904L Tubing (UNS N08904)

904L tubing is OD-sized, round instrumentation tube drawn from super-austenitic stainless 904L (UNS N08904, W.Nr. 1.4539), a copper-bearing stainless running roughly 20Cr-25Ni-4.5Mo-1.5Cu. It carries process fluid or gas between components and seats into a compression fitting's ferrule set to make a leak-tight, make-and-break joint. Crestflo supplies 904L tube seamless to ASTM B677 and welded to ASTM B673, in both imperial and metric sizes, shipped solution-annealed so it bends and cones cleanly into a ferrule. You reach for 904L tube when a line runs dilute-to-moderate sulfuric or phosphoric acid, warm chlorides, or seawater and brine, the service where 316 stainless pits or stress-corrosion cracks, but the duty doesn't yet justify the cost of a 6-molybdenum super-austenitic or a nickel alloy. Standard items ship from stock; specials are built to order, with delivery running 6-8 weeks. Request a quote to price your run.

Reviewed by the Crestflo Engineering Team

Swagelok® and Parker® are trademarks of their respective owners; Crestflo is not affiliated, and interchange is dimensional.

Why Specify 904L Tubing

Tube is the long, continuous wetted surface of an instrument hookup. Unlike a fitting or a valve, it has no dead legs or packing bores, but it has length, every inch of it exposed to the media, and it has to survive the cold work of bending and ferrule make-up without cracking. On a corrosive acid or chloride line that rules out a lot of materials. A stainless tube that pits or stress-corrosion cracks midway along a run is as dead as one that fails at the fitting.

904L is a super-austenitic stainless steel, carrying roughly double the molybdenum of 316L along with much higher nickel and a deliberate copper addition. That chemistry is tuned for the reducing-acid and chloride problem. The copper is the signature element: it gives 904L a genuine edge in dilute-to-moderate sulfuric acid and in phosphoric acid, both reducing environments where 316 and plain 304 struggle. The high molybdenum and chromium drive pitting and crevice resistance, taking its PREN to about 34 against roughly 24 for 316L, and the high nickel content underwrites strong resistance to chloride stress-corrosion cracking, the failure mode that most often limits 304 and 316 in warm chloride service. One of the lowest carbon limits of any austenitic grade keeps that corrosion resistance intact in the weld and the heat-affected zone of a welded tube, rather than letting the weld become the first thing to attack.

Be precise about where 904L sits, though, because it is easy to over-sell. It is a fully austenitic stainless, not a duplex and not a nickel-base alloy. Its strength is moderate: 904L yields at a level comparable to 316, not double it the way a duplex does, so there is no thinner-wall advantage to claim, and the case for 904L is corrosion resistance, not pressure-per-wall. Being fully austenitic does buy two real things. It is essentially non-magnetic in the annealed condition, which is itself a reason to specify it where magnetic permeability matters, and it keeps its toughness down to cryogenic temperatures with no ductile-to-brittle transition, so it is not ruled out of cold duty. Its corrosion service ceiling sits around 350-400 °C (660-750 °F), environment-dependent; this is not a high-temperature strength grade.

What makes 904L the tube to specify is where it sits on cost. It delivers reducing-acid, chloride, and chloride-SCC performance well beyond 316 without paying for a 6Mo super-austenitic or a high-nickel alloy. Where the service turns to hotter seawater or higher chloride than 904L comfortably handles, a 6Mo grade such as 254 SMO or AL-6XN (PREN ~43) is the move; where it is concentrated or hot sulfuric acid, Alloy 20 is the specialist; and for the harshest wet-chlorine and hot contaminated acid, Hastelloy C-276 steps up. 904L is the one you reach for when the duty outruns 316 but stops short of those.

The full metallurgical picture, composition ranges, mechanical and physical properties, PREN, and corrosion-by-media data, lives on the 904L alloy grade page. This page stays on the tube: how it's made, sized, finished, tested, and matched to the fitting.

Also Specified As: Alloy 904L Tube, 904L Seamless Tubing, UNS N08904 Tube

Buyers and specifiers call this tube several ways, and each one points to the same super-austenitic stainless. A requisition might read "904L seamless tubing," "Alloy 904L tube," "N08904 instrument tube," "1.4539 tube," "Type 904L tubing," or "SAE 904L tube," and every one of them lands here. 904L, Alloy 904L, Type 904L, and SAE 904L are the common forms; the material is registered as UNS N08904 and EN / Werkstoff 1.4539, with the EN steel name X1NiCrMoCu25-20-5. The welded form is often written "welded-and-drawn tube," the seamless form "cold-drawn seamless tube." UNS N08904 is the US number and 1.4539 is the European one; they describe one and the same alloy, and a tube labeled "904L" is routinely certified to both at once.

