Technology from Europe
SWEDEN / CASE STUDY

Fire safety retrofit using flexible-pipe deluge system avoids production downtime

HANS-LEO HALS, Trelleborg Offshore

Workers install the flexible piping system aboard Maersk’s Ngujima-Yin FPSO.

The fire deluge system is critical for ensuring safety onboard any offshore production facility. However, traditional carbon steel-fabricated deluge systems are prone to corrosion when carrying saltwater, which can restrict or even block flow as rust forms. As a consequence, the industry has suffered from costly shutdowns and repairs, and in the worst case, risk of failure in an emergency. To prevent these issues, operators are investigating corrosion-
free alternatives.

One recent example of this occurred aboard Maersk’s Ngujima-Yin FPSO in Vincent field off Western Australia. The vessel commenced operation in 2008 and has a daily production capacity of 120,000 bbl of oil and 100 MMcf of gas. The existing carbon steel seawater deluge system became corroded two years after installation and required a significant number of man-hours to carry out regular maintenance, cleaning and testing. A replacement was therefore required to reduce the long-term cost of ensuring essential fire protection at all times.
The challenge with the installation was to replace the existing fire deluge system throughout the FPSO modules, without affecting the safety of the vessel as it continued output. The system required about 1,600 m (5,250 ft) of pipe work, from 1-in. to 8-in. diameters, and associated fittings and accessories.

System considerations. Several factors had to be considered prior to specifying a replacement system. As the FPSO is a live production vessel, it must operate within a stringent set of safety regulations, requiring complete deluge coverage at all times. A temporary system would therefore have to be rigged up while the existing pipes were removed and installation of the new system was undertaken.

Replacing a deluge system with another conventional system requires hot work such as welding, cutting, brazing, soldering and grinding, which pose a number of issues when carried out on a live hydrocarbon facility. Any activity that generates heat, sparks, flames or other potential sources of ignition in an atmosphere that may be flammable requires a hot work permit. This is only granted after an in-depth risk assessment and also requires ongoing monitoring. To secure a permit, it may be necessary to isolate part of the hydrocarbon systems on a vessel, shut down production modules or use special habitat equipment. As such, hot work is usually only carried out as a last resort.

A number of material options were considered, including rigid copper-nickel and flexible synthetic rubber. Copper-nickel has an extensive field record and is cheap to purchase; however, it requires significant pre-fabrication and onboard construction. In contrast, synthetic rubber is easier to install and can be bent to a radius equal to five times its diameter, meaning it can negotiate minor clashes and obstructions as the installation progresses, while maintaining its structural integrity.

Compared with deluge systems that use rigid pipe, less detailed isometric construction drawings are required with a synthetic rubber system, and the need for accurate measurements is reduced, as the system can be designed and modified on location. This means that a module deluge system using flexible synthetic rubber can be installed on an FPSO in less than three months, while the installation time for an equivalent typical copper-nickel system would be significantly longer.

Taking these factors into account, Maersk contracted Trelleborg Offshore as an engineering, procurement, construction and installation (EPCI) supplier to install its synthetic rubber Elastopipe deluge system on the FPSO.

Corrosion-free fire protection. The system was developed as a result of both customer and industry feedback. Its design incorporates three core layers: the fire shield, pressure liner and inner layer. These combine to give the system high tolerance to impact, jet fire (1,400°C/2,552°F for one hour), explosion and water hammer. The system is lightweight, durable, and easy to cut, fit and install.

Compared with a conventional carbon steel-based deluge system, which will require more frequent testing and maintenance and must be replaced at regular intervals over the lifetime of the platform or vessel, rubber deluge systems deliver a very low total life cost.

The flexible piping system offers a 30-year minimum maintenance life, and its corrosion-free performance means system testing frequency can be reduced to statutory requirements.

Installation. The regulatory bodies governing deluge systems for FPSOs and similar structures did not have specific regulations to cover the flexible piping system, so there were early inquiries from independent verification societies into its concept and feasibility.

For the project to proceed, Trelleborg had to obtain approval from a number of national and industry authorities. As the Ngujima-Yin is a Danish-registered FPSO, the Danish Maritime Authority (DMA) had to approve the use of the flexible piping system onboard the vessel.

The project also required approval by the National Offshore Petroleum Safety Authority (NOPSA), as the FPSO was producing oil in Australian waters. Finally, the installation had to be approved by Lloyd’s Register, which classified the vessel. All authorities involved approved the solution proposed.

The materials required for the first module and the temporary deluge system were air freighted to Australia and were onboard the vessel within a week. The system, which comprises about 1,600 m of flexible piping, titanium fittings, nozzles, pipe supports, valves and strainers, was pre-fabricated onboard the FPSO. This assembly included cutting pipe runs to the required length and fitting the necessary ancillary components.

The first installation on the M60 module required 278 m of flexible pipe and was completed in less than two weeks. The synthetic rubber-based flexible piping system was installed without any welding, high-speed cutting or other hot work, which could compromise the safety of the vessel. The rubber was cut using a specialist handheld pipe cutter, while joins were made mechanically using air-operated hand tools and proprietary clips. Without the risk of sparks or naked flames, production and processing could continue unaffected.

Trelleborg installed a temporary deluge system for each module, removed the existing steel pipes, then completed the permanent flexible pipe work and fixings and moved the temporary deluge system on to the next module. This method ensured that full fire protection was retained throughout the project.

The fast-track project was carried out by 10 expert rope access pipe fitters and two supervisors, and no lost time incidents  were reported during installation. The supply company team worked independently, without disturbing activity onboard or impacting production. The installation team implemented the full scope of activity in full compliance with both Woodside’s golden safety rules and Maersk’s divisional management system, which includes the Maersk permit-to-work system.

The flexibility and light weight of the deluge system allowed very rapid installation, compared with a rigid pipe system, as it could be swiftly configured to confined spaces. The first two modules were completed in just a month, and all seven modules were completed and tested at full scale within three months, with no disruption to oil and gas production.

“Trelleborg Offshore provided the complete survey, design, engineering, supply and installation package, as well as removing the old installation,” said Christian Eilersen, Maersk director of FPSO projects. “It was important that operation of the FPSO was not affected in any way, and that safety was considered of paramount importance. Trelleborg Offshore ensured not only a quick and effective, but also a safe installation.”

Conclusions. Safety on offshore oil and gas installations is of paramount importance, and having an effective and reliable deluge system is vital to ensuring onboard safety. With corrosion a constant risk, steel-based systems require regular maintenance and periodic replacement, which is not only disruptive but also costly. The synthetic rubber deluge system not only has demonstrated advantages of corrosion resistance and lower maintenance, but—as demonstrated in the Ngujima-Yin installation—is also easier, quicker and safer to install than even corrosion-resistant options such as copper-nickel and rigid polymer pipework, making it particularly well-suited to retrofit operations aboard operating production facilities, where the cost of lost production during a shut-in is a major factor.

HANS-LEO HALS is the Elastopipe Product Group Manager at Trelleborg Offshore and has over 20 years of experience in the oil and gas industry. / hans-leo.hals@trelleborg.com