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Certifications: EN 10204 3.1 / 3.2 material test certificates, NACE MR0175 / ISO 15156 compliance, TPI inspection coordination, and complete export documentation packages.
ANSI B16
Flanges,
Fittings & Valves
A world-class technical reference for EPC contractors, piping and mechanical engineers, procurement heads, and TPI inspection agencies specifying ANSI/ASME B16 series flanges, fittings, gaskets, and valves — covering pressure-class rating logic, dimensional standards, material grade selection, manufacturing route, inspection protocol, and the specific interchangeability rules that govern ANSI B16 hardware on Oil & Gas, Power, Petrochemical, and LNG projects.
Pressure Classes
& Rating Logic
ANSI B16 is the dimensional and pressure-rating framework governing virtually every flanged, welded, and threaded pipe connection in North American and internationally-referenced EPC piping systems — the umbrella designation covers flanges, fittings, gaskets, bolting, and valves as a single interoperable dimensional system.
1.1 — What “ANSI B16” Actually Covers
“ANSI B16” is not a single document — it is a family of dimensional and pressure-rating standards originally issued by the American National Standards Institute and now maintained and published exclusively by ASME (the American Society of Mechanical Engineers). The legacy prefix “ANSI B16.x” and the current designation “ASME B16.x” refer to the identical standard body of work; procurement specifications frequently still cite “ANSI B16.5” interchangeably with “ASME B16.5,” and EPC engineers must treat the two designations as equivalent unless a specific revision date creates a material difference. The B16 family defines the face-to-face dimensions, bolt circle diameters (BCD), bolt hole patterns, flange outside diameters, thicknesses, facing types, and pressure-temperature ratings for flanges (B16.5, B16.47), butt-weld and forged fittings (B16.9, B16.11, B16.28), gaskets (B16.20, B16.21), flanged and butt-welding end valves (B16.34), orifice flanges (B16.36), and spectacle blinds / line blanks (B16.48) — together forming the dimensional backbone that allows a flange manufactured in one country, under one manufacturer’s forge, to bolt up correctly against a valve, fitting, or another flange manufactured anywhere else in the world, provided both parties conform to the same B16 standard and pressure class.
This interchangeability is the entire commercial and engineering value of the B16 system: an EPC contractor sourcing a Class 300 RF weld-neck flange from a supplier in India will mate correctly, without field modification, to a Class 300 RF valve manufactured in the United States and a Class 300 RF blind flange manufactured in South Korea — provided all three components are certified to the applicable B16 standard, NPS, and pressure class. Any deviation from the governing B16 dimensional table — even a difference of 1–2 mm in bolt circle diameter or bolt hole size — renders the component non-interchangeable and creates a bolt-up failure at site, which is why B16 compliance verification (dimensional inspection against the published tables) is a mandatory QC checkpoint on every EPC flange and fitting shipment, not a formality.
1.2 — Why Flanged Joints Are Specified Over Threaded or Welded Connections
Maintainability & Disassembly
Flanged joints (B16.5 / B16.47) are the only pipe connection method that permits repeated disassembly and reassembly without cutting the pipe — essential at valve connections, equipment nozzles, strainers, and any point in the circuit requiring periodic maintenance, inspection, or component replacement. Threaded joints degrade on repeated make/break cycles (thread galling, sealant breakdown); welded joints require cutting and re-welding for any disassembly. Flanged connections are mandatory at all equipment tie-in points, control valve stations, and any location identified for future maintenance access in the P&ID.
Pressure-Temperature Range & Large Bore
Threaded (NPT/BSPT) connections are limited by ASME B16.5 Note guidance and B31.3 to smaller NPS (typically ≤ 2″) and to pressure classes with adequate wall thickness at the thread root — threads inherently remove material and create a stress concentration that limits pressure-temperature capability. Flanged joints extend the full B16.5 pressure-temperature envelope (Class 150 through 2500) across the complete NPS 1/2″–24″ range, and B16.47 extends flanged connections to NPS 60″ — no equivalent threaded or socket-weld solution exists at these bore sizes.
Thermal Cycling & Fatigue Tolerance
Welded joints in high-thermal-cycling service (steam, thermal oil, cryogenic LNG) accumulate fatigue damage at the weld toe over repeated heat-up/cool-down cycles — a properly torqued flanged joint with a correctly selected gasket (spiral wound per B16.20) accommodates thermal expansion differential between the flange and bolting through elastic bolt stretch without the crack-initiation risk inherent to a welded heat-affected zone. Flanged joints are preferred at expansion loops, thermal cycling equipment nozzles, and any point identified for high-cycle fatigue service in the piping stress analysis.
