ASTM B111 C68700 Complete Data Sheet

ASTM B111 C68700 aluminum brass tube contains 76-79% copper, 19-22% zinc, and 1.5-2.5% aluminum. Tensile strength ranges from 550 to 750 MPa depending on temper. This data sheet covers chemical limits, mechanical properties, physical properties, and test methods.

We successfully supplied ASTM B111 C68700 aluminum brass tubes to a customer in India for shell & tube condenser applications. During the project, the customer visited our facility for production inspection and quality verification. All tubes were manufactured in accordance with ASTM B111 requirements and delivered with complete Material Test Certificates (MTC), ensuring full heat number traceability and verified chemical and mechanical properties.

Download ASTM B111 C68700 MTC (PDF)

Per ASTM B111 / ASME SB111, C68700 aluminum brass must meet these chemical limits:

Why aluminum matters: The 1.5-2.5% aluminum content is the key difference between C68700 and standard brass. Aluminum forms a protective oxide film that blocks dezincification. Below 1.5% Al, dezincification rate doubles. Above 2.5% Al, the alloy becomes brittle.

GNEE quality control: Every batch is tested with optical emission spectrometry (OES). Results reported on EN 10204 3.1 certificate. Buyers can request independent lab verification.

C68700 is available in three tempers. Each has different strength and ductility:

Selection guide:

O60 – Use for tube sheet expansion (condensers, heat exchangers). The lower yield strength allows 15-20% expansion without cracking.

H80 – Use for straight piping with mechanical couplings. Do not expand H80 tubes – they will crack.

Aged – Use for high-pressure or high-temperature service (up to 300°C). Aging increases hardness by 15-20% but reduces ductility.

GNEE stock: O60 is stocked in all sizes. H80 and aged are made to order (15-20 day lead time).

Key takeaway for engineers: Thermal conductivity (105 W/m·K) is double that of C70600 (45 W/m·K) and triple that of titanium (22 W/m·K). For heat exchangers, C68700 transfers heat much more efficiently.

Per ASTM G48 (dezincification test) and ASTM G73 (erosion test):

GNEE note: The <0.025 mm/year dezincification rate means a 2.0 mm wall tube loses less than 0.5 mm after 20 years. Always use this number for life calculations.

Per ASTM B111, seamless C68700 tubes must meet these tolerances:

Length tolerances:

Cut lengths under 6,000 mm: ±1.5 mm

Cut lengths over 6,000 mm: ±3.0 mm

Coils (no cut): No tolerance, but ends must be square

GNEE guarantee: All tubes are 100% eddy current tested (ASTM E243) and hydrostatically tested to 6.0 MPa minimum.

When purchasing ASTM B111 C68700 from GNEE (China), request these tests:

For critical applications (nuclear, offshore, desalination): Request ASTM G48 dezincification test on every heat. GNEE includes this as standard for seawater orders.

GNEE recommendation: C68700 is the best balance of strength, thermal conductivity, and corrosion resistance for seawater. Only downgrade to C44300 for freshwater. Only upgrade to C70600 for ammonia or >80°C.

C68700 aluminum brass tube meets these standards:

GNEE certificates provided:

EN 10204 3.1 mill certificate (traceable to heat number)

EN 10204 3.2 certificate (third-party verified) – extra cost

NORSOK M-650 (for offshore) – extra cost

Minimum order quantity: 500 kg for stock sizes. 200 kg for nano-treated. Sample orders (50-200 kg) accepted for new buyers.

Lead time: Stock sizes: 7-10 days. Custom: 20-25 days. Nano-treated: add 5 days.

Q1: What is the exact ASTM B111 C68700 chemical composition requirement?
A: Cu 76-79%, Zn 19-22%, Al 1.5-2.5%, Fe max 0.06%, Pb max 0.09%.
The aluminum content is critical. Below 1.5% Al, the alloy does not meet C68700 classification. Above 2.5% Al, the alloy becomes brittle. GNEE targets 2.0% Al for optimal balance. Request the mill certificate to verify each heat's composition.

