Hydraulic Flanges
A world-class engineering reference for EPC contractors, piping engineers, procurement heads and TPI inspection agencies. Covers sealing principles, dimensional standards, material grades, manufacturing process, inspection protocols and full project documentation.
Industry Context, Sealing Principles & Load Characteristics
Role of Hydraulic Flanges in EPC and High-Pressure Systems
Hydraulic flanges constitute the primary demountable joint type in high-pressure hydraulic circuits operating above 250 bar (3,625 psi). In EPC project environments — spanning offshore topsides, refinery skids, LNG loading arms, power plant turbine lube systems and heavy industrial presses — they function as the engineered interface between fixed piping infrastructure and dynamic equipment requiring periodic maintenance access or field modification during commissioning.
Unlike threaded or socket-weld connections, flanged joints provide a geometry-controlled, repeatable sealing interface that accommodates thermal cycling, vibration loads and pressure transients without requiring re-welding or field NDT recertification. This makes them indispensable in classified hazardous areas where hot work permits are costly or impractical, and in systems where documentation traceability to ASME B31.3 or ISO 15649 is a contractual requirement.
In a representative FEED study for an offshore hydraulic power unit (HPU), flanged connections account for approximately 68% of all high-pressure joints above DN50. Their selection over butt-weld connections is driven by commissioning flexibility, maintainability, and regulatory demountability requirements under ATEX/IECEx zone classifications.
Flanged Joints vs. Threaded and Welded Alternatives
The selection of a flanged joint over threaded connections (BSPP/NPT) or welded connections is governed by engineering constraints, not preference. Threaded connections in sizes above DN25 and pressures above 350 bar exhibit unacceptable stress concentration at thread roots, particularly under fatigue loading. Welded connections eliminate leak paths but prevent field disassembly — in systems requiring periodic valve, actuator or instrumentation replacement, every welded joint represents a future hot-work cost. Hydraulic flanges address both limitations: the O-ring face seal eliminates the thread-form leak path while the bolted joint allows complete disassembly with defined retorque procedures.
- Operating pressure exceeding 250 bar (3,625 psi) with cyclic loading
- Pipe or hose bore ≥ DN25 where threaded connection torque is unmanageable in-field
- Locations subject to vibration-induced loosening — compressor skids, marine environments
- Classified zones (ATEX Zone 1/2) prohibiting hot work for re-weld repair
- Multi-vendor skid interfaces requiring dimensional interchangeability per SAE J518
- Systems requiring EN 10204 3.1/3.2 material traceability without field welding
O-Ring Face Seal (ORFS) Sealing Mechanics
The sealing mechanism of a hydraulic flange connection employs a precision O-ring groove machined into one mating face, receiving a nitrile (NBR), fluorocarbon (FKM/Viton) or EPDM O-ring that is compressed radially within the groove as the flanges are drawn together by bolt load. When bolted, the O-ring undergoes controlled diametric compression — typically 15–25% of cross-section diameter — generating a sealing contact stress that exceeds the fluid pressure across the sealing band. Groove geometry is specified per SAE J518 Table 3 and must be maintained within ±0.05 mm on groove width and ±0.025 mm on groove depth. Face flatness must be ≤ 0.013 mm per 25 mm of face width (Ra ≤ 0.8 µm).
O-ring material selection: NBR for mineral oil to +100°C; FKM for synthetic esters and elevated temperatures to +200°C; EPDM for water and steam to +150°C, incompatible with petroleum-based fluids. Metal-to-metal sealing in ultra-high pressure applications (above 700 bar) requires faces lapped to Ra ≤ 0.4 µm with a soft metal gasket — annealed copper, aluminium or PTFE-coated steel.
