RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, ASTM A105N / A182 / A350 grades, Third-Party Inspection (SGS / BV / DNV / Lloyds), and complete EPC export documentation packages.
Blind Flange
A world-class technical reference for EPC contractors, piping and pressure vessel engineers, procurement heads, TPI inspection agencies, and global project buyers specifying blind flanges for pipe end closures, vessel nozzle blanking, pressure testing isolation, manway covers, and future tie-in points across Oil & Gas, Power Generation, Petrochemical, Offshore, LNG, and Industrial Construction sectors.
Design Principles
& Structural Behaviour
Blind flanges are solid, bore-less flanges bolted to a mating flanged connection to permanently or temporarily close the end of a pipe, vessel nozzle, or equipment connection. They are the primary pressure-retaining closure component used across all pressure classes and material grades in EPC and process plant construction — unique in being the only flange type available in all pressure classes from Class 150 through Class 2500 without structural limitations.
1.1 — Technical Definition and Functional Role
A blind flange (BF) is a solid disc-shaped forged flange — identical in outer geometry (bolt circle diameter, bolt hole count and size, facing type, and OD) to the mating pipe flange of the same NPS and pressure class, but with no central bore. Bolted to the mating flange with a gasket between the two facing surfaces, the blind flange closes the connection and contains the full design pressure with its flat plate body acting as a uniformly loaded circular membrane under internal pressure. Because the blind flange carries no pipe weld, it is the simplest and most reliable flanged closure in piping engineering.
In EPC and industrial piping construction, blind flanges serve six primary roles: (1) permanent or temporary closure of operating pipe ends; (2) blanking future expansion tie-in stubs installed in Phase 1 for Phase 2 connections; (3) pressure testing isolation — blanking open flanged connections during hydrostatic or pneumatic pressure testing of pipe sections; (4) vessel nozzle blanking for uncommissioned nozzles; (5) manway and handhole covers on pressure vessels; and (6) instrument connection blanking for uncommissioned instrument nozzles during initial plant start-up.
RR Hydraulic manufactures blind flanges under all applicable international standards with full EN 10204 3.1 / 3.2 material traceability and project documentation.
1.2 — Blind Flange vs Other Closure Methods
| Method | Pressure Class | Removability | NDE | Sealing Reliability | Primary Application |
|---|---|---|---|---|---|
| Blind Flange (BF) | All — Cl.150–2500 | Fully removable (unbolt) | Face + gasket only | Highest — full bolted gasket | Operating; test; future tie-in; vessel nozzle |
| Pipe Cap (welded) | All schedules | Destructive (cut out) | Full weld RT/UT | High — welded | Permanent pipe end closures |
| Spectacle Blind / Spade | Class 150–600 | Pivot or swing out | None added | Moderate | Process isolation during maintenance |
| Threaded Pipe Plug | Very low pressure | Removable (unscrew) | None | Moderate (thread sealant) | Temporary instrument blanking |
| Weld-in Plate | All — custom | Destructive | Full weld NDE | High — welded | Non-flanged vessel custom closures |
| Manway Cover | Per vessel design | Removable (unbolt) | Face only | Highest — bolted gasket | Pressure vessel internal access |
1.3 — Structural Behaviour and Design Basis
Flat Plate Bending Under Pressure
The blind flange acts as a uniformly loaded circular flat plate simply supported at its bolt circle. Internal pressure creates bending stress across the plate diameter, with maximum stress at the centre. ASME VIII Division 1 Appendix 2 and ASME B16.5 dimensions already incorporate the minimum plate thickness for pressure containment at each NPS/class combination. For non-standard designs, the ASME VIII UG-34 flat cover formula governs the required minimum thickness.
Hydrostatic End Force
The blind flange resists the full hydrostatic end force generated by system pressure acting on the pipe cross-section: F_end = P × (π × D²/4). For a 12″ NPS at 100 bar: F_end ≈ 823 kN. This force must be entirely absorbed by the bolts in tension — adequate bolt area, bolt grade, and preload are essential. For large-bore, high-pressure blinds, bolt load calculation is the governing design constraint and must be documented in the bolted joint design analysis.
