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Cargo hoses for chemical tankers - Care and maintenance

A modern cargo hose represents skilled engineering and, unless wrongly used, can be relied upon to contain the cargo. Nevertheless, it should always be treated as the weakest link in the cargo containment and transfer system, so correct handling and use of hoses is important.

Use and handling may differ from type to type of hose, or by manufacturer. The types of hoses normally encountered are either metallic, composite, PTFE (polytetrafluorethylene) or polypropylene. A ship's own cargo hoses are frequently used on board chemical tankers, during loading and discharge of cargo at a terminal, during cargo transfers between ships and during tank cleaning. A ship should have on board appropriate manufacturers' material describing the hoses carried, and specifying any limitations in their use.

chemical tanker navigation at sea
Certificates, marking and testing of cargo hoses

A ship's own cargo hoses must be tested and certified as required. The minimum requirements for the construction and testing of ships' cargo hoses are specified in the MCI Codes. All cargo hoses are required to be designed for a bursting pressure not less than 5 times the maximum pressure that the hose Will be subjected to during cargo transfer operations. New lengths of cargo hose, before being placed in service, should be tested hydrostatically at ambient temperatures to a pressure not less than IX times its specified maximum working pressure, but not more than two fifths of its bursting pressure.

A manufacturer's test certificate will provide information about the hose's construction method, its performance range and its nominal sizes. While in service, hoses should regularly be visually inspected, and they should be pressure tested at least annually. Test results should be recorded in a cargo hose condition log book.

Cargo hoses are required to be marked with their specified maximum working pressure, which should not be less than 10 bar gauge. Hoses used in the transfer of cargoes at other than ambient temperature should be marked with the applicable minimum and maximum service temperature range.

Cargo compatibility

Hoses used for the transfer of chemical liquids and vapours during cargo handling operations should be compatible with the nature and temperature of the chemical. Any limitations of the cargo properties and temperatures listed by the hose manufacturer should always be observed.

Handling, connection and use

When a hose is being moved about the ship it should always be lifted and carried. It should not be dragged over the ship's fittings such as pipework or walkways, or rolled in a manner that twists the body of the hose, nor hoisted on a crane or derrick using a single wire strop about its mid-length. Hoses should not be allowed to come into contact with hot surfaces such as steam pipes.

connecting loading arm at chemical tanker

Fig: Connecting shore loading arm to the ship’s manifold onboard a tanker.

Cargo transfer hoses may contribute to cargo contamination therefore hoses should be properly cleaned in between different cargoes.

To ensure cargo tank readiness, thorough check by senior officer must be carried out prior tendering Notice of Readiness for loading.

Cargo lines are the main concern while loading high specification cargoes. It is important that cargo lines, drains and dead ends are adequately cleaned along with the cargo tanks.

Octopus flanges (if fitted) are to be opened for additional checks and to verify the condition of the cargo lines. On completion of steaming the cargo lines, the quality of the effluent condensate at the flange will provide a good indication of the line cleanliness.

Octopus flange at chemical tanker

Fig: Octopus flange at a chemical tanker

Before connection, cargo hoses should be examined for any possible defects that may be visible inside the hose or on the outer covering. These may include signs of blistering, abrasion, flattening or evidence of leaks. Hoses with any damage should be assessed and a positive decision made on whether they can continue to be used safely. Seriously damaged or leaking hoses should not be used.

Gaskets used between hoses and at the ship's manifold should be checked for suitability before use. Flanges on both the hose and manifold should be checked for cleanliness and good condition. Bolts and nuts used should be of the correct size and material, with a bolt fitted to every hole in the flange and tightened correctly.

Cargo hose support

Fig:Cargo hose support

When in use, a cargo hose should be properly supported along its length to avoid excessive bending of the hose or its weight hanging from the manifold connection. This is especially important when significant tidal or draught variations can cause the relative heights of the ship and shore manifolds to alter a great deal, and the hose support to require frequent adjustment.

Fendering, stools or chocks can be used to provide support under the hose, particularly at the manifold and at the shipside rail. When a hose is supported from above, bridles and saddles should be used to spread the load, and may require more than one supporting point. A single wire strop should not be used to support a cargo hose near its midlength. Protection should be provided at points along the hose where chafing or rubbing could occur.

Hoses should not be subjected to pumping pressures that exceed the rated working pressure. If this happens, the hose should be replaced by another, and retested before any further use. After use, hoses should be depressurised and drained before disconnection.

Ship / shore insulation, earthing and bonding

It is essential that the cargo hose does, not provide the primary path for static electricity between the ship and the jetty, otherwise there is a possibility of a static electricity discharge at the manifold when offering up the hose for connection or when breaking the connection after the cargo transfer. The necessary electrical discontinuity should be achieved with an insulating flange or a single length of non-conducting hose in the hose string between the ship and the shore.