σ_contact ≥ P_op × SF // Must exceed operating pressure × safety factor across seal band
δ = (d_wire − d_groove) / d_wire × 100% // Compression ratio target: 15–25%
// ── WORKED EXAMPLE: 2″ Code 62 flange @ 6,000 psi (41.4 MPa), 4× M16 bolts, lubricated K=0.17 ──
F_sep = 41.4 MPa × (π × 0.0508² / 4) = 83,800 N // Hydraulic separating force
F_bolt_min = 83,800 × 2.5 = 209,500 N // SF = 2.5 for Code 62
F_per_bolt = 209,500 / 4 = 52,375 N
T_lubricated = 0.17 × 0.016 × 52,375 = 142 N·m // T = K × d × F
T_dry = 0.22 × 0.016 × 52,375 = 184 N·m
Bolt Preload Behaviour — Embedment, Thermal Cycling & Vibration
Embedment relaxation occurs within the first 24–72 hours as surface asperities on mating threads and bolt heads plastically deform. Typical loss is 5–15% of initial preload. Retorque at first service interval is standard practice in critical systems. Thermal cycling generates differential expansion between bolt and flange body. For applications above 150°C, Belleville washers or thread-locking compounds maintain preload within the operational range. Vibration loosening is the dominant failure mode on HPU skids and mobile machinery — quantified by Junker testing per DIN 65151. Nyloc inserts, Loctite 243/270 or split-ring lock washers are specified depending on thermal class and disassembly frequency.
Leak Prevention Chain — Sequential Engineering Requirements
1. O-ring compound selected for fluid and temperature compatibility → 2. O-ring groove to SAE J518 / ISO 6162 verified on CMM → 3. Flange face flatness ≤ Ra 0.8 µm confirmed by profilometry → 4. O-ring installed without twist or cut — visual + dimensional check → 5. Flange faces drawn parallel using cross-torque sequence → 6. Bolt torque applied in three stages to target value per lubrication condition → 7. Bolt preload verified by turn-of-nut or ultrasonic measurement on critical applications → 8. System pressure test at 1.5× MWP minimum for 30 minutes → 9. Retorque at first service interval (100–500 operating hours)
Static vs. Dynamic Load Handling — Fatigue and Pressure Cycling
The hydrostatic separating force must be reacted by total bolt clamping force with a minimum safety factor of 2.0 for Code 61 and 2.5 for Code 62 at rated pressure. Fatigue failure initiates at three primary locations: (1) the O-ring groove root radius, where stress concentration factors of 2.5–4.0 apply under cyclic loading; (2) the first engaged thread of bolts, where 50–60% of bolt load is transferred; (3) the bolt head-to-flange face fillet radius under bending-dominated loading. Pressure cycling performance is evaluated against Miner’s cumulative damage rule (Σni/Ni ≤ 1.0). Flanges for cyclic-duty above 10,000 full-pressure cycles must be manufactured from normalised or Q&T material with certified Charpy impact values, with O-ring groove root radius minimum 0.4 mm.
| Bore Size | Bore (mm) | Code 61 Max WP (psi) | Code 61 Max WP (bar) | Code 62 Max WP (psi) | Code 62 Max WP (bar) |
|---|---|---|---|---|---|
| 1/2″ | 12.7 | 6,000 | 414 | 9,000 | 621 |
| 3/4″ | 19.1 | 6,000 | 414 | 9,000 | 621 |
| 1″ | 25.4 | 5,000 | 345 | 9,000 | 621 |
| 1-1/4″ | 31.8 | 4,000 | 276 | 9,000 | 621 |
| 1-1/2″ | 38.1 | 3,500 | 241 | 6,000 | 414 |
| 2″ | 50.8 | 3,000 | 207 | 6,000 | 414 |
| 2-1/2″ | 63.5 | 3,000 | 207 | 6,000 | 414 |
| 3″ | 76.2 | 3,000 | 207 | 5,000 | 345 |
| 3-1/2″ | 88.9 | 3,000 | 207 | 5,000 | 345 |
| 4″ | 101.6 | 3,000 | 207 | 4,500 | 310 |
Source: SAE J518 (2011) / ISO 6162-1:2018 / ISO 6162-2:2018. Ratings are bore-dependent.
| Bolt Size | Grade | Code | Dry Torque (N·m) | Lubricated Torque (N·m) | Target Preload (kN) | Notes |
|---|---|---|---|---|---|---|
| M10 × 1.5 | 10.9 | 61 | 52 | 39 | 28 | K=0.22 dry / K=0.17 lub. |
| M10 × 1.5 | 10.9 | 62 | 65 | 49 | 35 | Higher preload for Code 62 |
| M12 × 1.75 | 10.9 | 61 | 90 | 68 | 42 | |
| M12 × 1.75 | 10.9 | 62 | 112 | 84 | 52 | |
| M16 × 2.0 | 10.9 | 61 | 218 | 163 | 82 | |
| M16 × 2.0 | 10.9 | 62 | 272 | 204 | 102 | Verify torque wrench calibration |
| M20 × 2.5 | 10.9 | 61 | 426 | 320 | 128 | |
| M20 × 2.5 | 10.9 | 62 | 533 | 400 | 160 | |
| M24 × 3.0 | 10.9 | 61 | 740 | 555 | 192 | |
| M24 × 3.0 | 10.9 | 62 | 925 | 694 | 240 | Hydraulic torque tool recommended |
T = K × d × F. Apply in three equal stages, cross-pattern sequence. Lubrication: MoS₂ grease or SAE 30 oil on threads and nut bearing face.