Dissimilar Material & Equipment Tie-In
Flanged joints are the standard method for connecting dissimilar pipe materials (carbon steel to stainless, carbon steel to duplex) without a dissimilar-metal weld — bolting a carbon steel flange to a stainless steel flange through an appropriate gasket avoids the metallurgical complications (galvanic corrosion, differential thermal expansion cracking, weld filler metal compatibility) of a direct dissimilar-metal weld. All equipment nozzles (pumps, vessels, heat exchangers, valves) are supplied with flanged connections as the universal EPC tie-in interface.
1.3 — Pressure Class System: The Foundation of B16.5 / B16.47
ASME B16.5 and B16.47 do not rate flanges by a single maximum working pressure — they rate flanges by pressure class (150, 300, 400, 600, 900, 1500, 2500), and each pressure class carries a pressure-temperature rating table specific to the material group of the flange (e.g., Group 1.1 for A105 carbon steel; Group 2.8 for A182 F316/F316L stainless). The allowable working pressure of a given pressure class decreases as service temperature increases, because material yield and creep strength decrease with temperature — a Class 300 A105 flange rated 51.1 bar (740 psi) at 38°C (100°F) is rated only 20.4 bar (296 psi) at 425°C (800°F). The engineer must always verify the flange rating against the specific design temperature and material group from the applicable B16.5 Table 2 (or B16.47 Table) — never assume the “Class number” alone (e.g., “Class 300”) represents a fixed pressure value independent of temperature and material.
1.4 — Static vs. Dynamic Load Handling and Bolt Preload Behaviour
A B16.5/B16.47 flanged joint achieves sealing through compressive preload applied by the stud bolts (per B16.5 / ASME PCC-1 recommended bolting practice), compressing the gasket (spiral wound per B16.20, or ring-type joint per B16.20 for RTJ facings) between the two flange faces. The joint must maintain sufficient residual bolt preload — after accounting for gasket creep relaxation, thermal cycling, and internal pressure “hydrostatic end thrust” that attempts to separate the flanges — to keep the gasket compressed above its minimum seating stress (m and y factors per the applicable code, or Gb/Gs per ASME PCC-1 Appendix O) throughout the service life of the joint. Vibration loosening (bolt back-off under cyclic mechanical vibration, common on reciprocating compressor and pump piping) and thermal cycling relaxation (differential thermal expansion between bolt and flange material causing progressive preload loss) are the two dominant B16 flanged-joint failure modes in EPC service, and both are mitigated by correct initial bolt torque/tension (calculated, not “feel”-based), by bolt material selection matched to service temperature (A193 B7 studs with A194 2H nuts for standard service; B7M/2HM for NACE sour service; B16/4 for high-temperature creep service), and by periodic re-torque inspection on critical high-vibration or high-thermal-cycling flanged connections identified in the piping engineer’s bolted-joint integrity programme.
1.5 — Fatigue, Pressure Cycling and Miner’s Rule Reference
Flanged joints and the associated fittings in cyclic pressure service (compressor discharge lines, pulsating pump discharge, batch process piping) accumulate fatigue damage proportional to the number and magnitude of pressure cycles experienced over the design life. ASME B31.3 Chapter II, Part 5 (and B31.1 Appendix V for power piping) requires a fatigue evaluation using stress range and allowable cycle data where the number of significant pressure/thermal cycles exceeds the code threshold (typically 7,000 full-range cycles over design life, per B31.3 302.3.5). Where multiple stress ranges of differing magnitude occur, the linear cumulative damage rule (Miner’s Rule: ΣNi/Ni,allow ≤ 1.0, where Ni is the number of cycles actually experienced at stress range i, and Ni,allow is the number of cycles allowable at that stress range per the applicable fatigue curve) governs the acceptability of the joint and adjoining piping for the specified design life. B16.5/B16.47 flanges themselves are not independently fatigue-rated by the B16 standard — the fatigue evaluation is performed at the system level per B31.3/B31.1 using the flange neck and weld transition geometry as the governing stress concentration location, with the flange treated as a rigid boundary condition in the piping flexibility and stress model.