Bolt Load and Gasket Seating
The bolted joint must provide two conditions: (1) minimum gasket seating load during assembly (W_m2) to deform the gasket into surface irregularities; and (2) operating load (W_m1) to maintain minimum residual gasket compression under design pressure minus the hydrostatic end force. Both conditions are verified per ASME B16.5 bolting data tables and ASME VIII Appendix 2. Spring washers or Belleville disc springs are used on high-temperature thermal cycling blind flange connections to maintain gasket stress.
Service Categories — No Restriction on Blind Flanges
Unlike slip-on flanges (excluded from Category M lethal fluid service) and socket weld flanges (small bore only), blind flanges carry no service category restriction in ASME B31.3 — they may be used in all services including Category M lethal fluid connections, severe cyclic service, and any pressure class. This universality makes blind flanges the default closure for all EPC project piping regardless of service severity or fluid classification.
Pressure Testing Applications
Blind flanges used for hydrostatic testing must be rated for the test pressure — typically 1.5× design pressure per ASME B31.3. A Class 150 A105N blind flange at 20°C is rated at 19.6 bar and has a hydrostatic test pressure allowable of approximately 29 bar — adequate for most utility piping test conditions. For high-test-pressure sections: specify Class 300 or Class 600 blind flanges. Track test blind flange locations on the hydro-test record; remove after testing.
Manway Cover Design Compliance
When blind flanges serve as pressure vessel manway or handhole covers, ASME VIII UG-34 flat cover design rules apply in addition to ASME B16.5 — the more restrictive governs minimum plate thickness. Large manway covers (e.g., 20″×16″ elliptical) require detailed stress analysis. UG-45 nozzle minimum thickness must also be verified for the vessel nozzle to which the blind flange bolts. Always check both standards when specifying blind flanges as vessel access covers.
1.4 — ASME VIII Flat Cover Thickness Design Formula
d = Diameter of the bolt circle (mm) — as the governing diameter for ASME B16.5 blind flanges
C = Factor depending on edge condition = 0.3 (fixed edges, full gasket contact across bore)
P = Design gauge pressure (MPa)
S = Allowable stress of flange material at design temperature (MPa) — per ASME II Part D
E = Weld joint efficiency (1.0 for solid plate — no welds through the plate section)
ASME B16.5 Note: Standard ASME B16.5 blind flange dimensions already satisfy the
minimum plate thickness at the rated class pressure for each NPS. UG-34 calculation is required
for non-standard sizes, pressures above the class rating, or vessel-code-governed nozzle covers.
Class 300 at 150°C (Group 1.1): 45.1 bar g → 45 bar ≤ 45.1 bar ✓ — within class rating.
ASME B16.5 Class 300 NPS 12 min thickness = 50.8 mm — no separate UG-34 calculation required.
For P > class rating or non-standard bore: use UG-34 with S from ASME II Part D Table 1A.
Submit your NPS, pressure class, material, facing type, and quantity for a documented RFQ within 24 hours.
Pressure Ratings &
Standards Compliance
Blind flange dimensions — OD, bolt circle, bolt count and size, raised face diameter, and minimum plate thickness — are fully tabulated in ASME B16.5 (NPS ½–24) for all pressure classes 150–2500. All applicable standards are supported with full certification at RR Hydraulic.
