Discover the key specifications, handling procedures, and maintenance practices for LNG and LPG cargo hoses in Ship-to-Ship (STS) operations. Ensure safety and efficiency in your transfers with our expert insights on hose inspection and ship’s hose management.
The use of cargo hose is prevalent in some trades. For small terminals receiving pressurised product its use is quite common. For some larger scale operations, such as ship-to-ship (STS) transfers, at present there is little alternative to the use of hose. Accordingly, this section addresses these issues. However it should be noted that cargo hose problems, when they occur, can be severe and attention is required to the matters discussed.
In some regions of the world the use of hose, even for small scale liquefied gas handling, is disallowed. Such regulations are often established as a result of individual Hazard Analysis (such as the Safety Report guidance framed under the European Seveso Directive Major accident hazards of certain industrial activities.x) rather than by central law making. This section concludes that, at the dock face, accidents due to human error are more common when hoses are used – as compared to the longer lasting hard-arms.
Readers of this section should note that the use of hoses for the transfer of liquefied gas products has caused deaths. The problems, as discovered, suggest that poorly specified hose and inadequate maintenance is responsible.
The observations in this section provide an outline of the necessary procedures to ensure safe cargo transfer by hose. Discussion centres on hose purchase, handling, testing and retirement. It ts clear from accident data that for some terminals a better knowledge of hose standards is necessary and SIGTTO recommend that this aspect forms a part of terminal training programmes.
Hose Specification
A review of accident information (see Appendix 1***) shows that, especially at smaller terminals and especially those in the third world, there can be a tendency to use cargo hose of unsuitable quality. The use of ship’s nose has also been shown as a source of problems (see Appendix 1***).
Liquefied or chemical gases may be handled:
- At high pressure;
- At low temperature;
- With properties corrosive to some hose materials.
At the time of hose purchase it is absolutely necessary for it to be properly specified for the products to be handled. In this regard the damaging nature of the cargo properties must also be addressed and this may mean special hoses having special linings for special grades.
Procedures to cover this aspect should be developed by individual terminals. For example, rubber hoses must be compatible with the liquefied gas being handled in respect of pressure, temperature and materials of construction. For some of the chemical gases this is not always feasible for rubber hose and composite hose, having a more wide-ranging lining, is used as an alternative. Flexible metallic hoses, being of stainless steel construction, do not present problems tn thts respect, but they are susceptible to salt corrosion pitting problems and it is usual for the most suitable grade of stainless steel (316) to be specified to reduce this effect. It is also worthy of note that a hose suitable for LPG may not be suitable for ammonia LPG hose usually has a nitrile lining but that used for ammonia requires a butyl lining. Ammonia hose is described in a standard produced by the International Standards Organisation (see Appendix 1***).
As suggested in the foregoing paragraph, there are three main types of cargo transfer hoses for refrigerated and pressurised LPG. They are:
- Rubber hose;
- Composite hose;
- Flexible stainless steel hose.
Additionally, a high quality type of floating hose for off-shore use is in current development specifically for LPG application. This hose-type has yet to be fully specified. Also, it is of interest to note, that composite and stainless steel hoses have been developed for cryogenic Ship to Ship (STS) Preparation and Manifold Connection for Transfer OperationLNG transfer but, at least for large scale bulk Operations, at present it is only composite hose that is used and then only for emergency situations. Hoses of the composite type have been found more satisfactory. This may be an important development for future terminal operations.
It should be noted that an older practice, sometimes found in the inter-island pressurised LPG trades, of using long lengths of lightweight rubber hose for fioating-hose discharge from off-shore berths is not safe. It is recommended that such operations be carried out using suitable hose to a manifold on the sea-bed and, thereafter, via a steel submarine pipeline.
In all three main hose-types, the method for securing the hose carcass to the flange fittings is of particular importance. In other words it is not just the hose carcass which should be specified but it is the whole hose assembly; including end flanges, which, as a unit, has to meet the appropriate design. This limits any risk of the end fittings becoming dislodged and ensures that the proper flange pressure-rating or Class (ASTM 150 Ib or ASTM 300 lb) can be specified. The use of the recommended standard covers this point. Apart from this document, the design of hoses can be governed by some other national criteria: the United States Coast Guard regulations provide an example.
Terminals should have a procedure available covering hose selection criteria. For dock-side use a standard is available and, in the absence of other suitable guidance, this one is recommended. As defined within this standard, rubber hose for LPG transfer should only be of Hose-Types 5 or 6. This provides for a maximum working pressure of 25 bar and allows for the fact that the hose will be successively pressurised and de-pressurised. The standard requires the hose to be suitable for a temperature range from -50 °C to +45 °C. By this means, pressure and temperature requirements will closely match the design for the pipeline system and provide a measure of security against pressure surges when cargo flow is interrupted (the stated maximum working pressure of the hose should not be exceeded !n pressure surge conditions – see Section 8***). At the time of purchase the need for either electrically continuous or electrically discontinuous hose should also be specified.
