Mitigating Risk for FPSOs With Hose &Coupling Solutions

As the search grows for better cost efficiencies, operators are turning to FPSOs more than ever before, leveraging the economical and efficiency benefits of floating production that storage and offloading vessels can deliver. New design concepts, fabrication and integration innovations, creative financing options and industry partnerships are all contributing to an upswing in orders.

As the global FPSO pipeline continues to grow, so too does the need for companies to invest in safe practices to guarantee the successful and reliable performance of the facility. Equipment needs to be able to endure the harshest environments. Selecting the right hose, for example, can ensure the highest safety standards, without compromising on optimizing service life.

By Vincent Lagarrigue, Director, Trelleborg Oil and Marine

In order to maximize safety and technical integrity, as well as cut costs and reduce the environmental impact of operations worldwide, organizations like the American Petroleum Institute (API) have developed set standards that represent the industry’s collective wisdom and best practices. These standards are designed to assist industry professionals improve the efficiency of their operations and mitigate the risks of equipment failure.

At present, API maintains over 700 standards and recommended practices. API Spec 17K is the most stringent of these applicable to a bonded marine hose. To meet the specifications laid out by this standard, hoses undergo rigorous testing and full-scale fatigue tests under the simulation of real-life conditions. The tests can accurately compute stresses and strains in every component of marine hoses, which in turn provides customers with the security that their selection is well suited to the environment in which the hoses will operate.

In addition, the aging of the materials used for each application, and the evolution of their mechanical properties over time, are verified through small-scale tests and compared with feedback from real applications. This reduces the amount of maintenance required for each solution and reduces lifecycle costs – enabling API Spec 17K hoses to be certified with a service life of up to 25 years in even the most challenging weather conditions.

These API Spec 17K hoses also have two particularly important applications in FPSO operations: it enables both reeling and safe operations at greater pressures and depths.

Reeling

When a hose is wrapped around a reel, to be wound in or out during an operation, it is called reeling. There are several functions on an FPSO that require reeling. Uses for this task include ship to ship (STS) transfers in the bow loading and tanker midship manifold configurations, as well as other applications. By its nature, a reeled hose poses additional challenges to an FPSO.

There are a number of inherent safety risks that operators of FPSOs must mitigate. For offloading transfers, these include a collision between the FPSO and the tanker vessel, tanker drift-off, unexpected pressure surges, and transfer failure. All of these can result in asset damage, injury to operational personnel, or product spill. To mitigate these risks, operators often use a marine breakaway coupling (MBC) or an emergency release coupling (ERC).

While superficially similar, there are some fundamental differences of which operators should be aware. Unlike the ERC, the MBC requires no manual activation from personnel, eliminating the potential for possible operator failures. At the same time, the MBC is more equipped to mitigate the risk of surge pressure and offers greater overall protection of the offloading hose in the event of tanker drift-off.

However, despite its advantages, there are a number of challenges when using MBCs in combination with a hose reel – specifically the unintended parting of the MBC during the reeling operation. This often happens when an operator uses a standard double carcass nipple hose that, when an MBC is added, has a stiff section that is longer than 1.7m. When the hose is stored on the reeling application, the stress placed upon the stiff section becomes too great, resulting in the unexpected release of the MBC. A number of FPSO projects have faced this challenge in the last years when using stiff double carcass nipple hoses.

To overcome this challenge, solutions were developed specifically for reeling applications on FSPOs. Using a nippleless design, REELINE dual carcass hoses contain reinforced compact flanges and integrated bending stiffeners – which means more flexibility, higher resistance to tension and collapse, and no stress concentration in the flange area. Even when operating in challenging sea conditions, the offloading solution has a long service life, making offloading operations safer and more reliable. An example of this solution is Trelleborg REELINE hose.

REELINE dual carcass hoses are designed to allow an MBC to be seamlessly integrated into the offloading line. Not only is an MBC vital to ensure that the risk of failure is mitigated, it is important that an MBC is properly integrated into the design of the hose to minimize the risk that the MBC will be accidentally activated as the hose is being reeled or unreeled during operations.

An MBC offers greater protection from the risk of product failure than the manually activated ERC, while using a hose designed to integrate seamlessly with MBCs also reduces the risk to equipment. At the same time as providing better protection, it also significantly reduces maintenance and overall operating costs.

Seawater Intake

Another area where fluid handling equipment is vital to ensuring safe, efficient operations is seawater intake. Used to bring huge quantities of cold water onto floating production platforms to absorb the heat generated when natural gas is compressed and liquified, seawater intake risers are an important part of any FPSO operation. In some cases, as much as 40,000 cubic meters of water per hour is needed to absorb the calories exhausted, requiring systems with high flow rates and a long lifespan of up to 25 years.

One of the trends emerging as a result of the challenging market environment is an increased demand for hybrid seawater intake risers using a combination of high-density polyethylene (HDPE) plastic pipes and rubber hose technology. While these hybrid solutions can offer capital cost savings, there are a number of risks involved that must be considered when choosing the right solution.

From a technical standpoint, the use of HDPE is challenging due to its buoyant nature. The density of the plastic is less than 1 kg/m3, therefore an HDPE riser must be weighted down to stop it from floating in the water and to ensure the strainer is at the lowest possible depth. Ballast weighting is also required for stabilizing purposes. All of this puts a huge amount of stress on the riser, posing a risk to both the vessel and the assets on the seabed if the plastic were to break.

There are also operational challenges inherent in hybrid systems, when compared with complete rubber hose solutions. For example, Trelleborg Swiline hoses are designed to be used in lengths of up to 600m or even more, enabling the use of seawater from greater depths, which can be up to 20ºC/68ºF cooler than water at the surface. In contrast, hybrid systems will operate in much shallower depths, resulting in warmer water being used during the liquefaction process.

For an effective cooling process, it is crucial that seawater is as cold as possible. Therefore, it is worthwhile to consider using a solution consisting solely of rubber hoses rather than a hybrid solution to maximize long term performance.

Seawater intake hose solutions, such as Telleborg’s Swiline hose, incorporate an integrated bending stiffener with a continuous inner liner and rubber outer cover to minimize the risk of corrosion while offering optimal thermal insulation. The combination of steel cables in a rubber matrix minimizes creep and offers typical tensile strength as high as 1,600 tons for 40-inch ID hose– a key attribute when the higher weights required to maintain the position of the hose in high currents are considered.

Swiline hoses can be easily installed vertically from the FPSO deck. Assembly can take place beside the hull with connection on the intake flange by divers, or in the riser caisson. Hydraulic simultaneous tightening of the flange ensures reliable, homogeneous per-loading of the bolts for optimum performance.

Final Thoughts

Hoses and couplings on FPSOs must operate under the harshest conditions and cope with incredibly high stresses and pressures. These forces act both externally, from the extreme environments that FPSOs operate in, as well as internally from the inherent pressures of fluid transfer.

Under these conditions, proper hose selection is vital. The risk of accident – which could cause damage to important assets, environmental damage or injury – is high. Using appropriate and specially designed hoses can mitigate these risks, while also providing better long-term value by reducing the operational expenditure needed for repairs and maintenance.