Scope: this is round, OD-sized instrumentation and fluid-system tube for compression and tube-fitting connections. It is not oilfield coiled tubing for downhole well intervention, not structural or ornamental tube, and not pipe specified by nominal pipe size (NPS) and schedule. It is also not watch-case steel; "Oystersteel" is a watch-industry trade name for a 904L variant, a different world entirely. Crestflo supplies 904L in instrumentation tube, fitting, and valve forms only, not mill bar, sheet, plate, or pipe.

Seamless vs Welded 904L Tubing

Both constructions are built to their own high-alloy stainless tube specification, and both accept a compression fitting the same way. Seamless 904L tube is cold-drawn from a hollow with no longitudinal weld, which makes it the default where you want maximum integrity for higher-pressure, cyclic, or critical service. Welded-and-drawn 904L tube is formed from strip, seam-welded, then cold-drawn to size; it is dimensionally consistent and cost-effective for general instrument and fluid-system work. The grade's very low carbon limit (0.020% max) is what keeps corrosion resistance intact in the weld and the heat-affected zone, so welded 904L holds up in service that would sensitize a leaner austenitic. Because 904L is fully austenitic rather than duplex, there is no ferrite-balance check to run on the weld, which is one fewer acceptance step than a 2205 or 2507 tube carries.

Not sure which construction to call out? The deep dives on seamless tubing and welded tubing walk through the trade-off before you commit a spec.

904L Tube Attributes at a Glance

904L Tube Sizes: OD, Wall & Imperial/Metric

Instrument tube is specified by its actual outside diameter and wall thickness, given in both imperial and metric units, never by NPS and schedule. The common instrument range runs fractional 1/8″ to 1″ and metric 6 to 12 mm; smaller 1/16″ small-bore tube and larger diameters up to 2″ (50 mm) are available to order. Wall thickness is chosen to carry the pressure and to suit the ferrule, and both OD and wall are held to the tolerances of ASTM B677 (seamless) or B673 (welded). Because 904L is a moderate-strength austenitic rather than a high-strength duplex, it earns no thinner-wall credit: size the wall to the same pressure math you would run for any austenitic stainless. Working pressure is not a single blanket figure: it is calculated from OD, wall thickness, and the alloy's allowable stress per ASME B31.3, so it is stated per size and wall rather than as one rating for the grade.

Values per applicable standard; customizable to requirement. For how to work back from a target pressure to a wall thickness, see the tube sizing and wall thickness guide, and for the full dimensional matrix across the range, the tubing size chart.

Temper & Hardness: Solution-Annealed for Bending and Ferrule Seating

The single most important mechanical property of instrument tube is not its peak strength but its softness. 904L is a solid-solution austenitic grade that does not age-harden, so it comes in one working condition, solution-annealed, and that condition is what lets the tube bend around a radius and cone down under a ferrule without cracking, so the joint seats and seals the way a compression fitting is designed to. In the solution-annealed condition 904L carries a tensile minimum around 71 ksi (490 MPa) with a 0.2% yield near 32 ksi (220 MPa) and elongation above 35%, with hardness in the annealed band (typically ≤ ~90 HRB). That yield is comparable to 316, not double it, which is the honest reason 904L buys no thinner-wall advantage. Being fully austenitic, it has no ferrite phase to balance and no ductile-to-brittle transition, so the same temper that makes it workable also keeps it tough from cryogenic temperatures up through its corrosion service range. Specify the hardness or condition to your own standard on the RFQ and it is confirmed on the certificate.

Finishes & Cleanliness: Bright-Anneal, Electropolish & Oxygen-Clean

904L tube ships in a mill/bright-annealed finish as standard. For high-purity gas, analytical, and oxygen service, passivation, electropolishing (EP), and oxygen/UHP cleaning with capped-and-bagged packaging are available. Electropolishing lowers surface roughness and smooths the inner diameter, which matters where particle generation, moisture dry-down, or deposit build-up is the concern. Standard UHP electropolish surface-roughness targets can be specified right on the RFQ to your own standard; electropolished tubing and oxygen and UHP cleaning cover the options in detail. Finish and cleanliness figures follow the applicable standard and are customizable to requirement.

