EN 10253-4 Type B 904L · X1NiCrMoCu25-20-5 PRE ~35 · 4.5% Mo + Cu

1.4539 (904L) Pipe Fittings

EN 10253-4 Type B buttweld pipe fittings in 1.4539 — 904L high-alloy austenitic stainless steel (X1NiCrMoCu25-20-5, N08904). 4.5% Mo and 1.5% Cu give PRE ~35 — bridging the gap between 316L (PRE ~24) and duplex (PRE ≥35). The copper addition provides specific resistance to reducing acids, particularly sulphuric acid. PRE equivalent to Duplex 2205 but fully austenitic, no sigma phase risk.

PRE (approx.)

~35

Mo + Cu

4.5% Mo · 1.5% Cu

ASTM UNS

N08904

Chemistry (EN 10088-4)

Element	Min	Max	Function
C (Carbon)	—	0.020%	Ultra-low C — avoids sensitisation
Cr (Chromium)	19.0%	21.0%	Passive film
Ni (Nickel)	24.0%	26.0%	High Ni — SCC immunity, austenite stability
Mo (Molybdenum)	4.0%	5.0%	PRE contributor: 3.3×4.5% ~15 pts
Cu (Copper)	1.2%	2.0%	Reducing acid resistance (H₂SO₄, H₃PO₄)

1.4539 (904L) vs Alternatives

Grade	PRE	Structure	Cu	When to Choose
1.4404 (316L)	~24	Austenitic	None	Mild service — lower cost
1.4539 (904L)	~35	Austenitic	1.5%	H₂SO₄, H₃PO₄, seawater — need Cu + PRE ~35
1.4462 (Duplex)	≥35	Duplex	None	PRE ≥35, no temperature ceiling concern, no acid need
1.4547 (254 SMO)	≥43	Austenitic	0.5–1%	Higher PRE needed; 6Mo + Cu

Key Applications

Sulphuric acid (H₂SO₄) process piping — Cu provides reducing acid resistance where 316L fails
Phosphoric acid (H₃PO₄) wet-process plants
Seawater cooling at moderate temperatures (PRE ~35, below duplex where cost is a constraint)
Marine applications where austenitic structure preferred over duplex (no sigma ceiling)
Scrubbers handling SO₂ + moisture (FGD pre-treatment)

Cross-References

W.Nr.	1.4539
EN Name	X1NiCrMoCu25-20-5
ASTM UNS	N08904
Common Name	904L

Welding

Filler: ERNiCrMo-3 (Inconel 625 filler) is widely used for 904L — matches or exceeds corrosion resistance. Dedicated 904L filler (ER320LR) also available. No PWHT required.

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Testing & Inspection

✓ Chemical analysis against EN 10216-5 / EN 10253
✓ Tensile test, with impact test where the standard or your order requires it
✓ PMI confirming Mo and Cu content
✓ PMI (positive material identification) on every order
✓ Visual and dimensional inspection to EN 10253
✓ NDT (UT, RT, MT or PT) when your order or code calls for it
✓ EN 10204 3.1 certificate as standard; 3.2 with TÜV, Lloyd's Register, Bureau Veritas, DNV or your own inspector

Size Range

DN15–DN600 and larger. Outside diameters follow the EN 10220 / EN ISO 1127 pipe series; wall thickness is matched to your connecting pipe.

Size	OD (mm)
DN 15	21.3
DN 20	26.9
DN 25	33.7
DN 32	42.4
DN 40	48.3
DN 50	60.3
DN 65	76.1
DN 80	88.9
DN 100	114.3
DN 125	139.7
DN 150	168.3
DN 200	219.1
DN 250	273.0
DN 300	323.9
DN 350	355.6
DN 400	406.4
DN 450	457.0
DN 500	508.0
DN 600	610.0

Export Documents & Packing

✓ Commercial invoice, packing list and certificate of origin
✓ EN 10204 certificates with heat-number traceability
✓ PED 2014/68/EU and AD 2000-Merkblatt W0 documentation for European projects
✓ Seaworthy wooden cases or pallets, bevel ends protected, marked to your instructions
✓ FOB, CFR or CIF delivery terms

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Frequently Asked Questions: 1.4539 (904L) Fittings

Where does 904L (1.4539) sit between 316L and duplex?

With 4.5% molybdenum and 1.5% copper its PRE is about 35, bridging 316L (about 24) and duplex (35 and above).

What is the designation of 1.4539?

X1NiCrMoCu25-20-5 (UNS N08904).

Why does 904L contain copper?

The copper addition gives specific resistance to sulphuric acid.