Corrosion-free alternative for onboard safety SAFETY is a key priority for the offshore oil and gas industry, and ensuring safety onboard any production facility is absolutely vital. Critical to delivering onboard safety is the fire deluge system which, designed to protect areas where fire is likely to spread rapidly, is now commonplace on offshore facilities.
However, traditionally used carbon steel-fabricated deluge systems are prone to corrosion when carrying saltwater, which can restrict or even block flow as rust forms, in turn reducing the effectiveness of the system.
Corrosion-free alternatives prevent such issues and give peace of mind to the offshore oil and gas sector. Presented in this white paper is a case study demonstrating the benefits that can be gained by specifying these alternatives.
TRADITIONAL TECHNOLOGY
Active fire protection systems, such as the fire deluge system, are essential for onboard safety and are designed to activate either mechanically or electronically in order to extinguish fires. While relatively simple in design and installation, their operation is essential for the safety of onboard personnel, asset protection and preventing event escalation.
In the offshore oil and gas industry, the risk of rapid fire spread is greater than most and as such, the fire deluge system needs to provide full assurance to the onboard team that it will not fail to deliver on any critical firewater or utility piping installations.
Traditionally, carbon steel-fabricated deluge systems have been installed to ensure onboard safety, however, the continual flow of water may cause potential blockages of small diameter pipe work and discharge nozzles. These are prone to corrosion that can cause vital systems to fail. This has resulted in the industry suffering from costly shutdowns and repairs, and in the worst-case scenario, risk of failure in an emergency. In addition, traditional systems also require constant maintenance, cleaning and testing, meaning additional unnecessary and costly downtime for the facility.
NEXT-GENERATION ALTERNATIVE
The problems encountered with traditional systems have since spurred the development of a new generation of fire-deluge systems that use synthetic rubber instead of traditional materials such as rigid steel, titanium, copper nickel and fiber glass piping.
By utilising synthetic rubber, systems can now be created that are non-corroding and can withstand jet fires with a heat flux of 390kW/m2, temperatures above 2552 deg F/ 1400 deg C and flame speeds that exceed the speed of sound. This makes it an ideal material choice for use in deluge and sprinkler systems on offshore oil and gas installations and ships, as well as other hazardous environments.
Due to its flexible characteristics, this new technology can be used to either partly or completely replace old systems and is also an ideal solution for temporary deluge systems when high safety levels need to be maintained during modification work to existing systems. The flexibility of the system allows it to be moved and reused (if temporary). Compared with rigid pipe systems, it requires fewer construction drawings, and the need for accurate measurements is reduced as the system can be designed and modified on site.
PROVEN SOLUTION
A recent example of how a traditional carbon steel-fabricated deluge system failed and was successfully replaced by a new, synthetic rubber alternative can be seen on Maersk’s FPSO Ngujima-Yin, a floating production storage and offloading (FPSO) vessel located in the Vincent Field off Western Australia. The vessel commenced operation in 2008 and has a daily production capacity of 120,000 barrels of oil and 100 million standard cubic feet of gas. The existing carbon steel seawater deluge system became corroded only 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 approximately 5,249 ft (1,600 metres) of pipe work, from 1 inch to 8 inches (25 mm to 200 mm) diameters, and associated fittings and accessories.
SYSTEM CONSIDERATION
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 have to be rigged up while the existing pipes were removed and installation of the new system was undertaken.
Replacing a conventional deluge system requires hot work such as welding, cutting, brazing, soldering and grinding, which poses 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-proven 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 rigid pipe systems, fewer detailed isometric construction drawings are required with a synthetic rubber system, and the need for accurate measurements is reduced as it can be designed and modified on site. This means a flexible synthetic rubber FPSO module deluge system can be installed in less than three months, whereas the installation time for an equivalent typical rigid 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™ corrosion-free fire safety deluge system on the FPSO. CORROSION-FREE PROTECTION The Trelleborg Offshore 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 (2,552 deg F / 1,400 deg C 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 requires more frequent testing and maintenance and needs replacing 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, approval from a number of national and industry authorities needed to be obtained. As the Maersk Ngujima-Yin is a Danish registered FPSO, the Danish Maritime Organization (DMO) had to approve the use of the flexible piping system onboard the vessel.
National Offshore Petroleum Safety Authority (NOPSA) approval was also required as the FPSO was producing oil in Australian waters. Finally, the installation had to be approved by Lloyd’s Register, which classed the ship. All authorities involved approved the solution proposed. The materials 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 approximately 5,249 ft of flexible piping, titanium fittings, nozzles, pipe supports, valves and strainers, was pre-fabricated on board the Maersk Ngujima-Yin. This included cutting pipe runs to the required length and fitting the necessary ancillary components.
The first installation on the M60 module required 912 ft of flexible pipe and was completed in less than two weeks. The synthetic rubber-based flexible piping system was installed without any welding or other hot work, such as high-speed cutting, which could compromise the safety of the vessel. The rubber was cut using a specialised hand-held pipe cutter, while joints 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.
A temporary Elastopipe deluge system for each module was installed before the existing steel pipes were removed and the permanent flexible pipe work and fixings were completed. 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. No lost time incidents (LTIs) were reported during installation.The installation team worked independently, without disturbing activity onboard or impacting production. The 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 to 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 full-scale tested within three months, with no disruption to oil and gas production.
CONCLUSION
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.In the harsh offshore and onshore oil and gas industry, you need the assurance of a material that delivers proven performance for your critical firewater and utility piping installations, without fail.
Source : Oil & Gas News Online
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