Composition: what exactly is ASTM B111 C68700?
C68700 is classified by the Copper Development Association as an arsenical aluminum brass - a copper-zinc base alloy, not a copper-nickel and not an aluminum bronze. Per the copper.org alloy database and ASTM B111/B111M (seamless condenser and heat-exchanger tubes), the nominal composition is:
| Element | Min (%) | Max (%) | Role in service |
|---|---|---|---|
| Copper (Cu) | 76.0 | 79.0 | Base metal; high intrinsic corrosion resistance in seawater |
| Aluminum (Al) | 1.8 | 2.5 | Forms the protective aluminum-oxide surface film (erosion resistance) |
| Arsenic (As) | 0.02 | 0.06 | Dezincification inhibitor (prevents selective zinc leaching) |
| Iron (Fe) | - | 0.06 | Impurity limit |
| Lead (Pb) | - | 0.07 | Impurity limit |
| Zinc (Zn) | Balance (nominally ~20.5%) | Remainder of the copper-zinc alloy | |
For technical specifications, visit our [ASTM B111 C68700] . For other power plant alloy options, see our [ASTM B111 heat exchanger tubes] page.
Customer Visit & Project Reference – India
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.
Why are power-plant condensers demanding on tube materials?
| Operating condition | Typical value | Stress imposed on tubes |
|---|---|---|
| Cooling-water velocity | 1.5–2.5 m/s (clean seawater) | Erosion-corrosion / impingement attack |
| Water temperature | 15–35 °C inlet | Moderate; scale & biofouling risk |
| Tube-side pressure | Full vacuum to ~5 psig | Collapse / buckling risk |
| Steam-side temperature | 35–50 °C | Condensation-side corrosion, air-in-leakage zones |
| Water quality | Seawater or brackish | Chloride pitting, dezincification (brasses) |
| Duty cycle | Continuous (24/7/365) | No rest for protective films; debris/silt periods |
Two failure modes dominate: erosion-corrosion from turbulent, sand-bearing high-velocity water, and dezincification of unprotected brasses in chloride media. C68700 was engineered against both.
How does C68700 behave in high-velocity seawater?
| Alloy | Max recommended seawater velocity | Key protective mechanism |
|---|---|---|
| C12200 (phosphorus-deoxidized copper) | ~1.0 m/s | Copper oxide film; low mechanical strength, fast erosion |
| C44300 (admiralty brass, inhibited) | ~1.5 m/s | Tin-inhibited; zinc oxide film, moderate impingement resistance |
| C68700 (aluminum brass) | ~2.5 m/s | Aluminum-oxide film - best erosion resistance among brasses |
| C70600 (90/10 copper-nickel) | ~3.5 m/s | Stable, self-healing protective film; highest velocity tolerance of the four |
Why C68700 beats copper and admiralty brass on velocity: the 1.8–2.5% aluminum forms a thin, hard, self-repairing aluminum-oxide layer that resists impingement far better than the copper/zinc oxide films on C12200 or C44300.
The minimum-velocity caveat: below roughly 1 m/s the film may not form or sustain; under-deposit attack and pitting can then initiate. C68700 is a "flow-loving" alloy - dead legs and low-flow periods are its weakness, which is exactly where C70600 is chosen instead.
C68700 vs C70600 for power-plant condensers
| Comparison factor | C68700 (aluminum brass) | C70600 (90/10 Cu-Ni) |
|---|---|---|
| Relative tube cost | 1.0× (baseline) | ~1.5–2.0× (industry estimate; varies with LME prices) |
| Max seawater velocity | ~2.5 m/s | ~3.5 m/s |
| Minimum velocity required | ~1.0 m/s to keep film | None - tolerant of low flow |
| Polluted / sulfide-bearing water | Poor | Good |
| Ammonia resistance | Fair (avoid ammonia carryover) | Good |
| Thermal conductivity | ~100 W/m·K (23% IACS) | ~45 W/m·K (9% IACS) |
| Biofouling resistance | Good | Excellent (copper-ion release) |
| Erosion (impingement) resistance | Excellent among brasses | Good |
| Typical condenser life (clean seawater) | 15–25 years | 20–30+ years |
Practical selection guide:
Clean seawater, stable high flow → C68700 (best value: lower cost + better heat transfer).