1.6 — Design Safety Factors by Application Category
| Application Category | Governing Code | Typical Design Margin Practice | Notes |
|---|---|---|---|
| General process piping | ASME B31.3 | Pressure class selected ≥ 1.0× MAWP at design temperature per B16.5 Table 2 rating | No arbitrary “extra” factor — code table rating is the governing allowable |
| Power piping (boiler / steam) | ASME B31.1 | Class selection includes allowance for steam-side thermal transients and creep at elevated temperature | B16.34 valve ratings referenced for flanged/BW valves |
| Sour service (H₂S) | NACE MR0175 / ISO 15156 | Hardness-limited material selection (≤ 22 HRC carbon steel; per-alloy limits for CRA); no separate pressure margin but material toughness/hardness controls | Governs material and heat treatment, not dimensional class |
| Cryogenic / LNG | ASME B31.3 Ch. IX | Low-temperature impact-tested material (Charpy V-notch per material spec) at minimum design metal temperature (MDMT) | Flange material impact testing mandatory below threshold temperature |
| Offshore / subsea | API 6A / API 17D + B16.5 hybrid | Class often up-rated one level above process requirement for corrosion allowance and TPI redundancy margin | Project-specific engineering standard governs final class selection |
Submit your class, NPS, facing, material grade, and quantity for a documented RFQ within 24 hours.
Facings, Dimensions
& Governing Standards
Every ANSI B16.5 and B16.47 flange type, facing, and pressure class carries a fixed dimensional table governing outside diameter, bolt circle, bolt hole size and count, thickness, and hub dimensions. RR Hydraulic manufactures to the complete applicable dimensional standard with full BCD/OD/thickness verification on every lot.
Submit class, NPS, facing, material grade, quantity, and application to sales@rrhydraulics.com for a certified offer.
2.1 — B16.5 Flange Types
Weld Neck (WN)
The highest-integrity B16.5 flange type — a tapered hub transitions smoothly from the flange body into the pipe wall thickness, butt-welded to the pipe, distributing bending stress gradually and minimising the stress concentration at the weld. Specified for all critical, high-pressure, high-temperature, cyclic, and severe-service piping. Full radiographic examination of the butt weld is standard practice on critical service WN flange installations.
Slip-On (SO)
The pipe is inserted into the flange bore and fillet-welded both inside and outside — lower cost and easier field fit-up than weld neck, but with a fatigue strength approximately 1/3 that of an equivalent weld-neck flange due to the discontinuous load path through two fillet welds. Used for low-pressure, non-cyclic, non-critical utility and low-hazard service piping where the cost saving outweighs the fatigue strength reduction.
Socket Weld (SW)
The pipe is inserted into a machined socket in the flange and fillet-welded at the hub — used for small-bore piping (typically NPS ≤ 2″) at higher pressure classes where a smooth internal bore (no weld root protrusion) is required, such as instrument and hydraulic lines. A 1.6 mm (1/16″) gap must be maintained between the pipe end and the socket bottom before welding to accommodate thermal expansion differential and prevent weld root cracking.
Threaded (THD)
Internally threaded to NPT (ASME B1.20.1) taper thread form, allowing a welder-free connection for low-pressure utility service, or for hazardous-area piping where welding (hot work) is restricted. Limited to lower pressure classes and smaller NPS per B16.5 Note guidance; not recommended for cyclic or high-temperature service due to thread root stress concentration and thermal cycling loosening risk.
Lap Joint (LJ)
A loose backing flange that rotates freely around a separate butt-welded stub end (per B16.9) — the flange itself never contacts the process fluid. Used where the flange must be rotated to align bolt holes without re-welding (frequent disassembly/reassembly points), or where the flange material must differ from the wetted stub-end material for cost or corrosion reasons (carbon steel LJ flange over a stainless stub end). Lower pressure rating than an equivalent WN flange due to the non-continuous load path.
Blind (BL)
A solid disc flange with no bore, used to seal the end of a piping run, a branch connection, or a vessel/equipment nozzle that is not currently in service. Blind flanges experience full internal pressure loading across the unsupported disc area and are checked for bending stress across the diameter per the flange design code — always the thickest flange type in a given pressure class and NPS.
2.2 — B16.47 Large-Diameter Flanges: Series A vs. Series B
Series A (formerly MSS SP-44)
Heavier, thicker flanges with a larger bolt circle diameter and larger/fewer bolts than Series B at the same NPS and class — originating from the API/MSS large-diameter flange standard, favoured on high-pressure and critical transmission pipeline applications (cross-country gas transmission, refinery high-pressure headers) where the additional wall thickness margin and bolting robustness are preferred despite the higher weight and material cost.
Series B (formerly API 605)
Lighter, more compact flanges with smaller bolt circle diameter and more, smaller-diameter bolts than Series A at the same NPS and class — originating from the API refinery large-diameter flange standard, favoured in refinery and petrochemical plant piping where weight and cost savings are prioritised and the service conditions do not demand the heavier Series A margin. Series A and Series B flanges are NOT interchangeable — a Series A flange will not bolt up to a Series B flange or valve at the same NPS/class due to differing BCD and bolt hole patterns.
