Why Forging for Flanges
Forging compresses the steel, closing porosity and aligning the grain flow with the part’s shape — which is why flanges, rings and high-strength fittings are forged rather than cast or cut from plate wherever pressure and fatigue matter. Carbon steel flange forgings are typically ASTM A105; low-temperature service uses A350 LF2; pipeline grades A694 F42–F70; stainless and nickel alloys use A182 (F304/304L, F316/316L, F51 duplex and up).
Flange Types and Facings
| Type | Where It Wins |
|---|---|
| Weld neck (WN) | High pressure/temperature; the neck transfers stress smoothly into the pipe |
| Slip-on (SO) | Low/medium pressure; cheaper, easier alignment |
| Blind (BL) | Closes a line end or nozzle |
| Lap joint (LJ) + stub end | Alloy savings — cheap backing ring with alloy contact face |
| Socket weld / threaded | Small-bore, Class 150–9000 per B16.11-related practice |
Facing is raised face (RF) for most process work, flat face (FF) for mating to castings, and ring-type joint (RTJ) for high pressure. Dimensions and pressure classes 150–2500 follow ASME B16.5 through NPS 24 and B16.47 above.
What Goes Wrong and How to Prevent It
The recurring issues in imported flanges: dimensional drift on drilling and raised-face serration (affects gasket seating), hardness above 22 HRC where NACE MR0175 applies (A105 needs restricted chemistry/heat treatment for sour), and mixed heat lots inside one shipment. Prevent with: 3.1 certificates traceable to heat numbers, a dimensional check against B16.5 at pre-shipment inspection, and explicit sour-service requirement in the PO.
Frequently Asked Questions
What does A105 actually specify?
Carbon steel forgings for piping components with nominal (ambient) rating — chemistry, mechanicals, grain size and heat treatment (normalizing or normalizing + tempering for NACE-typed material).
When do I need A350 LF2 instead of A105?
Below roughly −29°C design temperature: LF2 carries Charpy impact testing for low-temperature toughness, A105 does not.
Are cast flanges acceptable?
For pressure piping, forged (or wrought-bar) is the norm; cast flanges appear in low-risk utility service per project spec. When in doubt, follow the piping class, not the price.
CREATEEL supplies B16.5/B16.47 flanges in A105, LF2, A694 and A182 grades with full certification and sour-service options.
Standards & references: ASME B16.5/B16.47 · ASTM A105/A350/A182 · NACE MR0175
Need a quotation? CREATEEL supplies carbon steel, alloy and stainless pipes to API, ASTM and EN standards with EN 10204 3.1/3.2 certification. Contact us for a fast offer.
