Fully Welded Triple Offset Metal Hard Seal Butterfly Valve Worm Gear Operated

The fully welded triple offset metal hard seal butterfly valve is a pipeline isolation valve engineered for high-temperature, high-pressure and fire-safe duty where conventional flanged joints would create dead zones, thermal bridges or leak paths at the pipe-to-valve interface. Manufactured by Trekre Valve at our Wuxi production facility, this welded-end butterfly valve integrates a triple-eccentric disc geometry with a bubble-tight metal-to-metal seat pairing. The valve body is permanently welded into the line, eliminating flange gaskets and bolted connections that can fail under cyclic thermal loading or during emergency fire exposure.

Triple offset (triple eccentric) geometry positions the disc sealing surface on a conical path that lifts away from the seat before rotation, minimizing friction and wear during each stroke. On final closing degrees, the disc achieves a mechanical wedging action against the metal seat, producing the tight shut-off required for steam mains, refinery transfer lines, district heating networks and critical process headers. Worm gear manual operation is supplied as standard on larger nominal sizes to manage seating torque; electric multi-turn and pneumatic actuators can be integrated for remote or automated service on the same welded body assembly.

Fully welded triple offset butterfly valve construction

Connection type: fully welded end (butt weld or socket weld per project specification); no body flanges

Structure: triple offset (triple eccentric) butterfly valve with metal hard seal

Size range: 3″ to 60″ (DN80 to DN1500); intermediate and non-standard sizes on request

Pressure rating: ANSI Class 150 / 300 / 600; EN PN16 / PN25 / PN40 (size and standard dependent)

Body material: carbon steel WCB, low-alloy steel, stainless steel CF8 / CF8M, duplex or project-specified alloys

Disc material: stainless steel with Stellite, hard-chrome or nitrided facing for erosive media

Seat material: metal hard seal; laminated stainless / graphite composite optional for high-temperature cycling

Operation: worm gear manual (standard); pneumatic double-acting or electric multi-turn actuator optional

Design standards: API 609 Category B, EN 593, MSS SP-67, GB/T 12238 (project specified)

Leakage class: bubble-tight metal seat within rated temperature envelope per API 598 / EN 12266

Why specify a welded-end metal seated butterfly valve

Process and utility engineers select fully welded butterfly valves when the installation must remain permanently integral with the piping system. Refinery heater outlet lines, steam distribution headers, LNG transfer manifolds and high-integrity water injection systems often prohibit flanged body connections because gasket maintenance is impractical inside insulated or buried runs. Welding the valve directly into the spool piece removes two flange pairs and their associated leak paths, reducing the total joint count in a critical circuit.

The absence of body flanges also simplifies external insulation and jacketing. On high-temperature steam or thermal-oil circuits, contractors can wrap or weld insulation directly against the valve body profile without navigating bolt heads, flange gaps or raised-face steps. For buried district heating and long-distance hot-water transmission, a welded triple offset butterfly valve presents a smooth envelope that accepts polyethylene or mineral-wool cladding without cold spots at bolted flanges.

Metal hard sealing extends the operating window beyond resilient elastomer seats. While EPDM or NBR seats suit water and HVAC service up to roughly 120 °C, metal-to-metal triple offset pairs maintain shut-off integrity at elevated temperatures where soft materials would extrude or lose recovery. The Trekre welded series is therefore specified on superheated steam branches, hot condensate return headers and high-temperature heat-transfer loops where fire-safe behavior and post-fire operability are part of the hazard review.

Triple offset sealing mechanism explained

In a concentric butterfly valve, the disc rotates about a shaft centered in the pipe bore, and the seat wraps the disc edge at a constant diameter. High-performance double-offset designs shift the shaft behind the disc centerline and add a second angular offset to reduce seat scrubbing. Triple offset adds a third offset by machining the disc sealing surface on a conical plane inclined relative to the pipe axis. During opening, the disc lifts off the seat immediately; during closing, the final few degrees create a cam-like wedge rather than a sliding shear across the seat face.

This geometry delivers three practical benefits for welded high-integrity service. First, low operating torque over most of the stroke reduces gearbox size and actuator cost on large diameters. Second, repeatable bubble-tight closure is achievable because contact occurs on a narrow line rather than across a broad rubbing surface. Third, the metal seat tolerates brief over-temperature excursions and particulate carryover better than soft seats, which matters on steam systems with scale or on process lines with catalyst fines.

