Detailed Product Description
Application & Compliance
ASTM A182 F321H WNRF and BLRF flanges are specified for connections on shell and tube heat exchangers, heat exchanger tubesheets, high-temperature pressure vessels, and steam piping where the operating temperature falls within or above the chromium carbide precipitation range of 427°C to 816°C (800°F to 1500°F). In refinery fired heaters and reformer outlet piping, F321H flanges connect tubes and headers that operate continuously above 537°C (1000°F), where standard 304/304L or 316/316L flanges would sensitize at the grain boundaries and suffer intergranular corrosion. In heat exchanger channel and shell connections, the WNRF flange provides a butt-weld transition from pipe to flange, allowing full radiographic examination of the pressure boundary joint. In blanking and isolation service, the BLRF flange closes nozzles, manways, and test openings on the heat exchanger shell or channel without imposing a flow path.
Problem Solved
The F321H flange addresses the sensitization and high-temperature strength degradation that limit standard austenitic stainless flanges. When unstabilized grades such as 304 or 316 are exposed to temperatures in the 427°C to 816°C range during welding, hot forming, or service, chromium carbides precipitate at the grain boundaries, depleting the adjacent matrix of chromium and leaving it vulnerable to intergranular corrosion.
F321H contains titanium at a minimum ratio of four times the carbon plus nitrogen content (Ti ≥ 4 * (C + N)), which preferentially combines with carbon to form titanium carbides, keeping chromium in solid solution and preserving intergranular corrosion resistance through the sensitization range and beyond. The controlled carbon range of 0.04–0.10% in F321H, higher than the 0.08% maximum of F321, provides the creep rupture strength needed for sustained service above 537°C (1000°F), where the lower-carbon grade would deform under steady load. For the BLRF configuration, the blind design eliminates any through-bore, allowing the flange to seal a vessel opening without introducing a potential leak path through the pressure boundary.
Material Specification – ASTM A182 F321H
ASTM A182 F321H is a titanium-stabilized austenitic stainless steel forging grade. The “H" designation indicates a controlled higher carbon content for elevated-temperature strength, distinguishing it from the standard F321 grade (UNS S32100). F321H is designated UNS S32109 and EN 1.4878.
Chemical Composition (per ASTM A182 / ASME SA182 F321H)
| Element | Requirement (%) |
|---|---|
| Carbon (C) | 0.04 – 0.10 |
| Manganese (Mn) | 2.00 max |
| Phosphorus (P) | 0.045 max |
| Sulfur (S) | 0.030 max |
| Silicon (Si) | 1.00 max |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 12.0 |
| Titanium (Ti) | 4 * (C + N) min, 0.70 max |
| Iron (Fe) | Balance |
Mechanical Properties (per ASTM A182 / ASME SA182 F321H, Solution Annealed)
| Property | Requirement (min) |
|---|---|
| Tensile Strength | 515 MPa (75 ksi) |
| Yield Strength (0.2% offset) | 205 MPa (30 ksi) |
| Elongation in 50 mm | 40% |
| Hardness, Rockwell B | 95 HRB max |
| Hardness, Brinell | 217 HBW max |
Heat Treatment
F321H forgings are supplied in the solution-annealed condition. Solution annealing is performed at a temperature sufficient to dissolve titanium carbides and any chromium carbides that may have formed, followed by rapid cooling to retain carbon and titanium in solution. This treatment restores the corrosion resistance of the matrix and produces the uniform austenitic structure required for high-temperature service and subsequent welding. The titanium stabilization ensures that the alloy does not rely on rapid cooling alone to prevent sensitization: even after slow cooling through the 427–816°C range, the titanium preferentially forms carbides, leaving chromium available for the passive film.
Flange Design and Dimensions – WNRF and BLRF per ASME B16.5
The WNRF (Weld Neck Raised Face) flange features a long tapered hub that transitions the pipe wall thickness gradually into the flange ring. This geometry reduces stress concentration at the shell or channel connection and allows the butt-weld joint between pipe and flange to be fully radiographed, making WNRF the preferred choice for heat exchanger nozzles, high-pressure shell connections, and cyclic service where fatigue life depends on minimizing stress risers. The bore is matched to the specified pipe schedule so that the internal transition is flush. The BLRF (Blind Raised Face) flange is a solid disc with no bore, used to close nozzles, manways, and inspection openings on the heat exchanger shell, channel, or tubesheet side. The raised face provides a defined gasket seating surface; the blind design eliminates the through-bore as a potential leak path.
Dimensions follow ASME B16.5 for NPS 1/2″ through 24″. The raised face height is 1.5 mm up to Class 300 and 6.4 mm from Class 400 upward; the RF diameter tolerance is ±0.8 mm for the 1.6 mm raised face and ±0.5 mm for the 6.4 mm raised face. Flange outside diameter, thickness, bolt circle, bolt hole diameter, and number of bolts are per the ASME B16.5 tables for each size and class. Sizes up to 48″ and Classes beyond the B16.5 range are available to ASME B16.47 upon request.
Size Range and Pressure Classes
WNRF and BLRF flanges are available from NPS 1/2″ through 24″ per ASME B16.5, with larger sizes per ASME B16.47. Pressure classes include 150, 300, 400, 600, 900, 1500, and 2500. Facing options include Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ). Custom bore matching, special facings, and non-standard drilling are available per approved drawings.
Manufacturing Process
The manufacturing sequence for F321H flanges includes billet selection and verification, hot forging or rolling to near-net shape, solution annealing, machining of the raised face, bolt circle, bore (for WNRF), and weld bevel, followed by final dimensional inspection, marking, and surface protection. Heat treatment is performed before final machining to avoid distortion and to ensure that the delivered hardness and mechanical properties reflect the solution-annealed condition.
Testing and Quality Control
Each lot is subjected to chemical composition analysis to verify carbon, chromium, nickel, and titanium contents; tensile testing for tensile strength, yield strength, and elongation; hardness testing to confirm the 95 HRB / 217 HBW maximum; and Positive Material Identification (PMI) for grade verification. Non-destructive examination includes Ultrasonic Testing (UT) for internal soundness on WNRF forgings, Magnetic Particle Testing (MT) or Liquid Penetrant Testing (PT) on machined surfaces, and radiographic examination of the weld bevel when specified. Dimensional inspection verifies flange OD, thickness, bolt circle, bolt hole size and count, raised face diameter and height, bore (WNRF), and weld bevel geometry per ASME B16.5. Hydrostatic testing is performed when specified by the purchase order.
Documentation
Each shipment is supplied with Mill Test Certificates (EN 10204 Type 3.1 or 3.2), heat treatment records (solution annealing charts), mechanical test reports, hardness test reports, NDE reports (UT, MT/PT, PMI), dimensional inspection reports, and material traceability records.
For a rapid quotation on ASTM A182 F321H WNRF or BLRF Flange, please provide the following information:
Quantity (number of pieces) and flange type (WNRF or BLRF)
Nominal pipe size (NPS) and pressure class
Facing type (RF, FF, or RTJ)
Bore match to pipe schedule (for WNRF)
Special dimensional requirements (if any)
NACE requirement (if applicable)
Delivery period required