Dimensional Design Logic, Flange Types,
Standards & Compliance
Dimensional Design Logic
The dimensional architecture of a SAE hydraulic flange is engineered around three coupled constraints: (1) bore area, which determines the separating force at rated pressure; (2) bolt circle diameter (BCD) and bolt size, which together determine available clamping capacity; and (3) overall flange thickness, which must accommodate the O-ring groove depth plus minimum wall thickness without yielding under maximum bolt preload and fluid pressure acting simultaneously. As bore increases, pressure rating decreases because the separating force grows as d², while bolt capacity grows only as nbolts × dbolt².
| Bore (in) | Bore (mm) | Bolt Size | No. Bolts | BCD (mm) | Flange OD (mm) | Thickness C61 (mm) | Thickness C62 (mm) |
|---|---|---|---|---|---|---|---|
| 1/2″ | 12.7 | M10 × 1.5 | 4 | 42.9 | 57.2 | 17.5 | 22.2 |
| 3/4″ | 19.1 | M10 × 1.5 | 4 | 50.8 | 65.1 | 19.1 | 25.4 |
| 1″ | 25.4 | M12 × 1.75 | 4 | 60.3 | 79.4 | 22.2 | 28.6 |
| 1-1/4″ | 31.8 | M12 × 1.75 | 4 | 69.9 | 88.9 | 22.2 | 31.8 |
| 1-1/2″ | 38.1 | M16 × 2.0 | 4 | 79.4 | 101.6 | 25.4 | 34.9 |
| 2″ | 50.8 | M16 × 2.0 | 4 | 98.4 | 127.0 | 27.0 | 38.1 |
| 2-1/2″ | 63.5 | M20 × 2.5 | 4 | 120.7 | 152.4 | 31.8 | 44.5 |
| 3″ | 76.2 | M20 × 2.5 | 4 | 139.7 | 177.8 | 34.9 | 50.8 |
| 3-1/2″ | 88.9 | M20 × 2.5 | 4 | 158.8 | 196.9 | 38.1 | 54.0 |
| 4″ | 101.6 | M24 × 3.0 | 4 | 177.8 | 219.1 | 41.3 | 57.2 |
SAE J518 (2011) / ISO 6162-1:2018 / ISO 6162-2:2018. Verify against current revision for procurement.
Flange Types — Engineering Descriptions
Rated up to 6,000 psi (414 bar) at minimum bore, decreasing to 3,000 psi (207 bar) at 4″ bore. Flat-faced O-ring groove with four-bolt mounting. Code 61 is the dominant type in industrial hydraulic systems, mobile equipment and process plant auxiliary circuits below 350 bar. Dimensionally interchangeable across manufacturers when manufactured to full SAE J518 / ISO 6162-1 specification including O-ring groove tolerances and face flatness.
Shares the same bolt hole pattern and BCD as Code 61 for each bore size, but features increased body thickness, larger O-ring groove section and higher-grade bolting to achieve 6,000–9,000 psi (414–621 bar). Mandatory in subsea accumulator circuits, high-pressure test stands and applications above 350 bar. The increased groove depth requires a larger cross-section O-ring (AS568B series) — not interchangeable with the Code 61 O-ring size.
Two separate clamp halves encircle the flange head of a tube, hose fitting or port adapter. Provides critical installation advantages in confined spaces where a solid flange cannot be rotated, and during modifications where adjacent piping remains under pressure. Fully dimensional-compatible with solid flanges per SAE J518 Table 5.
Deviate from circular body geometry to facilitate direct bolting to manifold blocks, valve bodies and subplate-mounted components. Not covered by a single universal standard — engineering drawing control, material certification and interface verification are mandatory. FAI and first-off approval against customer drawing are required before production release.
