RFQ Today
Certifications available: EN 10204 3.1 / 3.2 MTRs, NACE MR0175 compliance, ASTM A105N / A182 grades, Third-Party Inspection (SGS / BV / DNV / Lloyds), and complete EPC export documentation packages.
Slip-On Flange
A world-class technical reference for EPC contractors, piping engineers, procurement heads, TPI inspection agencies, and global project buyers specifying slip-on flanges in general process piping, utility systems, low-pressure hydrocarbon lines, water, air, and non-critical service across Oil & Gas, Power Generation, Petrochemical, Chemical, and Industrial Construction sectors worldwide.
Design Principles
& Structural Behaviour
Slip-on flanges are plain-bore flanges with an inside diameter slightly larger than the outside diameter of the pipe, allowing the pipe to slip through before welding. Two fillet welds — one at the pipe bore on the flange face side, and one at the back of the hub — secure the flange to the pipe. They are among the most widely used flange types in global EPC construction for general and utility piping services.
1.1 — Technical Definition and Functional Role
A slip-on flange (SOF) is a flanged pipe connection component with a bore diameter machined slightly larger than the nominal pipe outside diameter — typically pipe OD + 1.5 mm — allowing the flange to slip over the pipe end before welding in position. The flange is secured to the pipe by two circumferential fillet welds: an inner weld at the bore face of the flange (preventing fluid bypass between pipe OD and flange bore), and an outer weld at the back of the hub. This two-weld design provides structural connection and pressure containment, but places the primary load path through two fillet welds rather than a single full-penetration butt weld as in a weld neck flange.
In EPC and industrial piping construction, slip-on flanges are specified for: cooling water systems, instrument air and plant air distribution, fire water rings, drain headers, general utility steam (low-pressure), non-critical hydrocarbon service (Class 150–300), flare and vent headers, chemical dosing lines, HVAC piping, and any general service application within Class 150–600 where the structural limitations of a fillet-welded connection are acceptable for the design conditions. They are not used in severe cyclic, lethal fluid, or Category M services.
RR Hydraulic manufactures slip-on flanges under all applicable international standards with full EN 10204 3.1 / 3.2 material traceability and project documentation.
1.2 — Slip-On Flange vs Other Flange Types
| Parameter | Slip-On (SOF) | Weld Neck (WNF) | Socket Weld (SWF) | Blind (BF) | Engineering Implication |
|---|---|---|---|---|---|
| Attachment weld | 2 fillet welds | 1 butt weld (full penetration) | 1 fillet weld (socket) | No pipe attachment | WNF stronger; SOF adequate for standard service |
| Fatigue life | Lower — fillet weld SIF | Highest — butt weld, tapered hub | Moderate | N/A | SOF: not for severe cyclic pressure |
| NDE on weld | MT/PT fillet weld only | Full RT/UT on butt weld | MT/PT fillet | No weld | SOF: lower NDE cost; limited flaw detection |
| Pressure class range | Class 150–600 | Class 150–2500 | Class 150–2500 (small bore) | All classes | SOF: limited to Class 600 max |
| Bore alignment | Adjustable before weld | Exact — matched to pipe schedule | Exact — socket depth | No bore | SOF: field adjustment possible |
| Installation ease | High — slip and weld | Moderate — butt fit-up required | Moderate | High — bolt directly | SOF: faster site installation |
| Cost | Lower — simpler profile | Higher — complex forging | Moderate | Low–Moderate | SOF: preferred for high-volume utility work |
| Crevice between pipe/bore | Yes — corrosion risk | No crevice | No crevice | No crevice | SOF: not for corrosive fluid where crevice = attack |
| Lethal / Category M | Not permitted | Required | Not permitted | Any type | SOF: excluded from most severe services |
1.3 — Structural Behaviour and Limitations
Dual Fillet Weld Load Path
The slip-on flange transfers all pressure, bending, and shear loads through two fillet welds — the bore-face fillet and the hub-back fillet. Fillet welds have an inherently higher stress intensification factor (SIF) than a full-penetration butt weld, resulting in lower fatigue life under cyclic pressure loading. For this reason, ASME B31.3 assigns a lower joint efficiency (E = 0.80) to slip-on fillet welds compared to butt welds (E = 1.0), which must be accounted for in pressure design calculations.
