Monel 400 Tube Fittings (Alloy 400 / Nickel-Copper Alloy 400, UNS N04400)
Monel 400 tube fittings are mechanical-grip compression fittings machined from nickel-copper Alloy 400 (UNS N04400), a solid-solution alloy of roughly 67% nickel and 30% copper. One or two ferrules swage onto the tube's outside diameter, giving a leak-tight, gas-tight seal and a firm grip on the tube itself. That is exactly what makes a Monel 400 fitting the practical pick for hydrofluoric-acid alkylation lines, seawater and brine service, and sour (H₂S) hydrocarbon instrumentation, the places where 316 stainless pits, cracks, or simply corrodes away. Crestflo carries these fittings from 1/8-inch through 2-inch (50 mm) tube OD, in both single and double (twin) ferrule versions. They are qualified to ASTM F1387 and offered to NACE MR0175 / ISO 15156 for sour service. Standard items ship from stock; specials are built to order, with delivery running 6-8 weeks. Request a quote to price out your configuration.
Monel® is a registered trademark of Special Metals Corporation. Crestflo supplies UNS N04400 to standard chemistry and is not affiliated with or endorsed by Special Metals Corporation.
What Monel 400 Compression Tube Fittings Are
A Monel 400 compression tube fitting is built for fluid-system instrumentation work: a body, a nut, and one or two ferrules that bite into the tube's outer diameter as the nut is torqued down. The result is a joint you can take apart and put back together without losing integrity. No flaring, no welding, no elastomer seal in the leak path. The seal is metal-to-metal, so the joint's service window comes from the alloy, not from an O-ring giving out first.
Scope matters here. These are instrumentation compression tube fittings in Alloy 400, not plumbing pipe fittings, not marine fasteners, and not electrical wire ferrules. They tie into small-bore instrument tubing on analyzers, transmitters, sample lines, chemical-injection systems, and process taps, anywhere hydrofluoric acid, seawater, chlorides, or H₂S push stainless out of the running.
Also Known As: Alloy 400, Nickel-Copper Alloy 400, N04400, Werkstoff 2.4360
Buyers and specifiers write the same alloy several ways, but they all point to the same Ni-Cu material. It is commonly written as Monel® 400, Alloy 400, or Nickel-Copper Alloy 400, and appears in ordering variants such as Monel-400, 400 Monel, and N04400 Monel. It is registered as UNS N04400 and Werkstoff 2.4360, with the German descriptive designation NiCu30Fe and the British designation BS NA13. Fitting feedstock is covered by the wrought nickel-copper specifications ASTM B164 (rod and bar) and ASTM B366 (wrought fittings).
| Designation type | Value |
|---|---|
| Common names | Monel 400, Alloy 400, Nickel-Copper Alloy 400, 400 |
| UNS number | N04400 |
| Werkstoff / EN | 2.4360 |
| Descriptive designation | NiCu30Fe |
| British Standard | BS NA13 |
| Wrought feedstock specifications | ASTM B164 (rod/bar), B366 (wrought fittings) |
Because these names all point to the same product, asking for "Alloy 400 tube fittings," "Monel 400 ferrule fittings," or "N04400 tube fittings" gets you exactly what's described on this page. The terms are interchangeable.
Why Choose Monel 400 for Instrumentation Tube Fittings
Alloy 400 is a binary nickel-copper solid solution, roughly 67% nickel, 30% copper, with minor iron and manganese, strengthened by solid solution rather than by age hardening. Nickel and copper are mutually soluble across the full range, which gives the alloy a single-phase structure and its standout resistance to chloride stress-corrosion cracking, the failure mode that limits austenitic stainless in seawater and brine. It is the industry benchmark alloy for hydrofluoric acid, and it holds up well in seawater, neutral and alkaline salts, caustics, and dilute reducing acids such as sulfuric and hydrochloric.
