Nickel Alloy Flanges - Grades, Pressure Classes & Standards
Date: 2025年9月12日 Categories: News Views: 344
By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Quick Answer: How Do You Specify a Nickel Alloy Flange?
A nickel alloy flange is specified by four things: the alloy grade (for example Inconel 625, UNS N06625), the dimensional and material standard (ASTM B564 forgings rated to ASME B16.5 or EN 1092-1), the pressure class or PN rating at service temperature, and the facing type with its matching gasket.
Key Takeaways
- Grade selection follows the service, not the price. Chloride and reducing-acid duty points to Ni-Cr-Mo (C-276, UNS N10276); strongly oxidizing media to C-22 or Alloy 20; cryogenic and seawater duty to Nickel 200 or Monel 400; high-temperature strength to Inconel 625 or 718.
- Forgings are the default for flanges above Class 300. ASTM B564 is the governing material specification for nickel alloy forgings; plate may be used only for blind and reducing flanges without hubs, where the standard permits it.
- Pressure class is a temperature-dependent rating, not a fixed pressure. A Class 150 nickel alloy flange that carries about 20 bar at ambient carries almost nothing at 550 °C, and ASME B16.5 sets a maximum service temperature per alloy — 675 °C for N10276 and 538 °C for N08825.
- Face finish and gasket choice cause more plant leaks than material grade does. RF, FF, RTJ and tongue-and-groove faces are not interchangeable, and the surface finish of the raised face must match the gasket the piping engineer specified.
- The certificate is not the verification. EN 10204 3.1 and 3.2 documents plus positive material identification is the only way to prove that the flange on the pallet is the alloy on the drawing.
- Standard systems do not convert automatically. An ASME B16.5 Class 150 flange and an EN 1092-1 PN 20 flange are rated differently and are not guaranteed to bolt up even when the DN and bolt circle look close.
Which Nickel Alloy Grades Are Used for Flange Forgings?
Flange forgings are made from seven families of nickel-base alloy, and each family exists because one service condition defeats the others. The nickel-chromium-molybdenum family handles chlorides and reducing acids; the nickel-chromium-iron family handles high temperature and oxidation; the nickel-iron-chromium family handles sulphuric and phosphoric acid at moderate cost; the nickel-copper family handles seawater, hydrofluoric acid and cryogenic service; pure nickel handles caustic; and the niobium-stabilised austenitic Alloy 20 handles sulphuric acid where its copper addition is the deciding feature. Choosing between them is a corrosion and temperature decision, and the flange standard is chosen afterwards.
The most important practical point is that a nickel alloy flange is a forging in almost every case. A forging consolidates the ingot, closes porosity and produces the metal flow that ASME B16.5 asks for in the hub and the fillet. Plate is permitted only for blind and reducing flanges without hubs in the material groups that allow it, and it is not acceptable for a welding-neck flange in wet chloride or cyclic service because the through-thickness properties and the short-transverse ductility are simply poorer. In ASME B16.5 the nickel alloys sit in their own material groups, and the Ni-Cr-Mo and Ni-Cr-Fe grades used for flanges are rated in group 3.8, whose governing documents are ASTM B564 forgings and ASTM B462, ASTM B575 and ASTM B443 plate.
| Alloy (common name) | UNS | W.Nr | Chinese designation | Typical flange service | Grade family |
|---|---|---|---|---|---|
| Inconel 625 | N06625 | 2.4856 | GH3625 (per GB/T 14992) | Wet chloride, mixed acid, high-temperature oxidation, subsea | Ni-Cr-Mo-Nb |
| Inconel 718 | N07718 | 2.4668 | GH4169 | High-strength bolting-linked flanges, cryogenic, aerospace-adjacent | Ni-Cr-Fe-Nb |
| Inconel 600 | N06600 | 2.4816 | GH3600 | Caustic, high-temperature, general corrosion | Ni-Cr-Fe |
| Hastelloy C-276 | N10276 | 2.4819 | NS334 (verify current grade list) | Chlorides, reducing acids, flue-gas desulphurisation | Ni-Cr-Mo-W |
| Hastelloy C-22 | N06022 | 2.4602 | (verify) | Wet chlorine, hypochlorite, ferric and cupric chloride | Ni-Cr-Mo-W |
| Incoloy 825 | N08825 | 2.4858 | NS142 | Sulphuric and phosphoric acid, seawater-cooled exchangers | Ni-Fe-Cr-Mo-Cu |
| Incoloy 800H / 800HT | N08810 / N08811 | 1.4958 / 1.4959 | GH1280-series (verify) | Steam reformer, cracking furnace, high-temperature ducting | Ni-Fe-Cr |
| Monel 400 | N04400 | 2.4360 | NCu30 (verify) | Hydrofluoric acid, seawater, cryogenic | Ni-Cu |
| Monel K-500 | N05500 | 2.4375 | (verify) | Pump and valve trim, high-strength wet service | Ni-Cu-Al-Ti |
| Nickel 200 / 201 | N02200 / N02201 | 2.4066 / 2.4068 | N6 / N7 (per GB/T 2054) | Caustic soda, high-purity chemical, electronic-grade | Commercially pure Ni |
| Alloy 20 (Carpenter 20Cb-3) | N08020 | 2.4660 | NS1403 | Sulphuric acid, mixed acid, pickling lines | Ni-Cr-Fe-Cu-Nb |
Table note: Grade designations are the commonly published equivalents. UNS numbers are the American designation per ASTM E527; W.Nr numbers are the German/European designation; Chinese designations are quoted from the GB/T 14992 superalloy designation system and from the GB/T 2054 nickel and nickel alloy plate and sheet standard. Cross-system designations are equivalent in intent and chemistry family, not identical in every element limit, so the controlling specification must be named on the drawing. Items marked (verify) should be confirmed against the current edition of the Chinese grade list before the designation is printed on a purchase order.
What changes when you move from one family to another? The nickel-chromium-molybdenum grades resist localised attack in chloride because their molybdenum content is high; the molybdenum is also what makes them expensive and what makes them difficult to hot-work into a hub. The nickel-iron-chromium grades (825, 800H) are cheaper and easier to forge, but they top out in chloride service and are not an appropriate substitute for C-276 in a wet chlorine header. The nickel-copper family is unique in resisting hydrofluoric acid and in staying ductile to cryogenic temperatures, which is why Monel 400 flanges appear on LNG and HF alkylation lines where no stainless grade is acceptable. If you are comparing families for a specific stream, our Hastelloy and Inconel product pages list the stock forms and grades, and the technical knowledge centre holds the corrosion tables behind these recommendations.
What Are the Standard Chemical Composition Limits for Nickel Alloy Flanges?
Composition limits for a nickel alloy flange come from the forging specification named on the order — normally ASTM B564, with ASTM B637 for the precipitation-hardening grades — and those limits are the same chemistry table used for the wrought product of the same alloy. The limits below are the published ranges and maxima for the grades most often bought as flanges, and the table gives the source standard for each. Only the principal discriminators are shown; every specification also carries limits for cobalt, copper, phosphorus and sulphur that a substituting supplier tends to overlook.
