Forged Flanges & Fittings for Petrochemical Industry

ASME B31.3 and ASME B16.5 specify several face types for different service conditions:

• Raised Face (RF): Standard for Class 150–2500 LB, most process piping service. Gasket confined to raised face bore area. Most common in refineries.
• Ring Type Joint (RTJ): Preferred for Class 900 LB and above, high-pressure, high-temperature service (>300°C / 100 bar+). Metal ring seal, superior leak integrity.
• Flat Face (FF): Used with cast iron or non-metallic flanges and low-pressure utility systems. Rarely used in process piping.
• Tongue & Groove (T&G): Used in heat exchanger nozzles and where full gasket confinement is required.

For cryogenic service (LNG), RTJ or double-jacketed spiral-wound gaskets in RTJ grooves are preferred to maintain sealing integrity during thermal cycling.

API RP 941 (Nelson Curves) defines the boundary conditions above which carbon and low-alloy steels are susceptible to HTHA (High Temperature Hydrogen Attack — irreversible decarburization and fissuring). Selection process:

1. Determine the H₂ partial pressure (bar) and operating temperature (°C)
2. Plot on the Nelson Curve chart for the target material. The operating point must be below the curve by the required safety margin.
3. Carbon steel: typically safe below 230°C / H₂ PP <7 bar
4. 1¼Cr-½Mo (F11): extends safe zone to ~310°C
5. 2¼Cr-1Mo (F22): extends to ~370°C — standard for hydrocrackers
6. 9Cr-1Mo-V (F91): for the most severe HTHA conditions to ~450°C

Note: Austenitic stainless steels (316, 321H, 347H) are not subject to HTHA and are used in hot H₂ piping above the Nelson Curve boundaries for alloy steels.

LNG service flanges require special qualification beyond standard mechanical testing:

• Charpy V-notch impact test: at design minimum temperature (-162°C for LNG, -196°C for LOX/LN₂). Minimum 27 J average, 20 J individual (per EN 1092-1 / ASME requirements)
• Cryogenic tensile test: Yield and tensile strength at design temperature. Austenitic steels gain strength at low temperature.
• BS 6364 / EN 1089-3: Specifies testing conditions for cryogenic valves and accessories including flanges
• Ferrite content measurement: For austenitic stainless, FN ≤ 8 per WRC-1992 diagram (excess delta ferrite can become magnetic and brittle at cryogenic temperatures)
• Helium leak test: For LNG terminal flanged joints to API 598 or equivalent

All test records are traceable to heat / lot number and supplied as part of the EN 10204 3.1 documentation package.

Polythionic Acid Stress Corrosion Cracking (PTA-SCC) is a form of intergranular cracking that can occur in sensitized austenitic stainless steel exposed to polythionic acids (H₂SₓO₆) during shutdown and maintenance. The mechanism:

• Sensitization occurs when austenitic steel operates between 425–850°C — chromium carbides precipitate at grain boundaries, depleting adjacent zones of Cr protection
• During shutdown, moisture + residual sulfur deposits form polythionic acids that attack the sensitized grain boundaries
• Susceptible grades: 304, 304H, 316, 316H — sensitized by service or welding
• Resistant grades: 321, 321H, 347, 347H (Nb/Ti stabilized — prevent carbide precipitation)

JIAJI recommends F347H or F321H flanges for all refinery furnace outlet and high-temperature piping applications where sensitization is a risk. Per ASTM A262 Practice E / ASTM A193/A194 bolt material requirements for polythionic acid service.

Yes. JIAJI FORGING manufactures forged flanges in Hastelloy C276 (UNS N10276 / EN 2.4819) as both ASME B16.5 and EN 1092-1 configurations:

• Standards: ASTM B564 (bar/forging stock), ASTM B574 (rod), ASTM B575 (plate)
• Available types: Weld Neck, Blind, Slip-On, Threaded, Socket Weld (all ASME B16.5 classes)
• Certification: EN 10204 3.1 MTC, PMI (XRF analysis), IGC test (ASTM G28 Method A/B)
• Lead time: 6–12 weeks depending on stock availability and size

Typical applications include flue gas desulfurization (FGD), wet SO₂ scrubbers, chloride-containing chemical reactors, and organic acid service in specialty chemical plants.

For European projects under the Pressure Equipment Directive (PED 2014/68/EU), our standard documentation package includes:

• CE Declaration of Conformity (DoC)
• EN 10204 Type 3.1 Material Test Certificate (by notified body for 3.2)
• Proof of conformity to EN 1092-1 (flanges) or ASME B16.5 with PED material equivalence
• Certificate of conformance to PED Module H1 or D1 (as applicable)
• Design calculation or documentation of pressure-temperature ratings
• Quality plan and inspection test plan (ITP)
• PMI certificates (XRF/OES analysis)
• Weld procedure qualification record (WPS/PQR) if welded items

Additional documentation per Shell DEP, BP GIS, or Total GS standards available on request. We work with third-party inspection agencies (Bureau Veritas, Lloyd's, SGS, TÜV) as required by project specifications.