Specified when standard bore sizes, pressure classes or mounting geometries do not satisfy system requirements: non-standard bore sizes, combined port thread types on the same body, extended neck lengths for insulation clearance, duplex material specification, integral instrumentation ports. Custom flanges require FEA validation if operating above 80% of standard rated pressure, and a First Article Inspection (FAI) report is mandatory before production release.
Standards and Compliance
SAE J518 / ISO 6162-1 / ISO 6162-2 define O-ring groove geometry, flange face flatness, bolt hole diameter and tolerance, BCD, overall dimensions and pressure ratings for bore sizes 1/2″ through 4″. Interchangeability conditions: Two flanges from different manufacturers are interchangeable if and only if manufactured to the same code and bore size, with O-ring groove dimensions within SAE J518 Table 3 tolerances and bolt hole BCD within ±0.25 mm.
ISO 4413 specifies system-level requirements and is mandatory on CE-marked hydraulic systems for the EU market. ISO 10474 specifies inspection document types equivalent to EN 10204. DIN 2353 governs bite-type tube fittings frequently co-referenced with SAE J518 in the same piping specifications. DIN 65151 is the accepted test method for bolt vibration-loosening resistance.
| ASTM Standard | Product Form | Material Grade | Application |
|---|---|---|---|
| A105 | Forgings | Carbon steel | Flanges, fittings ≤ 260°C non-corrosive service |
| A182 F304/316 | Forgings | Austenitic SS | Corrosive service flanges, general chemical plant |
| A182 F51 | Forgings | Duplex 2205 | Sour service, chloride exposure, offshore |
| A182 F53/F55 | Forgings | Super Duplex | Severe chloride, high pressure subsea circuits |
| A193 B7 | Bolting | Alloy steel Cr-Mo | High-strength stud bolts for all hydraulic flanges |
| A194 2H | Nuts | Carbon steel Q&T | Mating nuts for A193 B7 studs |
| A320 L7 | Bolting | Alloy steel low-temp | LNG, cryogenic service to −101°C |
| A350 LF2 | Forgings | Carbon-Mn steel | Low-temperature flange bodies to −46°C |
| Thread Type | Standard | Form | Sealing Method | Common Application |
|---|---|---|---|---|
| BSPP (G) | ISO 228-1 | Parallel | Face O-ring / bonded seal | European hydraulic equipment |
| BSPT (R) | ISO 7-1 | Taper | Thread sealing (PTFE/compound) | Pipe connections, legacy systems |
| NPT | ASME B1.20.1 | Taper | Thread sealing (PTFE/compound) | North American systems |
| UNF/UNC | ASME B1.1 | Parallel | O-ring on boss (SAE J1926) | SAE port connections |
| Metric (M) | ISO 724 | Parallel | O-ring on boss / compression | DIN/ISO hydraulic equipment |
| SAE ORB | SAE J1926 | Parallel UNF | O-ring on machined boss | SAE component ports |
Material Grades, Heat Treatment
& Manufacturing Process
| Material | Standard | UTS (MPa) | Yield (MPa) | Elong. (%) | Hardness | Corrosion | Primary Use |
|---|---|---|---|---|---|---|---|
| A105 CS | ASTM A105 | 485 min | 250 min | 22 | ≤187 HB | Low | General industrial, non-corrosive |
| A350 LF2 | ASTM A350 | 485 min | 250 min | 22 | ≤197 HB | Low | Low-temperature service to −46°C |
| AISI 4140 | ASTM A193 B7 | 862 min | 724 min | 16 | ≤321 HB | Low | High-strength bolting, custom flanges |
| 316L SS | ASTM A182 F316L | 485 min | 170 min | 30 | ≤217 HB | High | Corrosive service, offshore, chemical |
| Duplex 2205 | ASTM A182 F51 | 620 min | 450 min | 25 | ≤293 HB | Very High | Sour gas, chloride, subsea |
| Super Duplex | ASTM A182 F53/F55 | 795 min | 550 min | 15 | ≤310 HB | Extreme | Severe sour service, high-chloride offshore |
| Inconel 625 | ASTM B564 N06625 | 827 min | 414 min | 30 | ≤241 HB | Extreme | High-temperature, highly corrosive service |
| Service Medium | A105 CS | 316L SS | Duplex 2205 | Super Duplex |
|---|---|---|---|---|
| Mineral hydraulic oil | Excellent | Excellent | Excellent | Excellent |
| Water-glycol fluid | Marginal | Excellent | Excellent | Excellent |
| Seawater / chlorides | Not suitable | Marginal | Good | Excellent |
| Sour gas (H₂S) | NACE required | Susceptible | Good | Excellent |
| Phosphate ester fluid | Not suitable | Excellent | Excellent | Excellent |
| LNG / Cryogenic | Not suitable | Excellent | Good | Good |
| Hydrogen (high purity) | H-embrittlement risk | Good | Good | Good |
NACE MR0175 / ISO 15156 Requirements
For hydraulic flanges in sour service (H₂S-containing environments), NACE MR0175 / ISO 15156 mandates maximum hardness of 22 HRC (237 HB) throughout the full cross-section — not just at the surface. This eliminates as-forged carbon steel from sour service without subsequent heat treatment. Hardness must be verified by Vickers mapping of the full cross-section, not spot measurements. Duplex and super duplex alloys are acceptable within the partial pressure limits of NACE MR0175 Part 3, but must be solution annealed with PREN (pitting resistance equivalent number) verified per batch chemistry.