2.3 — Flange Facing Types and Surface Finish
| Facing | Designation | Typical Ra Finish | Gasket Type Used | Application |
|---|---|---|---|---|
| Raised Face (RF) | Standard — 1.6 mm (1/16″) raised height, Class 150/300; 6.4 mm for higher classes | 3.2–6.3 µm (125–250 µin) serrated concentric or spiral | Spiral wound (B16.20), non-metallic (B16.21) | Default facing — majority of general process service |
| Flat Face (FF) | Full face, no raised portion | 3.2–6.3 µm | Full-face non-metallic or rubber gasket | Mating to cast iron flanges / low-pressure equipment nozzles (avoids overstressing brittle CI flange) |
| Ring Type Joint (RTJ) | Machined groove per B16.5 Table for oval or octagonal ring | 0.4–0.8 µm (16–32 µin) precision-machined groove | Metallic ring gasket (soft iron, low-carbon steel, SS, or alloy per service) | High-pressure / high-temperature critical service (Class 600 and above typical) |
| Male-Female (MF) | Raised male face + matching recessed female face | 3.2–6.3 µm | Confined flat gasket | Positive gasket location; moderate pressure critical joints |
| Tongue-Groove (TG) | Raised tongue + matching recessed groove | 3.2–6.3 µm | Confined flat or metal-jacketed gasket | Positive gasket confinement; prevents blow-out |
2.4 — Flatness Tolerance and Bolt-Up Quality
B16.5 specifies flange face flatness tolerance to ensure uniform gasket compression across the full face area — a warped or non-flat flange face causes localised gasket under-compression at one point of the circumference and over-compression at the opposite point, leading to a leak path even at full design bolt torque. Standard manufacturing practice controls flange face flatness within 0.05 mm per 25 mm of face diameter (or the tighter tolerance specified in the project piping material specification for critical or high-pressure service), verified by straight-edge and feeler gauge or optical flatness measurement prior to final QC release. RTJ groove machining tolerance is significantly tighter — typically ±0.05 mm on groove depth and width — because the metallic ring gasket relies on precise groove geometry for the initial cold-flow seating that creates the metal-to-metal seal.
2.5 — Dimensional Reference: Class 150 & Class 300 Weld Neck Flanges
| NPS | Class | Flange OD (mm) | Bolt Circle Ø (mm) | No. of Bolts | Bolt Size | Flange Thickness (mm) |
|---|---|---|---|---|---|---|
| 2″ | 150 | 152.4 | 120.7 | 4 | 5/8″ | 19.1 |
| 2″ | 300 | 165.1 | 127.0 | 8 | 5/8″ | 22.4 |
| 4″ | 150 | 228.6 | 190.5 | 8 | 5/8″ | 22.4 |
| 4″ | 300 | 254.0 | 200.0 | 8 | 3/4″ | 30.2 |
| 6″ | 150 | 279.4 | 241.3 | 8 | 3/4″ | 23.9 |
| 6″ | 300 | 317.5 | 269.9 | 12 | 3/4″ | 36.6 |
| 8″ | 150 | 342.9 | 298.5 | 8 | 3/4″ | 25.4 |
| 8″ | 300 | 381.0 | 330.2 | 12 | 7/8″ | 41.1 |
| 10″ | 150 | 406.4 | 362.0 | 12 | 7/8″ | 28.4 |
| 10″ | 300 | 444.5 | 387.3 | 16 | 1″ | 47.8 |
| 12″ | 150 | 482.6 | 431.8 | 12 | 7/8″ | 30.2 |
| 12″ | 300 | 521.1 | 450.9 | 16 | 1 1/8″ | 50.8 |
2.6 — Pressure Rating Reference (Group 1.1 Carbon Steel A105)
| Temperature | Class 150 | Class 300 | Class 600 | Class 900 | Class 1500 | Class 2500 |
|---|---|---|---|---|---|---|
| 38°C (100°F) | 19.6 | 51.1 | 102.1 | 153.2 | 255.4 | 425.6 |
| 100°C (212°F) | 17.7 | 46.5 | 92.9 | 139.4 | 232.4 | 387.3 |
| 200°C (392°F) | 15.3 | 39.9 | 79.8 | 119.8 | 199.6 | 332.6 |
| 300°C (572°F) | 13.4 | 35.4 | 70.8 | 106.2 | 177.0 | 295.0 |
| 400°C (752°F) | 11.2 | 30.6 | 61.2 | 91.9 | 153.2 | 255.4 |
| 425°C (797°F) | 9.7 | 28.4 | 56.9 | 85.3 | 142.2 | 237.0 |
Values indicative and rounded for engineering reference — always verify against the current-edition ASME B16.5 Table 2 for Material Group 1.1, and confirm the specific certified material grade and specification revision applicable to the project before final design use.