| Element (wt %) | Inconel 625 N06625 | Inconel 718 N07718 | Hastelloy C-276 N10276 | Incoloy 825 N08825 | Monel 400 N04400 | Nickel 200 N02200 | Alloy 20 N08020 | Per standard |
|---|---|---|---|---|---|---|---|---|
| Ni | 58.0 min (bal.) | 50.0-55.0 | balance | 38.0-46.0 | 63.0 min | 99.0 min (+Co) | 32.0-38.0 | ASTM B564 / B637 / B462 |
| Cr | 20.0-23.0 | 17.0-21.0 | 14.5-16.5 | 19.5-23.5 | — | — | 19.0-21.0 | ASTM B564 / B637 |
| Fe | 5.0 max | balance | 4.0-7.0 | 22.0 min | 2.5 max | 0.40 max | balance | ASTM B564 |
| Mo | 8.0-10.0 | 2.80-3.30 | 15.0-17.0 | 2.5-3.5 | — | — | 2.0-3.0 | ASTM B564 / B637 |
| Cu | — | 0.30 max | — | 1.5-3.0 | 28.0-34.0 | 0.25 max | 3.0-4.0 | ASTM B564 / B462 |
| Nb (+Ta) | 3.15-4.15 | 4.75-5.50 | — | — | — | — | 8 x C min, 1.00 max | ASTM B564 / B637 |
| W | — | — | 3.0-4.5 | — | — | — | — | ASTM B564 / B575 |
| Ti | 0.40 max | 0.65-1.15 | — | 0.6-1.2 | — | — | — | ASTM B564 / B637 |
| Al | 0.40 max | 0.20-0.80 | — | 0.2 max | — | — | — | ASTM B564 / B637 |
| C | 0.10 max | 0.08 max | 0.010 max | 0.05 max | 0.30 max | 0.15 max | 0.07 max | ASTM B564 |
| Mn | 0.50 max | 0.35 max | 1.00 max | 1.00 max | 2.00 max | 0.35 max | 2.00 max | ASTM B564 |
| Si | 0.50 max | 0.35 max | 0.08 max | 0.50 max | 0.50 max | 0.35 max | 1.00 max | ASTM B564 |
| S | 0.015 max | 0.015 max | 0.030 max | 0.030 max | 0.024 max | 0.010 max | 0.035 max | ASTM B564 |
| Product condition | annealed | solution + aged | solution annealed | annealed | annealed | annealed | stabilized annealed | ASTM B564 |
Table note: Limits are the values published for the corresponding grades in ASTM B564 (nickel alloy forgings), ASTM B637 (precipitation-hardening nickel alloy bars and forgings), ASTM B462 (Ni-Cr-Fe and Ni-Cu alloy forgings) and ASTM B575 (low-carbon Ni-Cr-Mo plate) — verify against the current edition of the controlling specification before release. "balance" means the element is not separately limited and makes up the remainder. Carbon and sulphur limits are shown because they are the two numbers that separate a genuine flange forging from a downgraded or re-melted substitute, and the tungsten column in C-276 is what separates it from C-4 or from an Alloy 59 type that is chemically similar but not identical.
Why the chemistry table matters at the flange and not just at the mill. A flange is the highest-stress, highest-restraint item in most piping systems, and it is also the item most likely to be sourced from a second-tier forge shop when a project is running late. Two failure patterns follow. First, a supplier substitutes a lower-molybdenum Ni-Cr-Mo grade that passes a visual inspection and a hardness check but has no tungsten and a different molybdenum range, and the flange then suffers crevice corrosion under the gasket within the first year. Second, a precipitation-hardening grade such as 718 is supplied in the solution-treated rather than the aged condition, which passes the chemistry check and fails the strength requirement. Both are caught by the same two actions: read the certificate against the specification table, and verify the actual heat by X-ray fluorescence on receipt. Our Monel and pure nickel product lines are released against the mill certificate and re-checked before dispatch for exactly this reason.
Mechanical Properties at Room and Elevated Temperature
Room-temperature requirements for a nickel alloy flange are the minimum tensile properties published in the forging specification, and they apply in the heat-treatment condition that specification names. Elevated-temperature behaviour is a different question: the specification sets no high-temperature minimum for most of these grades, so the high-temperature design basis is the allowable stress in ASME B31.3 or ASME Section II Part D, and the pressure-temperature rating in ASME B16.5. The table below separates the two so that nobody mistakes a standard minimum for a design allowable.
| Grade / UNS | Condition (heat treatment) | Temp | UTS | 0.2% yield | Elongation | Per standard |
|---|---|---|---|---|---|---|
| Inconel 625, N06625 | Annealed | 20 °C | 827 MPa (120 ksi) min | 414 MPa (60 ksi) min | 30% min | ASTM B564 |
| Inconel 718, N07718 | Solution treated + aged | 20 °C | 1240 MPa (180 ksi) min | 1035 MPa (150 ksi) min | 12% min | ASTM B637 |
| Hastelloy C-276, N10276 | Solution annealed | 20 °C | 690 MPa min | 283 MPa min | 40% min | ASTM B564 / B575 |
| Incoloy 825, N08825 | Annealed | 20 °C | 586 MPa min | 241 MPa min | 30% min | ASTM B564 / B425 |
| Monel 400, N04400 | Annealed | 20 °C | 550 MPa min | 240 MPa min | 30% min | ASTM B564 |
| Nickel 200, N02200 | Annealed | 20 °C | 462 MPa min | 148 MPa min | 40% min | ASTM B564 |
| Alloy 20, N08020 | Stabilised annealed | 20 °C | 551 MPa min | 241 MPa min | 30% min | ASTM B462 / B473 |
| Inconel 625, N06625 | Annealed | 600 °C | 550-700 MPa (typical) | 350-430 MPa (typical) | 40-60% (typical) | Typical producer data, not a standard minimum |
| Inconel 718, N07718 | Solution treated + aged | 650 °C | 950-1100 MPa (typical) | 750-850 MPa (typical) | 15-25% (typical) | Typical producer data, not a standard minimum |
| Hastelloy C-276, N10276 | Solution annealed | 400 °C | 560-620 MPa (typical) | 200-250 MPa (typical) | 50%+ (typical) | Typical producer data, not a standard minimum |
Table note: Room-temperature values are the minimum requirements stated in the cited ASTM product specifications for the condition shown, and the two precipitation-hardening grades require the ageing treatment specified in the standard before those minima apply. Elevated-temperature values are typical published producer data reported for information; they are not standard minima, and a design must use the allowable stress from ASME B31.3 or ASME Section II Part D, or the flange rating from ASME B16.5. Always verify minima against the current edition of the controlling specification — values are revised when the standard is revised.
What the pressure-temperature rating does at temperature. A flange rating is not a constant. ASME B16.5 rates each material group against temperature, and for the nickel alloys in group 3.8 the fall-off with temperature is steep for the low-chrome grades and gentler for the high-strength ones. The same group table also fixes the maximum service temperature for each alloy, and those limits matter more than the pressure curve at the top of the range.
| ASME B16.5 Class | −29 to 38 °C | 100 °C | 300 °C | 400 °C | 500 °C | 538 °C | 600 °C |
|---|---|---|---|---|---|---|---|
| Class 150 | 20.0 bar | 17.7 | 10.2 | 6.5 | 2.8 | 1.4 | 0 (not rated) |
| Class 300 | 51.7 bar | 51.5 | 42.9 | 36.5 | 28.2 | 25.2 | 21.6 |
| Class 600 | 103.4 bar | 103.0 | 85.7 | 73.3 | 56.5 | 50.0 | 42.9 |
| Class 900 | 155.1 bar | 154.6 | 128.6 | 109.8 | 84.7 | 75.2 | 64.2 |
| Class 1500 | 258.6 bar | 257.6 | 214.4 | 183.1 | 140.9 | 125.5 | 107.0 |
| Class 2500 | 430.9 bar | 429.4 | 357.1 | 304.9 | 235.0 | 208.9 | 178.5 |
Table note: Rating values for ASME B16.5 group 3.8 materials (nickel alloy forgings per ASTM B564 and ASTM B462, including UNS N06625, N10276, N06022, N06200, N08825), quoted for guidance in bar; design must use the current edition of ASME B16.5. Applicable temperature limits in the same group: N10276 not above 675 °C, N06625 not above 645 °C, N08825 not above 538 °C. Note the Class 150 column — a Class 150 flange in this group has no pressure rating at all above about 538-550 °C, which is one of the most common specification errors we see on high-temperature nickel alloy lines.
