Blind flanges are solid, circular pipe flanges with no bore — used to seal the end of a pipe, valve outlet, or vessel nozzle. They provide a leak-tight closure while maintaining full pressure integrity. Available in sizes from NPS ½″ to NPS 60″ (DN 10 to DN 1500) across ASME B16.5, ASME B16.47, and EN 1092-1 standards, blind flanges are one of the most widely used isolation components in oil & gas, chemical, water treatment, and power generation piping systems.
HT PIPE manufactures blind flanges in carbon steel, stainless steel, alloy steel, duplex, and nickel alloys. All flanges are tested and supplied with material test reports (MTR / EN 10204 3.1) as standard.
Types of Blind Flanges
Blind flanges are classified by their face type — the sealing surface geometry that mates with the gasket. Selecting the correct face type is critical for leak-free performance.
| Face Type |
Code |
Description |
Typical Application |
| Flat Face |
FF |
Full-face gasket surface, completely flat. Requires full-face gasket. |
Low-pressure water, HVAC, non-critical service |
| Raised Face |
RF |
Concentric raised ring (~1.6 mm for Class 150). Gasket seats on raised portion only. |
Oil & gas, chemical, most standard industrial applications |
| Ring Type Joint |
RTJ |
Octagonal or oval metallic gasket groove. Metal-to-metal seal under high pressure/temperature. |
High-pressure oil & gas, sour gas (NACE), high-temperature steam |
| Tongue & Groove |
TG |
Male/female machined surfaces interlock. Centering provided. |
Chemical processing, vacuum service |
| Lap Joint (LJJ) |
LJ |
Smooth bore with a backing ring; no gasket load on flange face. |
Corrosive service, low-pressure slurry lines |
.png)
Pressure-Temperature Ratings
Blind flange pressure ratings vary by standard and class. The table below summarizes the standard rating ranges for the three most referenced standards.
| Standard |
Size Range |
Pressure Classes |
Region of Use |
| ASME B16.5 |
NPS ½″ – 24″ |
Class 150 / 300 / 400 / 600 / 900 / 1500 / 2500 |
Global (US, Americas, Middle East, Asia-Pacific) |
| ASME B16.47 |
NPS 26″ – 60″ |
Class 150 / 300 / 400 / 600 / 900 |
North America, LNG, offshore platforms |
| EN 1092-1 |
DN 10 – 2000 |
PN 2.5 / 6 / 10 / 16 / 25 / 40 / 63 / 100 / 160 / 250 / 320 / 400 |
Europe, Middle East, Africa, APAC (European projects) |
Note on PN vs Class: ASME Class and EN PN ratings are not directly interchangeable. Class ratings are based on US customary units and reference the 38°C (100°F) design basis. PN values are nominal pressure ratings in bar that vary with temperature per EN 1092-1 Annex A tables. For critical applications, always verify the pressure-temperature rating against the applicable code.
Materials for Blind Flanges
Material selection depends on the process fluid, temperature, pressure, and corrosion environment. HT PIPE supplies blind flanges in all major grades per ASTM/ASME and EN material specifications.
| Material Family |
Common Grades |
Max Temp |
Typical Service |
| Carbon Steel |
ASTM A105, A350 LF2, A694 F52–F70 |
~425°C (800°F) |
Water, steam, oil, gas, air |
| Stainless Steel |
304/304L, 316/316L, 321, 347, 904L |
~540°C (1000°F) |
Corrosive chemicals, food, pharma, seawater |
| Alloy Steel |
ASTM A182 F5, F9, F11, F22, F91 |
~600°C (1100°F) |
High-temp refinery, hydrocracker, reformer |
| Duplex / Super Duplex |
S31803 (2205), S32750 (2507), S32760 |
~300°C (570°F) |
Offshore, seawater, desalination, subsea |
| Nickel Alloy |
Monel 400, Inconel 600/625, Incoloy 825, Hastelloy C276 |
~800°C (1470°F) |
Sour gas, acid service, offshore topside |
| Copper Alloy |
CuNi 90/10, CuNi 70/30 |
~230°C (450°F) |
Desalination, shipbuilding, seawater cooling |
Blind Flange Weight Estimation
Blind flange weight is determined by the flange outside diameter, thickness, and material density. The following formula provides a first-pass estimate:
Approximate Weight Formula:
Weight (kg) ≈ π × (OD/2)² × Thickness × Density / 1,000,000
Carbon Steel density: 7.85 g/cm³ | Stainless Steel density: 7.98 g/cm³ | Duplex density: 7.81 g/cm³
Actual weight varies slightly by standard (bore geometry, hub reinforcement). Reference the dimension tables linked below for exact calculated weights per size and pressure class.