For a compression fitting, that chemistry translates directly into where you can put it: HF alkylation units in refining, seawater and produced-water systems offshore, chlor-alkali and reducing-acid process lines, and sour oil-and-gas duty. Alloy 400 does have a hard limit, it is attacked by strongly oxidizing media. Nitric acid, oxidizing salts, wet chlorine, and ferric or cupric chlorides will corrode it, so where the stream is oxidizing, a stainless or a Hastelloy grade is the right call. For the full metallurgical picture, composition, mechanical and physical properties, and corrosion-by-media data, see the Monel 400 grade page. We've summarized the reference composition below for convenience when writing specs. The values follow the applicable alloy standard, and Crestflo verifies actual heat chemistry on the material test certificate.
| Element | wt % (UNS N04400) |
|---|---|
| Nickel (Ni) | 63.0 min |
| Copper (Cu) | 28.0–34.0 |
| Iron (Fe) | 2.5 max |
| Manganese (Mn) | 2.0 max |
| Carbon (C) | 0.3 max |
| Silicon (Si) | 0.5 max |
| Sulfur (S) | 0.024 max |
Because Alloy 400 carries no chromium or molybdenum, PREN, the pitting-resistance index used to rank stainless and duplex grades, does not apply; its corrosion suitability is judged by service medium instead. For the higher-strength, age-hardenable version of the same nickel-copper base, see Monel K500, and for a head-to-head against the nickel-chromium alloys, see the Inconel vs Monel selection guide.
Monel 400 Tube Fitting Sizes (1/8-inch to 2-inch OD): Imperial & Metric
Crestflo machines Alloy 400 tube fittings in both imperial fractional and metric tube-OD series, with end connections up to 2-inch (50 mm) OD. The size chart below covers the standard imperial and metric range. Working pressure for any given fitting depends on size, wall thickness, and temperature. It comes from standard tube-fitting pressure data for the tube OD and wall, following ASTM/ASME practice, and the exact rated pressure for your configuration is confirmed on the quotation. Values follow the applicable standard and can be customized to requirement.
| Tube OD, imperial | Tube OD, metric | Availability |
|---|---|---|
| 1/8", 1/4", 3/8", 1/2" | 6 mm, 8 mm, 10 mm, 12 mm | Standard range |
| 5/8", 3/4", 1" | 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 25 mm | Standard range |
| up to 2" (50 mm) | up to 50 mm | Made-to-order |
Monel 400 Tube Fitting End & Thread Connections: NPT, BSPP, JIC & Weld
Fittings come with tube-OD compression ends, tapered or parallel threads, or weld ends. All fittings are available in national, international, and custom thread types.
| End type | Thread / connection standards |
|---|---|
| Tube-OD (compression) | Fractional inch and metric OD |
| Male / female tapered thread | NPT, NPTF, BSPT |
| Male / female parallel thread | BSPP, ISO parallel, SAE ORB |
| Flare / port | JIC 37°, SAE ORB |
| Weld end | Socket-weld, butt-weld, orbital |
Single vs Double Ferrule & Hardened vs Non-Hardened Options
Alloy 400 fittings come in single-ferrule and double (twin) ferrule designs, and hardened or non-hardened ferrules are supplied depending on what the job calls for. This choice shapes gripping action, vibration resistance, and how many times the fitting can be reassembled. One caution specific to this alloy: Monel 400 can gall against itself, so nut and thread finish matters, Crestflo applies anti-galling measures such as silver plating on request to keep make-up smooth on repeated assembly.
| Configuration | Description | When it is used |
|---|---|---|
| Double (twin) ferrule | Front ferrule seals, back ferrule grips | General instrumentation, vibration, gas-tight service |
| Single ferrule | One ferrule seals and grips | Simpler assemblies, certain hydraulic and OEM designs |
| Hardened ferrule | Case-hardened grip surface | Harder tube materials, maximum hold |
| Non-hardened ferrule | Softer grip surface | Thin-wall or softer tubing |
For guidance on making the right choice, see single vs double vs ferrule-less fittings and hardened vs non-hardened ferrules. Replacement nuts and ferrules are stocked separately, and so are single-ferrule fittings and double-ferrule fittings.