Five-Nation Standard Cross-Reference for Nickel Alloy Flanges
A nickel alloy flange can be ordered to American, Chinese, Japanese, German/European or Russian documents, and the systems are only partly interchangeable. In practice the dimensional standard and the material standard are separate choices, and they must be stated separately on the purchase order: it is entirely normal to buy an ASTM B564 forging machined to EN 1092-1 dimensions, and it is a serious error to assume that a PN number and a Class number mean the same thing. The table below maps the documents by function across the five systems.
| Function | US (ASTM / ASME / MSS) | China (GB / HG) | Japan (JIS) | Germany / EU (DIN / EN) | Russia (GOST) |
|---|---|---|---|---|---|
| Flange dimensions and ratings, NPS 1/2-24 (Class system) | ASME B16.5 | GB/T 9124.1 and the GB/T 9112-9124 series | JIS B2220 (10A-1500A, 5K-40K) | EN 1092-1, PN designated | GOST 33259-2015 (verify current edition) |
| Large-diameter flanges, NPS 26-60 | ASME B16.47 Series A (MSS SP-44) and Series B | GB/T 9124 series, large DN sizes | JIS B2220 (largest sizes) | EN 1092-1 (large DN) | GOST 33259-2015 |
| Orifice flanges | ASME B16.36 | HG/T 20592 (verify) | — | — | — |
| Weld-neck, slip-on, blind, lap-joint and threaded flange geometry | ASME B16.5 | GB/T 9115, GB/T 9116, GB/T 9119 and companion parts | JIS B2220 | DIN 2630 series (weld-neck PN 6-PN 40) and companion DIN types | GOST 12820-80 (flat welded), GOST 12821-80 (butt welded) |
| Flange face finish, RF and FF | MSS SP-6, ASME B16.5 | GB/T 9124.1 | JIS B2220 | EN 1092-1 | GOST 33259-2015 |
| Ring-joint groove geometry | ASME B16.5, ASME B16.20 | HG/T 20592 (verify) | JIS B2220 | EN 1092-1 | GOST 33259-2015 |
| Nickel alloy forgings, chemistry and mechanical properties | ASTM B564; ASTM B637 for the PH grades; ASTM B462 for Ni-Cr-Fe and Ni-Cu | GB/T 15007 (corrosion-resistant alloy grades), GB/T 2054 (nickel and nickel alloy plate and sheet) | JIS G3214 (stainless steel forgings for pressure vessels — verify applicability to nickel alloys) | EN 10095 and the relevant material data sheet for 2.xxxx grades | GOST 5632 (grade list, verify current edition) |
| Grade designation system | UNS (ASTM E527) | GB/T 14992 superalloy designation, GB/T 2054 for pure nickel | JIS grade designations | W.Nr / EN numeric designation | GOST grade designation |
| Inspection documents | ASTM E1476 PMI guide; mill certificate | GB/T 18253-type inspection documents (verify) | JIS mill certificate | EN 10204 (3.1 / 3.2) | GOST certificate with mill and third-party signatures |
| Gaskets for flanged joints | ASME B16.20 (metallic), ASME B16.21 (non-metallic) | HG/T 20612-series (verify) | JIS B2404 (verify) | EN 1514-1 and EN 1514-2 | GOST gasket standards (verify) |
Table note: Cross-references are given by function and scope; the documents are equivalents in intent, not interchangeable in every dimension, tolerance or rating value. Flange dimensions, bolt-hole pitch and face geometry differ between the ASME Class system and the EN PN system even where the nominal size matches, so the two systems must never be mixed on one joint. Items marked (verify) and every standard number in this table should be confirmed against the current edition of the document, and against the project's own material and dimensional specification, before it is printed on a purchase order. GB/T 9112-9124 is a series of standards and the exact part number depends on the flange type required.
How to use the cross-reference without creating a problem. Two rules cover almost every case. First, pick one dimensional system per piping system and stay in it: an ASME B16.5 Class 300 flange and an EN 1092-1 PN 50 flange may have similar pressure capability at ambient, but their outside diameters, bolt circles, bolt sizes and face diameters are not the same, and a joint made from one of each will not seal. Second, pick one material specification per flange and name it: "ASTM B564 UNS N06625, annealed" and "GH3625 to the Chinese superalloy grade list" describe the same alloy family, but only one of them is a legally controlling document in a given contract. Where the project spans both worlds — a Chinese fabrication to an American process licence, for example — the practical answer is to write the purchase specification against the American material standard and the buyer's dimensional standard, and to state the equivalence in a note rather than relying on it. Fabricators comparing routes for a flanged spool will find the same logic applied to wrought product on our Incoloy and Nimonic pages.
Pressure Classes and Temperature-Pressure Ratings: Class 150-2500 vs PN
A pressure class is not a pressure. Every Class or PN number in the standards is the label on a table, and the number you may actually use is read off that table at the design temperature, for the specific material group, from the current edition of the standard. The two label systems in worldwide use are the American Class system (Class 150, 300, 400, 600, 900, 1500, 2500, defined in ASME B16.5 for NPS 1/2 to 24 and in ASME B16.47 for NPS 26 to 60) and the European PN system (PN 2.5 through PN 400, defined in EN 1092-1 for steel flanges). They overlap in capability at ambient temperature and diverge steadily as the temperature rises and as the material changes.
The table below sets out the equivalence that engineers use in practice, together with the ambient-temperature working pressure for each class. The pressure figures are the well-established values for the carbon and low-alloy steel reference group and the group 3.8 nickel alloy values are given in the previous section, which shows how much lower they run at high temperature.
| ASME Class | Common EN 1092-1 PN equivalent (verify) | Group 1.1 ambient ceiling (psig) | Group 1.1 ambient (bar) | Typical nickel alloy use |
|---|---|---|---|---|
| Class 150 | PN 20 (PN 16 or PN 25 in some tables) | 285 | 19.6 | Utility and low-pressure chemical, DFF, water |
| Class 300 | PN 50 | 740 | 51.1 | General process, most chemical plant piping in nickel alloys |
| Class 400 | PN 64 (non-preferred in ASME) | 990 | 68.3 | Rarely specified; check availability before choosing |
| Class 600 | PN 100 | 1480 | 102.1 | High-pressure chemical, hydrogen, offshore process |
| Class 900 | PN 150 | 2220 | 153.1 | High-pressure process and wellhead-adjacent piping |
| Class 1500 | PN 250 | 3705 | 255.5 | Severe service, compact high-pressure skids |
| Class 2500 | PN 420 | 6170 | 425.5 | Extreme pressure, small DN only in nickel alloys |
Table note: Pressure figures are the ambient-temperature ratings for ASME B16.5 group 1.1 materials, which are quoted for scale only; the rating that applies to a nickel alloy flange is the one read from the material group table in the current edition of ASME B16.5 (group 3.8 for the Ni-Cr-Mo and Ni-Cr-Fe grades used for flanges). PN equivalences are the widely used engineering correspondence and are not a conversion defined by either standard — the class and PN systems have different rating equations, so confirm the exact figure in EN 1092-1 and ASME B16.5 before substituting one for the other.
What this means when you write a specification. Three consequences follow from the way the ratings work, and they cause most of the arguments we see between buyers and forge shops. First, specifying "Class 300" is incomplete; the flange is only rated to Class 300 at temperatures and in material groups where the table says so, and a nickel alloy flange in group 3.8 that holds 51.7 bar at ambient holds 21.6 bar at 600 °C. Second, a Class 150 nickel alloy flange is effectively a low-temperature item: at or above about 550 °C its rating collapses to zero in the group 3.8 table, so a high-temperature line needs Class 300 or better regardless of the modest pressure. Third, Class 400 exists in ASME B16.5 but is not a stock item in nickel alloys anywhere in the world; if a drawing calls for it, expect a long lead time or a substitution, and raise the question early rather than at the delivery date.
