VALVE MAGAZINE Fall 2025

ADVANCED SEALING TECHNOLOGIES FOR SUBSEA

Seal Combination

Key Characteristics

Subsea Applications and Relief Requirements

Configuration

Seals against pressure from either di rection; automatically relieves cavity pressure to the lower pressure side. Does not provide double isolation if one seat fails. Provides true double isolation with bidirectional sealing on both seats. Traps cavity pressure, requiring external relief.

Used in subsea pipelines for maintenance or non-critical isolation; self-relieving design eliminates need for external relief, simplifying system design.

DBB

Both seats SPE

Critical for subsea applications requiring maximum isolation (e.g., high-pressure gas lines); requires external relief systems (e.g., relief valves or vent piping) to man age cavity pressure. Suitable for subsea systems needing strong isolation with partial self-relief; ex ternal relief may be needed depending on valve orientation and pressure conditions.

DIB-1

Both seats DPE

DPE seat provides bidirectional isola tion; SPE seat allows self-relief on one side, reducing cavity pressure issues.

One seat SPE, one seat DPE

DIB-2

Double block and bleed DBB valves, designed to provide two sealing barriers and a bleed point, are often used in flowline applications where cost and simplicity are prioritized, ensuring effective isola tion with a single valve body. Double isolation and bleed • DIB-1 valves, which offer bidirectional sealing on one seat and unidirectional sealing on the other, are suited for subsea trees where enhanced isolation is needed under specific flow conditions. • DIB-2 valves, with both seats providing bidirectional sealing, are typically specified for critical emergency shutdown valves (ESDVs) to ensure fail-safe isolation regardless of pressure direction, minimizing the risk of fluid loss or environmental damage.

Explanation of SPE and DPE seats • Single piston effect (SPE) seats: SPE seats, also known as unidirectional or self-relieving seats, seal primarily against pressure from one direction, typically upstream. Upstream pressure forces the seat against the ball or gate, forming a tight seal. If cavity pressure exceeds upstream pressure, the seat disengages, venting pressure upstream to prevent over-pressurization. This design limits sealing against reverse pressure, making SPE seats less suitable for bidirectional isolation in subsea appli cations with multidirectional pressure sources. • Dual piston effect (DPE) seats: DPE seats, or bidirec tional seats, seal against pressure from both upstream and cavity sides. Pressure from either direction presses the seat against the closure element, ensuring robust To withstand subsea extremes — pressures depths up to 9,500 ft and internal pressures up to 10,000 psi, temperatures up to 400°F, and aggressive media like sour gas — SPE and DPE seats incorporate advanced sealing technologies such as spring-energized seals and V-ring live loaded seals. Sealing technologies used in SPE and DPE subsea valves • Spring-energized seals : These fluoropolymer-based seals, often featuring PTFE alloy jackets, are ener gized by metal springs which help ensure seal contact stresses to aid in sealing. This spring cavity also acts as a pressure energization feature, allowing system pressure to contribute to the overall sealing force. This style is commonly used in stem seals due to the tight sealing, low friction and stable performance over the life of the seal. Advantages : Internal spring energization generates lower friction than other options; pressure energization isolation. However, this can trap cavity pressure, requiring external relief systems to prevent valve damage under high-pressure subsea conditions.

An engineer reviews unidirectional seat seal design.

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FALL 2025

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