For quick reference, approximate weights of ASME B16.5 Class 150 carbon steel blind flanges (raised face):
| NPS (in) |
DN (mm) |
Weight – CL150 (kg, CS) |
Weight – CL300 (kg, CS) |
| ½ |
15 |
0.5 |
0.7 |
| 1 |
25 |
1.1 |
1.6 |
| 2 |
50 |
2.3 |
4.4 |
| 4 |
100 |
6.5 |
13.5 |
| 6 |
150 |
12.0 |
26.0 |
| 8 |
200 |
19.5 |
43.0 |
| 10 |
250 |
31.5 |
66.0 |
| 12 |
300 |
43.0 |
90.0 |
| 16 |
400 |
76.0 |
158.0 |
| 24 |
600 |
165.0 |
355.0 |
For complete dimension tables including exact weights for all pressure classes, refer to:
Surface Finish Options
Blind flange face finish affects gasket performance and leak tightness. HT PIPE offers the following standard surface finishes:
| Finish Type |
Roughness (Ra) |
Gasket Compatibility |
| Stock Finish (As-machined) |
3.2 – 6.3 μm |
Soft gaskets (rubber, PTFE, graphite) |
| Smooth Finish (Grinding) |
1.6 – 3.2 μm |
Standard spiral wound, compressed fiber |
| Spiral Serrated (30°–45°) |
1.6 – 3.2 μm |
Spiral wound gaskets with centering ring |
| Concentric Serrated |
1.6 – 3.2 μm |
Soft gaskets, compressed sheet |
Coatings and Corrosion Protection
For carbon steel blind flanges in atmospheric or buried service, surface coatings extend service life and simplify handling. Standard coating options include:
- Red oxide primer / vanish – shop primer for atmospheric storage and transit
- Yellow paint (epoxy) – standard industrial coating for outdoor storage
- Anti-rust oil – temporary protection for short-term indoor storage
- Hot-dip galvanizing (HDG) – for buried or exposed-to-atmosphere service
- FBE / 3LPE coating – fusion bonded epoxy for pipe-to-flange coating continuity
- Electroplated zinc – atmospheric protection, aesthetics
Common Applications
Blind flanges are selected across a wide range of piping applications:
- End-of-line isolation – seal dead ends of pipelines in plants, terminals, and offshore platforms
- Hydrostatic testing – temporary or permanent test blanks during commissioning
- Manway / access cover – vessel nozzles, tanks, and pressure vessels
- Spool piece blanks – isolation of spool pieces during tie-in or shutdown maintenance
- Drain and vent connections – temporary or permanent blanking of small branch lines
- Instrument impulse lines – pressure gauge and transmitter isolation
Sour Gas (NACE) Service: For hydrogen sulfide (H₂S) containing environments, HT PIPE supplies blind flanges in accordance with NACE MR0175 / ISO 15156 material requirements. Common grades include A350 LF2 ( Class 150–600) and ASTM A105 with controlled chemistry. RTJ face type is typically specified for sour gas applications.
How to Order
When requesting a blind flange quotation, include the following information to ensure accurate pricing and manufacturing:
- Standard – ASME B16.5, B16.47 Series A/B, EN 1092-1 Type A/B, or project-specified standard
- Size – NPS (inches) or DN (mm)
- Pressure Class – ASME Class or PN rating
- Face Type – RF, FF, RTJ, TG, or GF
- Material Grade – carbon steel, stainless steel, alloy, or project specification
- Quantity – number of pieces per size
- Testing / Certification – requirements: MTR (EN 10204 3.1), hydrostatic test, PMI, UT, DWT
- Coating / Surface Finish – for carbon steel: primer, paint, galvanizing, or bare
HT PIPE supplies blind flanges to ASME B16.5, ASME B16.47, EN 1092-1, JIS, KS, GOST and custom project specifications. All flanges are manufactured under an ISO 9001:2015 quality management system and are available with third-party inspection (SGS, BV, DNV, LR, ABS) upon request.
Reference Standards: ASME B16.5-2022 (Pipe Flanges and Flanged Fittings, NPS ½ through NPS 24) · ASME B16.47-2020 (Large Diameter Steel Flanges, NPS 26 through NPS 60) · EN 1092-1:2018 (Flanges and their joints — Circular flanges for pipes, valves, fittings and accessories) · ASTM A105 / A182 / A350 / A694 (Material Specifications) · ISO 15156 / NACE MR0175 (Sour Gas Service)
Disclaimer: Dimensions and weights shown are for reference only. Verify against the current edition of the applicable standard and project specifications. HT PIPE assumes no liability for the use of this data.
(1)_300x225.jpg)