Submit NPS, pressure class, material, facing, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — ASME B16.5 Class 150 Blind Flange Dimensional Table
| NPS | Flange OD (mm) | BCD (mm) | Bolts × Dia | RF Dia (mm) | Min Thickness (mm) | Approx. Weight (kg) |
|---|---|---|---|---|---|---|
| ½” | 88.9 | 60.5 | 4×½” | 34.9 | 11.2 | 0.3 |
| ¾” | 98.6 | 69.9 | 4×½” | 42.9 | 12.7 | 0.5 |
| 1″ | 108.0 | 79.4 | 4×½” | 50.8 | 14.2 | 0.6 |
| 1½” | 127.0 | 98.6 | 4×½” | 73.2 | 15.7 | 0.8 |
| 2″ | 152.4 | 120.7 | 4×⅝” | 91.9 | 17.5 | 1.4 |
| 3″ | 190.5 | 152.4 | 4×⅝” | 127.0 | 19.1 | 2.5 |
| 4″ | 228.6 | 190.5 | 8×⅝” | 157.2 | 20.6 | 4.1 |
| 6″ | 279.4 | 241.3 | 8×¾” | 215.9 | 22.4 | 7.0 |
| 8″ | 342.9 | 298.5 | 8×¾” | 269.9 | 23.9 | 11.5 |
| 10″ | 406.4 | 362.0 | 12×⅞” | 323.9 | 25.4 | 17.5 |
| 12″ | 482.6 | 431.8 | 12×⅞” | 381.0 | 25.4 | 25.0 |
| 14″ | 533.4 | 476.3 | 12×1″ | 412.8 | 27.0 | 32.0 |
| 16″ | 596.9 | 539.8 | 16×1″ | 469.9 | 28.6 | 45.0 |
| 18″ | 635.0 | 577.9 | 16×1⅛” | 533.4 | 31.8 | 57.0 |
| 20″ | 698.5 | 635.0 | 20×1⅛” | 584.2 | 34.9 | 76.0 |
| 24″ | 812.8 | 749.3 | 20×1¼” | 692.2 | 39.7 | 115.0 |
2.2 — ASME B16.5 Multi-Class Blind Flange Thickness and Bolt Reference
| NPS | OD Cl.300 (mm) | Thick Cl.300 (mm) | Bolts Cl.300 | OD Cl.600 (mm) | Thick Cl.600 (mm) | Bolts Cl.600 | Thick Cl.900 (mm) | Thick Cl.1500 (mm) |
|---|---|---|---|---|---|---|---|---|
| 2″ | 165.1 | 25.4 | 8×⅝” | 165.1 | 30.2 | 8×¾” | 38.1 | 47.8 |
| 3″ | 209.5 | 28.6 | 8×¾” | 209.5 | 38.1 | 8×¾” | 47.8 | 63.5 |
| 4″ | 254.0 | 31.8 | 8×¾” | 273.1 | 44.5 | 8×⅞” | 57.2 | 82.6 |
| 6″ | 317.5 | 36.6 | 12×¾” | 355.6 | 57.2 | 12×1″ | 79.4 | 117.5 |
| 8″ | 381.0 | 41.4 | 12×⅞” | 419.1 | 66.7 | 12×1⅛” | 98.6 | 152.4 |
| 10″ | 444.5 | 47.8 | 16×1″ | 508.0 | 82.6 | 16×1¼” | 117.5 | 190.5 |
| 12″ | 520.7 | 50.8 | 16×1⅛” | 584.2 | 95.3 | 20×1¼” | 139.7 | 228.6 |
| 16″ | 647.7 | 57.2 | 20×1¼” | 704.9 | 114.3 | 20×1½” | 171.5 | — |
| 20″ | 774.7 | 66.7 | 24×1¼” | 857.3 | 139.7 | 24×1⅝” | 209.6 | — |
| 24″ | 914.4 | 76.2 | 24×1½” | 1022.4 | 165.1 | 24×2″ | 247.7 | — |
2.3 — ASME B16.5 Pressure Rating — All Classes (Group 1.1 / A105N)
| Temp (°C) | Class 150 | Class 300 | Class 600 | Class 900 | Class 1500 | Class 2500 |
|---|---|---|---|---|---|---|
| −29 to 38 | 19.6 | 51.1 | 102.1 | 153.2 | 255.3 | 425.5 |
| 50 | 19.2 | 50.1 | 100.2 | 150.3 | 250.5 | 417.5 |
| 100 | 17.7 | 46.6 | 93.2 | 139.8 | 233.0 | 388.3 |
| 150 | 15.8 | 45.1 | 90.2 | 135.3 | 225.5 | 375.8 |
| 200 | 13.8 | 43.8 | 87.6 | 131.4 | 219.0 | 365.0 |
| 300 | 10.2 | 39.8 | 79.6 | 119.4 | 199.0 | 331.6 |
| 400 | 6.5 | 36.5 | 73.0 | 109.5 | 182.5 | 304.2 |
| 450 | 5.1 | 31.6 | 63.2 | 94.8 | 158.0 | 263.3 |
| 480 | — | 26.5 | 53.0 | 79.5 | 132.5 | 220.8 |
| 538 | — | 20.5 | 41.0 | 61.5 | 102.5 | 170.9 |
2.4 — Applicable Standards and Compliance Framework
ASME B16.5
Pipe Flanges and Flanged Fittings, NPS ½–24, Class 150–2500. The primary standard governing blind flange dimensions, pressure–temperature ratings by material group, facing types (RF, FF, RTJ, LM/LF), bolt data, and tolerances. Blind flanges are available in all seven pressure classes (150 to 2500) without the service restrictions that apply to other flange types — the most universally applicable flange standard for blind flange specification on global EPC projects.