2.7 — Standards Compliance Framework
ASME B16.9 — Butt-Welding Fittings
Factory-made wrought butt-welding fittings (elbows, tees, reducers, caps, crosses) in NPS 1/2″–48″, dimensionally matched to B16.5 and B16.47 flange bore diameters and wall (schedule) thickness for direct butt-weld connection into piping systems without field fabrication of the fitting geometry.
ASME B16.11 — Forged Fittings
Forged socket-weld and threaded fittings (elbows, tees, couplings, unions, plugs) for small-bore piping (typically NPS ≤ 2″) at Class 2000, 3000, 6000, and 9000 socket-weld/threaded pressure classes — a separate class designation system from the B16.5 flange pressure classes, specific to small-bore forged fitting wall thickness.
ASME B16.20 / B16.21 — Gaskets
B16.20 governs metallic gaskets (spiral wound, ring-type joint, metal jacketed) for use with B16.5 flanges — dimensions, winding materials, and filler materials keyed to the flange facing and pressure class. B16.21 governs non-metallic flat gaskets (compressed fibre, PTFE, rubber) for lower-pressure RF and FF flange applications. Gasket selection is dictated by the flange facing type, pressure class, temperature, and process fluid compatibility.
ASME B16.25 — Buttwelding Ends
Standardises the bevel angle, root face, and wall thickness transition at the weld end of butt-welding fittings, flanges (WN and LJ stub ends), and valves — ensuring a consistent, weldable joint geometry regardless of manufacturer, matched to the pipe schedule per ASME B36.10M (carbon/alloy steel) or B36.19M (stainless steel).
ASME B16.34 — Valves, Flanged/Threaded/Welding End
Governs pressure-temperature ratings, materials, dimensions, and testing for flanged-end, butt-welding end, and threaded-end steel valves — the valve equivalent of the B16.5 flange rating table, using the identical pressure class and material group structure so that a B16.34 valve and a B16.5 flange of the same class and material group are directly rating-compatible.
ASME B16.36 & B16.48 — Orifice Flanges & Spectacle Blinds
B16.36 governs orifice flanges — a WN flange pair with tapped and drilled radial connections for orifice-plate flow measurement, dimensionally based on the parent B16.5 flange class. B16.48 governs spectacle blinds and line blanks (figure-8 blinds and spacers) used to positively isolate a piping section for maintenance, matched to the mating B16.5 flange OD, BCD, and thickness.
Heat Treatment &
Production Route
ANSI B16 flanges, fittings, and valves are manufactured from forged or hot-rolled steel in carbon, low-alloy, stainless, and duplex grades governed by ASTM material specifications, with heat treatment and manufacturing controls that determine mechanical performance and NACE compliance. See our complete materials reference for grade selection guidance.
3.1 — Material Grade Selection
ASTM A105 — Carbon Steel Forgings
The default material for B16.5/B16.47 flanges in general process, oil & gas, and power piping — normalized carbon steel forging, UTS 485 MPa min, yield 250 MPa min, elongation 22% min. Good weldability, widely available, cost-effective. Not suitable below -29°C without supplementary low-temperature impact testing; not suitable for sour/H₂S service above NACE hardness limits without normalizing heat treatment control.
ASTM A182 F-Grades — Alloy & Stainless Forgings
Covers forged flanges, fittings, and valve parts in low-alloy (F5, F9, F11, F22, F91) and austenitic stainless (F304, F304L, F316, F316L, F321, F347) and duplex/super duplex (F51, F53, F55) grades. F11/F22 chrome-moly grades for elevated-temperature hydrocarbon service (resist hydrogen attack per Nelson curves); F304/F316 for general corrosion resistance; F51 (2205 duplex) and F53 (2507 super duplex) for chloride-bearing and sour offshore service requiring higher strength and superior pitting/crevice corrosion resistance than austenitic grades.
ASTM A350 LF2 / LF3 — Low-Temperature Carbon Steel
LF2 (Class 1/2) and LF3 (3.5% Ni) carbon/low-alloy steel forgings for low-temperature service — LF2 impact-tested to -46°C, LF3 impact-tested to -101°C, both per Charpy V-notch testing on production test coupons. Specified for cryogenic and LNG-adjacent piping, cold climate installations, and any application where the minimum design metal temperature (MDMT) falls below the standard A105 impact-test-exempt threshold.
