Tapped blind flanges – blind flanges with a threaded (tapped) hole in the center or off-center – in carbon steel and stainless steel, 1/2″ – 24″, class 150 – 2500. Custom tap sizes, positions and orientations machined to order.
What Is a Tapped Blind Flange?
A tapped blind flange is a standard blind flange with one or more threaded holes machined into its face. The tap lets you mount instruments and accessories directly on the blank: pressure gauges, thermowells, sample valves, drain or vent needles. It gives you a sealed line termination with a service connection in one part – instead of blanking the line and tee-ing off separately.
Typical Tapping Options
| Option | Detail |
|---|---|
| Tap size | 1/4″ NPT to 2″ NPT, BSP/BSPP, metric on request |
| Position | Center tap, off-center, or multiple taps at any clock position |
| Base flange | Class 150 – 2500 blind, RF or FF facing, NPS 1/2″ – 24″ |
| Materials | A105, A350 LF2, A182 F304/F304L/F316/F316L |
| Extras | Reinforcement boss (welded or integral) for high-pressure taps |
Where Tapped Blinds Are Used
Common uses: pressure gauge connections at line ends, thermowell insertion for temperature monitoring, chemical injection points, drain and vent ports on vessel nozzles and piping low points, and sample connections on process lines. On skid systems a tapped blind at the header end often replaces an extra tee and plug, saving welds and installation time.
Design Notes
- A center tap reduces the effective sealing area – for higher classes we add an integral boss so the tap does not weaken the blind
- Tap orientation matters for gauge readability: tell us the clock position (e.g. 12 o’clock) required after installation
- Taps are cut after heat treatment where specified, and threads are gauge-checked
- For repeated instrument removal we can fit a half-coupling instead of a direct tap
FAQs
Can you tap a stainless blind flange?
Yes – A182 F304/F316 blinds are tapped with the same NPT/BSP threads; for chloride service we can discuss thread coatings or seal-weld options.
What tap size do I need for a pressure gauge?
Most process gauges use 1/4″ or 1/2″ NPT male connections – a 1/2″ NPT tapped blind is the common choice. Confirm your gauge connection size and we will machine to match.
How close to the bolt circle can the tap be?
The tap must clear the gasket seating area and bolt holes; as a rule we keep the tap center inside the raised face diameter. Send your position requirement and we will confirm feasibility on the drawing.
Send us the base flange spec plus tap size and position for a fast quotation.
Related Blind Flange Products
Standard Blind Flanges (blank flanges) · Spectacle Blinds · Spade / Paddle Blinds · RTJ Blinds · Tapped Blinds · All Flange Types