Available Monel 400 Fitting Shapes & Connectors
Alloy 400 covers the full geometry range, so you can build a complete instrument run in a single material:
- Union, elbow, tee, cross, and reducer fittings
- Male connectors, female connectors, and adapters for joining mismatched threads
- Bulkhead unions, port connectors, caps, and plugs for sealing off unused lines
- Weld connectors (socket, butt, and orbital)
Alloy 400 comes in related fitting families too, including 37° JIC flare fittings and DIN 2353 bite-type fittings, all combinable within the same instrument tubing system. For the geometry range and ferrule design, start at the tube-fittings product hub.
Corrosion & Service: Hydrofluoric Acid, Seawater, Brine & Sour (H₂S) Duty
What a fitting actually sees in service is the whole reason to specify Monel 400 over stainless. The table below sums up how Alloy 400 behaves against the media that drive fitting selection. These are the alloy's published, standard-referenced characteristics, not a per-fitting rating; the corrosion allowance and suitability for a specific stream stay the specifier's call.
| Media / service | Alloy 400 behavior | Note |
|---|---|---|
| Hydrofluoric acid (HF) | Excellent | The industry benchmark alloy for HF service, including HF alkylation |
| Seawater / brine | Excellent | Low general corrosion; resists chloride pitting well |
| Chloride stress-corrosion cracking | Excellent | Immune where austenitic stainless cracks, the key marine/offshore advantage |
| Caustics / alkalis | Excellent | Strong resistance across concentrations |
| Reducing acids (dilute H₂SO₄, HCl) | Good | Depends on concentration, temperature, and aeration |
| Sour service (H₂S) | Suitable | Acceptable under NACE MR0175 / ISO 15156 in the annealed condition |
| Nitric & oxidizing acids | Poor | Choose stainless or Hastelloy instead |
| Wet chlorine, ferric/cupric chloride | Poor | Oxidizing chlorides attack the alloy |
Where a stream runs strongly oxidizing, carries wet chlorine, or contains ferric or cupric chlorides, look instead to Hastelloy C-276 for mixed oxidizing-reducing and wet-chlorine service. Where the driver is high-temperature strength or oxidizing acids, a nickel-chromium grade is the better fit, the Inconel vs Monel guide lays out the trade-offs.
Standards, Testing & NACE MR0175 Sour-Service Compliance
Crestflo qualifies its compression tube fittings to ASTM F1387, the performance standard for mechanically attached fittings. That's the basis for dimensional interchange and mechanical-integrity claims. For sour service, Alloy 400 fittings are offered to NACE MR0175 / ISO 15156. Nickel-copper alloy N04400 is accepted for sour service in the annealed condition; confirm the certified hardness limits and any environmental restrictions on H₂S partial pressure, temperature, and chloride content in the standard against your application. We hold the standard approvals that apply to instrumentation tube fittings.
| Standard / certification | Scope | Applies here |
|---|---|---|
| ASTM F1387 | Mechanically attached fitting performance | Yes |
| NACE MR0175 / ISO 15156 | Sour-service materials | Yes |
| EN 10204 MTC 3.1 / 3.2 | Material test certification | Yes |
| ASTM B164 / B366 | Nickel-copper bar & wrought-fitting feedstock forms | As applicable |
| ISO 9001 / 14001 / 45001 & PED | Quality, environmental, safety, pressure | Certified |
These fittings go through a wide battery of tests. Hydraulic proof, burst, and impulse come first. Then there's pneumatic, flexure-fatigue, rotary-flex, vibration, and thermal-cycling work, plus pull-out and vacuum checks. Positive material identification (PMI) confirms the alloy on every piece, which matters for a high-nickel grade where substitution is a real risk. NDT is standard and done in-house. Destructive testing goes out to labs accredited under ISO/IEC 17025. Third-party inspection is available on request.