ASTM A193 / A194 — Bolting Materials
A193 governs alloy and stainless steel bolting material (studs) for high-temperature/high-pressure service: B7 (chrome-moly, standard general service), B7M (lower hardness, NACE MR0175 sour service), B8/B8M (stainless, for CRA flange bolting or cryogenic service). A194 governs the mating nuts: 2H (standard, matched to B7), 2HM (matched to B7M for sour service), 8/8M (stainless). Bolting material selection must match both the flange material group compatibility and the process NACE/sour service requirement.
3.2 — Heat Treatment Requirements
Normalizing
Heating the forged flange/fitting above the upper critical transformation temperature (typically 900–930°C for carbon steel) followed by air cooling, refining the grain structure for improved toughness and more uniform mechanical properties compared to the as-forged condition. Standard heat treatment for A105 flanges intended for NACE sour service (per ISO 15156 Part 2) and for any application requiring guaranteed Charpy impact values.
Quenching & Tempering (Q&T)
Used for low-alloy Cr-Mo grades (F11, F22, F91) and high-strength bolting (A193 B7) — quenching from austenitizing temperature followed by tempering at a controlled temperature to achieve the specified combination of strength and toughness. F91 (modified 9Cr-1Mo) requires precise Q&T control (normalize at ~1040-1080°C, temper at 730-800°C) to achieve the creep-strength-enhanced microstructure required for its elevated-temperature power/HRSG service rating.
Solution Annealing (Austenitic Stainless)
Heating austenitic stainless (F304, F316 etc.) to 1040–1150°C followed by rapid water quench, dissolving chromium carbides back into solid solution to restore full corrosion resistance and prevent sensitization (grain boundary chromium depletion that causes intergranular corrosion). Mandatory heat treatment step after hot forging of all stainless B16.5 flanges before final machining.
Solution Annealing (Duplex / Super Duplex)
Duplex (F51) and super duplex (F53/F55) require tightly controlled solution annealing (1020–1100°C for duplex; 1040–1120°C for super duplex) followed by rapid water quench, to achieve the target 50/50 austenite-ferrite phase balance. Incorrect annealing temperature or insufficiently rapid quench allows precipitation of embrittling intermetallic phases (sigma phase) that severely reduce impact toughness and corrosion resistance — duplex/super duplex heat treatment records and post-treatment ferrite content verification (per ASTM E562 or magnetic ferrite measurement) are mandatory QC checkpoints.
Stress Relieving (PWHT)
Post-weld heat treatment applied to welded fabrications incorporating B16.5/B16.47 flanges (e.g., flanged spool pieces) where wall thickness, material grade, or service (sour, cyclic, low-temperature) requires stress relief per the applicable code (ASME B31.3 Table 331.1.1) to reduce residual welding stress and, for certain sour-service applications, to meet NACE MR0175 hardness requirements in the weld and heat-affected zone.
NACE MR0175 / ISO 15156 Hardness Control
For H₂S-containing (sour) service, all pressure-boundary materials — including B16.5 flanges, B16.9 fittings, and bolting — must meet maximum hardness limits (typically 22 HRC for carbon/low-alloy steel; alloy-specific limits for CRA materials) verified by production hardness testing per ISO 15156 Part 2/3. This drives the requirement for normalized (not as-forged) carbon steel, and for controlled PWHT of any welded assembly, to keep the heat-affected zone hardness within the sour-service limit.
3.3 — Manufacturing Process: Forging vs. Bar Stock / Plate
| Route | Grain Flow | Typical Use | Governing Spec | Engineering Note |
|---|---|---|---|---|
| Closed-die forging | Continuous, radial grain flow following flange contour — optimal fatigue/impact properties | Standard for all critical-service B16.5/B16.47 flanges | ASTM A105 / A182 (forged) | Preferred and, in most project specifications, mandatory route for pressure-retaining flanges |
| Plate / bar stock machined | Rolled grain flow, not radially oriented to flange geometry — lower transverse toughness | Non-critical, low-pressure, large-diameter special/custom flanges where forging is impractical | ASTM A105 (plate) with project engineering approval | Requires explicit project specification deviation approval — many EPC specs prohibit plate flanges for pressure service above Class 300 |
Closed-die forging produces a continuous, uninterrupted grain flow that follows the contour of the flange hub and bolt circle — this grain orientation provides superior transverse toughness and fatigue resistance compared to a flange machined from plate or bar stock, where the rolling grain direction is fixed and does not align with the hoop and radial stress directions the flange experiences in service. Virtually all EPC piping material specifications mandate forged construction (ASTM A105, A182) for B16.5 and B16.47 flanges in pressure service; plate or bar-stock flanges are restricted to low-pressure, non-critical, or large special-diameter applications where a suitable forging die does not exist and a documented engineering deviation has been approved.
