What Is a Blind Flange? Applications

A blind flange is a solid disc with bolt holes but no bore. It bolts to the end of a piping run, nozzle, or valve to seal the system completely. Despite having no flow path, blind flanges must withstand full system pressure—and in fact endure the highest bending stresses of any standard flange type because there is no hub to transfer load.

When to Use a Blind Flange

Blind flanges serve several purposes:

• Dead-ending a pipe run that will be extended in a future phase
• Isolating equipment for maintenance (alternative to closing a valve)
• Hydrostatic testing of piping systems—blinds seal the test boundary
• Blanking off unused nozzles on vessels, heat exchangers, or headers
• Access points for periodic internal inspection (unbolt, inspect, re-seal)

Property	Detail
Standard	ASME B16.5 (NPS 1/2-24), ASME B16.47 (NPS 26-60)
Pressure classes	150 through 2500
Face types	RF, RTJ, FF
Common materials	A105 (CS), A182 F304/F316 (SS), A350 LF2 (low-temp CS)
Bore	None (solid disc)
Connection	Bolted to a mating flange with gasket

Pressure Considerations

Because a blind flange is an unsupported flat plate, it experiences higher bending stress than hubbed flange types. ASME B16.5 accounts for this by specifying greater thickness for blind flanges at the same NPS and pressure class. For example, a Class 300 NPS 8 blind flange per ASME B16.5 has a minimum thickness of 44.5 mm (1.75 in), compared to 55.6 mm hub height for a weld neck flange of the same rating.

Common Mistake

Do not use a blind flange as a permanent pressure boundary if the design calls for a spectacle blind. A spectacle blind is figure-8 shaped and allows quick switching between open flow and blanked-off positions. Blind flanges require full bolt removal to open the line.

Specs and Comparison

NPS	Class 150 Thickness (mm)	Class 300 Thickness (mm)	Class 600 Thickness (mm)
4	24.0	33.4	47.8
8	28.4	44.5	63.5
12	31.8	50.8	73.2
16	36.6	57.2	82.6

Values from ASME B16.5-2020, raised face configuration.

Pro Tip

On large-diameter blind flanges (NPS 16+), the weight becomes significant. A Class 300 NPS 24 A105 blind flange weighs approximately 215 kg (475 lb). Plan rigging and handling accordingly during installation and hydrotesting.

Blind flanges use the same stud bolt pattern and gasket as the mating flange, which simplifies procurement. They are one of the most commonly ordered flange types across all industries.

Read the full guide to flanges