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Simplifying Complexity. Delivering Safety.
Simplifying Complexity.
Delivering Safety.

Development of hazardous area Electrodeionization systems


Working with a Norwegian engineering consultancy to develop hazardous area water treatment systems for installation on Floating Production Storage & Offloading (FPSO) vessels



FPSOs are self-contained floating vessels used by the offshore oil and gas industry for the production, processing and storage of hydrocarbons, prior to offloading via a pipeline or tanker. In a similar way to fixed production platforms, many areas onboard an FPSO will be classified as hazardous, requiring all equipment and systems to be certified for safe use. This case outlines one such project.


Project Brief

Our client, a specialist engineering consultancy company based in Norway, needed to source certified Electrodeionization (EDI) systems to provide ultra-pure process water onboard several FPSOs. EDI cells and their control systems are readily available for safe area applications, but no suitable hazardous area systems exist. Due to the physical size and weight of the cells, a Purged and Pressurized (Ex p) enclosure was the only feasible protection method. The client contacted Expo as the clear leader in this field.


  • Due to footprint limitations, each pressurized enclosure system would be required to contain 2 off EDI cells and associated controls, hence large enclosures would be required, suitable for unusually heavy contents, each cell having an empty weight in excess of 150kg.
  • Thermal management had to be considered as the FPSOs would be deployed to warm climates.
  • The EDI process generates small quantities of both hydrogen and oxygen, which are normally piped away safely to vent. However, in the event of a leak into the pressurized enclosure, a potentially dangerous situation could occur. Mitigation was therefore required.
  • The systems were to be designed to be suitable for Zone 1certification.
  • A joint feasibility study was carried out with the client, prior to agreeing the final enclosure design.
  • The specially reinforced enclosures featured sliding rail systems to allow the EDI cells to be loaded inside, one above the other, before being locked into place.
  • Special flanged connections were provided for the water feed and return flows, as well as the vent gas piping.
  • To mitigate the risk of hydrogen or oxygen leakage, hazardous area certified gas leak detection systems were installed to monitor both upper and lower EDI cell compartments.
  • A Type-X Minipurge was fitted, with internal distribution piping to ensure full purging of the upper controls enclosure and the two EDI cell compartments in series.
  • Custom sun shields were installed on most available external surfaces to limit the impact of direct sunlight once the FPSOs were deployed.
  • After final fit-out, the enclosures will be inspected & certified by Expo


Expo products and services
  • Engineering consultancy to develop the overall solution
  • Custom enclosure design & manufacture
  • MiniPurge type X
  • Populated enclosure certification service



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