3.4 — CNC Machining Tolerances for Critical Features
- Bore diameter: Machined to the schedule/wall thickness specified for the mating pipe, per B36.10M/B36.19M — bore tolerance typically ±0.4 mm for standard NPS, tighter for critical instrument or orifice-adjacent bores
- Raised face height and diameter: Per B16.5 Table dimensions — raised face height 1.6 mm (Class 150/300) or 6.4 mm (Class 400 and above), controlled to ±0.4 mm
- Bolt hole diameter and position: Bolt circle diameter (BCD) held to ±0.4 mm; bolt hole diameter per B16.5 Table (typically bolt diameter + 1.6–3.2 mm clearance); angular bolt hole spacing controlled to prevent cumulative error around the full circle that would prevent bolt-up
- RTJ groove dimensions: Groove depth, width, and angle machined to ±0.05–0.10 mm — the tightest tolerance on the flange, since the RTJ metallic gasket relies on precise cold-flow seating geometry for the seal
- Flange face flatness: Controlled within 0.05 mm per 25 mm of face radius, verified by dial indicator sweep or optical flatness gauge before final release
- Hub/neck taper (weld neck flanges): Taper angle and transition length per B16.5 Table, verified by profile gauge or CMM on critical service flanges
3.5 — Surface Finish and Hydraulic Cleanliness for Bore Surfaces
While B16.5/B16.47 flanges are not typically subject to the ISO 4406 hydraulic fluid cleanliness classification applied to hydraulic system components, flanges supplied for hydraulic power unit manifolds, control valve stations, and instrument piping in hydraulic and lubrication systems require bore and face cleaning to remove machining swarf, cutting fluid residue, and mill scale before shipment. Standard practice: bore and face degreasing (solvent wipe or vapour degrease), followed by visual and, for critical hydraulic service, white-cloth wipe verification, with bore caps and flange face protectors fitted immediately after cleaning to prevent recontamination during transit and site storage.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified forging heat to finished, tested, and packed ANSI B16 flange, fitting, and valve component shipment. Dimensional verification, NDT, PMI, hardness, hydrostatic testing, and complete export documentation are standard on all project-grade B16 supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 Material Test Certificate Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific test report | Not acceptable for EPC pressure components | Never for pressure-retaining B16 flanges, fittings, or valves |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report, self-certified by manufacturer’s QC | Mandatory — all EPC B16 hardware | All process, hydrocarbon, and utility piping components |
| 3.2 (EN 10204) | 3.1 report + independent third-party inspection agency countersignature | Offshore critical; sour service; high-hazard piping classes | Class 900 and above typical; sour/NACE service; offshore/subsea; owner-specified critical line list items |
4.3 — Applications by Industry
4.4 — Torque and Preload Reference
| Bolt Size | Class | Dry Torque (N·m) | Lubricated Torque (N·m) | Approx. Bolt Preload (kN) |
|---|---|---|---|---|
| 5/8″ | 150 | 95 | 68 | 48 |
| 5/8″ | 300 | 105 | 75 | 53 |
| 3/4″ | 150 | 170 | 122 | 71 |
| 3/4″ | 300 | 190 | 136 | 79 |
| 7/8″ | 150 | 270 | 193 | 97 |
| 7/8″ | 300 | 300 | 215 | 108 |
| 1″ | 150 | 410 | 293 | 127 |
| 1″ | 300 | 460 | 329 | 142 |
Indicative values for engineering reference only — final bolt torque must be calculated per ASME PCC-1 Appendix O (or the project’s bolted-joint procedure) using the actual gasket factor, target seating stress, friction coefficient, and lubricant condition for the specific joint, and verified by a calibrated torque or tensioning tool at site.
K = Nut factor / friction coefficient (typ. 0.20 dry steel-on-steel; 0.14–0.16 lubricated)
D = Nominal bolt diameter (m)
F = Target bolt preload / axial tension (N)
Design check — gasket seating and separating force:
The total bolt preload around the joint must exceed the sum of (a) the minimum gasket seating load (m × gasket contact area, per the applicable gasket factor) and (b) the hydrostatic end force generated by internal pressure acting on the gasket effective area (F_H = P × π/4 × G², where G is the gasket reaction diameter), with an additional safety margin to prevent joint separation under pressure and thermal transients.