ASME B16.47 Series A/B
Large Diameter Steel Flanges, NPS 26–60. Series A (formerly MSS SP-44 — for higher-pressure service) and Series B (formerly API 605 — lower-pressure). Large bore blind flanges per B16.47 are used on vessel nozzles, large-bore pipe ends, and manway connections NPS 26 and above. Series A and B dimensions differ significantly — specify the correct series on the purchase order and verify with the mating equipment flange drawing.
ASME VIII Division 1
Appendix 2: design of bolted flange connections including blind flanges as vessel nozzle closures. UG-34: minimum thickness of flat heads and covers — governs where the blind flange is used as a pressure vessel cover. UG-45: nozzle neck minimum thickness. When specifying blind flanges as vessel manway or nozzle covers, verify both the ASME B16.5 class rating AND the ASME VIII UG-34 thickness requirement — the more demanding governs the actual minimum plate thickness.
EN 1092-1 Type 05
Type 05 is the EN 1092-1 designation for blind flanges (blanking flanges), available in PN 6 through PN 400 for all standard NPS equivalents. The European standard for blind flanges in CE-marked pressure equipment under PED 2014/68/EU. EN 1092-1 Type 05 blind flanges are dimensionally compatible with EN 1092-1 Type 01/11 pipe flanges at the same PN and NPS within the standard tolerance range — no dimensional modification is required when mating EN blind flanges to EN pipe flanges.
ASTM A105N
Carbon steel forgings for piping components — normalised condition. A105N is the standard material for carbon steel blind flanges across all pressure classes. The “N” normalising designation reduces hardness to ≤187 HB — mandatory for NACE MR0175 sour service compliance. Non-normalised A105 (without the N suffix) frequently exceeds 22 HRC and is NOT acceptable in H₂S sour service. Always verify the N designation on all sour service blind flange purchase orders.
ASTM A182
Forged or rolled alloy and stainless steel pipe flanges and fittings. Covers all alloy and SS grade blind flanges: F304L / F316L (austenitic SS), F51 (Duplex 2205), F53 (Super Duplex S32750), F11 / F22 (Cr-Mo for elevated temperature), F91 (9Cr-1Mo-V for ultra-high temperature), and speciality grades. The governing material standard for all non-carbon steel blind flange grades in EPC O&G, chemical, and power generation projects.
ASTM A350 LF2 / LF3
Forgings for piping components requiring notch toughness. LF2 (Charpy at −45°C) for low-temperature service to −46°C; LF3 (Charpy at −101°C) for cryogenic service. Required for blind flanges on LNG process connections, ethylene plant piping, and carbon steel piping with minimum design temperature below −29°C. Individual Charpy specimens from each production forging heat — lot specimens are not acceptable for LF2 or LF3 certification.
NACE MR0175 / ISO 15156
For blind flanges in H₂S sour service: A105N normalised (≤187 HB mandatory); F316L SS (NACE-compliant); F51 Duplex (≤28 HRC); Inconel 625 (NACE-compliant). Non-normalised A105, A182 F22 exceeding 241 HB, and surface-hardened alloy grades are NOT acceptable in sour service. Blind flanges at production separator nozzles, amine plant piping, sour crude handling, and well-head connections all require NACE-certified material with individual hardness documentation.
2.5 — Facing Types and Gasket Selection
Raised Face (RF) — Standard
Standard facing for most EPC applications in all pressure classes. 2 mm raised ring height (Class 150/300); 7 mm (Class 600 and above). Serrated concentric phonograph-groove finish 125–250 µin Ra per ASME B16.5. Compatible with spiral wound, compressed asbestos-free (CAF), and soft full-face gaskets. Most common blind flange facing type in global EPC piping supply across all pressure classes and material grades.
Ring-Type Joint (RTJ)
Precision octagonal ring groove per ASME B16.20. Required for Class 600–2500 high-pressure service: well-head connections, high-pressure separator nozzles, reactor nozzle blinds, and pressure relief valve isolation blinds. Provides highest integrity metal-to-metal sealing. Ring number must be specified (e.g., R-49 for 6″ Class 900). RTJ blind flanges are standard on Class 900+ EPC upstream O&G and refinery pressure piping.