Large-diameter and specialised flanges. Above NPS 24 the governing American document is ASME B16.47, which has two series: Series A, whose dimensions follow MSS SP-44, and Series B, which follows the older API 605 practice. The two series are not interchangeable and the bolt counts differ, so a purchase order must state the series. Orifice flanges for flow measurement are dimensioned in ASME B16.36 rather than B16.5, and they carry the same pressure class table plus the jack-screw and pressure-tap details. On the European route, EN 1092-1 covers steel flanges from small DN up to very large diameters and defines both the dimensions and the material groups, while the older DIN 2630 series (weld-neck, PN 6 to PN 40) is still quoted on replacement work in process plants built to German practice. Russian projects are commonly written to GOST 33259-2015, which consolidated the older GOST 12820-80 and GOST 12821-80 flange standards; the legacy numbers still appear on as-built drawings and must be recognised rather than refused.
Which Facing and Gasket Combination Should You Specify?
The facing is the machined surface that carries the gasket, and it must be chosen together with the gasket and with the mating flange. The four facing types in common use are the raised face (RF), the flat face (FF), the ring-type joint (RTJ) and the tongue-and-groove pair (T&G), with the male-and-female pair (M&F) as a fifth, older variant. The single most common field error on a nickel alloy flange is a facing mismatch — an RF flange offered to an FF flange of the same nominal size, or an RTJ flange ordered where the mating item is RF. Both look plausible on a pallet and neither will seal.
| Facing | Where it is used | Typical gasket | Face finish / detail | Standard |
|---|---|---|---|---|
| Raised face (RF) | Default for process piping in Classes 150-2500 | Spiral-wound with inner and outer rings, graphite or PTFE filler; Kammprofile; sheet | 125-250 µin Ra AARH typical for the raised face; serrated spiral finish | ASME B16.5, MSS SP-6 |
| Flat face (FF) | Low-pressure cast-iron or bronze mating flanges, some pump casings | Full-face non-metallic sheet gasket | Full-face contact; thinner and less efficient than RF at the same bolts | ASME B16.5, MSS SP-6, ASME B16.21 |
| Ring-type joint (RTJ) | High pressure, high temperature, hydrocarbon and hydrogen service | Solid metal ring, oval or octagonal (R, RX or BX profile) | Machined groove, typically 63 µin Ra; metal-to-metal seal | ASME B16.5, ASME B16.20 |
| Tongue and groove (T&G) | Aggressive or highly toxic service where a confined gasket is wanted | Flat or sheet gasket confined by the tongue and groove | Groove and tongue machined as a pair; the pair must be ordered together | ASME B16.5, MSS SP-6 |
| Male and female (M&F) | Legacy piping and some special services | Sheet or soft-metal gasket in the female recess | Older variant; gasket fully confined | ASME B16.5, MSS SP-6 |
| Large male-female | Available in several Classes as an alternative to RF | Soft gasket confined in a wide recess | Deep recess, larger gasket diameter | ASME B16.5 |
Table note: Facing dimensions, groove geometry and finish requirements are those published in ASME B16.5, with face finish practice referenced to MSS SP-6 and gasket dimensions to ASME B16.20 for metallic gaskets and ASME B16.21 for non-metallic flat gaskets. Verify the current edition before machining, and note that a 125-250 µin AARH finish is a range, not a target — a spiral-wound gasket and a PTFE sheet gasket in the same joint want different finish windows.
Gasket selection for nickel alloy flanges deserves one more decision. Spiral-wound gaskets are the default on RF flanges in Classes 300 to 900 and are normally specified with an inner ring to prevent buckling and an outer ring to centre the gasket on the bolt circle; the winding material and the filler are chosen separately, and on a nickel alloy flange the winding is usually the matching alloy or a 316L winding with flexible graphite filler, both of which are covered by ASME B16.20. Ring-type joints are chosen where the pressure or the thermal cycling exceeds what a spiral-wound gasket will tolerate, and the ring material is selected for hardness as well as for corrosion — a ring that is too hard damages the flange groove, and a groove that has been damaged by a previous hard ring will never seal again without re-machining. PTFE and expanded-graphite sheet gaskets are used at lower pressures and where chemical compatibility rules out a metal winding; on nickel alloys they are usually specified for caustic (Nickel 200 flanges) or for very dilute acid duty. Our Monel alloy and stainless steel ranges cover the matching winding and ring materials that these joints usually need, and the news and technical guides section carries worked examples of gasket selection on flanged joints that failed.
How Are Nickel Alloy Flanges Manufactured, Heat Treated and Inspected?
A nickel alloy flange is normally a hot-forged item, subsequently solution annealed or aged, then machined, then verified by a defined sequence of non-destructive and destructive checks. The commercial alternatives are ring rolling for large-diameter rings and closed-die forging for high-volume standard sizes; both are legitimate, and both must meet the same material specification. Whatever the route, the two process steps that decide whether the flange performs are the forging reduction and the heat treatment, and both are visible in the certificate only if the mill actually records them.
| Process step | What is done | Practical control | Reference |
|---|---|---|---|
| Cutting and billet preparation | Saw or plasma cut billet from a wrought bar or ingot, ends squared, surface defects ground out | Material traceability transferred by hard stamping or by a tag that survives heating | Mill route card |
| Heating | Charge to the hot-working temperature for the grade; C-276 and 625 are hot-worked in a narrow window | Furnace atmosphere controlled; no sulphur-bearing fuel or marking in contact with the metal | Manufacturer practice |
| Forging | Open-die upsetting and drawing, or closed-die forging, or ring rolling for large diameters | Minimum forging reduction and metal flow direction recorded; no work below the minimum finishing temperature | ASME B16.5 material group rules; ASTM B564 |
| Solution anneal / ageing | Heat to the temperature the specification names and quench or air cool as required; PH grades then aged | Furnace chart per heat; quench rate for C-276 is a specification item, not an option | ASTM B564, ASTM B637 |
| Machining | Face, bore, hub and bolt holes; groove or raised face cut to the standard | Facing finish and groove profile checked with a comparator and a profile gauge | ASME B16.5, MSS SP-6 |
| Non-destructive examination | Ultrasonic, radiographic, dye penetrant or magnetic particle depending on the grade and the contract | Nickel alloys are non-magnetic (except some Ni-Cu), so MT is generally replaced by PT | ASTM E165 (PT), ASTM E1742 (RT), ASTM A388-type UT practice (verify), ASTM E709 (MT) |
| Mechanical testing | Tensile per heat or per lot, hardness on the finished part | Test frequency per the material specification, not per the shop's convenience | ASTM E8/E8M, ASTM E21, ASTM E18/E10/E92 |
| Positive material identification | XRF or OES check of every piece before dispatch | Recorded per serial number; rejects quarantined and not returned to stock | ASTM E1476 (guide) |
| Marking and certification | Grade, UNS, heat number, class, size, facing and manufacturer's mark stamped or stencilled | Marking must not create a notch in a stressed area; low-stress stamps on thin hubs | ASME B16.5, MSS SP-25 |
Table note: Steps, controls and the standards they reference reflect normal commercial forging practice and the requirements of the cited ASTM and ASME documents; the specific forging reduction, finishing temperature and inspection extent are set by the material specification, the purchase order and the project specification, so they must be taken from those documents rather than from this table. Alloy-specific thermal cycles (for example the solution-anneal window for C-276 and the solution-plus-double-age cycle for 718) should be confirmed against the current edition of the applicable ASTM specification.
Why the heat treatment is not a formality. Two processing failures account for a disproportionate share of nickel alloy flange problems in the field. The first is an inadequate quench after solution annealing on a Ni-Cr-Mo grade: if the material cools slowly through the precipitation range, molybdenum-rich phases form at the grain boundaries, the corrosion resistance drops and the ductility falls, and the flange passes a chemistry check and a hardness check while failing in service. The second is a precipitation-hardening grade supplied in the solution-treated condition without the ageing treatment, which halves the yield strength and is invisible to a dimensional inspection. In practice we treat the furnace chart and the quench record as part of the material certificate for these grades, and we do not accept a flange whose certificate simply states "heat treated" without the cycle parameters and the quench medium.
