The fire safe double offset butterfly valve is a quarter-turn valve engineered for high-performance pipeline isolation and flow control in oil and gas, refining, petrochemical, chemical, and process applications where fire exposure, high pressure, and media containment are critical.
The double-offset shaft arrangement removes continuous contact between the disc and seat during operation. This reduces friction at the sealing surface, ensures predictable operating torque, and significantly extends seat wear life during repeated opening and closing cycles.
Product Selection at a Glance
|
Parameter |
Specification Options |
|
Valve Type |
Fire Safe Double Offset Butterfly Valve |
|
Design Standards |
API 609 (Category B), EN 593 |
|
Nominal Sizes |
DN50 to DN1200 (NPS 2" to 48") |
|
Pressure Class |
ASME Class 150, 300, 600 / PN10 to PN100 |
|
Body Style |
Wafer, Lug, Double Flanged |
|
Fire Test Standards |
API 607, ISO 10497 |
|
Leakage & Pressure Testing |
API 598, ISO 5208, EN 12266-1 |
|
Top Flange Mounting |
ISO 5211 direct mount pad |
|
Operation Options |
Manual Lever, Manual Gearbox, Pneumatic Actuator, Electric Actuator |
|
Primary Media |
Oil, Gas, Hydrocarbons, Petrochemicals, Chemicals, Process Fluids |
Key Features & Design Engineering
First Offset: The shaft is located behind the seat sealing plane, providing a continuous, unbroken seat surface.
Second Offset: The shaft centerline is offset from the valve centerline, causing the disc to lift off the seat immediately upon opening (within 1 to 3 degrees of rotation).
Primary Soft Seat: Ensures bubble-tight shutoff (Class VI / Rate A) under normal operating conditions.
Secondary Metal Seat: Made from high-nickel alloys (such as Inconel) or stainless steel. If the primary soft seat is damaged during a fire, line pressure forces the disc against the secondary metal seat to maintain fire-safe shutoff.
ISO 5211 Direct Mounting: Top flange designed for direct mounting of manual gearboxes, pneumatic actuators, or electric actuators without external brackets.
Anti-Blowout Stem: Internal stem retaining design prevents stem ejection under high operating pressure, enhancing field safety.
Material Grade Options
To simplify procurement and technical evaluation, standard body, trim, and seat material combinations are detailed below:
|
Valve Component |
Carbon Steel Option |
Stainless Steel Grade |
Low Temp / Duplex Alloy |
|
Body |
ASTM A216 WCB / LCC |
ASTM A351 CF8 / CF8M |
ASTM A995 4A (Duplex) / 5A (Super Duplex) |
|
Disc |
ASTM A351 CF8M |
ASTM A351 CF8M / 316 |
Duplex 2205 / Super Duplex 2507 / Monel |
|
Stem |
17-4PH (UNS S17400) |
17-4PH / AISI 316 |
Duplex 2205 / Inconel 718 |
|
Primary Seat |
RPTFE / PTFE / Devlon |
RPTFE / PEEK |
PEEK / Metal-to-Metal |
|
Secondary Seat |
Inconel 718 / 316SS |
Inconel 718 / 316SS |
Inconel 625 / Inconel 718 |
|
Gland Packing |
Flexible Graphite |
Flexible Graphite |
Flexible Graphite (Fire-Safe) |
Technical Specifications & Industry Standards
|
Engineering Parameter |
Applicable Standard / Criteria |
|
Design & Manufacture |
API 609 (Category B), MSS SP-68, EN 593 |
|
Face-to-Face Dimensions |
API 609, ISO 5752, EN 558 |
|
Flange Drilling |
ASME B16.5 (Class 150-600), EN 1092-1 (PN10-PN100) |
|
Pressure-Temperature Rating |
ASME B16.34 |
|
Fire Test Qualification |
API 607, ISO 10497 |
|
Testing & Inspection |
API 598, ISO 5208, EN 12266-1 |
|
Fugitive Emission Testing |
ISO 15848-1 / API 641 (Optional upon request) |
Plant Maintenance & Valve Replacement Guide
When replacing existing valves during plant maintenance, verify the following 10 critical parameters prior to order release:
Valve Size (NPS / DN)
Pressure Class (ASME Class or PN Rating)
Face-to-Face Dimension (API 609 / EN 558 series)
End Connection Type (Wafer, Lug, or Flanged)
Flange Drilling & Facing (RF, RTJ, Smooth Finish)
Seat Material & Temperature Limits
Stem Drive Dimensions & ISO 5211 Pad Size
Required Breakaway Torque under Maximum Differential Pressure
Fire-Safe Standard & Certification Requirements
Installation Space & Actuator Orientation
FAQ
Q: What is the difference between a Double Offset and a Concentric Butterfly Valve?
A: A concentric butterfly valve has the stem centered in the middle of the disc and seat, leading to continuous 360-degree contact during rotation. A double-offset valve offsets the shaft in two axes, causing the disc to lift away from the seat immediately upon opening.
Q: Does a double-offset butterfly valve automatically have fire-safe certification?
A: No. Double offset refers to the mechanical geometry of the valve. Fire-safe qualification requires a specific dual-seat design (primary soft seat combined with a secondary metal seat) and must be independently tested and certified according to standards such as API 607 or ISO 10497.
Q: How should I select the right actuator for a double offset butterfly valve?
A: Actuator sizing must be based on the valve breakaway torque at the maximum differential pressure (Delta P). The sizing calculation should consider the process medium, operating temperature, seat material, operating frequency, and a required safety factor (typically 20% to 30%).
Q: What documentation can be provided for project procurement?
A: Standard project documentation includes Material Test Reports (EN 10204 3.1), pressure and leakage test reports (API 598), API 607 fire-test certificates, General Arrangement (GA) drawings, and Certificates of Conformity.
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