Annular Crevice — Corrosion Risk
The gap between the pipe OD and the flange bore creates an annular crevice that can trap process fluid and promote crevice corrosion, microbiologically influenced corrosion (MIC), and chloride stress corrosion cracking in SS grades. The bore-face inner fillet weld seals one end of this crevice but cannot eliminate it entirely. Slip-on flanges should not be specified for corrosive fluid services where even a short unprotected crevice would initiate service-life-limiting corrosion.
Pressure Class Limitation
Slip-on flanges are generally limited to ASME B16.5 Class 150 through Class 600 in standard carbon and alloy steel. At Class 900 and above, the structural requirements exceed what a fillet weld attachment can reliably provide under the combined bolt preload and pressure end force — weld neck flanges are mandated. Some project specifications further restrict slip-on flanges to Class 150 and 300 for critical process lines even when ASME B16.5 permits Class 600.
Bore Alignment Flexibility
The slip-on bore clearance of approximately +1.5 mm over pipe OD allows rotational and axial positioning adjustment before tack welding — an advantage on large-bore pipe erection where exact bore-to-bore alignment is critical. The pipe can be set to the correct face-to-face pipe spool dimension before the flange is tacked; small adjustments are possible that would not be available with a fitted socket-weld or butt-weld-prepared weld neck flange bore.
Service Exclusions
Slip-on flanges are excluded from multiple service categories per ASME B31.3: lethal fluids (Category M) — mandatory weld neck; severe cyclic conditions (more than 1000 full pressure cycles per year) — weld neck preferred; services requiring full radiographic examination (Category D with RT required) — fillet welds are not RT-inspectable; and high-pressure (Class 900+) service. Project piping specifications routinely add further restrictions beyond the code minimum.
PWHT Considerations
Post-weld heat treatment (PWHT) of slip-on flange fillet welds is required for: carbon steel when weld throat thickness exceeds 19 mm (¾”) or when P-number grouping requires PWHT regardless of thickness (P4, P5, P6); chrome-moly alloy steels regardless of thickness; and any material where the ASME B31.3 service conditions mandate PWHT. The PWHT procedure must heat the complete flange assembly uniformly — local banding PWHT on a large bore slip-on flange risks distortion of the flange face.
1.4 — Pressure-Temperature Rating and Design Basis
P_class = Class rating base pressure at 20°C (MPa) — per ASME B16.5 material group table
S_allow,T = Allowable stress of flange material at temperature T (MPa) — from ASME B16.5 Table A
S_allow,20°C = Allowable stress at 20°C (MPa)
ASME B31.3 pipe pressure design (for companion pipe):
t_min = (P × D) / (2 × S × E + 2 × P × Y)
P = Design pressure; D = Pipe OD; S = Allowable stress; E = Joint efficiency (0.80 for SOF fillet weld);
Y = Temperature coefficient (0.4 for ferrous materials ≤480°C)
Base pressure Class 150 at 38°C: 19.6 bar g
S_allow at 100°C for Group 1.1 ≈ 17.7 bar g (derated per ASME B16.5 Table 2-1.1)
The lower pressure at 100°C is the governing design pressure for Class 150 at 100°C.
Submit your line list, NPS, pressure class, material, facing type, and quantity for a documented RFQ within 24 hours.
Pressure Ratings &
Standards Compliance
Slip-on flange dimensions — flange OD, bolt circle diameter, bolt hole count and size, raised face diameter, flange thickness, hub dimensions, and bore — are fully defined by ASME B16.5 (NPS ½–24), ASME B16.47 (NPS 26–60), and EN 1092-1 (PN rated). All applicable standards are supported at RR Hydraulic with full certification.
Submit NPS, pressure class, material, facing type, and quantity to sales@rrhydraulics.com for a fully certified offer.
