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The evolution of subsea sealing

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oil rig illustrationSince the world’s first subsea well was brought into production in 1961, offshore development has moved forward in leaps and bounds.

The oil & gas industry has extended to the exploration of ultra-deep waters upwards of 10,000ft into the ocean. Offshore exploration and production is pursuing resources in remote reservoirs characterised by extreme pressure and temperature – all of which is testing the limits of current subsea sealing technology.

Stringent new industry standards in line with these high temperature, high pressure  (HTHP) advancements have caused OEMs to develop new components for subsea production systems; these include trees, wellheads, BOPs, manifolds, gate, ball and choke valves, flow meters and couplings.

As a result, OEMs are searching for alternative seals to an interference-type seal (O-ring).

Initially an O-ring with two back-up rings would have been used in subsea applications. If the direction of media was unknown, two back-up rings prevented incorrect installation.

Back-up rings also prevented the elastomer O-ring from extruding into the hardware at high-pressure. Extrusion doesn’t instantly lead to seal failure, but after time could be a factor of regular leaks. Leaks or technical issues with subsea equipment could have critical consequences, harming people or the environment.

As wells got deeper, both pressures and the criticality of seals increased. Soon T-seals were replacing O-rings in HTHP applications.

T-seals comprise of an elastomer T-shaped cross section and two backup rings made from an engineering grade plastic, often PTFE or PEEK. This new shaped seal holds the backup rings in high pressure applications, whilst still maintaining high sealing efficiency at low pressures.

The design of the T-seal uses the system pressure to actively energise the backup rings, ensuring efficient extrusion resistance in single and bi-directional pressure applications, both in static and dynamic conditions.

However operators were still faced with the challenge of installing a three-component sealing system thousands of feet below sea-level, using a remote-operated-vehicle (ROV).

Factoring in all the application challenges, the spring seal was introduced.

Spring seals (also known as S-seals and all-in-one T-seals) comprise of a high modulus elastomer and two integrated anti-extrusion springs.

Spring SealThe homogenous seal features corrosive-resistant metal coil springs moulded into the exposed seal corners. The strategic position of these spring coils eliminated weak points around the seal's circumference.

The anti-extrusion design has versatile properties, sealing larger tolerances. In this case the anti-extrusion elements are often referred to as being active rather than passive, as is the case with more traditional thermoplastic back-up rings.

The spring seal is concentric to the hardware, removing the need to manipulate the anti-extrusion elements (back-up rings), minimising complexity of installation and reducing the risk of damaging the seal elements.

The evolution of sealing didn’t stop there. Precision Polymer Engineering identified that while the profile of the seal had changed, the material hadn’t.

Precision Polymer Engineering were the first to launch spring seals in a unique low temperature Perfluoroelastomer FFKM material, fully qualified to industry, OEM and supermajor approvals.

Designed to combat deeper and harsher operating conditions, involving the most extreme low and high operating temperatures, FFKM spring seals demonstrated the capability to meet the future demands of Oil & Gas exploration and production for OEMs.

FFKM spring seals deliver reliable performance under pressures exceeding 20,000 psi and temperatures of -29°C to 204°C. The material also demonstrates exceptional durability against aggressive process media and operating fluids.

With numerous advantages for the OEM, the evolution of the FFKM spring seal makes for reduced cost of ownership, full traceability, ease of installation and safer operations.

Explore the full potential of PPE's FFKM spring seals here, or contact our team of engineers today to discuss your subsea sealing requirements.

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