Storage and maintenance

After they have been used for cargo transfer, hoses should be washed out, drained and dried. They should be stored horizontally on solid supports. If hoses are stored in the open, they should be protected from direct sunlight. No attempt should be made on board to repair damaged or leaking hoses.

Related Info:
  1. Cargo line leakage countermeasures
    There are many reason that may lead to cargo line failure on board chemical tanker. Galvanic corrosion in the cargo and stripping pipelines may cause several leakage. One of the sources of such corrosion in pipelines is variation in corrosion resistance at adjacent points in the piping.

  2. Checklist for handling dangerous liquid chemicals in bulk
    Is information available giving the necessary data for the safe handling of the cargo and, where applicable, is a manufacturer's inhibition certificate available? Information on the product to be handled should be available on board the ship and ashore before and during the operation.

  3. Recommended temperature monitoring equipments onboard
    Temperature sensors are fitted so that the temperature of the cargo can be monitored, especially where required by the IBC Code. It is important to know the cargo temperature in order to be able to calculate the weight of cargo on board, and because tanks or their coatings often have a maximum temperature limit. Many cargoes are temperature sensitive, and can be damaged by overheating or if permitted to solidify. Sensors may also be fitted to monitor the temperatures of the structure around the cargo system.

  4. Practical example of solving tank cleaning problems
    Tank cleaning is essential on-a chemical tanker, but it must be recognised as a potentially hazardous operation, and rigorous precautions should be observed throughout the process. Together with gas freeing, it is probably the most hazardous operation routinely undertaken on a chemical tanker.
    Pre-cleaning /washing of cargo tanks

  5. Pre-cleaning /washing of cargo tanks
    Washing between different grades of cargo is the most common reason for tank cleaning. In most cargo sequences on chemical tankers, this cleaning may consist of no more than a simple hot or cold seawater wash. A simple water wash will disperse many types of chemicals and has been found effective between clean petroleum products such as gas oil and kerosene.

  6. Final cleaning of cargo tanks prior loading
    Method of final cleaning to be used depends on both previous cargo and cargo to be loaded. As a general rule the tanks and piping shall be completely drained of water or residues before loading. The bottom of the tanks may have to be dried up with rags.

  7. Tank cleaning and posoning hazards
    Certain substances affect the tissues locally as an irritant (cashew nut shell oil) or cause grave damage to the eyes, skin or mucous membranes (e g strong acids and caustic). Other substances may be absorbed by contact to the skin without local effects (e g nitrobenzene, aniline).

  8. Testing of tanks and cargoes
    Most common tests and checks for oil and chemical cargoes include testing tank walls for cleanliness. Testing is normally carried out by independent surveyors who, according to local practice or a written agreement in the charter party, are accepted by shipper, receiver and owner.

  9. Practical tank cleaning methods for various noxious liquid cargo
    Tanks that may have contained monomer or drying oils should first be cleaned with sufficient cold water quantities to avoid polymerization of cargo residues. In some cases, it is necessary to employ tank cleaning chemicals, but their use is generally limited as it may be difficult to dispose of slops.

  10. Special tank cleaning method
    If a special method involving cleaning agents is to be used, it may create an additional hazard for the crew. Shipboard procedures should ensure that personnel are familiar with, and protected from, the health hazards associated with such a method. The cleaning agents may be added to the wash water or used alone. The cleaning procedures adopted should not entail the need for personnel to enter the tank.

  11. Determining proper tank cleaning by acid wash method
    The acid wash method is used if there is any suspicion that a cargo of aromatics may have been contaminated by a previous oil cargo. The method is also used as a check that a tank is sufficiently cleaned before loading aromatics.

  12. Supervision of all tank cleaning and gas freeing operations
    Tank cleaning is essential on-a chemical tanker, but it must be recognised as a potentially hazardous operation, and rigorous precautions should be observed throughout the process. Together with gas freeing, it is probably the most hazardous operation routinely undertaken on a chemical tanker.

  13. Disposal of tank washings, slops and dirty ballast - safe method
    During normal operations of a chemical carrier, the main need to dispose of chemical residues, slops or water contaminated with cargo will arise during or immediately after tank cleaning. Final disposal of slops or washwater should be in accordance with the ship's P&A Manual. Tank washings and slops may be retained on board in a slop tank, or discharged ashore or into barges.

  14. PV valves -function and maintenance requirements
    Pressure/Vacuum valves are designed to provide protection of all cargo tanks against over/under pressure and provide for the flow of small volumes of tank atmosphere resulting from temperature variations in the cargo tank(s) and should operate in advance of the pressure/vacuum breaker, where IG system is in use....

