriate design codes and standards, to sound engineering principles and to be fit for purpose. Jetties should be of sound construction, preferably made of non-combustible materials, and be of sufficient strength to withstand normal berthing forces.

The design should take into account the following:

In addition to the correct design of the jetty installation the facility should also be subjected to an adequate maintenance and inspection programme designed to ensure that the integrity of the facility is maintained during operation.

Additional consideration should be given to the precautions that should be taken at jetties since there may be a number of different ‘authorities’ which may have a controlling influence. These include the harbour operator, the jetty operator and the master of the ship. There should be a clear definition of the roles and responsibilities of all parties concerned. Consideration may also be needed in respect of other jetties in the vicinity and the impact on management arrangements in the case of interaction arising from domino effects, communication links, etc.

General siting considerations

As part of the fundamental design process the following strategic factors should be taken into account in the choice of the site and the design of the facility:

Civil and structural design considerations

Jetties should be designed in accordance with BS 6349 – Code of Practice for Maritime Structures. Part 2 provides advice on the design of quay walls, jetties and dolphins.

For the civil and structural engineering design consideration needs to be given to the following:

Impact protection

Guidance for the approach of a ship towards a jetty is outside the scope of this document since it will depend upon the specific details of the waterway, tidal flows, sea/river bed layout etc. However the aim of the approach will be to bring the ship (either by the use of tugs or her own engines) gently alongside the jetty according to the procedures laid down elsewhere. Should these procedures not be adhered to by the pilot/master of the ship and the ship collides with the jetty at excessive speed or at an inappropriate angle then severe damage is likely to result to the jetty and/or the ship. Impact protection for a jetty is normally confined to normal berthing forces and not for the scenario described above.

Due to the inherent difficulties in positioning a large ship alongside a jetty it is essential that some form of protection be available associated with the jetty to protect the jetty from the ship and vice versa. Such protection is essential when the ship is being manoeuvred into mooring position alongside the jetty and when the ship is moored and the ship may be being pushed onto the jetty by the tides, winds, currents etc.

BS6349: Part 4 : 1994 gives guidance on types of fenders, fendering systems and layouts, mooring devices and ropes, mooring system layouts for commercial vessels, and recommendations as to their suitability for various applications and locations.

The function of a fendering system is to protect the jetty structure against damage from ships approaching, lying alongside or leaving the jetty and to limit the reactive forces to the ship’s hull to acceptable values. Fender systems design varies considerably and should be integrated with the jetty design. Consideration should be given to the types of vessels to be moored and their hull designs and upon the characteristics of the location. These will vary depending upon whether the jetty is to be situated on the coast, in an estuary, in a tidal basin or elsewhere.

Vessel Anchorage/Mooring

Adequate facilities should be provided at a jetty for safe and secure mooring. The installation should take into account the range of sizes and types of ship, local tidal variations, foreseeable weather conditions and the nature of the cargo and ballasting operations. Close liaison is required between all parties concerned (ship’s crew, harbour master, jetty operator etc.) to ensure that the mooring is done safely and an adequate watch is kept on the moorings while the ship is alongside and particularly during cargo transfer. Local conditions may place additional requirements on vessel mooring.

Account needs to be taken of the rise and fall of ships in relation to the jetty as a result of the changing tidal patterns. The extent of tidal fluctuations will vary from location to location and should be considered on an individual basis. In addition the displacement of the ship in the water will also rise and fall as the ship is emptied/filled and this should also be taken into account in the mooring systems.

Insufficient depth of water to accommodate the ship in approach or at the jetty, or to accommodate mooring at low tides may result in the ship running aground. This may result in a loss of containment of the hazardous substances and lead to a major accident.

Consideration should be given at the design stage to the possibility of berth silting at the jetty leading to an increasing possibility of a vessel running aground.

