UNS C71520 (CuNi 70/30) Copper-Nickel Open-Die Forgings & Tubesheets
Summary
UNS C71520 is a 70/30 copper-nickel alloy (CuNi 70/30) with a minimum 65 % copper and 29-33 % nickel, supplied under ASTM B171/B171M for pressure vessels, condensers and heat exchangers. It is the low-impurity, weldable version of C71500. Zinc is capped at 0.50 % instead of 1.0 %, and lead, phosphorus and sulfur are each capped at 0.02 %, so the material can be welded without hot cracking. In the M20 and O25 tempers, plate and forged flat products 60 mm and under must reach 345 MPa (50 ksi) tensile strength, 140 MPa (20 ksi) yield and 30 % elongation.
Jiangyin Jiangnan Metal Co., Ltd. forges C71520 into tubesheets, seamless rolled rings, flanges, discs, hollow bars and round bars up to 12,000 kg at its plant at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Enquiries: sales@steelforgepieces.com, +86 189 2135 9659.
Classification note: C71520 is a copper-nickel alloy, not an alloy steel. There is no iron base. Iron is present only as a 0.40-1.0 % addition that improves resistance to impingement attack. Buyers who look for it as a steel grade are in fact looking for a copper-base material in the UNS Cxxxxx series.
What is UNS C71520?
UNS C71520 is a single-phase, solid-solution copper-nickel alloy containing nominally 70 % copper and 30 % nickel, with deliberate additions of iron and manganese. The iron addition of 0.40-1.0 % gives the 70/30 family its resistance to erosion-corrosion and impingement attack in fast-moving seawater. Manganese acts as a deoxidiser and improves hot workability.
Copper and nickel are mutually soluble across the whole composition range, so C71520 cannot be hardened by heat treatment. It is strengthened only by cold work, and it is supplied either as-worked or annealed. That single-phase structure is also why the alloy is essentially immune to chloride stress-corrosion cracking, the failure mode that limits austenitic stainless steels in seawater service.
ASTM B171/B171M is the governing specification for plate, sheet and circles cut from plate for pressure vessels, condensers and heat exchangers. Material under B171 is manufactured by hot rolling or forging, then finished by whatever cold working and annealing is needed to reach the required dimensions and properties. An open-die forge is therefore a compliant source of C71520 tubesheets and heavy flat products, in the same way a rolling mill is.
C71520 compared with C71500
C71500 and C71520 have the same copper and nickel content and the same mechanical requirements. They differ only in the permitted level of four impurity elements, and that difference exists to make the material weldable. If a fabrication will be welded, C71520 is the grade to specify.
| Element | C71500 | C71520 | Why it is restricted |
|---|---|---|---|
| Zinc, Zn | 1.0 | 0.50 | Fume and porosity in the weld pool |
| Lead, Pb | Not specified | 0.02 | Liquid-metal embrittlement, hot cracking |
| Phosphorus, P | Not specified | 0.02 | Low-melting films at grain boundaries |
| Sulfur, S | Not specified | 0.02 | Hot shortness during welding |
| Carbon, C | 0.05 | 0.05 | Carbide formation, reduced corrosion resistance |
In older editions the same restricted limits appear as a footnote to C71500 covering subsequent welding applications. C71520 makes those limits mandatory rather than optional.
Ordering C71500 and hoping it will weld is a gamble on the residuals in the heat. Ordering C71520 puts the low-impurity chemistry on the mill certificate as a contractual requirement. For welded tubesheet-to-shell assemblies, clad overlay work and any fabrication that may involve weld repair, specify C71520.
Chemical composition
| Element | Symbol | Composition (%) |
|---|---|---|
| Copper | Cu | 65.0 min |
| Nickel | Ni | 29.0-33.0 |
| Iron | Fe | 0.40-1.0 |
| Manganese | Mn | 1.0 max |
| Zinc | Zn | 0.50 max |
| Carbon | C | 0.05 max |
| Lead | Pb | 0.02 max |
| Phosphorus | P | 0.02 max |
| Sulfur | S | 0.02 max |
Copper is reported as copper plus silver. Nickel may be reported as nickel plus cobalt. Total named elements plus copper must meet the 99.5 % minimum stated in the specification.