| Grade | UTS (MPa) | 0.2% Yield (MPa) | Elongation (%) | Charpy @ −20°C (J) |
|---|---|---|---|---|
| A105 (Normalised) | 485–580 | 250–330 | 22–26 | ≥27 (typical) |
| A193 B7 (Q&T) | 862 | 724 | 16 | ≥47 |
| A182 F304 | 515 | 205 | 30 | N/A — austenitic |
| A182 F316L | 485 | 170 | 30 | N/A — austenitic |
| A182 F51 Duplex | 620 | 450 | 25 | ≥45 @ −40°C |
| A182 F53 S-Duplex | 795 | 550 | 15 | ≥40 @ −40°C |
| A350 LF2 | 485 | 250 | 22 | ≥20 @ −46°C |
| Condition | Grade | UTS (MPa) | Yield 0.2% (MPa) | Elong. (%) | CVN @ −20°C (J) | Max Hardness |
|---|---|---|---|---|---|---|
| As-Forged | A105 | 485 | 250 | 22 | Not guaranteed | 187 HB |
| Normalised | A105 | 500–580 | 280–330 | 22–26 | ≥27 J | 187 HB |
| Q&T | A105 (Q&T) | 550–690 | 380–480 | 20–24 | ≥40 J | 197 HB |
| Normalised | A350 LF2 | 485 min | 250 min | 22 | ≥20 J @ −46°C | 197 HB |
| Solution Annealed | F316L | 485 min | 170 min | 30 | N/A | 217 HB |
| Solution Annealed | F51 Duplex | 620 min | 450 min | 25 | ≥45 J @ −40°C | 293 HB |
PWHT per ASME VIII Div.1 UCS-56 or BS EN 13480 required for weld-neck attachments on carbon steel ≥ 32 mm thickness.
Manufacturing Process
Hydraulic flanges above DN25 in Code 62 pressure class must be manufactured from closed-die forgings per ASTM A105 or equivalent, not from bar stock. Forgings produce a continuous grain flow aligned with the principal stress direction, resulting in superior fatigue resistance and impact toughness compared to bar-machined parts where grain flow is transverse to the sealing face.
- Bore diameter: ±0.025 mm (H7 fit where transitioning to tube OD)
- O-ring groove width: +0.05 / −0.00 mm
- O-ring groove depth: ±0.025 mm
- O-ring groove corner radius: 0.4 mm minimum — prevents O-ring extrusion under pressure
- Flange face flatness: ≤ 0.013 mm per 25 mm of face diameter
- Flange face Ra: ≤ 0.8 µm (1.6 µm permitted for Code 61 at ambient non-cyclic duty)
- Bolt hole diameter: +0.25 / −0.00 mm clearance for standard hex bolt
- Bolt hole BCD: ±0.13 mm · Overall thickness: ±0.25 mm
Post-machining, all hydraulic flanges must be cleaned to ISO 4406 cleanliness Class 16/13 minimum prior to preservation and packaging. This requires ultrasonic cleaning or high-pressure flushing with filtered solvent, followed by dried compressed-air purge. Particle counting per ISO 11500 on a sample wash test confirms compliance. Bore caps and flange face protectors must be installed immediately after cleanliness verification.