Flat Face (FF)
No raised ring — full face flush with the flange OD. Required when mating to flat face equipment connections: cast iron pump bodies, rubber-lined vessels, non-metallic equipment, and GRP piping flanges. Full face gasket extends to bolt holes. Common in offshore seawater systems where the blind flange mates to GRP piping with flat face flanges. Also used in fire water systems where the downstream component is cast iron.
Ring-Type Joint — Octagonal vs Oval
ASME B16.20 defines both octagonal (standard for new installations) and oval ring gaskets for RTJ joints. Octagonal rings provide higher contact stress and are preferred for all new EPC designs. Oval rings are available for replacement of existing oval-groove flanges only. Verify ring groove geometry — octagonal grooves accept octagonal rings only; oval grooves accept both types. Specify ring type and ring number explicitly on all RTJ blind flange purchase orders.
Heat Treatment
& Manufacturing Process
Blind flange material is specified to match the connected piping system material class — same ASTM grade, same pressure class, same corrosion and temperature requirements. RR Hydraulic manufactures blind flanges in all standard and exotic material grades from A105N through Super Duplex and Inconel 625, with full EN 10204 3.1 / 3.2 material traceability.
3.1 — Material Grade Overview and Mechanical Properties
| Material | Spec | UTS (MPa) | Yield (MPa) | Temp Range (°C) | Max HB | NACE | Application |
|---|---|---|---|---|---|---|---|
| Carbon Steel (N) | ASTM A105N | 485 | 250 | −29 to +538 | 187 | Yes | General EPC; all classes; all standard service |
| CS Low-Temp LF2 | ASTM A350 LF2 | 485 | 250 | −46 to +345 | 197 | Cond. | Low-temp; LNG utility; −46°C service |
| CS Cryogenic LF3 | ASTM A350 LF3 | 450 | 240 | −101 to +345 | 197 | Cond. | Cryogenic; LNG storage; −101°C |
| 1.25Cr-0.5Mo | ASTM A182 F11 | 485 | 275 | −29 to +593 | 217 | Yes | High-temp; reformer nozzles; heater piping |
| 2.25Cr-1Mo | ASTM A182 F22 | 415 | 205 | −29 to +649 | 241 | Yes | Hydrocracker; reactor inlet nozzles |
| 9Cr-1Mo-V (P91) | ASTM A182 F91 | 585 | 415 | −29 to +649 | 250 | Yes | Ultra-high temp; power plant steam lines |
| SS 304L | ASTM A182 F304L | 450 | 170 | −196 to +425 | 192 | Yes | Corrosive; food/pharma; cryogenic |
| SS 316L | ASTM A182 F316L | 450 | 170 | −196 to +425 | 192 | Yes | Marine; offshore; chloride; chemical |
| Duplex 2205 | ASTM A182 F51 | 620 | 450 | −50 to +315 | 293 | Yes | Offshore; sour+Cl⁻; seawater injection |
| Super Duplex | ASTM A182 F53 (S32750) | 750 | 550 | −50 to +260 | 310 | Cond. | Seawater; high chloride; aggressive sour |
| Inconel 625 | ASTM B564 N06625 | 827 | 414 | −196 to +980 | — | Yes | Extreme corrosion; very high-temp nozzles |
3.2 — Corrosion Resistance Matrix
| Material | H₂S Sour* | CO₂ / Wet Gas | Cl⁻ / Seawater | Acids | Caustic | High Temp >400°C | Cryogenic |
|---|---|---|---|---|---|---|---|
| A105N CS | Cond.* | Fair | Poor | Poor | Good | Good to 538°C | Not suitable |
| A350 LF2 / LF3 | Cond.* | Fair | Poor | Poor | Good | Limited | Excellent |
| A182 F11 / F22 / F91 | Cond.* | Good | Poor | Poor | Good | Very Good–Excellent | Not suitable |
| F304L SS | Fair | Good | Poor (SCC) | Fair | Very Good | Good | Excellent |
| F316L SS | Good | Very Good | Fair | Good | Very Good | Good | Excellent |
| F51 Duplex | Very Good | Excellent | Very Good | Very Good | Very Good | Limited >315°C | Good to −50°C |
| F53 Super Duplex | Excellent | Excellent | Excellent | Excellent | Excellent | Limited >260°C | Good to −50°C |
| Inconel 625 | Excellent | Excellent | Excellent | Excellent | Excellent | Excellent to 980°C | Excellent |
3.3 — Manufacturing Process
3.3.1 — Forging — Mandatory for All Pressure Service
All blind flanges for pressure piping and vessel service must be manufactured by hot forging from ingot, billet, or bar stock conforming to the applicable ASTM material specification. Plate-cut blind flanges — machined from flat plate rather than forged — are NOT acceptable for any pressure-retaining application under ASME B16.5 or ASME B31. Plate-cut components have grain flow perpendicular to the loading direction, reduced through-thickness toughness, and lower UTS compared to forged product, and they cannot be certified to ASTM A105N or A182 material specifications which require forging as the manufacturing process.