2.1 — ASME B16.5 Class 150 Slip-On Flange Dimensional Table
| NPS | Pipe OD (mm) | Flange OD (mm) | BCD (mm) | Bolts × Dia | RF Dia (mm) | Flange Thick (mm) | Bore (mm) | Hub OD (mm) |
|---|---|---|---|---|---|---|---|---|
| ½” | 21.3 | 88.9 | 60.5 | 4×½” | 34.9 | 11.2 | 23.0 | 38.1 |
| ¾” | 26.7 | 98.6 | 69.9 | 4×½” | 42.9 | 12.7 | 28.4 | 47.8 |
| 1″ | 33.4 | 108.0 | 79.4 | 4×½” | 50.8 | 14.2 | 35.1 | 57.2 |
| 1½” | 48.3 | 127.0 | 98.6 | 4×½” | 73.2 | 15.7 | 50.0 | 76.2 |
| 2″ | 60.3 | 152.4 | 120.7 | 4×⅝” | 91.9 | 17.5 | 61.9 | 92.1 |
| 3″ | 88.9 | 190.5 | 152.4 | 4×⅝” | 127.0 | 19.1 | 90.6 | 127.0 |
| 4″ | 114.3 | 228.6 | 190.5 | 8×⅝” | 157.2 | 20.6 | 116.1 | 157.2 |
| 6″ | 168.3 | 279.4 | 241.3 | 8×¾” | 215.9 | 22.4 | 170.2 | 215.9 |
| 8″ | 219.1 | 342.9 | 298.5 | 8×¾” | 269.9 | 23.9 | 220.9 | 269.9 |
| 10″ | 273.1 | 406.4 | 362.0 | 12×⅞” | 323.9 | 25.4 | 274.9 | 323.9 |
| 12″ | 323.9 | 482.6 | 431.8 | 12×⅞” | 381.0 | 25.4 | 325.6 | 381.0 |
| 14″ | 355.6 | 533.4 | 476.3 | 12×1″ | 412.8 | 27.0 | 358.8 | 412.8 |
| 16″ | 406.4 | 596.9 | 539.8 | 16×1″ | 469.9 | 28.6 | 409.6 | 469.9 |
| 18″ | 457.2 | 635.0 | 577.9 | 16×1⅛” | 533.4 | 31.8 | 460.4 | 533.4 |
| 20″ | 508.0 | 698.5 | 635.0 | 20×1⅛” | 584.2 | 34.9 | 511.2 | 584.2 |
| 24″ | 609.6 | 812.8 | 749.3 | 20×1¼” | 692.2 | 39.7 | 612.8 | 692.2 |
2.2 — ASME B16.5 Class 300 Slip-On Flange Dimensional Table
| NPS | Flange OD (mm) | BCD (mm) | Bolts × Dia | RF Dia (mm) | Flange Thick (mm) | Bore (mm) |
|---|---|---|---|---|---|---|
| 1″ | 123.8 | 88.9 | 4×⅝” | 50.8 | 19.1 | 35.1 |
| 1½” | 155.7 | 114.3 | 4×¾” | 73.2 | 22.4 | 50.0 |
| 2″ | 165.1 | 127.0 | 8×⅝” | 91.9 | 25.4 | 61.9 |
| 3″ | 209.5 | 168.3 | 8×¾” | 127.0 | 28.6 | 90.6 |
| 4″ | 254.0 | 200.2 | 8×¾” | 157.2 | 31.8 | 116.1 |
| 6″ | 317.5 | 266.7 | 12×¾” | 215.9 | 36.6 | 170.2 |
| 8″ | 381.0 | 330.2 | 12×⅞” | 269.9 | 41.4 | 220.9 |
| 10″ | 444.5 | 387.4 | 16×1″ | 323.9 | 47.8 | 274.9 |
| 12″ | 520.7 | 450.8 | 16×1⅛” | 381.0 | 50.8 | 325.6 |
| 16″ | 647.7 | 571.5 | 20×1¼” | 469.9 | 57.2 | 409.6 |
| 20″ | 774.7 | 685.8 | 24×1¼” | 584.2 | 66.7 | 511.2 |
| 24″ | 914.4 | 812.8 | 24×1½” | 692.2 | 76.2 | 612.8 |
2.3 — ASME B16.5 Pressure Rating Table — Slip-On Flanges
| Temp (°C) | Class 150 | Class 300 | Class 400 | Class 600 | Service Limitation Note |
|---|---|---|---|---|---|
| −29 to 38 | 19.6 | 51.1 | 68.1 | 102.1 | SOF max Class 600; WNF for Class 900+ |
| 50 | 19.2 | 50.1 | 66.8 | 100.2 | — |
| 100 | 17.7 | 46.6 | 62.1 | 93.2 | — |
| 150 | 15.8 | 45.1 | 60.1 | 90.2 | — |
| 200 | 13.8 | 43.8 | 58.4 | 87.6 | — |
| 250 | 12.1 | 41.9 | 55.9 | 83.9 | Verify creep allowable for carbon steel |
| 300 | 10.2 | 39.8 | 53.0 | 79.6 | — |
| 375 | 7.4 | 36.4 | 48.5 | 72.9 | Check NACE if H₂S present |
| 425 | 6.1 | 33.7 | 44.9 | 67.4 | Review Nelson Curves (API 941) for H₂ service |