The manufacture of composite hose is defined in the same standard. This type of hose is also designed for temperatures ranging from -50 °C to +45 °C. Other specifications should be similar to those described above. With regard to electrical continuity it should be noted that composite hose is electrically continuous and therefore insulation flanges always must be fitted at the shore manifold. An advantage of this type of hose is its light weight – so easing handling operations – however, due to its lighter construction tt is more prone to damage than rubber hose and the frequency of visual inspections should be enhanced accordingly. Manufacturers usually recommend checking for:
- Displacement of the internal and external reinforcing wire helixes;
- Impact damage;
- Abrasion or corrosion of the outer wire and abrasion of the outer cover;
- Displacement or damage to end fittings.
Certified hoses are available for most products carried on liquefied gas carriers or handled at terminals and it is only approved equipment which should be used. An obvious example of an incorrect procedure is to use a hose certified for ambient temperatures when refrigerated product is to be transferred.
Following from the arguments in Section 4***, good practice for hose usage dictates that for ports having special risks (see Section 4***), the addition of a Break-Away Coupling at the shore manifold is necessary. This matter is discussed further in Section 7 1.3***.
Hose Handling and Operation
Because of the added risks in the use of hoses it is always good practice to keep hose lengths to a minimum. Cargo manifolds at terminals should be positioned as close as possible to the jetty face while allowing sufficient room for handling and storage.
During cargo handling all types of hose should be correctly supported in hose-saddles or by multi-point slings. This helps to ensure that the minimum-bending-radius requirements (as specified by the manufacturer) are met.
Generally, hoses should not be allowed to rest on jetty decks or to touch sharp corners. This may cause abrasion. During connection and disconnection the hose should aiso be clear of the jetty as this affects safety regarding electrical continuity by short-circuiting essential ship/shore electrical insulation. During Cargo pumping, where operations require hoses to rest on jetty decking they are often best supported by hose trollies (or dollies).
Before cargo pumping starts the hose should be the subject of a joint inspection by ship and shore personnel. This Inspection should include a thorough visual review of hose condition. This should be carried out in accordance with Ship/Shore Safety Check List procedures. Such an inspection can include a mutual check of the hose test certificate.
During cargo pumping operations maximum flow rates, as recommended by hose manufacturers, should be observed.
Hose Inspection, Testing and Maintenance
Hoses should be tested at intervals as specified in an appropriate standard. If there are signs of weakness, or if the hose fails other tests in the series, the hose should be scrapped.
The method normally accepted for testing rubber hoses is for pressure tests and elongation (temporary and permanent) measurements to be taken out at six-monthly intervals and the findings recorded and found suitable against previous results. It should be noted that such tests should be carried out based on the maximum working pressure of the hose – and not based on the normal maximum working pressure experienced during operations; which may be considerably less (the testing of composite hose is similar; only measurements for temporary and permanent elongation are not necessary).
Read also: Ship-to-ship LNG transfer operations
An equally important adjunct to testing is a thorough internal and external visual inspection. Internal hose linings in LPG service have been known to blister – caused by trapped liquid in the carcass evaporating as the hose is de-pressurised. Inspection must prove the hose to be visually sound and good common sense must be applied at these times.
Apart from producing a new hose test certificate after each inspection, it is good practice to maintain a record in the terminal of all hoses. This can be used as a complete inventory of equipment and can provide a useful aide memoir for all hose details including the times of hose testing. A computer programme is available for doing this known as “Hosetrac” and details are available from the SIGTTO secretariat on request.
The electrical continuity of the hose should be checked during hose testing against design parameters. Inspection and testing dates should be clearly indicated on the hose. Visual inspection of composite hose is particularly important as the carcass is known to be subject to unexpected damage (see Section “Hose specification”).
Ship’s Hoses
Ship’s hoses are often specified to standards different from those specified ashore. This standard is somewhat less exacting that the other standards mentioned in Section 10***. Accordingly, where possible, the hoses recommended for dock-side use should be preferred.
A possible disadvantage of using shipboard hose is the higher chance, in some cases, of it not being subject to appropriate tests which are sometimes difficult to carry out at sea. A case of this type is recorded in Section “STS transfers”. If a ship’s hose is to be used, as a minimum, terminal personnel should check the hose test certificate and confirm the hose to be of a type suitable for handling the cargo.
Furthermore, the storage of hoses on board ships can be in unsatisfactory places resulting in early deterioration.
STS Transfers
Ship-to-Ship (STS) transfer operations are becoming a more common feature in many LPG trades. The procedures to adopt for these operations are described in another document. That publication also covers aspects relating to hose quality and its recommendations should be followed.
There is a case on record of a hose burst occurring during an STS operations (See Appendix 1***). This describes how the wrong hose happened to be specified. In such operations it is usually an STS Agency which arranges for the transfer equipment to be supplied. It is important for the principals, who set up such operations, to ensure that the STS Agency knows which hose to obtain.
In another case a ship’s hose was used and this failed during the transfer of refrigerated product it was found that hose testing had not been carried out (See Appendix 1***).
To date, STS transfer of a routine nature have been limited mainly to LPG. However, there are a few cases on record of LNG STS transfers having been carried out in emergency situations. These operations have all been serviced using composite type hose of special manufacture.