Mechanical properties
ASTM B171/B171M sets two thickness bands for C71520. Material 60 mm (2.5 in) and under must reach 345 MPa tensile and 140 MPa yield. Material over 60 mm up to 140 mm (5 in) must reach 310 MPa tensile and 125 MPa yield. Minimum elongation is 30 % in both bands.
| Thickness | Tensile strength, min | Yield strength, min | Elongation in 50 mm, min |
|---|---|---|---|
| 60.0 mm (2.5 in) and under | 345 MPa (50 ksi) | 140 MPa (20 ksi) | 30 % |
| Over 60.0 to 140.0 mm (2.5 to 5 in), incl. | 310 MPa (45 ksi) | 125 MPa (18 ksi) | 30 % |
Yield strength under this specification is the stress producing an elongation of 0.5 % under load, that is 0.254 mm (0.01 in) in a 50 mm (2 in) gauge length, rather than a 0.2 % offset. Tensile testing follows ASTM E8/E8M. Tempers available under B171 are as-hot-rolled (M20), hot-rolled and annealed (O25), hot-forged and annealed (O20) and as-hot-forged air-cooled (M10). Properties for forged tempers are confirmed on the mill test certificate at the time of order. Table numbering varies between editions of B171; the current edition governs.
Note on published figures: several grade databases list the elongation of C71520 as 430 %, and some swap the two thickness rows so that the thinner band appears to carry the lower strength. The correct minimum elongation is 30 %, and the thinner band carries the higher strength requirement, as shown above. An elongation of 430 % is not physically possible for a wrought copper-nickel alloy.
Physical properties
| Property | Metric | Imperial |
|---|---|---|
| Density at 20 °C | 8.94 g/cm³ | 0.323 lb/in³ |
| Melting range | 1170-1240 °C | 2140-2265 °F |
| Modulus of elasticity | 152 GPa | 22 × 10⁶ psi |
| Poisson's ratio | 0.325 | 0.325 |
| Thermal conductivity at 20 °C | 29 W/(m·K) | 17 Btu/(ft·h·°F) |
| Coefficient of thermal expansion, 20-300 °C | 16.2 × 10⁻⁶ /K | 9.0 × 10⁻⁶ /°F |
| Specific heat capacity at 20 °C | 377 J/(kg·K) | 0.09 Btu/(lb·°F) |
| Electrical conductivity, annealed | ≈ 4.6 % IACS | ≈ 4.6 % IACS |
| Electrical resistivity at 20 °C | ≈ 37 µΩ·cm | ≈ 224 Ω·cmil/ft |
| Machinability rating | 20 (C36000 = 100) | 20 |
| Max recommended seawater velocity | 4.5 m/s | 15 ft/s |
Physical properties are typical published values for the 70/30 copper-nickel family and are given for design guidance only. They are not acceptance criteria under ASTM B171/B171M, and they are not reported on the mill certificate unless separately agreed in the purchase order.
Equivalent grades and specifications
| System / region | Designation | Notes |
|---|---|---|
| UNS (USA) | C71520 | Restricted-impurity, weldable grade |
| UNS (USA) | C71500 | Base 70/30 grade; same Cu/Ni, looser residuals |
| EN / DIN (Europe) | CuNi30Mn1Fe · CW354H · 2.0882 | Nearest European equivalent |
| BS (UK) | CN107 | Legacy British designation |
| JIS (Japan) | C7150 | Nearest Japanese equivalent |
| ISO | CuNi30Mn1Fe | Composition designation |
| CDA | CDA 715 | Copper Development Association number |
| Specification | Product form |
|---|---|
| ASTM B171 / ASME SB-171 | Plate, sheet and circles cut from plate for pressure vessels, condensers, heat exchangers and tubesheets |
| ASTM B124 | Forging rod, bar and shapes |
| ASTM B283 / ASME SB-283 | Die forgings, hot pressed |
| ASTM B151 / ASME SB-151 | Rod and bar |
| ASTM B466 / ASME SB-466 | Seamless pipe and tube |
Equivalents are nearest-match designations for purchasing reference. They are not automatically interchangeable. Confirm the acceptance criteria of the governing specification before substituting a grade in a coded pressure application.
