ASTM A182 F51 Blind Flanges API 6A ASME B16.5

ASTM A182 F51 Blind Flanges Manufacturer

We are a professional manufacturer of ASTM A182 F51 blind flanges forged from duplex stainless steel (ASTM A182 F51, UNS S31803) — perfect for applications requiring strong resistance to corrosion, high pressure, and stress corrosion cracking.

What Are ASTM A182 F51 Blind Flanges?

ASTM A182 F51 blind flanges are forged blank flanges used to close the end of a pipeline or pressure vessel. These flanges enable convenient maintenance, pressure testing, or future expansion while delivering robustness, resistance to pitting, and resistance to chloride stress corrosion.
Made from duplex stainless steel, F51 (S31803) Blind flanges offers a unique combination of austenitic and ferritic microstructures

As a leading manufacturer of ASTM A182 F51 blind flanges, we follow the highest industry standards and rigorous quality controls during production. Our F51 blind flanges are forged, solution-annealed, and carefully inspected to guarantee.

Standard for A182 F51 Blind Flanges:

ASTM A182 — Standard Specification for Forged or Rolled Alloy Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
ASME B16.5 or ASME B16.47 — Dimensions and Pressure Classes for Steel Flanges

API 6A Type 6B Flanges:

Type 6B flanges are of the ring joint type and are not designed for face-to-face makeup. The connection make-up bolting force reacts on the metallic ring gasket. Type 6B flanges are of through bolted or studded design. Dimensions for 6B flanges blind type shall conform to Table 36, Table 37 & Table 38 with reference to figure no. 8 on pg. no. 108 of API 6A (19 th Edition, July 2004) as applicable.

API 6A Type 6BX Flanges:

Type 6BX flanges are of the ring joint type and are designed with a raised face. Depending on the tolerances, the connection make-up bolting force may react on the raised face of the flange when the gasket has been properly seated.

This support prevents damage to the flange or gasket from excessive bolt torque. Therefore, one of the flanges in the 6 BX connection shall have a raised face. Type 6BX flanges are of through bolted or studded design. Face-to-face contact is not necessary for the proper functioning of the 6BX flange. Dimensions for 6BX flanges blind type shall conform to Table 46 of API 6A (19 th Edition, July 2004) as applicable.

Chemical Composition of ASTM A182 F51

Element	Min	Max
Carbon (C)		0.03
Manganese (Mn)		2.0
Silicon (Si)		1.0
Phosphorus (P)		0.03
Sulfur (S)		0.02
Chromium (Cr)	21.0	23.0
Nickel (Ni)	4.5	6.5
Molybdenum (Mo)	2.5	3.5
Nitrogen (N)	0.08	0.20
Copper (Cu)		0.5
Iron (Fe)	Balance

ASTM A182 F51 Flange Mechanical Properties and Hardness

Property	Requirement
Tensile Strength	minimum 620 MPa (90 ksi)
Yield Strength (0.2% offset)	minimum 450 MPa (65 ksi)
Elongation in 50 mm	minimum 25%
Hardness (Brinell)	maximum 290 HB

Applications

ASTM A182 F51 blind flanges are frequently used in:

Oil and gas pipeline closures
Chemical processing facilities
Petrochemical and refining equipment
Seawater desalination and offshore platforms
Pulp and paper industry
Power generation stations
Heat exchanger applications

Size and Pressure Rating

We manufacture ASTM A182 F51 blind flanges in a wide range of sizes (1/2” to 48”) and pressure classes (150#, 300#, 600#, 900#, 1500#, 2500#) in compliance with ASME B16.5 and ASME B16.47 standards.

ASTM A182 F51 blind flange Inspection and Testing

Every ASTM A182 F51 blind flange we produce undergoes extensive quality control and testing:

✅ Chemical analysis
✅ Hardness testing (Brinell)
✅ Ultrasonic testing (UT)
✅ Liquid penetrant or magnetic particle testing (PT/MT)

✅ Dimensional checks against ASME standards
✅ Material test certificates (MTR) provided with delivery

ASTM A182 F51 Heat Treatment

Solution Annealing at 1040°C–1120°C (1900°F–2050°F)
Rapid Water Quenching afterwards
This guarantees a balanced microstructure (austenitic + ferritic) for desirable mechanical properties and resistance to stress corrosion.

Types of Flanges:

Blind Flanges (BL) — used to close pipeline ends or pressure equipment
Facing — typically Raised Face (RF), Ring Type Joint (RTJ), or Flat Face (FF) per ASME standard

Inspection and Testing:

✅ Chemical Analysis
✅ Hardness Testing (Brinell)
✅ Tensile and Yield Strength Tests
✅ Non-Destructive Inspection (Ultrasonic, Liquid Penetrant, Magnetic Particle)