Material Traceability & Certification
Every Alloy 400 part is marked with its own heat/lot number. Each shipment comes standard with an EN 10204 MTC 3.1 certificate, and 3.2 is available on request. PMI confirms grade at the part level, every time. That documentation backs solid audit trails for offshore, subsea, HF-alkylation, and sour-service work, the kind of jobs where a mis-specified alloy is not a small problem.
Drop-In Interchange with Swagelok, Parker & Hy-Lok
Crestflo Alloy 400 fittings are built as dimensional interchange / equivalent fittings for the major instrumentation brands, and that claim rests on ASTM F1387 performance qualification, not on marketing language. These aren't "compatible" or "intermix" parts. Brand names such as Swagelok®, Parker®, and Hy-Lok® remain trademarks of their respective owners, and Crestflo is not affiliated with them; the interchange is strictly dimensional. We don't publish a part-number table. Instead, we prepare interchange references per project: request your cross-reference, and our engineering team will map your existing part numbers to Crestflo Monel 400 equivalents.
Origin & US-Serving Positioning
Crestflo manufactures for the US market. Standard product comes from India; US or European melt is available on request, with full material traceability. Parts are engineered as US drop-in replacements and ship in 6-8 weeks. TAA/DFARS and domestic-melt requirements are handled straight, no hedging, on our US-origin compliance page. If a project calls for a specific melt origin, just specify it on the RFQ.
Applications & Industries for Monel 400 Tube Fittings
Monel 400 fittings show up wherever nickel-copper corrosion resistance is essential and stainless won't survive:
- HF alkylation in refining, hydrofluoric acid is the alloy's signature service; instrument and sample lines on HF units are a classic N04400 application.
- Offshore and marine systems, seawater, produced water, and high-chloride streams, where immunity to chloride SCC is the deciding factor.
- Chlor-alkali and reducing-acid process lines, caustics and dilute sulfuric/hydrochloric service in chemical plants.
- Sour oil and gas, H₂S-bearing instrumentation qualified to NACE MR0175 / ISO 15156.
Crestflo supplies N04400 instrumentation components into oil and gas and marine and shipbuilding applications, among others.
Why Crestflo for Monel 400 Tube Fittings
Crestflo operates as the instrumentation division of an export house with four decades behind it and formal recognition from the Government of India. That parent company has a proven delivery record across the Middle East. Its backing grounds a new, focused instrumentation brand built on a handful of clear advantages:
- Lead time of 6-8 weeks versus 20+ weeks typical of the majors.
- ASTM F1387 drop-in interchange proof that mill and trading suppliers rarely publish.
- Small MOQ and private label for distributors and OEMs.
- Both imperial and metric on every fitting, single or double ferrule, hardened or non-hardened.
- Heat-number marking plus MTC 3.1/3.2 on every order, PMI-confirmed.
- Cost-competitive after US duties and tariffs, ISO 9001 / 14001 / 45001 & PED certified.
We Engineer Confidence.
Request a Quote for Monel 400 Fittings
Give us the details: size, shape, ferrule, thread, and quantity. We'll price it out and get your order scheduled:
- Request a quote, the fastest path to pricing and lead time.
- Request a sample for qualification.
- Become a distributor for line-card and stocking programs.
Datasheets and CAD models are available to customers on request. Reach Crestflo's US sales desk at sales@crestflousa.com or +1 346 594 9005 (Houston, TX). Round out your system with the related Monel 400 instrumentation valves and Monel 400 tubing, and serve the corrosion-critical lines in oil and gas and marine and shipbuilding.
Frequently Asked Questions
Are Alloy 400 and Monel 400 the same?
Yes. "Alloy 400," "Nickel-Copper Alloy 400," and "Monel® 400" all point to the same material: UNS N04400, also listed as Werkstoff 2.4360, a nickel-copper alloy of roughly 67% nickel and 30% copper. Monel® is a registered trademark of Special Metals Corporation, while "Alloy 400," "N04400," and "400" are the generic designations for identical material. Crestflo supplies UNS N04400 to standard chemistry and is not affiliated with Special Metals Corporation.