| 480 | 5.2 | 28.3 | 37.7 | 56.5 | Upper limit for standard carbon steel A105N |
2.4 — Applicable Standards and Compliance Framework
ASME B16.5
Pipe Flanges and Flanged Fittings, NPS ½–24. The primary US and international standard for slip-on flanges in pressure class 150 through 2500. Defines dimensional requirements, pressure–temperature ratings (by material group), facing types (RF, FF, RTJ), bolt data, and tolerances. All EPC projects operating under ASME B31.1 / B31.3 specify flanges per ASME B16.5. Class 150 and 300 are the most common pressure classes for slip-on flange applications.
ASME B16.47
Large Diameter Steel Flanges, NPS 26–60. Series A (formerly MSS SP-44): for high-pressure piping; used with weld neck flanges primarily. Series B (formerly API 605): lower-pressure; slip-on type available. Large bore slip-on flanges (NPS 26+) per ASME B16.47 Series B are used in large-bore utility and cooling water systems. Dimensions differ significantly between Series A and Series B — specify the correct series on the purchase order.
EN 1092-1
Flanges and their joints — circular flanges for pipes, valves, fittings and accessories, PN designated. Type 01 (plate flange — no hub, flat faced) and Type 11 (weld neck) are the EN 1092-1 types. The EN 1092-1 slip-on equivalent is Type 01 (plate flange) or Type 02 (loose plate flange) for PN 6 to PN 40. European EPC projects under PED (2014/68/EU) reference EN 1092-1 as the flange standard for CE-marked equipment and piping.
DIN 2573 / 2576 / 2631
Legacy German standards for slip-on flanges: DIN 2573 (PN 6), DIN 2576 (PN 10), DIN 2631 (PN 16), DIN 2632 (PN 25), DIN 2633 (PN 40). Still widely specified in German-coded EPC projects and plant maintenance documentation. Dimensionally aligned with EN 1092-1 for equivalent PN ratings in the standard NPS range. Specify the DIN standard reference explicitly when German project documentation requires it.
ASTM A105N
Carbon steel forgings for piping components — normalised condition. A105N (normalised) is the NACE MR0175-compliant grade for slip-on flanges in sour service — hardness ≤ 187 HB after normalising heat treatment. The standard material for Class 150–600 carbon steel slip-on flanges in EPC Oil & Gas, petrochemical, and general process piping. Available in all sizes NPS ½–24 as standard stock items.
ASTM A182
Forged or rolled alloy and stainless steel pipe flanges and fittings. Covers all alloy and SS grades for slip-on flanges: F304L, F316L (austenitic SS), F51 (Duplex 2205), F53 (Super Duplex S32750), F11 and F22 (Cr-Mo for elevated temperature). The governing material standard for non-carbon steel slip-on flange material specification in EPC projects requiring corrosion resistance or elevated temperature service.
