While seawater is an effective and popular coolant in the offshore oil & gas (O&G) industry, it does bring a host of challenges including salinity and aggressive micro and macro marine growth. There are, however, effective solutions to minimise its impact on offshore assets. But what if there is nobody around? In this article, Rob Jones, Chloropac® System Sales Manager at Evoqua Water Technologies, discusses the design considerations for marine growth prevention (MGP) in protecting unmanned platforms.
When it comes to long-term viability within offshore O&G, minimising downtime and implementing cost-effective and cost-saving solutions are critical. While seawater has played an important role within the offshore industry for decades, it does introduce a series of complications and expense if left untreated. Seawater itself is home to vast quantities of bacteria and microbes that have long been lamented as the cause of substantial corrosion and damage through blockages in plant and equipment, resulting in downtime.
While, conventionally, technology systems could be monitored and maintained by personnel on the platform, the rise in unmanned platforms has highlighted a requirement for highly reliable, low-maintenance systems. Indeed, Equinor’s famous unmanned North Sea platform launched in 2019, has no living quarters and receives minimal visits per year. Not only do these unmanned platforms significantly reduce risk to personnel, but they also have the potential to increase efficiency, provide cost savings and reduce operational CO2 emissions, thanks to substantially reduced helicopter transport as well as the elimination of accommodation and living facilities.
Despite the absence of people, minimising the impact of damage caused by marine growth remains an essential part of maintaining profitability. This is particularly true for heat exchangers and cooling. Perhaps no system can contribute more to preventing plant degradation than effective marine growth prevention (MGP).
As ever longer periods between one technician visit to the next are envisaged, careful consideration should be given to the type of MGP technology to be employed. Preferably systems that have been specifical engineered for the unique offshore environment, with long term operational references, are good indicators of the level of practical reliability achievable in the field. Untested approaches are a risk not worth taking!
Although, potentially feasible for some late life platforms; liquid or powder disinfection chemicals introduce potential safety and pollution concerns, but also carry the inherent risk of bad weather preventing the replenishment of stocks in time.
In situ generation methods, such as electro-chlorination, have been employed for over 40 years in the offshore industry. Hypochlorite is generated in an electrolyser by applying an electrical field to seawater in the presence of a catalyst. Although care is required that the electrolyser type selected does not introduce the need for regular chemical cleaning to remove calcified deposits (an unavoidable by-product of the electrolysis process). A cell designed to use high internal seawater velocities is known as a concentric tube electrolyser (CTE) and are self-cleaning, albeit operational evidence is essential in the selection of the manufacturer.
An electrolyser system can feature, if required, a level of redundancy in order to minimise the risk of equipment failures. However, less obvious design factors lurk here! In variably, the equipment needs to be hazardous area approved and deal with very low seawater temperatures in ever more remote areas. Introducing purging air to the electrolyser and/or having to pre-heat seawater feed both add cost and additional services: Look for electro-chlorination systems that eliminate these complications.
Inevitably as the heart of any system, the electrolyser cell construction must offer a robust sealing design and stable electrical connections in the harsh ambient offshore conditions; improving overall reliability.
At Evoqua, we work closely with customers to understand their specific maintenance plans and ensure that MGP systems are well taken care of. We also offer remote monitoring and control, for total and complete oversight. We can provide customers with consumable spares, equipping them with stock should it be needed as close to the platform as possible, further reducing downtime and the complexity of logistics.
With any technology solution for offshore, performance and reliability are key but what sets the leading solutions apart from others, is the ability to operate unmanned and give engineers confidence in doing so. We stand by our technology, so our customers don’t have to.
 Equinor starts up unmanned North Sea rig (energy-reporters.com)