| Finish / Coating | Standard | Thickness (µm) | Protection | Max Temp (°C) | Application |
|---|---|---|---|---|---|
| Black oxide | MIL-DTL-13924 | 0.5–2 | Low | 200 | Internal storage, short-term |
| Phosphate + oil | MIL-DTL-16232 | 5–15 | Moderate | 120 | General industrial, pre-paint base |
| Zinc plating | ASTM B633 | 8–25 | Good | 150 | Mild corrosion environments |
| Zinc-nickel | ASTM B841 | 8–15 | Very good | 200 | Offshore, marine-adjacent |
| Hot-dip galvanise | ASTM A153 | 45–85 | Excellent | 200 | Structural, external piping |
| PTFE / Xylan | Whitford spec. | 15–30 | Good + low friction | 230 | Bolt threads, anti-galling |
| Electroless nickel | ASTM B733 | 15–50 | Very good, uniform | 300 | Complex geometry, bores |
| Bare 316L SS | ASTM A276 | N/A (passive) | High — passive film | 870 | Corrosive service — no coating needed |
Inspection, QC Protocols, Applications
& Export Documentation
EN 10204 3.1 vs 3.2 Material Test Certificates
EN 10204 Type 3.1: The MTC is validated by the manufacturer’s own authorised inspection representative, independent of production. Minimum standard for most onshore EPC projects and OEM supply. The certificate must reference the applicable standard, heat/lot number, chemical analysis results and mechanical test results — UTS, yield, elongation, hardness and Charpy impact where required.
EN 10204 Type 3.2: The MTC is co-validated by an independent third-party inspection body nominated by the purchaser — Bureau Veritas, DNV, Lloyds, SGS, TÜV. Mandatory for offshore installations, nuclear-adjacent systems and wherever the project ITP specifies TPI witness of material certification. The TPI inspector physically reviews and countersigns the certificate at the manufacturer’s works after witnessing mechanical testing.
NDT Methods and Application Criteria
Ultrasonic Testing (UT) — applied to forgings per ASTM A388 or EN 10228-3. Mandatory for Code 62 flanges in critical service and all custom flanges above DN50. UT is the only NDT method capable of detecting subsurface volumetric defects in the full flange cross-section. Magnetic Particle Inspection (MPI/MT) — applied to machined surfaces of carbon steel and low alloy steel flanges per ASTM E709 / EN ISO 17638. Demagnetisation to ≤ 2 mT residual field required post-inspection for flanges installed near flow instrumentation. Liquid Penetrant Inspection (LPI/PT) — applied to austenitic stainless steel, duplex and non-ferromagnetic alloys per ASTM E165 / EN ISO 3452. Particularly important on O-ring groove surfaces and bore-to-face transition radii. Positive Material Identification (PMI) — mandatory for all stainless steel, duplex and alloy steel flanges using XRF or OES spectrometry. Critical when multiple grades are in inventory simultaneously. Hardness Testing — grid mapping on the critical cross-section for sour service qualification per NACE MR0175 — spot hardness alone is insufficient.
First Article Inspection (FAI) and Pressure Test Parameters
For new part numbers, custom flanges or supply from a previously unqualified manufacturer, a First Article Inspection is mandatory before series production release. The FAI package must include: complete dimensional inspection (minimum 100% of critical features on CMM); O-ring groove profilometry trace; flange face Ra measurement; hardness map; PMI; mechanical test results from the same heat; and photographic record. FAI approval must be given in writing before purchase order release.
The minimum test pressure is 1.5× MWP per ASME B31.3 (hydrostatic) or 1.1× MWP per ASME B31.3 Chapter VIII (pneumatic). Test duration is minimum 10 minutes at sustained test pressure with zero visible leakage. For subsea or buried system flanges, test pressure is raised to 2.0× MWP with a 30-minute hold. Test medium is clean water with ≤ 50 ppm chloride for stainless steel systems.
Applications by Industry Sector
Wellhead control system (WCS) hydraulic lines, BOP accumulator skid piping, subsea tree hydraulic control umbilical terminations. Code 62 flanges in duplex 2205 or super duplex are the standard specification for subsea and offshore topside hydraulic control circuits. NACE MR0175 compliance, 3.2 MTC, TPI witness and HPHT material qualification are project-standard requirements.