C71520 forged products we manufacture
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, not a stockholder. C71520 parts are forged to order from cast cake or billet, so sizes follow the drawing rather than stock availability. The forms below are produced routinely.
| Product form | Typical size range | Usual specification |
|---|---|---|
| Tubesheets / tube plates | Ø 300-3,500 mm, thickness 20-400 mm | ASTM B171 |
| Baffles and support plates | Ø 300-3,000 mm, thickness 10-80 mm | ASTM B171 |
| Seamless rolled rings | OD 300-3,000 mm, height to 800 mm | ASTM B124 / B283 |
| Forged flanges | DN 50-DN 1600, to Class 2500 | ASTM B171 / B124 |
| Discs and blanks | Ø 100-2,500 mm | ASTM B171 / B124 |
| Round bars | Ø 20-800 mm | ASTM B151 / B124 |
| Hollow bars and sleeves | OD 100-1,200 mm | ASTM B124 / B283 |
| Shells, cylinders, housings | To 12,000 kg finished weight | Per drawing |
| Valve bodies and pump casings | To 3,000 kg finished weight | Per drawing |
| Clad / weld-overlay tubesheets | Carbon or low-alloy steel base with C71520 overlay | Per procedure qualification |
Size ranges are the normal working envelope of the plant. Larger or heavier pieces are reviewed case by case. Send the drawing for confirmation.
Clad and weld-overlay tubesheets
Where full-thickness copper-nickel is not economic, we supply tubesheets with a carbon or low-alloy steel backing and a C71520 weld overlay on the wetted face, typically 6-12 mm of deposited thickness after machining. This is common on large seawater condensers, where a solid C71520 tubesheet of 3 m diameter would be prohibitively expensive. Overlay work is carried out to a qualified WPS with PQR records, dye-penetrant examination of the finished face, and ultrasonic testing for bond integrity.
How we forge and verify C71520
Copper-nickel is unforgiving of loose process control. Its narrow hot-working window and its sensitivity to sulfur pickup mean that the practices used for carbon steel will produce cracked, gassy forgings in C71520. Our route is as follows.
- Material and traceability. Cast cake or billet is purchased to the ASTM B171 chemistry with a certified heat analysis. Each heat is stamped and tracked through to the finished part.
- Incoming verification. Chemistry is confirmed in-house by optical emission spectrometry before the material enters the furnace. Positive material identification (PMI) is applied to every piece to prevent grade mix-up with C70600 and C71500.
- Heating. Soaking takes place in a controlled, sulfur-free atmosphere. Sulfur pickup from fuel causes intergranular embrittlement in nickel-bearing copper alloys, so oil-fired heating on shared hearths is avoided for this grade.
- Forging. Open-die forging within the hot-working range, with reheats scheduled so the work never finishes below temperature. Reduction ratio is planned to break down the cast structure through the full section rather than only at the surface.
- Annealing. Solution anneal and controlled cool to the O20 or O25 temper as ordered. C71520 cannot be hardened by heat treatment, so the anneal exists to restore ductility and relieve forging stresses, not to develop strength.
- Non-destructive examination. Ultrasonic testing to ASTM B171 requirements or to the customer's acceptance class, plus dye-penetrant examination of machined faces and weld overlays.
- Mechanical testing. Tensile testing to ASTM E8/E8M from test locations agreed with the purchaser, with yield reported on the 0.5 % extension-under-load basis that B171 requires.
- Machining. Rough or finish machining in-house, including tube-hole drilling to the tube layout drawing, grooving for tube expansion, and gasket-face finishing.