  15. Deck seal, tank non return valves and tank gauging requirements
    On vessels fitted with an inert gas system it is a requirement to maintain a positive seal between the cargo tanks and the inert gas generation plant this is usually accomplished by the use of a non - return valve and a Deck Water Seal...

  16. Loading / stress computer
    This instrument is provided to supplement the stability booklet for the vessel. It allows the Officer responsible, to carry out the various complex calculations required to ensure that the ship is not overstressed or damaged during the carriage of the nominated cargoes..

  17. Various cargo handling safety equipments carriage requirements
    It is essential on chemical tankers that everyone knows his ship's safety equipments thoroughly prior handling noxious chemical cargo. Also the master/chief officer must assume responsibility for this.

  18. Vapour emission control requirement for chemical tankers
    Vessels fitted with a VEC system must have an independent overfill alarm providing audible and visual warning. These are to be tested at the tank to ensure their proper operation prior to commencing loading, unless the system is provided with an electronic self-testing capability. Fixed gauging systems must be maintained in a fully operational condition at all times. .....

  19. Draegar Chemical detector tubes use and reading correction guideline
    These instruments, often referred to as Draeger tubes, normally function by drawing a sample of the atmosphere to be tested through a proprietary chemical reagent in a glass tube. The detecting reagent becomes progressively discoloured if a contaminant vapour is present in the sample. The length of the discoloration stain gives a measure of the concentration of the chemical vapour which can be read from the graduated scale printed on the tube. Detector tubes give an accurate indication of chemical vapour concentration, whatever the oxygen content of the mixture

  20. Requirements of various grade chemical cargo heating
    : The voyage orders will contain heating information, if heating is required. As a rule the final heating instructions are given by the Shipper in writing to the Master / Chief Officer in the port of loading. If those written instructions are not given, the master should request them and issue a Letter of Protest if they are not received at departure. In the latter case the management office should be immediately informed.

  21. Recommended temperature monitoring equipments onboard
    :Temperature sensors are fitted so that the temperature of the cargo can be monitored, especially where required by the IBC Code. It is important to know the cargo temperature in order to be able to calculate the weight of cargo on board, and because tanks or their coatings often have a maximum temperature limit. Many cargoes are temperature sensitive, and can be damaged by overheating or if permitted to solidify. Sensors may also be fitted to monitor the temperatures of the structure around the cargo system.

  22. Cargo instruments
    :In order to maintain a proper control of the tank atmosphere and to check the effectiveness of gas freeing, especially prior to tank entry, several different gas measuring instruments need to be available for use. Which one to use will depend upon the type of atmosphere being measured.

  23. Liquid level gauges
    :The accuracy required of chemical carrier level gauges is high because of the nature and value of the cargo. To limit personnel exposure to chemicals or their vapours while cargo is being handled, or during carriage at sea, the IBC Code specifies three methods of gauging the level of a liquid in a tank - open, restricted or closed

  24. Overflow control
    :Certain cargoes require the designated tank to be fitted with a separate high level alarm to give warning before the tank becomes full. The alarm may be activated by either a float operating a switch device, a capacitive pressure transmitter, or an ultrasonic or radioactive source. The activation point is usually pre-set at 95% of tank capacity.

  25. Oxygen analysers
    :Oxygen analysers are normally used to determine the oxygen level in the atmosphere of an enclosed space: for instance, to check that a cargo tank can be considered fully inerted, or whether a compartment is safe for entry.

    Vapour detection
    :Ships carrying toxic or flammable products (or both) should be equipped with at least two instruments that are designed and calibrated for testing the gases of the products carried. If the instruments are not capable of testing for both toxic concentrations and flammable concentrations, then separate sets of instruments should be provided.

  26. Alarm circuit
    :An important feature of many modern measurement and control instruments is the ability to signal a particular situation. This can be a main operational alarm that gives an indication of a pre-set situation such as liquid level in a tank, or a malfunction alarm indicating a failure within a sensor's own operating mechanism. The designs and purposes of alarm and shutdown circuits vary widely, and their operating system may be pneumatic, hydraulic, electrical or electronic. Safe operation of plant and systems depends on the correct operation of these circuits and a knowledgeable reaction to them.

  27. Venting of cargo tanks safety procedure
    The cargo tank venting system should be set for the type of operation to be performed. Cargo vapour displaced from tanks during loading or ballasting should be vented through the installed venting system to atmosphere, except when return of the vapour to shore is required. The cargo or ballast loading rate should not exceed a rate of vapour flow within the capacity of the installed system. .....

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