3.3.2 — Machining and Face Finishing
- Face serration: Raised face machined with phonograph-groove concentric serration 125–250 µin Ra per ASME B16.5 — critical for gasket seating stress; smooth faces reduce contact stress and increase leakage risk
- Raised face height: 2 mm (Class 150 and 300); 7 mm (Class 600 and above) — verified by depth gauge on every blind flange
- Face flatness: Maximum 0.8 mm TIR across the raised face ring per ASME B16.5 — face out-of-flat creates non-uniform gasket stress and leakage risk; verified by dial gauge TIR measurement
- RTJ groove machining: Groove dimensions per ASME B16.20 ring number table — width, depth, and wall angle to ±0.05 mm tolerance; sealing wall Ra ≤ 1.6 µm (63 µin)
- Bolt hole drilling: ±0.8 mm on BCD; angular spacing ±0.5° per ASME B16.5; bolt holes straddle centreline; all holes drilled simultaneously on CNC multi-spindle drill for positional accuracy
- Identification marking: ASTM grade, NPS, pressure class, heat number, and manufacturer mark per ASME B16.5 marking requirements — stamped or vibro-engraved on OD hub face
3.3.3 — Heat Treatment by Grade
- A105N: Full normalising at 900°C / air cool; hardness ≤187 HB mandatory — NACE sour service compliance
- A350 LF2: Normalise + Charpy impact at −45°C (individual specimens per forging heat)
- A350 LF3: Normalise + Charpy at −101°C for cryogenic LNG service
- F11 / F22: Normalise + temper; hardness verified ≤217 / 241 HB per grade
- F91 (P91): Normalise at 1040°C + temper at 730–800°C; hardness 197–250 HB; PWHT of all field welds mandatory at 730–800°C
- F304L / F316L: Solution anneal ≥1040°C; L grades prevent sensitisation; no PWHT required
- F51 Duplex: Solution anneal 1020–1100°C + water quench; ferrite content 40–60% verified by metallographic examination
- F53 Super Duplex: Solution anneal 1025–1125°C + water quench; ferrite 40–50%; PREN ≥ 40 confirmed
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw forging heat to final packed shipment on all blind flange orders. Dimensional inspection, EN 10204 3.1 / 3.2 MTRs, hardness certificates, Charpy impact reports, NACE compliance statements, TPI witness capability, and complete EPC export documentation packages are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | Signatory | EPC Requirement | When Mandatory |
|---|---|---|---|---|
| 2.1 | Conformity declaration only | Manufacturer | Not acceptable for pressure service | Never acceptable for ASME B16.5 pressure flanges |
| 2.2 | Non-specific test results | Manufacturer | Not acceptable for EPC pressure service | Not acceptable for any pressure-retaining blind flange |
| 3.1 | Heat-traceable forging lot mech + chem | Manufacturer’s authorised QC | Minimum for all EPC pressure blind flanges | All Class 150+ blind flanges for pipe and vessel service |
| 3.2 | 3.1 + TPI countersign | Manufacturer + SGS / BV / DNV / Lloyds | NACE; cryogenic; offshore; Class 900+; vessel nozzle | Sour service; A350; Duplex; Class 900+; ASME VIII vessel |
4.3 — Applications by Industry
Future Tie-In Points — Phase 1 / Phase 2 EPC
The highest-volume blind flange use in EPC construction. A105N Class 150/300 RF blind flanges blank all future process tie-in connections, utility header branches, and expansion stubs installed in Phase 1 piping for Phase 2 connection. Blind flanges remain operational for 2–10 years until the Phase 2 expansion is executed. Material, class, and facing must match the pipe specification for the line to which the future connection will be made — specify the mating pipe spec on the blind flange purchase order to ensure compatibility.