Polluted, estuarine or sulfide-bearing water → C70600 (safer choice).
Low-flow or stagnant zones → C70600 (C68700 needs minimum flow).
Budget-constrained clean-seawater project → C68700.
Lifecycle-cost priority in marginal water → C70600.
Many coastal plants run C68700 in the main condenser and C70600 in auxiliary coolers where flow is lower or water dirtier - a proven, cost-effective split.
Design guidance for a long-lived C68700 condenser
| Design factor | Recommendation for C68700 | Why |
|---|---|---|
| Tube OD | 19.05 mm (3/4 in) or 25.4 mm (1 in) | Standard BWG sizes, widely stocked |
| Wall thickness | 18 BWG (1.245 mm) minimum; 16 BWG (1.651 mm) for aggressive water | Corrosion allowance for 15–25 years |
| Design flow velocity | 1.5–2.5 m/s, avoid > 2.5 m/s | Optimal film formation; stay under erosion threshold |
| Tube pitch | 1.25–1.30 × OD | Adequate support and cleaning access |
| Inlet inserts / ferrules | Yes, if sand or debris present | Prevents inlet erosion |
| Tube support spacing | < 1.0 m | Prevents flow-induced vibration |
| Waterbox design | Even flow distribution, no dead zones | Prevents stagnant zones that kill the protective film |
| Cleaning system | Sponge-ball (on-load) system | Keeps surfaces clean, restores film |
FAQ
Q1. Why is C68700 called "arsenical aluminum brass"?
"Arsenical" refers to the 0.02–0.06% arsenic added to inhibit dezincification (selective leaching of zinc from the brass). "Aluminum" refers to the 1.8–2.5% aluminum that forms the protective oxide film for erosion resistance. "Brass" indicates a copper-zinc base (nominally ~77.5% Cu, ~20.5% Zn). Together they make C68700 uniquely suited to seawater condenser service.
Q2. Can C68700 be used in nuclear power plant condensers?
Yes - C68700 has a long history in both PWR and BWR plant condensers (the alloy family is covered by ASME SB111, the code version of ASTM B111). Nuclear procurement normally adds: full melt-to-finished-tube traceability, certified mill test reports per heat, third-party inspection, and compliance with ASME Section III or the project code where required. Stricter water-chemistry control in nuclear plants generally benefits C68700 tube life.
Q3. What is the typical cost difference between C68700 and C70600 for a condenser?
As an industry estimate, C70600 typically costs about 1.5–2× more than C68700 for the same tube size and quantity (prices move with LME copper, nickel, and specification). For a large condenser with tens of thousands of tubes, this can be a seven-figure USD difference - the main reason C68700 remains the default for clean-seawater applications. Always run a lifecycle-cost analysis: in marginal water, C70600's longer life and lower maintenance can justify its premium.
Q4. How does C68700 handle chlorinated seawater for biofouling control?
Industry practice is to use intermittent chlorination (e.g., 1–2 h/day) rather than continuous dosing; continuous or excessive chlorine attacks the protective film and accelerates corrosion. Residual-chlorine limits of roughly 0.5 ppm for intermittent dosing are commonly cited in plant practice (to be confirmed against your plant's water-treatment spec). Combine chlorination with sponge-ball cleaning or other biofouling controls and monitor residuals.
Q5. What is the maximum tube length available for C68700 condenser tubes?
Seamless C68700 condenser tubes are typically supplied in lengths up to ~15 m (roughly 50 ft) as a standard industrial limit; some mills can go longer on request. Very long condensers are usually built with a divided waterbox or multiple tube sections rather than welded intermediate joints (welded butt joints are uncommon in B111 practice). Always confirm maximum length, straightness tolerances and transport constraints with your supplier before finalizing the design.
Q6. Can I retrofit an existing C70600 condenser with C68700 tubes?