ASTM A350 LF2
Forgings for piping components with notch toughness requirements — LF2 (impact tested at −45°C). Required for slip-on flanges on low-temperature and cryogenic process piping where carbon steel must be verified to impact-tested condition. Charpy impact testing per ASTM A350 Table S5 is mandatory. Used in ethylene plants, LNG facilities, and other low-temperature EPC services where standard A105N is not adequate below −29°C design temperature.
NACE MR0175 / ISO 15156
For slip-on flanges in H₂S sour environments: ASTM A105N (normalised, ≤187 HB mandatory); A182 F316L (NACE-compliant within ISO 3506 hardness limits); A182 F51 Duplex (NACE-compliant, ≤28 HRC). Non-normalised carbon steel (ASTM A105 without the N designation) may exceed 22 HRC and is NOT acceptable in sour service. Verify the “N” normalising designation is included in all NACE sour service purchase orders for slip-on flanges.
2.5 — Facing Types for Slip-On Flanges
Raised Face (RF) — Standard
Standard facing for Class 150 and 300 slip-on flanges. 2 mm raised ring height (Class 150/300); 7 mm for Class 600+. Serrated concentric finish 125–250 µin Ra per ASME B16.5. Compatible with spiral wound, CAF (compressed asbestos-free), and soft gaskets. The most common slip-on flange facing for EPC utility, chemical, and non-critical process service. Standard for the vast majority of slip-on flange supply in global EPC projects.
Flat Face (FF)
No raised ring — full face flush with the flange OD. Required when mating to flat face flanges on equipment with brittle body materials (cast iron, ductile iron, non-metallic). Full face gasket extends to bolt holes. Prevents the raised face of a steel flange from creating a bending moment across a cast iron companion flange face that could crack it. Commonly used for slip-on flanges on cooling water pump nozzle connections where the pump body is cast iron.
Ring-Type Joint (RTJ)
RTJ facing on slip-on flanges is uncommon but available for Class 600 high-pressure utility service. Precision-machined octagonal ring groove per ASME B16.20. Provides metal-to-metal sealing with an octagonal soft metal ring. Ring number must be specified for each NPS/class combination. For most slip-on flange applications, a raised face with an appropriate gasket is preferred; RTJ on slip-on flanges requires careful weld and PWHT management to maintain groove geometry.
Large Male / Large Female (LM/LF)
Male-female mating faces where the male flange has a protruding boss that fits into the female flange recess — the gasket is fully confined between the two faces. Used in heat exchanger channel-to-shell connections and where a confined gasket is required to prevent blowout under high-pressure dynamic loading. Must be ordered as matched pairs (one LM + one LF). Less common than RF but available as a standard ASME B16.5 facing option on slip-on flanges.
Heat Treatment
& Manufacturing Process
Slip-on flange material is selected to match the service fluid, temperature, and pressure conditions of the connected piping system. RR Hydraulic manufactures slip-on flanges in all standard and exotic grades — from ASTM A105N carbon steel through Super Duplex and Inconel — with full EN 10204 3.1 / 3.2 traceability.
3.1 — Material Grade Overview and Mechanical Properties
| Material | Spec | UTS (MPa) | Yield (MPa) | Elong (%) | Temp Range (°C) | Max HB | NACE | Primary Application |
|---|---|---|---|---|---|---|---|---|
| Carbon Steel (N) | ASTM A105N | 485 | 250 | 22 | −29 to +538 | 187 (N) | Yes | General EPC; utility; process lines |
| Low-Temp CS | ASTM A350 LF2 | 485 | 250 | 22 | −46 to +345 | 197 | Cond. | Cryogenic, low-temp service lines |
| 1.25Cr-0.5Mo | ASTM A182 F11 | 485 | 275 | 20 | −29 to +593 | 217 | Yes | High-temp; reformer; heater piping |