Pressure Testing Isolation
Temporary blind flanges isolate pipe sections during hydrostatic pressure testing at 1.5× design pressure per ASME B31.3. Class 150 A105N RF blind flanges for most utility hydro-test applications. For high-test-pressure conditions: Class 300 or 600 blind flanges verified against test pressure and test medium temperature. Track test blind flange locations on the pressure test record — all test blinds must be removed and replaced with the correct operational flange after test completion and prior to plant commissioning.
Pressure Vessel Nozzle Covers
A182 F316L or A105N blind flanges on vessel nozzles not commissioned during initial plant start-up — spare nozzles, future instrumentation, and temporarily blanked relief valve connections. Large-bore vessel nozzle blind flanges (NPS 12–24) in Class 600–900 RF or RTJ can weigh 100–250 kg — davit lift lugs are often required on the purchase drawing. Comply with both ASME B16.5 and ASME VIII UG-34 — the vessel code flat cover thickness calculation may govern over the B16.5 table minimum.
Offshore Well-Head and Subsea
A182 F316L, Duplex F51, or Super Duplex F53 RTJ blind flanges (Class 900–2500) on offshore well-head flowlines, subsea tree closures, and riser end terminations. All offshore blind flanges: EN 10204 3.2 with DNV or Lloyds TPI; PMI mandatory on every lot; individual hardness certificates for NACE sour service. RTJ facing is standard for all Class 900+ offshore blinds — octagonal ring provides the highest integrity seal under the high-pressure, high-cycle dynamic loading of an offshore production well-head.
LNG Plant and Cryogenic Service
A350 LF3 or A182 F304L blind flanges for LNG process and utility line end closures at temperatures to −165°C. Charpy impact testing at −101°C (LF3) or full cryogenic testing per project specification. A182 F304L austenitic SS preferred for LNG process nozzle blanking — austenitic SS retains ductility at cryogenic temperatures and does not require Charpy testing in most codes. EN 10204 3.2 with TPI for all LNG cryogenic blind flange supply. PMI on all SS and LF3 lots.
Pipeline Pig Launcher / Receiver Covers
Large-bore A105N or F316L Class 150–900 RF or RTJ blind flanges as closure heads on pig launcher and receiver barrels. Class 600–900 blind flanges for high-pressure transmission pipeline pig traps can exceed 200 kg for NPS 24 — structural davit lift lugs or monorail attachment points are specified on the fabrication drawing. Quick-opening closure (QOC) or conventional bolted blind flange type per the process safety requirements and maintenance access frequency for the pig trap location.
4.4 — Export Packaging Specification
- Blind flanges individually wrapped in VCI poly film — prevents atmospheric corrosion on machined face, bolt hole bores, and RTJ groove surfaces during ocean freight and extended site storage
- Raised face protection: cardboard or foam disc bonded to the raised face before packaging — prevents damage to the critical 125–250 µin serrated gasket contact surface during transit and site handling; a scored raised face requires re-machining which delays installation
- RTJ groove protection: foam bead or precision-fit plastic insert in every RTJ ring groove — damage to the precision sealing walls of an RTJ groove renders the flange unusable without re-machining; one impact during transit can destroy a Class 2500 blind flange worth thousands
- Identification: stainless steel or weatherproof tag per flange with ASTM grade, NPS, pressure class, facing, heat number, and PO item number — traceability maintained through site receiving inspection to flange installation record
- Palletising: face-to-face matched pairs where possible; NPS 12 and above individually crated on ISPM-15 heat-treated timber frames; heavy flanges (Class 600+, NPS 16+) with timber dunnage blocking and individual steel banding
- ISPM-15 heat-treated timber pallets and crates for all international export; outer labelling per project packing specification
- Documentation: EN 10204 MTC, dimensional inspection report, hardness certificate (A105N), Charpy report (A350), heat treatment records, ferrite count (Duplex), and TPI release note in waterproof document pocket on exterior crate face
4.5 — Complete EPC Project Documentation Package
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | Mandatory — all pressure service | Forging heat-traceable; one MTC per heat lot |
