Improving safety and efficiency in the ever-evolving STS transfer sector
20 April 2020
Ship-to-ship (STS) transfer is becoming increasingly popular throughout the shipping industry, opening up new trade routes and making new and more efficient logistics processes possible.
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Most of the headlines have tended to focus on large, milestone transfers, such as Scheldt River performing the first STS LNG bunkering operation in German waters last year; these underpin an ongoing, significant rise in the number of STS transfers taking place. This rise in oil transfers is evidenced by SafeSTS Middle East FZE, which stated at the end of 2018 that it had transferred nearly 2,334,000 barrels of oil in the Gulf of Oman by STS within its first six weeks of operation, and opened new premises in the region in November 2019.
One of the main forces driving demand is logistics efficiency. It is more efficient to use a very large ship to transfer liquid cargo for the bulk of a long journey, and transfer cargo to another, smaller ship either when draught restrictions require a smaller ship or if there are multiple offload points for the cargo at several ports.
This trend of using larger ships to reduce the cost of transporting liquid cargo, is evidenced in the sharp increase in the number of Very Large Crude Carriers (VLCCs). VLCCs are used to transport oil across oceans at a lower marginal cost, but are too large for most ports and some key channels – including much of the Gulf of Mexico. The economics of this have led to a boom in STS oil transfers taking place, often in designated STS locations designed to cope with the rise in demand.
Despite the clear benefits, STS transfer can be a particularly complex process. There are very real risks of a spill or a fire if an STS transfer is poorly planned or executed. It requires proper planning, coordination, equipment and approval to perform a transfer safely and ethically. There are clearly risks associated with operating equipment between two independently moving ships at the best of times, so planning must mitigate the risks of hazardous weather and hose management must mitigate the risks associated with the stresses exerted on the equipment by the external pressures alongside the internal pressure associated with the transfer.
A 2018 incident involving a faulty hose highlights the dangers of poor hose management in STS transfers. In that incident, a faulty hose ruptured and sprayed oil on deck and overboard, raising serious questions around the safety and operability standards of STS transfers around the world. The UK P&I Club, investigating the incident, noted that the hose used was not provided with valid records of test and inspection which contributed to the failure of the hose. The Club issued a recommendation stating that all cargo hoses must be fit for purpose and provided with valid records showing that they have been appropriately tested and inspected.
The incident demonstrates the need for all parties involved in an STS transfer operation to ensure that the process is conducted safely and efficiently. The investigation additionally highlighted the need for suppliers to ensure that they are helping to raise standards across the industry by contributing their expertise as much as their products.
In any liquid cargo transfer, equipment must improve both efficiency and safety while functioning in a way that is easy for a crew to operate. In STS transfers the need for efficiency, safety and ease of operations are heightened, while equipment must be rated to safely and efficiently operate in the face of environmental challenges.
Hose solutions for oil and LNG STS transfers require different specifications and features to ensure safety and efficiency due to their relative temperatures and viscosities. There are design philosophies whose benefits cover both LNG and oil. These designs are based on technology originally developed for truck tyres, with the internal carcass providing resistance to the internal pressure, and the outer carcass providing resistance from the external pressures and loads inherent in STS transfer while preventing leaks. This enables the hose to withstand accidental kinks or crushing forces that can occur during the process, and different designs using this philosophy create bespoke solutions for both LNG and oil transfers that optimise safety and efficiency.
Overcoming specific challenges in LNG transfer
LNG poses a unique challenge in STS transfers, especially in open seas. LNG needs to be kept at a low, cryogenic temperature which in itself can cause wear to some hoses. It also creates new risks in transfers, as any spillage is dangerously cold and rapidly changes state into an extremely flammable gas. Additional measures are required to ensure that a hose is more durable, and that there are adequate failsafe systems in place to capture and funnel off any leaked LNG.
This is why so much effort has been spent in developing robust means of safely loading and unloading LNG in STS operations. One example is floating cryogenic hoses, where vessels can be moored as much as 100 to 300 metres away from a storage unit, allowing for STS transfer in deeper waters in even the most challenging conditions.
During the development of our Cryoline hose-in-hose technology, several full-scale hose prototypes were successfully tested in both static and dynamic conditions – with most tests taking place in cryogenic conditions at -196 °C / -321 °F – demonstrating their ability to withstand fatigue resistance in even the most hazardous conditions.
Boil-off gas generation during transfer presents another challenge for operators in offshore conditions, often causing valuable energy loss during the transfer process. Technology has therefore been developed with insulated hoses that can reduce boil-off by as much as 60% – equating to a saving of 10 billion btu’s of energy saved over the course of 500 transfers.
Overcoming specific challenges in oil transfer
One specific challenge when it comes to STS oil transfer is how to handle internal pressure on a hose. Internal pressure can cause a hose to wear or rupture quickly, which in turn can cause a serious accident that either endangers crew or discharges oil into the environment. In an STS oil transfer, this is multiplied by the external pressures exerted on the hose as two ships move independently of each other and by accidental kinks or knots in the hose.
STS oil hoses are typically qualified to the EN 1765 standard, however some hoses are qualified to the higher GMPHOM 2009 standard. This standard requires more in-depth testing – including for higher torsion loads and pressures – and means that the hose has a longer than typical service life. A higher level of assessment provides a superior level of certainty and confidence when it comes to STS transfers, in line with best practice regulations, alongside better performance indicators offering more accurate estimates of service life and resistance. Capital expenditure investment in this higher specification ensures smoother operations, less expensive maintenance, and ultimately fewer expensive replacements over a project’s lifespan.
Standard STS oil transfers use hoses with nipples connecting sections of the tube. These long metal connectors create a sudden change in hose flexibility which concentrates bending stresses in particular, increasing the risk of failure. To combat this risk, the KLELINE STS hose has a unique nippleless design.
In contrast to a standard nipple hose design, there are no large, stiff metal connectors. Instead metal connectors between sections of hose are kept very compact compared to a nipple-design hose. This makes the hose more flexible, while the continuous inner liner and integrated gasket create a perfect sealing solution. The design means that there is no need for gaskets at each connection, increasing the simplicity of installation, resulting in a hose that can withstand stresses and strains for longer.
The nippleless hose design philosophy used in these hoses been constantly updated since 1975 and used around the world in offshore projects. The technology is now poised to have the same impact in improving safety and reliability standards in the STS market.
As suppliers, it is our duty to ensure that we are helping to raise standards across the industry. As experts, it is our duty to contribute our expertise alongside our products. Particularly in hoses, investing in higher specification products has a big impact; reducing the need for maintenance, increasing operability, and lessening the number of costly replacements over the lifecycle of a project reduces operational expenditure alongside reducing risk of accident. As the industry evolves, it is crucial we continually evaluate the long-term effectiveness of oil transfer solutions at each part of the value chain, along with operability.
About the author:
Nicolas Landriere is Product Manager for Trelleborg's oil hose applications, providing technical support to new and existing customers and expert advice throughout the various stages of each project. As a technical specialist for hoses and offshore offloading applications, Nicolas also contributes to the development of new products.
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