Jetty bollards and mooring arrangements should be designed to hold the ship in position once the ship has docked so that loading/offloading can take place safely. Inadequacies in the mooring arrangements could result in the ship breaking away from the moorings for example during a storm. Often it is necessary to hold the ship in place in relation to the jetty mounted off-loading facilities which may have limited flexibility in movement. This is achieved by restraining the movement to within acceptable limits by means of an adequate number of mooring lines compatible with the conditions of wind, tide, weather and previous operating experience of the facility.

Failure to properly restrain the ship in position which results in excessive movement may result in fracture of offloading pipework and subsequent loss of containment of hazardous substances.

Ship to shore transfer

The transfer from ship to shore inevitably involves the transfer of hazardous substances by pipework system suspended above a watercourse. See HS(G)186 The bulk transfer of dangerous liquids and gases between ship and shore which addresses many of the issues concerning design, operations and procedures at jetties.

All ship to shore connections should provide sufficient flexibility to allow for rise, fall and range of the vessel due to tide, wave and current effects and changes in displacement.

Flexible pipework should be manufactured to a standard suitable for the application and should be compatible with the substances to be handled (See Technical Measures Document – Design Codes - Pipework). It should be adequately supported (for example by slings, loading arms or saddles) so that it does not become kinked, overbent, abraided or trapped between the ship and the jetty. Where large hoses are used suitable cranes or hose rigs should be used. Care should be taken that hose slinging and securing equipment does not cause excessive curvature of flexible pipework systems.

Failure of the transfer lines during transfer could result in spillage of material into the watercourse or on to the jetty resulting in pollution, fire or explosion. This can happen for a variety of reasons and facilities should be available for pollution control should this occur.

Excessive movement of the ship which results in the pipework system being pulled apart, or the discharge pipework becoming trapped between the jetty and the ship, may result in fracture of the pipework connection and the release of hazardous substances.

When not in use hoses should be properly stored to avoid accidental damage, extremes of temperature and direct sunlight. It is good practice to provide blank ends for the additional sealing of couplings that are frequently broken and remade.

All hoses should be externally inspected for damage and deformation prior to use. A more detailed examination, including appropriate internal inspection and hydrostatic pressure testing should be carried out at least annually.

Additional features such as emergency release or breakaway couplings with automatic shut-off valves for isolation of the inventory can be installed to minimise the potential for spillage. It is also necessary to consider the ability to shut off transfers from both shore side and ship side, and necessary ship to shore communications arrangements.

For pipework transfer systems consideration should also be given to pressure relief, fire engulfment relief and the possibility of pressure surges causing ruptures to the hoses/flanges. Pressure surges in pipelines caused by closing valves too rapidly, may lead to failure of vulnerable parts such as flanges.

Pigging operations are often carried out to clean pipelines. The hazards associated with the pigging operations should be carefully assessed. Further guidance is available in HS(G)186 The bulk transfer of dangerous liquids and gases between ship and shore.

Special consideration should be given to installations where manifold systems are used to ensure that the correct connections between ship and storage tank are made.

In instances where the storage tanks are situated on land above the level of the jetty then consideration needs to be given to the control of gravity flow from the storage tanks. Suitable facilities for the isolation of the inventory should be included to avoid spillage and pollution.

As a precaution against spillage or other emergency on the jetty, shut-off valves should be considered at or near the shore end of all jetty pipelines which carry hazardous substances. Such valves should not introduce unacceptable surge pressures in the pipeline in the event of closure. Such valves should be fail safe and be capable of manual operation in an emergency.

Procedures and facilities should be in place for emptying out residual contents from flexible pipework systems after use and then cleaning pipework systems as necessary. Suitably designed areas which provide containment of releases to avoid pollution should be considered.

Maintenance

The integrity of the jetty system should be routinely checked and confirmed. The following items should be routinely inspected as a minimum requirement:

Status of guidance

Codes of Practice relating to design of Jetties

Further reading material

Lees, F.P., 'Loss Prevention in the Process Industries: Hazard Identification, Assessment and Control', Volumes 1-3, Second Edition, 1996, Butterworth Heinemann, ISBN 0750615478.

Case studies illustrating the importance of Design Codes - Jetties

2010-03-11