Ring rolling and closed-die forging. Ring rolling produces a circumferentially oriented grain flow, which is favourable for a flange because the hoop stress is the dominant stress. It is the usual route for large-diameter rings and for flanges above about NPS 24 where a forged ring cut and machined from plate would be a dimensional impossibility. Closed-die forging produces the hub and the flange body in one operation with good metal flow through the fillet, and it is the economic route for standard sizes in repeat production. Open-die forging remains the most flexible route for one-off and very large items, and it is perfectly acceptable provided the reduction ratio and the finishing temperature are controlled and recorded.
Procurement and Inspection: PMI, MTR, EN 10204 3.1/3.2 and Common Failures
Buying a nickel alloy flange is a document exercise as much as a materials exercise, and the documents must be verified independently of the seller. The minimum package is a mill test report traceable to the heat number actually stamped on the flange, a positive material identification check on the finished item, and a dimensional and visual inspection against the dimensional standard. Anything above that — an EN 10204 3.2 certificate, a witnessed third-party inspection, or a full destructive test — is a project decision and should be written into the purchase order rather than requested afterwards.
| Verification step | What it proves | Document or method | When we insist on it |
|---|---|---|---|
| Mill test report (MTR) to EN 10204 3.1 | The manufacturer's own inspection results, issued by the producing mill, with the heat number and the specification | EN 10204 type 3.1 | Every order; the default commercial document |
| Inspection certificate to EN 10204 3.2 | The same results, but countersigned by an independent inspector representing the purchaser or a nominated body | EN 10204 type 3.2 | Pressure, offshore, nuclear and any project where traceability is a contract requirement |
| Positive material identification | That the physical item is the alloy on the certificate, checked on the finished flange rather than on the raw bar | XRF or OES, per the ASTM E1476 guide | Every nickel alloy flange we ship, at no extra cost, with results recorded by serial number |
| Hardness survey | That the heat-treatment condition is consistent with the specified condition; also required for sour service | ASTM E18, ASTM E10, ASTM E92 | Precipitation-hardening grades, and all wet sour service to NACE MR0175 / ISO 15156 |
| Dimensional and facing inspection | That the flange meets the dimensional standard and the facing type ordered | ASME B16.5 tolerances, MSS SP-6 finish | Every order; facing and bolt circle are the two features most often wrong |
| Third-party inspection | Independent confirmation of the whole package, usually at the forge shop before dispatch | SGS, BV, TUV or the client's nominated inspector | Export projects, EPC packages and any order where the end user has not audited the mill |
| Corrosion or metallographic testing | That the material meets a specific corrosion or microstructure requirement beyond the specification minima | Project specification (for example ASTM G48 for pitting) | Seawater, chloride and other aggressive-duty flanges |
Table note: Documentation types are those defined in EN 10204; PMI, hardness, dimension and test methods are referenced to the ASTM documents shown. Which combination is required is set by the purchase order and the project specification, and the acceptance limits for any corrosion testing belong to the project specification rather than to the test method. Confirm the current edition of each document before quoting a requirement.
Common failures and how to avoid them. The failure list below is compiled from our own inspection records and from customer returns, and it is short because most flange problems are one of eight things.
| Failure or defect | Root cause | Consequence in service | Prevention |
|---|---|---|---|
| Grade substitution | Lower-molybdenum or lower-nickel grade supplied against a nickel alloy order | Crevice and pitting corrosion under the gasket within the first year | PMI on every piece; certificate checked against the chemistry table |
| Wrong heat-treatment condition | Slow quench after solution anneal, or ageing omitted on a PH grade | Low ductility, cracking, or yield strength well below the design basis | Furnace chart and quench record with the MTR; hardness survey |
| Facing mismatch | RF supplied against an FF mating flange, or RTJ against RF | Joint will not seal at any bolt load | Facing type stated on the order and verified at goods-in |
| Face finish out of range | Raised face machined too smooth or too rough for the gasket chosen | Gasket extrusion or insufficient seating stress, leak at first pressurisation | Finish checked with a comparator to MSS SP-6 |
| Over-torquing bolts | Bolt load calculated for the nominal class rather than for the gasket and the bolt material | Hub yielding, flange rotation, or bolt failure | Torque values from the gasket supplier, tightened in a controlled sequence |
| Crevice corrosion under the gasket | Gasket and flange material combination, or a design that leaves an accessible crevice | Leak path developing between inspection intervals | Alloy selection for the crevice condition, not just for general corrosion |
| Class or PN rating exceeded at temperature | Ambient rating assumed to hold at design temperature | Deformation, loss of joint integrity | Rating read at design temperature for the correct material group |
| Plate used where a forging is required | Cost reduction on a weld-neck or high-class flange | Poor through-thickness properties, risk of laminar tearing | Material form stated on the order; forging certificate and reduction record |
Table note: Failure modes, consequences and prevention measures come from our own dispatch inspection and customer-return records and are in-house observations, not standard requirements. The applicable acceptance criteria for each item come from the material specification, the dimensional standard or the project specification named on the purchase order.
What to put on the purchase order. A nickel alloy flange order that cannot go wrong states seven things: alloy grade and UNS number; material specification with its form (forging, per ASTM B564 or the applicable document); heat-treatment condition; dimensional standard including the series where relevant (ASME B16.5, or ASME B16.47 Series A or B, or EN 1092-1, or GOST 33259-2015); size, pressure class or PN, and facing; inspection documents required (EN 10204 3.1 or 3.2) and whether PMI and third-party witness are included; and marking and traceability requirements. We have written the technical basis for those seven lines into the FAQ below, and if you send us a drawing and a service description we will come back with a grade recommendation, a facing and gasket combination, and the documents that will be issued with the goods. Our contact and enquiry desk handles both quotations and technical review.