Only if the operating envelope fits C68700: 12 months of water-quality data showing clean seawater, actual flow velocities within 1.0–2.5 m/s, and no sulfide/pollution excursions. If the original C70600 choice was driven by polluted or low-flow conditions, switching to C68700 risks rapid failure. Evaluate existing tube failure modes and consult a materials engineer before retubing.
Q7. How does thermal conductivity affect condenser performance?
C68700's thermal conductivity is about 100 W/m·K (copper.org data), roughly 2.2× that of C70600 (~45 W/m·K, also copper.org). For the same heat duty, a C68700 condenser therefore needs less surface area (fewer tubes) than a copper-nickel unit - a real capex advantage on top of the lower alloy cost. Reference points: C12200 copper ~339 W/m·K; C44300 admiralty brass ~111 W/m·K.
Q8. What wall thickness is recommended for new C68700 condenser tubes?
18 BWG (1.245 mm / 0.049 in) is the common default for seawater condensers and offers a reasonable corrosion allowance for 15–25 years. For aggressive water (sand, higher velocity, marginally polluted), specify 16 BWG (1.651 mm / 0.065 in). Some plants use 20 BWG (0.889 mm) in very clean service to cut cost, accepting a shorter life. Balance cost against your expected unit lifetime.
Q9. Can C68700 tubes be used with titanium tubesheets?
Yes, but galvanic corrosion must be managed. Titanium is far more noble (cathodic) than C68700; in seawater the couple drives accelerated attack on the tube ends at the tubesheet. Mitigations: insulating coatings on the tubesheet face, non-conductive tube-end sleeves, keeping the water clean to minimize galvanic current, and planning for earlier retubing of tube ends. For new designs, prefer a tubesheet of C68700, C70600 or other copper alloy close in potential to the tubes.
Our Factory & Equipment
All ASTM C68700 tubes are produced and inspected on our in-house equipment, allowing full process control from billet casting to final packing.
Key equipment used for this lot:
• Induction melting furnace – precise alloying (Cu + Zn + Al + As)
• Horizontal continuous casting – uniform billet structure
• Extrusion press (800T / 1630T) – seamless tube forming
• Cold drawing bench (5–40m) – dimensional accuracy to ±0.02mm
• Online eddy current tester (FOERSTER / MAC) – 100% NDT
• Ultrasonic wall thickness gauge – real-time monitoring
• Annealing furnace (controlled atmosphere) – temper O61
In-house metrology: Micrometers, pin gauges, optical comparator, hardness tester (HV/HRB)
All equipment is calibrated quarterly. Production records are traceable by lot number.
Copper & Copper Alloy Products – Supply Range
| Product Form | Common Alloys / Grades | Size Range | Standards | Typical Applications |
|---|---|---|---|---|
| Tube / Pipe | C12200, C11000, C68700, C70600, C71500, C44300, C27000 | OD: 4mm – 219mm Wall: 0.5mm – 20mm Length: up to 15m |
ASTM B68, B75, B111, B280, B359, B466 | Heat exchangers, condensers, HVAC, plumbing, oil coolers |
| Plate / Sheet | C11000, C12200, C26000, C26800, C52100, C68700 | Thk: 0.5mm – 50mm Width: up to 1200mm Length: up to 4000mm |
ASTM B152, B169, B103, B465 | Electrical parts, roofing, gaskets, industrial panels |
| Rod / Bar | C11000, C26000, C36000, C46400, C48500, C63000 | Dia: 3mm – 120mm Length: 1m – 6m (or custom) |
ASTM B16, B124, B138, B150, B453 | Valve stems, shafts, fasteners, machined components |
| Wire | C11000, C16200, C17500, C26000, C52100, C64700 | Dia: 0.1mm – 12mm Coil weight: up to 100kg |
ASTM B1, B2, B3, B197, B206, B624 | Welding electrodes, electrical conductors, springs, mesh |
| Strip / Foil | C11000, C19400, C26000, C26800, C52100, C70250 | Thk: 0.05mm – 3.0mm Width: 5mm – 600mm |
ASTM B36, B465, B694, B888 | Connectors, terminals, battery tabs, shielding, stamping parts |
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