Typical applications and industry sectors

Power generation: main steam isolation, feedwater heater bypass, condenser cooling water headers where welded spool pieces are prefabricated in the shop

Oil and gas: pipeline block valves on high-integrity transfer lines, heater treater outlets, tank farm manifold isolation

Petrochemical: hot oil circulation, reactor charge lines, flare header isolation with metal seat fire-safe requirement

Metallurgy and mining: slurry and process water lines on autoclave circuits where welded construction resists vibration

District energy: buried hot-water transmission, central heating substation isolation with minimal external envelope

Fire protection: deluge and foam loop isolation where post-incident re-seating must be verified

Actuation and remote operation options

Worm gear operators with handwheel or chain wheel extension are the default for field-installed welded valves above 8″ nominal size. The gear reduction converts manageable rim pull into the seating torque required by metal triple offset discs under differential pressure. For valves mounted at height or inside pipe racks, a chain wheel driven from floor level provides safe manual operation without scaffolding.

Electric actuators with multi-turn output suit SCADA-linked isolation on steam and water utility headers. Pneumatic double-acting actuators deliver faster stroke times for emergency shutdown sequences. Trekre sizes each actuator for breakaway torque, running torque and seated torque at the specified differential pressure, including safety factors for degraded seat condition after long service.

Material selection and corrosion considerations

Carbon steel WCB bodies cover the majority of steam, condensate and neutral process applications within the standard pressure-temperature chart. Stainless steel CF8M is specified when the line carries mildly corrosive condensate, chlorinated cooling water or chemical traces that would attack carbon steel internals. For duplex or super-duplex piping systems, matching body and disc materials prevent galvanic couples at the welded end transitions.

Hard-facing on the disc sealing edge—Stellite 6, hard chrome or equivalent—extends service life when the medium carries abrasive solids or when frequent cycling causes metal seat wear. Seat rings are typically stainless steel with optional graphite laminate inserts to absorb thermal expansion mismatch between body and disc during rapid heating events.

Installation, welding and testing requirements

Shop fabrication of welded valve spool pieces is strongly recommended. The valve arrives with end preparations matching the parent pipe schedule; qualified welders join the valve using procedures qualified to ASME Section IX or EN ISO 15614 as applicable. Disc orientation marks and open/closed position indicators should remain accessible after insulation. Pre-installation inspection includes seat leakage test at 1.1 times rated pressure per project specification, shell hydrostatic test and dimensional check of weld bevels.

Post-weld heat treatment may be required on thick-wall carbon steel assemblies to relieve residual stresses. The valve must be positioned and thermally protected during welding and any required PWHT in accordance with the valve manufacturer’s instructions and the approved welding and heat-treatment procedures, protecting valve internals and stem seals from overheating. After field installation, a functional stroke test confirms gear operation and indicator alignment before the line is pressurized.

Selection checklist for procurement engineers

Confirm nominal size, pipe wall thickness and end preparation (BW/SW) before ordering. State design pressure and temperature, including upsets and hydrotest conditions. Specify leakage class, flow direction if unidirectional, and whether fire-safe or fire-tested documentation is required. Indicate actuator type, control signal, fail position and enclosure rating for hazardous areas. Provide insulation thickness so stem extensions and operator clearance are dimensioned correctly. Request material certificates, pressure test reports and weld procedure summaries with the delivery package.

Product parameters summary

Model series: fully welded triple offset metal hard seal butterfly valve

End connection: welded (butt weld / socket weld)

Nominal diameter: 3″–60″ (DN80–DN1500)

Pressure class: ANSI 150/300/600; PN16/25/40

Temperature range: −29 °C to 425 °C (material and seat dependent)

Seat type: metal hard seal, bubble-tight

Drive: worm gear manual; electric / pneumatic optional

Body / disc: WCB, CF8, CF8M or project alloy

Brand: Trekre Valve — industrial butterfly valves made in China

Contact Trekre Valve with your pipeline data sheet for fully welded triple offset butterfly valve sizing, actuator selection and delivery schedule from our Wuxi factory.