Q2: What is the tensile strength of C68700-O60 annealed tube?
A: 550-620 MPa – higher than C70600 CuNi 90/10 (350-520 MPa).
Many buyers assume copper nickel is stronger. It is not. C68700-O60 has 550-620 MPa tensile strength. C70600-O60 has only 350-420 MPa. For high-pressure seawater systems, C68700 is the stronger choice.

Q3: What is the hardness of aged C68700 after 300°C treatment?
A: 170-185 HB (Brinell hardness) – 15-20% harder than annealed.
Aging at 300°C for 1-2 hours precipitates aluminum-rich phases, increasing hardness. Do not exceed 350°C – over-aging softens the alloy. GNEE provides aged tubes for high-erosion applications like propeller shaft sleeves.

Q4: How does C68700 thermal conductivity compare to other heat exchanger alloys?
A: 105 W/m·K at 20°C – double C70600 (45) and triple titanium (22).
For energy-efficient heat transfer, C68700 is superior. A desalination plant using C68700 instead of C70600 saves 8-12% on pumping and heating energy. The only common alloy with higher thermal conductivity is C27000 yellow brass (120 W/m·K) – but yellow brass fails rapidly in seawater.

Q5: What is the maximum operating temperature for ASTM B111 C68700?
A: 300°C continuous, 350°C intermittent, based on mechanical property retention.
Above 300°C, the aluminum oxide film degrades. Above 350°C, dezincification accelerates significantly. For service above 300°C, GNEE recommends C70600 or C71500 copper nickel. For service up to 300°C, C68700 maintains 90% of room-temperature strength.

Q6: Does GNEE test each C68700 heat for dezincification per ASTM G48?
A: Yes – GNEE runs ASTM G48 Method A on every heat destined for seawater service.
The test takes 14 days. Maximum allowed dezincification depth is 0.03 mm/year (GNEE internal standard, stricter than ASTM's 0.05 mm/year). Test report is included with the mill certificate. Buyers may witness the test at GNEE's China lab.

Q7: What is the difference between ASTM B111 C68700 and C44300 admiralty brass?
A: C68700 has higher strength (550-750 vs 330-450 MPa) and better dezincification resistance.
C44300 (admiralty brass) contains tin and arsenic instead of aluminum. It resists dezincification moderately (0.05-0.10 mm/year) but has lower strength. For seawater, C68700 is preferred. For freshwater or low-stress applications, C44300 is acceptable and slightly cheaper.

Q8: How do I read a C68700 mill certificate from GNEE?
A: Check three items: aluminum content (1.5-2.5%), tensile strength (550-750 MPa for O60), and ASTM G48 depth (<0.03 mm/year).
GNEE's mill certificate also includes heat number, quantity, dimensions, and hydrostatic test pressure. If any of these three items is missing or out of range, reject the shipment. Contact GNEE immediately for replacement or refund.

Every lot of C68700 material undergoes a multi-step inspection protocol:
1) Chemical composition verified by Oxford Spectrometer (meeting ASTM B111/B135).
2) Mechanical properties tested via 300kN universal tester for tensile strength (≥370MPa) and hardness (80-110 HRB).
3) Dimensional accuracy checked by laser micrometer and pneumatic gauge.
4) Anti-corrosion validation includes mercurous nitrate test and dezincification depth analysis (≤200μm per ASTM B858).
5) Non-destructive testing – 100% eddy current or ultrasonic flaw detection.
We provide traceable mill test certificates (MTC) for each shipment, with third-party inspection (SGS/BV) available upon request.

Our C68700 (Aluminum Brass) production line is equipped with Germany-derived continuous extrusion presses, high-precision tandem cold rolling mills, and online solution heat treatment furnaces. The automated casting system ensures homogeneous distribution of aluminum and arsenic elements, while the in-line eddy current testing devices monitor surface defects in real time. With CNC-controlled straightening and cutting machines, we can supply C68700 tubes and rods in custom lengths (±0.5mm tolerance), supporting OD from 6mm to 219mm for condenser and heat exchanger applications.

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