904L Tube Standards: ASTM B677, B673 & ASME B31.3

904L tube is covered by the high-alloy stainless tube specifications, not the 300-series austenitic specs such as ASTM A269 or A213, and the construction decides which applies: seamless falls under ASTM B677, welded under ASTM B673, each with its matching ASME boiler-code SB- designation. Allowable working pressure for a given size and wall is calculated per ASME B31.3. Where sour service applies, the material can be supplied to NACE MR0175 / ISO 15156 as the application qualifies. Crestflo holds the standard approvals that apply to instrumentation tube and is ISO 9001 / 14001 / 45001 and PED certified.

The full family of 904L product-form specifications, including welded pipe (B674), bar (B649), and plate (B625), is set out on the 904L grade page; for tube, B677 and B673 are the two that apply.

Working Pressure: Calculated per ASME B31.3, Not Assumed

There is no single pressure rating for "904L tube," and any supplier who quotes one is skipping the engineering. Allowable internal pressure depends on three things: the tube OD, its wall thickness, and the alloy's allowable stress at the service temperature. ASME B31.3 sets the method, relating wall thickness to pressure, diameter, the allowable stress value S, the weld-joint quality factor E, and the coefficient Y. Seamless tube carries a higher joint factor than welded, which is part of why seamless is chosen for higher-pressure work. 904L is a moderate-strength austenitic, so its allowable stress sits near that of other austenitic stainless rather than above it, and it derates with temperature the way austenitics do; do not expect a duplex-style strength bonus. The thin-wall instrument sizes still carry ample pressure for analyzer, sample, and injection duty. Give us the OD, wall, temperature, and medium on the RFQ and the engineering team returns the calculated working pressure for your configuration. Values per the applicable standard; customizable to requirement.

Testing, NDT & Material Verification

Every length of 904L tube is verified before it ships. ASTM B677 and B673 require each tube to pass either a hydrostatic test or a nondestructive (eddy-current) electric test, and dimensional checks confirm OD, wall, and straightness against the ordered tolerances. Positive material identification (PMI) confirms the alloy on the material, which matters for a high-alloy stainless where the nickel, molybdenum, and copper content is exactly what buys the corrosion performance and must be verified, not assumed. NDT is done in-house; destructive testing, where a job calls for it, goes to ISO/IEC 17025-accredited labs, and third-party inspection is available on request.

For sour service, 904L tube material can be supplied to NACE MR0175 / ISO 15156 where the application qualifies. Confirm the hardness and material-condition limits in the standard against your application, H₂S partial pressure, temperature, and chloride content, and note the sour-service requirement on the RFQ.

Straight Lengths & Coiled 904L Tube

904L tube ships as straight lengths for racked and rigidly supported runs, and as continuous coils for heat-tracing, long analyzer and sample lines, and chemical-injection and hydraulic bundles where a joint-free run is the whole point. Coiled tube keeps the count of mechanical joints down, which on a corrosive, acid, or buried line is one fewer place to leak, and 904L's chloride-SCC resistance makes it a natural choice for the sample and injection cores that run in seawater and brine. Both forms are supplied solution-annealed; call out length or coil length on the RFQ. For long-run and tracing applications, see coiled tubing; for thicker-wall high-pressure control lines, hydraulic tubing.

Material Traceability & Certification

Every length of 904L tube carries its own heat/lot number, and each order ships with an EN 10204 MTC 3.1 certificate as standard, 3.2 available on request. PMI confirms the grade at the part level, every time. That documentation backs the audit trails that acid-plant, chemical, and chloride-service jobs demand, the kind of work where a mis-specified or under-alloyed tube in a long run is an expensive thing to discover in commissioning. Full detail is on the traceability page.

Applications for 904L Tubing

904L tube earns its place wherever reducing acids or chlorides rule 316 out of a long wetted run, but the duty doesn't yet justify a 6Mo or nickel alloy:

• Sulfuric and phosphoric acid processing, process, analyzer, and sample lines in dilute-to-moderate sulfuric and in phosphoric acid, the copper-bearing signature duty for 904L. See petrochemical and chemical processing.
• Pickling and acid-handling lines, dosing, sample, and transfer tube in mixed-acid and regeneration service.
• Flue-gas desulfurization (FGD) and pollution control, scrubber and absorber instrument lines in wet, reducing, chloride-laden condensate.
• Chloride process and seawater service, warm-chloride pitting and stress-corrosion environments on coastal and desalination plant, where 904L's chloride-SCC resistance beats 304 and 316.
• Pulp and paper, bleach-plant and chloride-bearing process instrument lines.
• Non-magnetic and cryogenic requirements, lines where low magnetic permeability or low-temperature toughness governs, both of which the fully austenitic structure provides.