K = 0.20, D = 0.01905 m, target preload F = 50,000 N
T = 0.20 × 0.01905 × 50,000 = 190.5 N·m — consistent with the Class 300 dry torque reference above.
This torque must be verified against the specific gasket’s minimum seating stress requirement and the joint’s calculated hydrostatic end force at design pressure before finalising the bolt-up procedure.
4.5 — Export Packaging Specification
- Flange bore, raised face, and RTJ groove surfaces coated with rust-preventive oil or VCI (vapour corrosion inhibitor) compound immediately after final QC release and before packing — bare machined carbon steel surfaces flash-corrode within days in humid ocean-freight container conditions
- Bore caps (plastic or plywood) fitted to all flange bores and threaded connections to prevent ingress of moisture, dust, and foreign material during transit and site storage — mandatory for all hydraulic, instrument, and critical process service flanges
- Individual wooden crating (ISPM-15 certified) for large-diameter (NPS ≥ 12″) and heavy flanges/valves; palletised and strapped packing for smaller NPS bulk shipments, with dunnage separating flange faces to prevent face-to-face contact damage during transit
- Each flange, fitting, and valve permanently stamped with heat number, NPS, class, material grade, and manufacturer identification per B16.5/B16.47 marking requirements — verified legible before packing, since heat number traceability is the link between the physical item and its material test certificate at site receiving inspection
- Documentation in a waterproof pouch attached to the crate/pallet exterior, and a duplicate set couriered separately: EN 10204 3.1/3.2 MTC, dimensional inspection report, NDT reports (UT/MPI/LPI), PMI report, hardness report, hydrostatic test certificate (valves), NACE compliance declaration (where applicable), TPI witness certificate (where applicable), packing list, and certificate of origin
4.6 — Complete Documentation Package for EPC Project Supply
| # | Document | Standard / Format | Mandatory / Conditional | Notes |
|---|---|---|---|---|
| 01 | Material Test Certificate | EN 10204 3.1 / 3.2 | Mandatory — all EPC supply | Heat-traceable; chemical + mechanical results |
| 02 | Dimensional Inspection Report | ASME B16.5 / B16.47 tables | Mandatory | OD, BCD, bolt holes, thickness, face height/flatness |
| 03 | Chemical Composition Report | ASTM A105 / A182 / A350 grade limits | Mandatory | Per heat; cross-referenced to MTC |
| 04 | Mechanical Properties Report | ASTM A370 | Mandatory | UTS, yield, elongation, Charpy (where specified) |
| 05 | Ultrasonic Testing Report | ASTM A388 | Mandatory — critical / high-pressure class | Volumetric forging integrity |
| 06 | MPI / LPI Surface NDT Report | ASTM E709 (MPI) / E165 (LPI) | Mandatory — critical service | Post-machining surface crack detection |
| 07 | PMI Report (XRF/OES) | Per project QA/QC procedure | Mandatory — alloy/stainless/duplex/CRA | Grade verification; 100% for alloy items |
| 08 | Hardness Test Report | ASTM E10 / E18; NACE MR0175 limits | Mandatory — sour service; conditional otherwise | Confirms heat treatment and NACE compliance |
| 09 | NACE MR0175 / ISO 15156 Compliance Declaration | ISO 15156 Parts 2/3 | Conditional — sour / H₂S service | Material and hardness compliance statement |
| 10 | Hydrostatic Test Certificate | API 598 / B16.34 | Mandatory — valves | Shell and seat test pressure, hold time, result |
| 11 | First Article Inspection (FAI) Report | Project-specific format | Mandatory — new project specifications | All parameters; before batch production |
| 12 | TPI Witness Certificate | SGS / BV / DNV / Lloyd’s / TÜV | Conditional — critical / offshore / owner-specified | Co-witness dimensional + NDT + hydro + PMI |
| 13 | ISO 9001:2015 Certificate | Third-party QMS certification | Mandatory — EPC projects | Scope covers flange/fitting/valve manufacture |
| 14 | Country of Origin + Packing List | Chamber of Commerce / item-level | Mandatory | HS tariff code; grade and class on packing list per item |
| 15 | Commercial Invoice + Bill of Lading | Per INCOTERMS 2020 | Mandatory | Freight forwarder issued |
Submit your class, NPS, facing, material grade, and quantity to RR Hydraulic for a complete, certified commercial offer.