An ASME B16.5 Class 400 Slip-On (SO) Flange is designed to slide directly over the outer diameter of the connecting pipe. It is secured using two fillet welds-one on the exterior hub profile and one inside the flange bore cavity. HT PIPE supply all different types and scales of flanges. Please feel free to contact us for further product information and pricing.
- The Raised Face (RF): Standard Class 400 flanges feature a 0.06-inch (1.6 mm) raised face, which is included in the total thickness specification. This surface contains specific serrated grooves to anchor the gasket under high bolt loads.
- Hub Taper: The hub provides structural reinforcement, minimizing the risk of flange distortion during the welding process.
- Bore Clearance: The internal bore is slightly larger than the nominal pipe outside diameter (OD) to allow smooth positioning before welding.
Fabrication & Field Installation Protocols
To guarantee the structural reliability of a Class 400 slip-on flange configuration, assembly teams should follow these technical field practices:
1. Dual Fillet Welding Strategy
Slip-on flanges must be welded both externally at the hub bevel and internally at the pipe end. The pipe must be set back from the flange face by a distance equal to the nominal wall thickness of the pipe plus approximately 1/16 of an inch. This gap prevents weld spatter from degrading the gasket seating surface.
2. Gasket Alignment & Surface Finish
Because Class 400 systems experience considerable mechanical loads, the surface finish of the raised face must be verified. ASME B16.5 mandates a concentrated circular or continuous spiral serration finish between 125 microinches and 250 microinches roughness. This texture prevents the gasket from extruding or shifting under high compression.
3. Star-Pattern Bolting
Uneven load distribution during flange make-up is a frequent cause of premature joint leakage. Technicians must apply a calibrated torque sequence using a star pattern, bringing the joint to full compression in incremental stages (typically 30%, 60%, and 100% of final calculated torque values).
Technical Sourcing & Quality Checklist
When reviewing manufacturing data sheets or inspecting inbound shipments, ensure the following markers are clearly stamped onto the outer rim of the flange body:
Origin Stamp & Heat Code: Provides traceability back to the original steel melt slab batch.
Material Conformance: Clear labeling of the forge grade (e.g., ASTM A105 or A182 F316L).
Dimensional Standard: Clear marking of ASME B16.5.
Class & Size Identifier: Explicitly stating the sizing parameters (e.g., 8" 400# SO).
ASME B16.5 Class 400 Slip-On Flanges dimension