Turbine lube oil supply and return piping, hydraulic governor actuator circuits and turning gear hydraulic drives. A105 normalised flanges with phosphate coating for mineral oil service below 120°C. For plants with phosphate ester fire-resistant hydraulic fluid (Fyrquel), 316L SS flanges with FKM O-rings are mandatory — phosphate esters degrade carbon steel surfaces and NBR elastomers.
Control valve actuators, hydraulic presses and catalyst injection circuits use 316L SS or alloy steel flanges with electroless nickel-coated bores for chemical resistance. For LNG terminal applications, A350 LF2 flanges with Charpy impact certification to −46°C are specified. In hydrogen generation and compression facilities, 316L SS or duplex 2205 are preferred — carbon steel flanges above 620 MPa yield strength are excluded from hydrogen-wetted circuits. ASME B31.12 requires helium leak testing by mass spectrometry at 1.5× MWP to confirmed zero leakage.
Mining equipment, offshore cranes, large presses and marine deck machinery. Code 62 in A105 normalised material with zinc-nickel coating. Split flanges preferred in confined cavities. Thread-locking compound and lockwire on bolt heads are standard assembly specifications for this duty class.
Export Packaging and Preservation
- Individual polyethylene bore caps installed on all bores and ports immediately post-inspection
- High-density polyethylene flange face protectors bolted or banded to each face
- VCI (Volatile Corrosion Inhibitor) poly film wrapping of each flange or batch
- Silica gel desiccant packets within sealed VCI bags — minimum 30 g per kg of metal
- Batch packing in polypropylene-lined steel or plywood boxes with foam void fill
- ISPM-15 heat-treated timber certification on all wood packing material for phytosanitary compliance
- Outer crate markings: PO number, item tag, material grade, heat number, quantity, gross weight, shipping marks
- MTC and packing list in waterproof envelope attached to exterior of crate
Hydraulic flanges in duplex, super duplex or Inconel alloys destined for certain countries may be subject to export control classification under EAR (Export Administration Regulations). Confirm end-use country and end-user declaration requirements with compliance team before committing lead time.
| # | Document | Standard / Reference | Minimum Requirement |
|---|---|---|---|
| 01 | Material Test Certificate (MTC) | EN 10204 3.1 / 3.2 | 3.2 mandatory for offshore / NACE service |
| 02 | Dimensional Inspection Report | SAE J518 / ISO 6162 | 100% critical features on FAI; AQL on production batches |
| 03 | Heat Treatment Certificate | ASTM A105 / A182 | All normalised and Q&T batches |
| 04 | Hardness Test Report | NACE MR0175 / project spec | Mandatory for NACE service; AQL for others |
| 05 | NDT Reports (UT, MPI, LPI) | ASTM E709 / E165 / A388 | As per approved Inspection and Test Plan (ITP) |
| 06 | Pressure Test Certificate | ASME B31.3 / ISO 4413 | All assemblies — 1.5× MWP minimum, 10 min hold |
| 07 | PMI Report | XRF / OES per project spec | 100% of SS, duplex and alloy steel items |
| 08 | First Article Inspection (FAI) Report | Project QAP | New part / new supplier / custom flange — mandatory |
| 09 | ISO 9001 Certificate | ISO 9001:2015 | Current; scope must include flange manufacture |
| 10 | Packing List / Material Traceability Record | Project MRB format | Batch / heat-number-level traceability to PO line item |
| 11 | Mill Certificates for Raw Material | EN 10204 3.1 (back-to-back) | Required for 3.2 MTC compliance chain |
| 12 | ATEX / CE Declaration (if applicable) | 2014/34/EU | Components within EU machinery directive scope |
| 13 | Corrosion Inhibitor / VCI Certificate | VCI supplier datasheet | Preservation-sensitive alloys in long-term storage |
| 14 | ISPM-15 Phytosanitary Certificate | IPPC / FAO | All wood packaging for international export |
RR Hydraulics manufactures hydraulic flanges — Code 61, Code 62, Split, Square, Rectangular and Custom — in carbon steel (A105), stainless steel (316L) and duplex grades (F51/F53) with full EN 10204 3.1/3.2 documentation capability and ISO 9001:2015 QMS. In-house CMM dimensional inspection, surface profilometry, PMI and hardness verification. Export packing and complete project documentation packages prepared to individual EPC project ITP requirements. TPI witness inspections by BV, DNV, Lloyds, SGS and TÜV routinely accommodated.