- Documentation. EN 10204 3.1 mill test certificate as standard, with 3.2 third-party inspection available. Reports cover heat chemistry, mechanical results, NDE records, dimensional inspection and heat-treatment charts.
Where C71520 is used
C71520 is specified where seawater or brackish water meets a requirement for both corrosion resistance and weldability. Typical service:
- Seawater condensers and heat exchangers: tubesheets, baffles and support plates in power stations and process cooling trains.
- Desalination plants: multi-stage flash and multi-effect distillation evaporators, brine heaters, tubesheets and waterboxes.
- Naval and commercial marine systems: seawater cooling piping, sea chests, valve and pump bodies, condenser tubesheets.
- Offshore platforms: firewater ring mains, cooling-water systems and heat exchangers on raw seawater duty.
- Oil and gas processing: coolers and exchangers in refinery and offshore service where the water is polluted or carries sulfides.
- Brackish and polluted water: conditions in which the higher nickel content of the 70/30 alloy outperforms 90/10 C70600 at high velocity or under sulfide contamination.
Choosing between C71520 and C70600
C70600 (90/10 copper-nickel) is cheaper and adequate for clean seawater at moderate velocity. C71520 costs more but tolerates higher flow rates, around 4.5 m/s against roughly 3.0 m/s for the 90/10 alloy, and it holds up better in polluted or sulfide-bearing water. It also carries the higher strength requirement, which matters on thick tubesheets that take a significant pressure differential. Where a system sees intermittent stagnation followed by high flow, the 70/30 alloy is the safer selection.
What we need to quote a C71520 forging
A drawing plus the governing specification is usually enough to return a price and lead time within two working days. The full checklist is below.
- Governing specification and edition, for example ASTM B171/B171M, or ASME SB-171 for coded work
- Temper required: O20 or O25 annealed, or M10 / M20 as-forged
- Drawing or full dimensions, including tube-hole layout for tubesheets
- Quantity and required delivery date
- Supply condition: as-forged, rough machined, or finish machined
- NDE requirements and acceptance class
- Certification level, EN 10204 3.1 or 3.2, and any third-party inspection body
- Whether the part will be welded in fabrication, and any customer WPS to be followed
- Marking, preservation and packing requirements for sea freight
Request a quotation for C71520 forgings
Send a drawing or a description of the part and we will confirm feasibility, weight, price and lead time. We quote in USD ex-works Jiangyin or on FOB Shanghai terms.
Jiangyin Jiangnan Metal Co., Ltd., Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Frequently asked questions
What is the difference between C71520 and C71500?
C71520 and C71500 have identical copper and nickel ranges and identical mechanical requirements. C71520 additionally restricts four impurities so the alloy can be welded: zinc to 0.50 % maximum instead of 1.0 %, and lead, phosphorus and sulfur to 0.02 % maximum each. Specify C71520 whenever the finished part will be welded, weld-overlaid or weld-repaired.
Is UNS C71520 a steel?
No. UNS C71520 is a copper-nickel alloy with a minimum 65 % copper and 29-33 % nickel. Iron is present only as a 0.40-1.0 % alloying addition to improve resistance to impingement attack. The UNS Cxxxxx prefix designates copper-base materials; steels carry G, K, S or T prefixes.
What is the tensile strength of C71520?
Under ASTM B171/B171M in the M20 and O25 tempers, C71520 up to 60 mm (2.5 in) thick must reach a minimum 345 MPa (50 ksi) tensile strength and 140 MPa (20 ksi) yield strength. Over 60 mm up to 140 mm (5 in), the minima are 310 MPa (45 ksi) tensile and 125 MPa (18 ksi) yield. Minimum elongation is 30 % in 50 mm for both thickness bands.
Why do some sources give the elongation of C71520 as 430 %?
The correct minimum elongation is 30 % in a 50 mm gauge length. The 430 % figure carried by several online grade databases is a transcription error, and that value is not physically possible for a wrought copper-nickel alloy. Annealed 70/30 copper-nickel typically shows about 40 % elongation in actual testing.