Standard Index
| Standard | Title / scope | Covers | Form |
|---|---|---|---|
| ASME B16.5 | Pipe flanges and flanged fittings, NPS 1/2 through NPS 24, metric/inch | Dimensions, pressure-temperature ratings by material group, facings, tolerances, marking | flanges, flanged fittings |
| ASME B16.47 | Large diameter steel flanges, NPS 26 through NPS 60 | Series A (MSS SP-44-derived) and Series B dimensions and ratings | large flanges |
| ASME B16.36 | Orifice flanges | Dimensions, pressure taps, jack screws, ratings by class | orifice flanges |
| ASME B16.20 | Metallic gaskets for pipe flanges | Ring-joint, spiral-wound and jacketed gasket dimensions | gaskets |
| ASME B16.21 | Non-metallic flat gaskets for pipe flanges | Dimensions and materials | gaskets |
| MSS SP-44 | Steel pipeline flanges | Dimensions for large pipeline flanges, basis of B16.47 Series A | large flanges |
| MSS SP-6 | Standard finishes for contact faces of pipe flanges and connecting-end flanges | Face finish ranges and visual comparators | facing finish |
| MSS SP-25 | Standard marking system for valves, fittings, flanges and unions | Marking content and method | marking |
| ASTM B564 | Nickel alloy forgings | Composition, mechanical properties, heat treatment, tolerances for flanges, fittings and valve parts | forgings |
| ASTM B637 | Precipitation-hardening nickel alloy bars and forgings | Composition and mechanical properties for 718 and similar grades | bar, forging |
| ASTM B462 | Ni-Cr-Fe and Ni-Cu alloy forgings | Composition and mechanical properties for Alloy 20 and Ni-Cu grades | forgings |
| ASTM B575 | Low-carbon Ni-Cr-Mo alloy plate, sheet and strip | Composition and mechanical properties for C-276 plate | plate, sheet |
| ASTM B443 | Ni-Cr-Mo-Nb alloy plate, sheet and strip (625) | Composition and mechanical properties | plate, sheet |
| ASTM E8/E8M | Tension testing of metallic materials | Test method for tensile properties | test method |
| ASTM E21 | Elevated temperature tension testing | Test method for high-temperature tensile properties | test method |
| ASTM E18 / E10 / E92 | Rockwell, Brinell and Vickers hardness | Test methods for hardness verification | test method |
| ASTM E112 | Determining average grain size | Microstructure verification | test method |
| ASTM E165 | Liquid penetrant examination | Surface defect detection on non-magnetic alloys | test method |
| ASTM E1476 | Guide for metals identification, sorting and grade verification | PMI practice with XRF and OES | test method |
| ASTM G48 | Pitting and crevice corrosion resistance in ferric chloride | Practice A pitting, Practice B crevice | test method |
| EN 1092-1 | Flanges and their joints, circular flanges, PN designated, steel flanges | Dimensions, material groups, pressure-temperature ratings | flanges |
| EN 10204 | Metallic products - types of inspection documents | Definition of inspection certificate types 3.1 and 3.2 | documentation |
| EN 10095 | Heat-resisting steels and nickel alloys | Grade list and properties for heat-resisting grades | material standard |
| DIN 2630 series | Weld-neck steel flanges, PN 6 to PN 40 | Dimensions of the classic German weld-neck flange range | flanges |
| GB/T 9112-9124 series | Steel pipe flanges (series of standards by flange type) | Dimensions and technical requirements for Chinese flanges | flanges |
| GB/T 9124.1 | Steel pipe flanges, Part 1: PN designated | Dimensions and technical requirements | flanges |
| HG/T 20592 | Steel pipe flanges (PN designated) for the chemical industry | Dimensions and technical requirements | flanges |
| GB/T 2054 | Nickel and nickel alloy plate and sheet | Grades, composition and properties for nickel and nickel alloy plate | plate, sheet |
| GB/T 15007 | Corrosion-resistant alloy grades | Grade designation and composition tables | grade system |
| GB/T 14992 | Classification and designation for superalloys and high temperature intermetallic materials | GH-series grade designation system | grade system |
| JIS B2220 | Steel pipe flanges | Dimensions and ratings from 10A to 1500A, 5K to 40K | flanges |
| JIS G3214 | Stainless steel forgings for pressure vessels (verify applicability to nickel alloys) | Forging requirements for pressure-vessel service | forgings |
| GOST 33259-2015 | Flanges for nominal pressure up to PN 250 (consolidating the earlier GOST flange series) | Dimensions and requirements | flanges |
| GOST 12820-80 | Steel plane welded flanges, PN 1 to PN 25 | Dimensions (legacy; superseded by GOST 33259-2015) | flanges |
| GOST 12821-80 | Steel butt-welded flanges, PN 1 to PN 25 | Dimensions (legacy; superseded by GOST 33259-2015) | flanges |
| GOST 5632 | Corrosion-resistant, heat-resistant and creep-resistant steels and alloys - grades (verify) | Russian grade designation list | grade system |
FAQ
Q1: What is the best nickel alloy for flanges in chloride service?
For wet chloride service the default is a nickel-chromium-molybdenum grade, and the two that dominate are Hastelloy C-276 (UNS N10276, W.Nr 2.4819) and Hastelloy C-22 (UNS N06022, W.Nr 2.4602). C-276 is the choice where the stream is reducing or mixed — hydrochloric acid, chlorinated hydrocarbons, flue-gas desulphurisation liquors — because its molybdenum and tungsten content gives it high resistance to both pitting and crevice attack. C-22 carries more chromium and less molybdenum, which makes it better in strongly oxidizing chloride such as wet chlorine, hypochlorite and ferric or cupric chloride solutions. Where the chloride is combined with sulphuric or phosphoric acid and temperatures stay moderate, Incoloy 825 (UNS N08825) can be the more economical answer, and Alloy 20 (UNS N08020) is frequently specified for sulphuric acid pickling lines. Two practical cautions: the crevice between the gasket and the flange face is the first place that fails, so the grade must be selected for crevice resistance and not only for general corrosion rate; and the companion flange, bolts and gasket ring should be selected at the same time so that a galvanic couple is not introduced at the joint. If you send us the chloride level, the pH and the temperature, we will shortlist two grades and explain the difference in expected life.
Q2: Which standard governs a nickel alloy flange forging?
The dimensional standard and the material standard are two separate documents and both must be named on the order. Dimensionally, most flanges worldwide are ordered to ASME B16.5 (NPS 1/2 to NPS 24), ASME B16.47 (NPS 26 to NPS 60, in Series A or Series B), or the European EN 1092-1 PN system; the Chinese GB/T 9112-9124 series and GB/T 9124.1, the Japanese JIS B2220 and the Russian GOST 33259-2015 are the equivalents in the other systems. For the material, the governing American specification is ASTM B564 (nickel alloy forgings), which covers the Ni-Cr-Mo, Ni-Cr-Fe, Ni-Fe-Cr, Ni-Cu and pure nickel grades and is the document that appears on the mill test report of a forged flange. Precipitation-hardening grades such as Inconel 718 are covered by ASTM B637, and the Ni-Cr-Fe and Ni-Cu grades used as forgings also appear in ASTM B462. In ASME B16.5 the pressure-temperature rating for these alloys is read from material group 3.8, whose forging specifications are ASTM B564 and ASTM B462. If a supplier quotes a flange without naming the material specification, that is the first thing to correct on the enquiry.
Q3: Is EN 1092-1 PN 16 the same as ASME B16.5 Class 150?
No, and treating them as interchangeable is a common and expensive mistake. The two systems use different rating equations and different dimensional tables, so a PN 16 flange and a Class 150 flange of the same nominal size have different outside diameters, different bolt circles, different bolt sizes and different face dimensions, and they will not bolt together even though both are described as low-pressure items. The rough engineering correspondence that people quote — Class 150 to about PN 20, Class 300 to about PN 50, Class 600 to about PN 100, Class 900 to about PN 150, Class 1500 to about PN 250, Class 2500 to about PN 420 — is a convenient memory aid, not a conversion, and the actual ratings diverge further at temperature and differ by material group. The correct approach is to choose one system for the whole piping system, to state the standard and the class or PN on every flange and gasket, and to check the mating equipment — pumps, valves, vessels — because that is where the two systems most often collide. If a spool must transition between systems, use a flange pair designed for the purpose or a spool piece with one flange of each standard, and record the decision on the isometric rather than relying on the site.
Q4: Why is a Class 150 nickel alloy flange not rated for high temperature?
Because the pressure-temperature rating for a flange is a table value, and for nickel alloys in ASME B16.5 group 3.8 the Class 150 entry falls away rapidly with temperature and reaches zero at about 550 °C. The material itself is still strong at that temperature — Inconel 625 retains several hundred megapascals of tensile strength — but the flange rating is limited by the joint: bolt load, gasket seating, flange stiffness and permissible bolt stress all interact, and the standard has decided that a Class 150 joint in this material group cannot be relied on above that temperature. That is why high-temperature nickel alloy lines are normally specified as Class 300 or Class 600 even where the operating pressure is only a few bar. The same group table also sets a maximum service temperature per alloy, and those limits are absolute: N10276 is not to be used above 675 °C, N06625 above 645 °C, and N08825 above 538 °C. Where the design temperature exceeds the class rating envelope, the answer is not a special flange but a higher class, a different joint type, or a design to ASME Section VIII Division 1 or ASME B31.3 rather than a standard flange table.
Q5: What is the difference between EN 10204 3.1 and 3.2 certificates?