Where the service steps past 904L, to hotter seawater and higher chloride, concentrated hot sulfuric, or wet chlorine, see the step-up grades in the next section.

Where 904L Stops: Stepping Up to 6Mo, Alloy 20 or C-276

904L sits a clear step above 316 but below the 6-molybdenum super-austenitics and the nickel alloys. Knowing where it stops is as important as knowing what it handles. Where the duty is hotter seawater or higher chloride than 904L comfortably manages, move to a 6Mo grade such as 254 SMO or AL-6XN (PREN ~43). Where it is concentrated or hot sulfuric acid, Alloy 20 is the purpose-built specialist. Where the stream turns to wet chlorine or hot contaminated acid, Hastelloy C-276 is the answer. For the baseline comparison that drives most 904L decisions, see 904L vs 316. Match the alloy to the media and don't over-specify.

Pairing 904L Tube With 904L Fittings and Valves

A tube is one part of the hookup, and the joint is only as corrosion-resistant as its weakest metal. For a matched instrument run, pair this tube with 904L tube fittings and 904L instrumentation valves so the whole assembly, tube, ferrules, and valve body, carries the same resistance and the same traceability. Crestflo supplies the tube alongside compression fittings tested to ASTM F1387, so the ferrule set seats correctly on the exact OD and wall you ordered, and the joint is a dimensional match rather than a mix of two suppliers' tolerances. Putting a 904L tube into a 316 fitting just moves the failure point to the ferrule. Because 904L is a high-nickel austenitic that work-hardens and can gall, anti-galling measures such as silver plating on the ferrule are offered on request where repeated make-up or high torque is expected.

Drop-In Interchange and the Tube-Plus-Fitting System

Crestflo 904L tube is cut and finished to standard OD and wall, so it drops into the compression fittings you already run, and the matching 904L fittings are built as dimensional interchange / equivalent parts for the major brands, with the fitting ends qualified to ASTM F1387. These are not "compatible" or "intermix" parts. Swagelok® and Parker® remain trademarks of their respective owners, and Crestflo is not affiliated; the interchange is strictly dimensional. Moving a run off a major brand? Request your Swagelok®/Parker® cross-reference and the engineering team maps your tube and fitting part numbers to Crestflo 904L equivalents. We don't publish a part-number table.

Origin & US-Serving Positioning

Crestflo manufactures for the US market. Standard product is of Indian origin; US or European melt is available on request, with full material traceability. Tube is engineered as a US drop-in and ships in 6-8 weeks, well under the 20+ weeks typical of the majors. If a project calls for a specific melt origin or TAA/DFARS handling, specify it on the RFQ and we'll address it straight, no hedging. See the US-origin compliance page for how we document it.

Why Crestflo for 904L Tubing

Crestflo operates as the instrumentation division of an export house with four decades behind it and formal recognition from the Government of India, with a proven Middle-East delivery record. That backing grounds a focused instrumentation brand built on a handful of clear advantages:

• Lead time of 6-8 weeks versus 20+ weeks typical of the majors, on standard stock and made-to-order specials alike.
• A matched system, tube plus F1387-tested fittings and ferrules that seat on the exact OD and wall you ordered.
• Both seamless and welded 904L tube, in both imperial and metric, straight or coiled.
• Heat-number marking plus MTC 3.1/3.2 on every order, PMI-confirmed, so a high-alloy super-austenitic is never taken on trust.
• NACE MR0175 / ISO 15156 material options where the sour-service application qualifies.
• ISO 9001 / 14001 / 45001 & PED certified, cost-competitive after US duties and tariffs, with small MOQs and private-label available.

We Engineer Confidence.

Request a Quote for 904L Tubing

Give us the details: seamless or welded, OD and wall, straight length or coil, finish and cleanliness, and the line conditions (media, pressure, temperature, sour-service requirement). We'll calculate the working pressure, confirm the spec, and schedule the run.

• Request a quote, the fastest path to pricing and lead time.
• Request a sample for qualification.
• Request your Swagelok®/Parker® cross-reference and we'll map your tube and fitting part numbers.

Datasheets and CAD 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 the system with 904L tube fittings and 904L valves, browse the tubing pillar for other grades and constructions, and see where this tube serves in petrochemical and chemical processing.

Frequently Asked Questions

Related Pages

• 904L alloy grade & corrosion data
• 904L tube fittings · 904L instrumentation valves
• Tubing pillar · Instrumentation tubing · Seamless tubing · Welded tubing
• 904L vs 316 · 254 SMO · Alloy 20
• ASME B31.3 · NACE MR0175 · EN 10204 MTC · Petrochemical & chemical