Butt Weld Swing Check Valve

Size: 2" - 24" (DN50 - DN600)

Pressure: Class 150 - 2500 / PN 10-420

Standard: API 6D, ASME B16.34, MSS SP-71

Body Materials: A182 F316 (forged), A182 F304 (forged), A182 F22/F91 (forged Cr-Mo for high-temperature). Forged body eliminates casting defects at high-pressure ratings.

Seat: Metal-to-metal with Stellite overlay standard—high-pressure applications demand harder seat surfaces that survive disc impact slamming force at Class 600+.

Disc: Swing disc on hinge pin, same mechanism as flanged swing check. Opening angle up to 80°. Gravity closure.

Design: Butt weld ends—valve welds directly into the pipeline. No flanged connections, no flange gasket leak paths. Forged body for high-pressure integrity. Bolted or welded body cover options (welded cover eliminates one more potential leak path for extreme pressure/temperature service).

Why Butt Weld Instead of Flanged

Two reasons. Both of them come down to the same thing: you don't want leak paths on a passive component that operates automatically with no manual intervention.

Reason one—high pressure. At Class 600 and above, flanged connections get expensive. The flanges are heavier, the bolting is larger, and the gaskets become a reliability liability. High-pressure gaskets cold-flow under sustained load. They creep. They leak. A flanged swing check at Class 900 with a leaking gasket means you have to shut down the line to re-torque or replace the gasket, because you can't tighten a flange on a running check valve—you can't access it safely under pressure. Butt welding eliminates the gasket entirely. The valve welds directly into the pipe. Permanent joint, zero gasket leak path.

Reason two—hazardous and high-temperature service. Hydrogen service, steam at 600°F and above, high-pressure gas lines. Every flanged joint is a potential emission point. The gasket, the bolt stress relaxation over thermal cycles, the flange face condition after years of service. On a check valve—a component that sits there passively, cycling automatically on flow direction—you have no opportunity to monitor or tighten a flanged connection during operation. Butt weld it in and the joint is permanent. No gasket to degrade. No bolts to relax. No flange faces to inspect.

Forged Body — No Casting Defects at High Pressure

Cast bodies work fine at Class 150 and 300. The casting process produces parts with adequate wall thickness and acceptable porosity levels for those pressure ranges. At Class 600 and above—Class 900, 1500, 2500—casting defects become unacceptable. Porosity in a cast body under sustained high pressure can leak through the body wall. Surface shrinkage cavities can initiate cracks under cyclic pressure loading.

Forged bodies eliminate those defects. The forging process compacts the metal grain structure, closes internal voids, and produces a body with uniform mechanical properties through the full wall thickness. No porosity. No shrinkage cavities. No internal defects that become leak paths under sustained high-pressure service.

That's why the material spec is A182—forged stainless and forged Cr-Mo alloy. F316 and F304 for corrosive service at high pressure. F22 and F91 for high-temperature service where you need Cr-Mo alloy strength at 600°F+ operating temperatures. All forged, all defect-free at the pressure ratings where casting can't guarantee integrity.

Stellite Overlay — Standard, Not Optional

On a flanged swing check at Class 150, Stellite overlay on the seat is optional because the disc impact force at low pressure is manageable. Base metal seating survives.

On a butt weld swing check at Class 600+, Stellite overlay on the disc face and seat ring is standard. Here's why: the slamming force increases with pressure rating. At Class 600, the disc hits the seat with significantly more force than at Class 150 because the backpressure driving the disc closure is higher. That higher impact force deforms the base metal seat surface faster—repeated cycling at Class 600+ pounds the seat ring every time the disc closes.

Stellite overlay resists that impact deformation. Cobalt-chromium alloy is harder than the base stainless or Cr-Mo steel, and it maintains its surface integrity under repeated high-force disc impact. On a butt weld swing check, you can't easily pull the valve out of the line to re-machine the seat—it's welded in. Stellite overlay from the start means the seat survives for years without seat repair.

Welded Cover — When You Need Zero Leak Paths

The body cover is the access point for the hinge pin and disc assembly during maintenance. Standard configuration is a bolted cover with a gasket—same leak path concern as any bolted flange joint.

For extreme service—high-pressure hydrogen, superheated steam, toxic or flammable gas at Class 900+—a welded cover option eliminates that gasket leak path too. The cover welds to the body, creating a second permanent joint. You lose the ability to open the cover without cutting the weld, but you gain a valve body with no gasket-sealed joints at all. Butt weld ends, welded cover—two potential leak paths eliminated. For the service conditions where even one leak path is unacceptable, that's the configuration to specify.

Disc impact force increases with pressure rating. At Class 600+, the disc slams into the seat with significantly higher force than at Class 150. Base metal seating deforms faster under that impact. Stellite overlay protects the seat surface from repeated high-force closure. Since butt weld checks are typically specified at Class 600+, Stellite comes standard.

Not recommended at Class 600+. Casting porosity can leak through the body wall under sustained high pressure. Forged bodies (A182 specification) eliminate internal defects and provide uniform mechanical properties through the wall thickness. At Class 150-300, cast bodies are acceptable; at Class 600 and above, forged is the correct specification.

Eliminates the gasket leak path at the cover joint. With butt weld ends and a welded cover, the valve has zero gasket-sealed joints—both end connections and the cover are permanent welds. This is specified for extreme-pressure, high-temperature, or hazardous service where even one gasket leak path is unacceptable.

Yes. Swing disc on a hinge pin, gravity closure, 80° maximum opening angle. The disc mechanism is identical. The difference is in the body construction—forged instead of cast, butt weld ends instead of flanged, and Stellite seating as standard instead of optional.

Class 150 through 2500 (PN 10-420). The forged body and butt weld construction support pressure ratings that flanged swing checks can't economically or reliably cover. At Class 150-300, flanged and butt weld are both viable; at Class 600+, butt weld becomes the preferred or required configuration.