Both are inspection certificates that report the actual test results for the material, and both are traceable to the heat number. The difference is who signs. A type 3.1 certificate is issued by the manufacturer's own inspection department — in practice, by the producing mill — and states that the material meets the order requirements on the basis of the manufacturer's own inspections. A type 3.2 certificate carries the same results but is also signed by an independent inspector representing the purchaser or a nominated third party, which means an organisation with no commercial interest in the outcome has witnessed or reviewed the testing. Most commercial orders for nickel alloy flanges are satisfied with a 3.1 certificate plus an independent positive material identification check, and that combination catches the two failures that matter most: a substituted grade and a heat-treatment condition that does not match the certificate. A 3.2 certificate is normally required on pressure equipment, offshore projects and any contract where the end user has not audited the mill. For reference, older document types 2.2, 2.3 and 3.1B exist in the same standard and are sometimes quoted by suppliers looking for a cheaper option; the specification should therefore name the document type explicitly rather than asking for "a mill certificate".
Q6: How does positive material identification work on flanges?
Positive material identification, usually shortened to PMI, is a surface chemical analysis performed on the actual item using a portable X-ray fluorescence or optical emission spectrometer. It takes seconds per piece, it is non-destructive, and it is the only practical way to prove that the flange in the crate is the alloy on the certificate. The ASTM E1476 guide describes the practice, including the need for a documented procedure, verified reference standards and a defined sampling plan. On nickel alloy flanges the discriminating elements are molybdenum, chromium, tungsten and niobium: C-276 reads about 15-17% molybdenum with 14.5-16.5% chromium and 3-4.5% tungsten, C-22 reads 12.5-14.5% molybdenum with 20-22.5% chromium, and 625 reads 8-10% molybdenum with a niobium-plus-tantalum figure near 3.15-4.15%. A piece that reads 21% chromium when the stencil says C-276 is either C-22 or a mixed-up crate. Two practical limits are worth knowing: XRF gives no reliable carbon figure, so PMI cannot confirm the low-carbon requirement of a Ni-Cr-Mo grade; and a heavily oxidised or painted surface can distort the reading, so the measurement point should be a clean machined or freshly ground area. We treat PMI as standard practice on every nickel alloy flange we ship and record the result against the serial number.
Q7: Which flange facing should I choose — RF, FF, RTJ or tongue and groove?
Choose the facing together with the gasket and the mating flange, because the three form one joint and cannot be selected independently. The raised face (RF) is the default for process piping in Classes 150 to 2500 and takes a spiral-wound gasket, usually with inner and outer rings, or a Kammprofile gasket at higher pressures. The flat face (FF) is used where the mating item is cast iron or a low-strength material, because a full-face gasket spreads the bolt load; it is not an efficient joint at high pressure and should not be substituted for RF simply to match an existing item. The ring-type joint (RTJ) is used for high-pressure, high-temperature and hydrocarbon or hydrogen service, and it seals metal-to-metal on a machined ring; it is dimensionally intolerant of a damaged groove, so handling and groove protection matter. Tongue-and-groove and male-and-female facings confine the gasket, which is valuable in aggressive or highly toxic service, and the pair must always be ordered as a matched set. Whichever you choose, tell us the facing on the order and we will machine and gauge it accordingly; the most common error we see is an RF flange ordered against an FF mating item.
Q8: Can nickel alloy flanges be supplied as plate instead of forgings?
Usually not, and the exceptions are narrow. The ASME B16.5 material group rules permit plate and flat bar to be used for blind flanges and for reducing flanges without hubs in the groups that allow it, but a welding-neck, slip-on or lapped flange is expected to be a forging or to be machined from a forged ring. The reason is metallurgical rather than bureaucratic: a forging consolidates internal porosity, refines the structure and produces metal flow oriented to resist the hoop and bending stresses in the hub and fillet, whereas a plate flange cut from a rolled slab has properties that vary through the thickness and short-transverse ductility that may be much lower than the longitudinal values on the certificate. For a low-pressure blind at ambient temperature the difference may be irrelevant; for a Class 600 weld-neck in wet chloride service or a flange subject to thermal cycling it is decisive, and a plate-built flange is also more likely to suffer laminar tearing at a weld. In practice, always ask the supplier to state the product form on the certificate. If the form is not stated, assume the worst and require a forging certificate with the reduction ratio and heat-treatment record before you accept the goods.
Q9: What should be on a nickel alloy flange purchase order?
Seven lines prevent almost every dispute. First, the alloy grade and its UNS number, written in full — for example Inconel 625, UNS N06625, W.Nr 2.4856. Second, the material specification and the product form, for example ASTM B564 forgings, annealed. Third, the heat-treatment condition, stated explicitly, particularly for the precipitation-hardening grades where solution-plus-age is not the same as solution-treated. Fourth, the dimensional standard, including the series where one exists — ASME B16.5, ASME B16.47 Series A or Series B, EN 1092-1, GB/T 9124.1, JIS B2220 or GOST 33259-2015. Fifth, the size, the pressure class or PN, and the facing, given as an example: NPS 6, Class 300, raised face, 125-250 µin finish. Sixth, the inspection documents required — EN 10204 3.1 or 3.2 — and whether PMI, hardness testing and third-party witness are included. Seventh, marking and traceability, including whether the heat number must be transferred to the finished flange. Send the list to our enquiry desk with the service data and we will confirm grade, class and documents in writing before the order is placed.
Q10: How are nickel alloy flanges marked and identified?
Marking on a flange is not decoration; it is the only link between the item and the documents that make it acceptable. ASME B16.5 sets the marking content and MSS SP-25 sets the marking system, and between them they require the manufacturer's name or mark, the material designation, the pressure class or rating, the size and the facing, and in most cases the heat number or a traceable code that leads to it. Marking is applied by low-stress stamping, by vibro-etch or by a durable paint stencil; on a nickel alloy flange with a thin hub or in a stressed location, heavy stamping is avoided because a deep stamp acts as a notch and can become a crack initiation site. The mark must remain legible after blasting, pickling and painting, and a supplier that removes or obscures a heat number is a supplier to be avoided. In our own dispatch we photograph the marking on each flange, record the PMI result against the same serial number and issue both with the EN 10204 certificate, so that a receiving inspector can match the physical item to the paperwork without opening the mill's file. If a flange arrives with no legible heat number, treat it as unidentified material and quarantine it: without traceability, none of the other documents mean anything.
Q11: What are the common failure modes of nickel alloy flanged joints?
Most flanged joint failures are not material failures at all, and the list is short. Grade substitution is the first: a lower-molybdenum alloy delivered against a C-276 order, which then corrodes in the crevice under the gasket. The second is a heat-treatment problem, either a slow quench after solution annealing on a Ni-Cr-Mo grade or an omitted ageing treatment on a precipitation-hardening grade, both of which pass a chemistry check and fail in service. The third is a facing mismatch, RF against FF or RTJ against RF, which cannot seal at any bolt load. The fourth is a face finish outside the range the gasket needs, leading to extrusion or to insufficient seating stress. The fifth is over-torquing, which yields the hub or the bolts and distorts the joint. The sixth is a genuine material problem — crevice corrosion, pitting or, in wet sour service, sulphide stress cracking — where the grade was chosen for general corrosion resistance and not for the local condition. The seventh is a rating error, where an ambient class rating was applied at a high design temperature. All seven are preventable with a correct order, a verified certificate and a PMI check, and none of them is fixed by tightening the bolts harder.
Q12: Does a nickel alloy flange need any special coating or surface treatment?
