Blind Flanges

Solid Disc Flange for Blanking, Isolation, and Pressure Testing

What Is a Blind Flange?

A blind flange is a solid disc with no bore, used to blank off the end of a piping system, valve, or pressure vessel. It is bolted to the mating flange to seal the line and must withstand full system pressure. Blind flanges are often the highest-stressed flange in a system because they have no pipe to share the bending load.

Blind flanges are designed per ASME B16.5 and B16.47 and are essential components for isolation, testing, and future expansion of piping systems.

Key Design Features

  • Solid forged disc with no center bore
  • Available in RF, FF, and RTJ facings
  • Handles the highest mechanical stress of any flange type
  • Can be drilled and tapped for NPT connections
  • Often modified to serve as test blinds or spectacle blind components

Common Applications

  • Blanking off unused nozzles and pipe ends
  • Pressure testing and hydrostatic testing
  • Future connection points (stub-outs)
  • Isolation of piping systems during maintenance
  • Flow reversal prevention

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Available Sizes and Pressure Classes

Under ASME B16.5, blind flanges are available in NPS 1/2 through 24 in Classes 150, 300, 600, 900, 1500, and 2500. ASME B16.47 Series A and Series B extend coverage from NPS 26 through 60.

Since there is no bore, blind flange dimensions are the same regardless of pipe schedule — only the outer diameter, bolt circle, and thickness matter.

Common Materials

  • Carbon Steel (A105) — the most common material for general-purpose service
  • Stainless Steel (A182 F304/F316) — for corrosion-resistant applications
  • Alloy Steel (A182 F11/F22) — for high-temperature service
  • Low-Temp (A350 LF2) — for cryogenic and low-temperature applications

Blind Flanges vs Pipe Caps

Both blind flanges and pipe caps seal pipe ends, but they differ in how they attach. Blind flanges are bolted to a mating flange, making them removable for future access or maintenance. Pipe caps are welded directly to the pipe end, creating a permanent closure.

Blind flanges are preferred where future access is needed or where pressure testing will occur. Pipe caps are lower cost for permanent dead ends where reopening is not anticipated.

Related References