| 2.25Cr-1Mo | ASTM A182 F22 | 415 | 205 | 20 | −29 to +649 | 241 | Yes | High-temp alloy; hydrocracker lines |
| SS 304L | ASTM A182 F304L | 450 | 170 | 30 | −196 to +425 | 192 | Yes | Corrosive; food; pharma; cryogenic |
| SS 316L | ASTM A182 F316L | 450 | 170 | 30 | −196 to +425 | 192 | Yes | Marine; chloride; offshore; chemical |
| Duplex 2205 | ASTM A182 F51 | 620 | 450 | 25 | −50 to +315 | 293 | Yes | Offshore; sour; seawater; high-Cl⁻ |
| Super Duplex | ASTM A182 F53 (S32750) | 750 | 550 | 15 | −50 to +260 | 310 | Cond. | Seawater injection; high chloride |
| Inconel 625 | ASTM B564 N06625 | 827 | 414 | 30 | −196 to +980 | — | Yes | Extreme corrosion; very high-temp |
3.2 — Corrosion Resistance Matrix
| Material | H₂S Sour* | CO₂ / Wet Gas | Cl⁻ / Seawater | Acids | Caustic | High Temp (>400°C) | Cryogenic |
|---|---|---|---|---|---|---|---|
| A105N CS | Conditional* | Fair | Poor | Poor | Good | Good to 538°C | Not suitable |
| A350 LF2 | Conditional* | Fair | Poor | Poor | Good | Limited | Excellent |
| A182 F11/F22 | Conditional* | Good | Poor | Poor | Good | Very Good | Not suitable |
| A182 F304L | Fair | Good | Poor (SCC) | Fair | Very Good | Good | Excellent |
| A182 F316L | Good | Very Good | Fair | Good | Very Good | Good | Excellent |
| A182 F51 Duplex | Very Good | Excellent | Very Good | Very Good | Very Good | Limited >315°C | Good to −50°C |
| A182 F53 S.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: Slip-On Flange
3.3.1 — Forging (Preferred) vs Fabrication
Slip-on flanges for pressure service must be manufactured by hot forging from ingot, billet, or bar stock conforming to the applicable ASTM material specification — ASTM A105N (carbon steel), ASTM A182 (alloy and SS), or ASTM A350 (low-temperature CS). The forging process produces continuous grain flow, superior impact toughness, and higher structural integrity compared to plate-cut or welded fabricated flanges. Fabricated plate flanges (cut from flat plate) are acceptable only for non-pressure-bearing attachments or for flanges outside the scope of ASME B16.5 — they must not be used as pressure-containing flanges in ASME B31 piping systems without specific engineering review.
3.3.2 — Bore Machining and Face Finish
- Bore diameter: Machined to pipe OD + 1.5 mm (standard) per ASME B16.5 bore tolerance table — bore must be concentric with the flange OD within 0.8 mm TIR to ensure correct pipe-to-flange alignment
- Raised face finish: Serrated concentric phonograph-groove finish 125–250 µin Ra (3.2–6.3 µm) per ASME B16.5 — produced by a lathe facing pass with a controlled feed rate; smooth faces are NOT acceptable as they reduce gasket seating stress by reducing surface area contact for standard gasket sealing
- Flange face flatness: Maximum 0.8 mm TIR across the full raised face ring per ASME B16.5 — flange face out-of-flat creates non-uniform gasket stress and leakage risk
- Bolt hole position: ±0.8 mm on bolt circle diameter; angular spacing ±0.5° per ASME B16.5 — bolt holes must straddle the flange centreline (no bolt hole at top or bottom of flange unless specifically requested)
- Hub geometry: Hub OD and bore parallel within 0.5 mm along the hub length; fillet at bore-to-hub transition machined to min 3 mm radius to reduce stress concentration at the inner fillet weld toepoint
3.3.3 — Heat Treatment
- ASTM A105N — Normalising: Full normalising heat treatment (900°C / air cool) mandatory — the “N” suffix in A105N specifies this condition; hardness verified ≤ 187 HB; critical for NACE sour service compliance
- A350 LF2: Normalised or normalised and tempered; Charpy impact test at −45°C mandatory per ASTM A350 Table S5
- A182 F11 / F22: Normalised + tempered; hardness verified ≤ 217 HB / 241 HB respectively; PWHT of field welds mandatory
- SS grades (F304L / F316L): Solution annealed at 1040°C minimum; use L grades to prevent sensitisation; no PWHT required