Generally no, and it is often better left untreated. Nickel alloys owe their corrosion resistance to the alloy itself rather than to a coating, so painting, galvanising or plating a nickel alloy flange adds nothing to its performance and can actively harm it — zinc from galvanising causes liquid metal embrittlement if welding or heating follows, and a plated surface can mask a substituted grade during a visual inspection. Where a coating is asked for, it is normally a project colour-code requirement rather than a corrosion measure, and it should be applied only to the outside diameter and never to the facing or the gasket contact area. Surface cleaning after machining is what matters: remove cutting fluid residues with a non-chlorinated solvent, avoid iron contamination from carbon steel brushes or tooling used elsewhere, and keep the facing free of oil. For stainless and nickel alloy items in hygienic or high-purity service, a pickled and passivated finish may be specified, but for high-molybdenum nickel alloys such as C-276 the industry practice is mechanical cleaning with dedicated tooling rather than acid passivation, because those alloys have limited resistance to nitric acid. Bolting is the item that does usually need a coating or a material upgrade, and it should be selected for the environment and for the flange material.
Q13: Which national standard should I specify for a nickel alloy flange?
Specify the standard that the rest of the piping system is built to, because a flange only works in a joint and the joint has to match on both sides. If the system is American practice — an ASME B31.3 process plant, an API pipeline, a US-licensed design — specify ASME B16.5 or ASME B16.47 dimensions with an ASTM B564 forging, and the material certificate will read in UNS numbers. If the plant is built to European practice, specify EN 1092-1 PN ratings with an EN 10095 or equivalent material route, and use W.Nr designations alongside the UNS number for clarity. Japanese projects typically use JIS B2220 dimensions, Chinese domestic projects use the GB/T 9112-9124 series or GB/T 9124.1 with HG/T 20592 for chemical industry work, and Russian and CIS projects use GOST 33259-2015, with the legacy GOST 12820-80 and GOST 12821-80 numbers still appearing on older drawings. The material standard does not have to match the dimensional standard: many projects worldwide buy an ASTM B564 forging machined to EN 1092-1 or JIS B2220 dimensions, and that is a perfectly sound arrangement as long as both documents are named on the order. What must never happen is combining one flange of each dimensional system in the same joint.
Q14: How long does it take to supply forged nickel alloy flanges?
Lead time depends far more on the heat-treatment route and the size than on the alloy, and the range is wide. Standard stock sizes in the common grades — Monel 400, Nickel 200, Incoloy 825, Inconel 625 and Hastelloy C-276 — in Classes 150 to 600 and NPS 1/2 to 12 are regularly held by distributors and speciality mills and can ship from stock in days. Non-stock sizes in the same grades typically need a forging and a solution anneal and run in the region of four to eight weeks depending on size and quantity, with large-diameter and high-class items at the longer end. The precipitation-hardening grades need an additional ageing cycle, and the rarer grades — C-22, Alloy 20 in large sizes, Monel K-500 — depend on whether the mill has a suitable billet in stock, which is the single biggest variable. Two things shorten lead time decisively: order the correct facing and finish first time, and settle the documentation requirement early, because a 3.2 certificate with witnessed testing needs to be scheduled before the heat is forged and cannot be added at the end. Hangbo Alloy keeps traceable stock of the common grades in bar and forged blanks, so send us the flange schedule and we will confirm what can ship from stock and what needs a forging cycle — WhatsApp (Lisa) at +86 13611656360, or email sales@hangboalloy.com.
Q15: How do you check a nickel alloy flange on receipt?
Receiving inspection takes about ten minutes per flange and catches nearly everything. Start with the paperwork: the mill test report must name the heat number, the material specification, the heat-treatment condition and the mechanical results, and that heat number must match the mark on the flange and, if the order required it, the EN 10204 certificate type. Then check the physical item: measure the outside diameter, the flange thickness, the bolt circle and the bolt hole diameter against the dimensional standard, and confirm the facing type and the raised-face height or groove profile. Check the facing finish with a comparator against MSS SP-6. Then carry out PMI on a clean area and compare the readings against the expected range for the grade — chromium, molybdenum, tungsten and niobium are the discriminators. Finally, inspect for damage: handling marks on an RTJ groove, arc strikes, deep stamping on a thin hub, or rust staining that would indicate iron contamination from shared tooling or storage. Any item that fails PMI or whose heat number cannot be traced should be quarantined immediately and not returned to stock. Our own dispatch documentation includes the PMI record and a photograph of the marking for every flange, so your inspection can be completed against our package rather than starting from scratch.
Conclusion: Specify the Grade, the Rating, the Facing and the Documents
A nickel alloy flange is a simple item that fails for four reasons: the wrong grade, the wrong heat-treatment condition, the wrong facing or rating, and a certificate that does not describe the metal in the crate. Getting it right means choosing the alloy family from the service chemistry and temperature, naming both a dimensional standard and a material specification on the order, reading the pressure class at the design temperature rather than at ambient, matching the facing to the gasket and to the mating flange, and requiring independent positive material identification on the finished item rather than accepting a photocopied mill certificate. Do those five things and a nickel alloy flange will outlast the pipe it is welded to; skip any one of them and the joint becomes the reliability limit of the line.
Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier — ISO 9001:2015, established 2012 — supplies forged nickel alloy flanges in Inconel 625, Inconel 718, Hastelloy C-276 and C-22, Incoloy 825 and 800H, Monel 400 and K-500, Alloy 20 and Nickel 200/201, machined to ASME B16.5, ASME B16.47, EN 1092-1, GB/T, JIS or GOST dimensions, with EN 10204 3.1 certification as standard, EN 10204 3.2 and SGS, BV or TUV third-party inspection on request, and PMI recorded against every serial number.
Email: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Send us the flange schedule with the service conditions — medium, concentration, temperature and pressure — and we will return a grade recommendation, the facing and gasket combination, the class rating at temperature and a document package, rather than a bare price.
Related Reading
- Hastelloy C-276 welding guide: filler metals, parameters and crack control — the weldability rules that apply where a C-276 flange is joined to C-276 pipe.
- Nickel alloy technical knowledge centre — corrosion tables, grade comparisons and standard interpretations behind the selections in this guide.
- Inconel alloys: 625, 718 and 600 product range — forged and wrought forms for high-temperature flanged connections.
- Hastelloy C-276 and C-22 plate, bar and forgings — the Ni-Cr-Mo grades most often specified for chloride and mixed-acid flanges.
- Incoloy 825 and 800H supply — the Ni-Fe-Cr family for sulphuric and phosphoric acid duty.
- Monel 400 and K-500 products — nickel-copper grades for hydrofluoric acid, seawater and cryogenic flanges.
- Pure nickel 200 and 201 — caustic soda and high-purity chemical service.
- Titanium and titanium alloy products — the alternative where chlorides and oxidising media allow a lighter material.
- Stainless steel and duplex products — the lower-cost route where the chloride level and temperature permit it.
- Request a quotation and technical review — flange schedules, data packs and third-party inspection arrangements.
Contact & Complete Product Range
Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier
Email: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com
All Grades
Ni: NI200-N6 | Monel: 400-502, K-500, R-405 | Inconel: 600-740H, X-750, 725 | Incoloy: 800-27-7MO | Hastelloy: C-276-HYBRID-BC1, N | Super Austenitic: 904L-AL-6XN | Chromium-Rich: Alloy 33 | High-Strength Stainless: Nitronic 50/60, PH13-8Mo | Chlorination: Alloy 45 | Nimonic: 75-263 | Haynes: 25-HR-160 | RA: 330/333 | Precision: 1J22-4J45 | High-Strength: 18Ni250-AerMet100 | Heating: Cr20Ni80/60 | Specialty: Alloy 20-602CA
Product Forms: Bars(6-500mm) | Tubes(OD 6-610mm) | Plates(0.1-100mm) | Forgings | Welded Pipes | Fittings | Wire(0.05-10mm) | Strip(0.02-4.0mm)
Flange forms supplied: weld-neck, slip-on, blind, lapped, threaded, orifice and large-diameter, in Classes 150 to 2500 and PN 6 to PN 400, with RF, FF, RTJ and tongue-and-groove facings.
SGS/BV/TUV. www.nickel-alloy.com