Can C71520 be hardened by heat treatment?
No. Copper and nickel form a continuous solid solution, so C71520 has no second phase to precipitate and cannot be hardened by heat treatment. It is strengthened only by cold work. Annealing is used to restore ductility and relieve forging stresses, not to raise strength.
What is the maximum seawater velocity for C71520?
Around 4.5 m/s (15 ft/s) is the commonly cited design limit for 70/30 copper-nickel, compared with roughly 3.0 m/s for 90/10 C70600. The protective cuprous oxide film that gives the alloy its corrosion resistance is removed by impingement above that velocity. The 0.40-1.0 % iron addition is there specifically to raise this threshold.
Does C71520 suffer chloride stress-corrosion cracking?
C71520 is highly resistant to chloride stress-corrosion cracking, which is the main reason it is chosen over austenitic stainless steel for seawater service. It is, however, susceptible to attack by ammonia and by sulfides, so condensers handling ammonia-contaminated steam or stagnant sulfide-bearing water need separate assessment.
Can C71520 tubesheets be supplied as forgings rather than rolled plate?
Yes. ASTM B171/B171M states that material shall be manufactured by hot rolling or forging, then finished by such cold working and annealing as needed to achieve the required dimensions and properties. Open-die forging is therefore a compliant route, and it is usually the only practical route for thick or large-diameter tubesheets where plate of the required thickness is not available. Jiangyin Jiangnan Metal Co., Ltd. forges C71520 tubesheets up to 3,500 mm diameter and 400 mm thick.
Which ASTM specifications cover C71520 forgings?
ASTM B171/B171M covers plate, sheet and circles for pressure vessels, condensers and heat exchangers, including tubesheets. ASTM B124 covers forging rod, bar and shapes; ASTM B283 covers hot-pressed die forgings; ASTM B151 covers rod and bar; ASTM B466 covers seamless pipe and tube. The ASME equivalents SB-171, SB-283, SB-151 and SB-466 are used for code work.
What is the minimum order quantity for C71520 forgings?
Jiangyin Jiangnan Metal Co., Ltd. forges to order from cast cake or billet rather than cutting from stock, so single-piece orders are accepted where the piece justifies a heat. For small parts a minimum lot weight generally applies so that one heat can be certified economically. Send the drawing to sales@steelforgepieces.com for confirmation of minimum quantity, price and lead time.
Where is your factory and what documentation do you supply?
The plant is at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Standard documentation is an EN 10204 3.1 mill test certificate covering heat chemistry, mechanical test results, NDE records, dimensional inspection and heat-treatment charts. EN 10204 3.2 certification with third-party inspection is available on request.
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China, producing forged rings, flanges, shafts, bars, blocks, tubesheets, valve parts and pipe components in carbon steel, alloy steel, tool steel, stainless steel, nickel alloys and copper-nickel alloys. Jiangyin sits in the Yangtze River Delta forging cluster in southern Jiangsu, roughly 150 km from the Port of Shanghai, which keeps export freight times short for heavy single pieces.
The company works to drawing and to specification rather than from a stock list, and supplies both as-forged blanks and finish-machined parts. Enquiries in English are handled directly by the sales engineering team at sales@steelforgepieces.com or +86 189 2135 9659.
Related grades
Sources
- ASTM B171/B171M, Standard Specification for Copper-Alloy Plate and Sheet for Pressure Vessels, Condensers, and Heat Exchangers. Published by astm.org
- ASTM B171 tensile property and chemistry tables, C71500 / C71520 rows: boltport.com
- Copper Development Association / CDA 715 alloy data sheet for 70/30 copper-nickel
- ASME SB-171 C71520 mechanical property summary: gravitycastindia.com
Technical data on this page is provided for engineering reference. The current edition of the governing specification takes precedence, and material is accepted against the mill test certificate issued for the specific heat supplied.