- Duplex F51: Solution annealed 1020–1100°C with water quench; ferrite content 40–60% verified by metallographic examination
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from raw forging heat to final packed shipment on all slip-on flange orders. Dimensional inspection, EN 10204 3.1 / 3.2 MTRs, hardness certificates, NACE compliance statements, 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 B31 piping flanges |
| 2.2 | Non-specific test results | Manufacturer | Not acceptable for O&G EPC | Not acceptable for any pressure service flange |
| 3.1 | Heat-traceable forging lot mech + chem | Manufacturer’s authorised QC | Minimum for all EPC pressure service flanges | All Class 150+ slip-on flanges for piping service |
| 3.2 | 3.1 + countersigned by TPI | Manufacturer + SGS / BV / DNV / Lloyds | NACE, cryogenic, offshore, nuclear | Sour service, A350, offshore, Duplex, nuclear Class 2/3 |
4.3 — Applications by Industry
Cooling Water and Utility Systems — EPC
The highest-volume slip-on flange application in EPC. NPS 2–24 A105N Class 150 RF slip-on flanges for open cooling water, closed cooling water, potable water, firewater, plant air, and instrument air systems. HDG or coal-tar epoxy external coating for buried or submerged cooling water headers. EN 10204 3.1 MTC standard. Bore verified against actual pipe OD schedule — cooling water systems routinely use standard wall pipe (Schedule 40 / 80) with defined OD per ASME B36.10.
Non-Critical Process Hydrocarbon Lines
NPS 2–12 A105N Class 150 or 300 RF slip-on flanges for Category D (non-flammable, non-toxic) or non-critical Category Normal fluid service within ASME B31.3. Common applications: fuel gas at low pressure, treated water injection, crude oil storage tank suction lines, and product blending headers where the process conditions are within the Class 150/300 P–T rating and the service is not classified as lethal or severely cyclic.
Offshore Seawater Systems
NPS 2–24 A182 F316L or F51 Duplex Class 150–300 FF (flat face, for compatibility with GRE piping) or RF slip-on flanges for offshore seawater lift, seawater injection, ballast water, and open-deck drain systems. SS F316L for standard offshore seawater service; Duplex F51 for seawater injection at higher pressures. All with EN 10204 3.2 and Lloyds/DNV TPI. PMI mandatory on all SS lots.
Chemical Plant Utility and Acid Lines
NPS 1–12 A182 F304L or F316L Class 150–300 RF slip-on flanges for chemical plant utility piping (dilute acids, caustic, brine, process water). F316L preferred for chloride-containing chemical environments. All SS slip-on flanges: passivation per ASTM A967 before dispatch; PMI on each lot. Bore machined to pipe OD + 1.5 mm standard; verify actual OD of SS or HDPE-lined pipe used in the chemical system against the slip-on bore tolerance range.
Low-Temperature and Cryogenic Utility
NPS 2–12 A350 LF2 Class 150–300 RF slip-on flanges for utility nitrogen, CO₂ purge headers, and low-temperature process streams down to −46°C. Charpy impact tested per ASTM A350 Table S5 at −45°C. For service below −46°C (LNG utility piping): ASTM A182 F304L slip-on flanges with cryogenic impact testing per project specification. EN 10204 3.2 with TPI witness for all cryogenic slip-on flange supply.
Fire Water and Deluge Systems
NPS 2–16 A105N Class 150 FF or RF slip-on flanges for fire water ring mains, deluge headers, and sprinkler systems. Flat face where mating to grooved or rubber-lined system components. Internal coating (epoxy or cement lining) for long-term corrosion protection of fire water headers. NFPA 13 / NFPA 15 design basis; UL/FM-listed flanges may be required for US-coded projects. External HDG for above-ground exposed headers; FBE or coal-tar epoxy for buried ring mains.