| 02 | Chemical Composition Report | Forging lot certified lab analysis | Mandatory | All elements per ASTM A105N / A182 / A350 |
| 03 | Mechanical Properties Report | UTS, yield, elongation, hardness | Mandatory | Per applicable ASTM grade specification |
| 04 | Hardness Test Report | ASTM E10 Brinell | Mandatory — A105N and NACE service | Individual flange results; A105N ≤187 HB |
| 05 | Charpy Impact Test Report | ASTM A370 / EN 10045 | Mandatory — A350 LF2 / LF3 | Test temp; individual + average J-values per heat |
| 06 | Dimensional Inspection Report | Per ASME B16.5 / B16.47 tables | Mandatory | All dimensional parameters including RF height, RTJ groove |
| 07 | Face Finish Report | ASME B16.5 Ra 3.2–6.3 µm | Mandatory | Ra measurement; flatness TIR; raised face height |
| 08 | RTJ Groove Inspection Certificate | ASME B16.20 ring groove table | Conditional — RTJ facing blind flanges | Ring number; groove dims ± 0.05 mm; Ra ≤1.6 µm |
| 09 | Heat Treatment Certificate | Furnace chart + HT procedure | Mandatory — A105N, A350, F11/F22/F91, Duplex | Normalising / solution anneal records per grade |
| 10 | NDE Report (UT / MT / PT) | ASTM A388 / E709 / E165 | Mandatory — Class 600+; NACE; vessel nozzle | Pre-machining UT; post-machining MT or PT |
| 11 | PMI Report (XRF) | Per lot — SS / duplex / alloy grades | Mandatory — non-CS grades | F316L vs F304L; F51 vs F53; alloy verification |
| 12 | Ferrite Content Report | Metallographic cross-section | Mandatory — F51 and F53 Duplex supply | 40–60% ferrite; PREN ≥ 40 for F53 |
| 13 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project line items | Released before batch production proceeds |
| 14 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 orders | Co-witness at manufacturer works |
| 15 | NACE Compliance Statement | Hardness + HT declaration | Conditional — sour service supply | A105N ≤187 HB normalised; heat number referenced |
| 16 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers forged flange manufacture |
| 17 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff code for customs classification |
| 18 | Packing List | Item-level per shipment | Mandatory | Cross-references MTC and TPI numbers |
| 19 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 20 | Bill of Lading / Air Waybill | Per freight mode | Mandatory | Issued by freight forwarder |
4.6 — ISO and Quality System Compliance
ISO 9001:2015
Quality Management System covering raw forging procurement, normalising/heat treatment process control, face serration machining and Ra measurement, bolt hole position CNC verification, hardness testing protocol, NDE qualification, and complete material traceability from forging heat to finished flange. Mandatory for all EPC, O&G, and ASME B31/VIII pressure service project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification with scope covering forged flange manufacture.
ASME B31.3 Process Piping
Blind flanges in ASME B31.3 process piping must comply with B31.3 material acceptance (Appendix A listed materials), pressure class selection (Appendix B), and test requirements (Chapter VI). Blind flanges carry no service category restriction in B31.3 — they may be used in all fluid categories including Category M (lethal fluid), Category D, and Category Normal service — the only flange type with universal applicability across all service categories.
ASME VIII Division 1
When blind flanges serve as pressure vessel nozzle covers or manway covers, UG-34 flat head thickness design and Appendix 2 bolted flange analysis apply in addition to ASME B16.5. The more restrictive governs minimum plate thickness. Large-bore, high-pressure vessel blind flanges must also satisfy UG-45 nozzle minimum wall thickness at the vessel nozzle neck. Always verify both codes for vessel nozzle blind flange applications.
PED 2014/68/EU
Pressure Equipment Directive — European regulatory framework for CE-marked pressure equipment. Blind flanges in European pressure systems must meet PED essential safety requirements. EN 1092-1 Type 05 blind flanges for European projects; ASME B16.5 blind flanges used under PED with appropriate conformity assessment. RR Hydraulic supplies PED-compliant blind flanges with Declaration of Conformity and CE marking documentation on request for all European EPC project blind flange supply.
Submit your line list, NPS, pressure class, material, facing, and quantity to RR Hydraulic for a complete, certified commercial offer.