Why use Monel 400 tube fittings instead of 316 stainless?
Monel 400 is the better choice where the stream is hydrofluoric acid, seawater, brine, caustics, or high in chlorides. It is the benchmark alloy for HF service, and it is immune to the chloride stress-corrosion cracking that limits 316/316L in marine and offshore work. Stainless still wins on oxidizing acids and cost, so the call comes down to the medium. For oxidizing service, use stainless or Hastelloy C-276 instead.
How much do Monel 400 tube fittings cost?
As a high-nickel alloy, Monel 400 fittings run more than stainless steel does, and the price shifts with size, shape, ferrule type, and quantity ordered. Crestflo stays cost-competitive even after US duties and tariffs, but it quotes per configuration. There's no live pricing posted anywhere. Request a quote to get a firm number.
What are Monel 400 tube fittings used for?
They handle corrosion-critical instrumentation lines wherever hydrofluoric acid, seawater, brine, chlorides, or H₂S rule out stainless: HF alkylation units in refining, offshore and marine seawater systems, chlor-alkali and reducing-acid process lines, and sour oil and gas service. In instrumentation terms, that's the fittings on HF, seawater, and sour analyzer, sampling, and process lines.
Are Crestflo Monel 400 fittings NACE-compliant?
Yes. Nickel-copper alloy N04400 is accepted for sour service under NACE MR0175 / ISO 15156 in the annealed condition. Crestflo offers Monel 400 fittings to that standard with material traceability backing project qualification; confirm the certified hardness and environmental limits in the standard against your application.
Do they interchange with Swagelok, Parker, or Hy-Lok fittings?
They're built as dimensional interchange and equivalent fittings, with performance backed by ASTM F1387 qualification. We don't call them "compatible" or "intermix," and every brand name mentioned belongs to its respective owner; Crestflo is not affiliated. Send us your cross-reference request and we'll map your part numbers.
What sizes are available?
Tube-OD sizes run from 1/8-inch up to 2-inch (50 mm), covering both imperial fractional and metric series, in single or double ferrule. Standard sizes span 1/8" to 1" and 6 mm to 25 mm; anything larger is made to order.
Is Monel 400 magnetic, and does that matter for a fitting?
Monel 400 is only weakly ferromagnetic near room temperature, with a Curie point around 20-50 °C that shifts with exact composition, so a given lot may read as faintly magnetic. For a compression fitting the effect is not a service concern; it is a metallurgical trait of the nickel-copper base rather than anything that affects the seal or grip.
Are single and double ferrule versions both offered?
Yes. Both single-ferrule and double (twin) ferrule designs are available, with hardened or non-hardened ferrules supplied depending on what's required. Because Monel 400 can gall against itself, anti-galling measures such as silver plating are offered on request for repeated make-up.
What material certification comes with the fittings?
Standard practice is an EN 10204 MTC 3.1 certificate, though 3.2 is available if you ask for it. Every part gets a heat/lot number stamped on it, and PMI confirms the alloy is genuinely N04400.
Are these made in the USA?
Crestflo manufactures for the US market. Standard product comes from India, though US or European melt is available on request, complete with full material traceability. It's engineered for a US drop-in fit and ships in 6-8 weeks. For TAA and origin specifics, see the US-origin compliance page.
What thread and end connections are available?
Tube-OD compression ends come standard, alongside NPT, NPTF, BSPT, BSPP, and ISO parallel threads. JIC 37° and SAE ORB fittings round out the lineup, and weld ends are available in socket, butt, and orbital styles. National, international, or custom thread, they're all supported.
What is the minimum order and lead time?
Small minimum order quantities apply, and lead time for US orders runs 6 to 8 weeks. Standard items ship from ready stock; specials are made to order. Private-label and custom or made-to-print options are also available.