4.4 — Export Packaging Specification
- Slip-on flanges individually wrapped in VCI poly film — prevents atmospheric corrosion on precision-machined bore, raised face, and bolt hole surfaces during ocean freight and site storage
- Raised face protection: cardboard or foam disc bonded to the raised face — prevents damage to the critical 125–250 µin serrated surface finish during transit and site handling; a scratched raised face requires re-machining which delays installation
- Bore protection: cardboard or foam plug in the bore — prevents foreign object ingress, surface damage, and moisture accumulation in the annular bore-hub area during transit
- Individual item tagging: stainless steel or weather-proof tag per flange with ASTM grade, NPS, pressure class, facing type, heat number, and PO item number — traceability through site receiving inspection
- Pallet arrangement: flanges palletised face-to-face in matched pairs where possible to protect raised faces; heavy flanges (NPS 12+) individually crated on ISPM-15 timber base frames; lighter flanges (NPS ≤ 8) bundled per size and class
- ISPM-15 heat-treated timber pallets and crates for all international export; outer labelling per project packing specification and UN transport requirements
- Documentation: EN 10204 MTC, dimensional inspection report, hardness certificate (A105N), Charpy report (A350), and TPI release note enclosed in waterproof document pocket on crate exterior and inside crate lid
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 |
| 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 material 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 | Test temp + individual + average J-values per heat |
| 06 | Dimensional Inspection Report | Per ASME B16.5 tolerance tables | Mandatory | All flange body dimensions + bore verified |
| 07 | Face Finish Report | ASME B16.5 Ra 3.2–6.3 µm | Mandatory | Ra measurement; flatness TIR; raised face height |
| 08 | Heat Treatment Certificate | Furnace records + HT procedure | Mandatory — A105N, A350, F11/F22, Duplex | Normalising / solution anneal records per grade |
| 09 | NDE Report (UT / MT / PT) | ASTM A388 / E709 / E165 | Mandatory — Class 600+; Conditional — 150/300 | Pre-machining UT; post-machining MT or PT |
| 10 | PMI Report (XRF) | Per lot — SS / duplex / exotic | Mandatory — non-CS grades | F316L vs F304L; F51 vs F53 differentiation |
| 11 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new line items | Released before batch production |
| 12 | TPI Witness Certificate | SGS / BV / DNV / Lloyds | Conditional — EN 10204 3.2 | Co-witness at manufacturer works |
| 13 | NACE Compliance Statement | Hardness + HT declaration | Conditional — sour service supply | A105N ≤187 HB normalised; heat number referenced |
| 14 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers forged flange manufacture |
| 15 | Country of Origin Certificate | Chamber of Commerce | Mandatory — all export | HS tariff code for customs |
| 16 | Packing List | Item-level per shipment | Mandatory | Cross-references MTC and TPI numbers |
| 17 | Commercial Invoice | Per INCOTERMS 2020 | Mandatory | Includes HS tariff code |
| 18 | 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, bore machining dimensional verification, raised face finish measurement, hardness testing, NDE qualification, and full material traceability through all production stages. Mandatory for all EPC, O&G, and ASME B31 pressure piping project procurement qualification. RR Hydraulic holds current ISO 9001:2015 certification with scope covering forged flange manufacture.
ASME B31.3 Process Piping
The primary design code for EPC process piping flanged connections. B31.3 defines joint efficiency factors (E = 0.80 for slip-on fillet welds vs E = 1.0 for butt welds), service restrictions on slip-on flanges (no Category M; no severe cyclic), and required NDE for each weld category. The slip-on flange specification, material grade, and weld procedure must all conform to B31.3 requirements for the assigned service category on the piping line list.
ISO 10474
Steel and steel products — inspection documents. Source framework for EN 10204 certificate types. Some legacy EPC project specifications and piping material specifications reference ISO 10474 Type 3.1.B (= EN 10204 3.1) for flange material certification. RR Hydraulic provides documentation in either format on request and cross-maps certificate types for legacy project compliance.
PED 2014/68/EU
Pressure Equipment Directive — European regulatory framework for pressure-retaining equipment above threshold pressures. Slip-on flanges used in European CE-marked pressure systems must comply with PED essential safety requirements; Category I–IV classification depends on fluid group and PS×DN product. EN 1092-1 flanges for European projects; ASME B16.5 flanges may be used under PED with appropriate conformity assessment. RR Hydraulic supplies PED-compliant slip-on flanges with CE marking documentation on request.
Submit your line list, NPS, pressure class, material, facing, and quantity to RR Hydraulic for a complete, certified commercial offer.