C68700 Aluminum Brass Tube Dezincification Performance: 15-Year Marine Field Report

ASTM B111 C68700 aluminum brass tube limits dezincification to less than 0.025 mm per year. After 15 years in actual seawater cooling systems, tubes show less than 0.4 mm penetration depth. This report covers test data, field performance, and purchasing recommendations from GNEE (China).

Dezincification is the selective leaching of zinc from brass alloys, leaving behind weak, porous copper. For ordinary brass (C27000, C36000), this causes pinhole leaks within 2–5 years in seawater.

C68700 aluminum brass tube solves this problem by adding 1.5–2.5% aluminum. The aluminum forms a protective oxide film that blocks zinc from dissolving.

Key data point: ASTM G48 testing shows C68700 dezincification depth = 0.025 mm/year maximum. Standard brass = 0.20–0.30 mm/year. That is 8–10 times better.

GNEE (China) tested C68700 seamless tubes per ASTM B111 and ASTM G48 (copper alloy dezincification standard). Conditions: artificial seawater, 50°C, 365 days.

Conclusion: C68700 aluminum brass tube retains structural integrity after 1 year. Standard brass loses over 20% of wall thickness.

A power plant in coastal China (GNEE customer) installed ASTM B111 C68700 tubes in 2010. Seawater conditions: temperature 25–35°C, flow velocity 2.5 m/s, chlorides 25,000 ppm. Inspections performed at 5, 10, and 15 years.

Actual field result: After 15 years, the deepest dezincification penetration was 0.41 mm. Original wall thickness was 2.0 mm. Remaining wall = 1.59 mm – still well above minimum required (1.0 mm for 3.5 MPa pressure).

Even with C68700's high resistance, certain conditions increase corrosion rate. Buyers must avoid these:

If your system has any of these conditions, specify nano-treated C68700 from GNEE. Nano-treatment adds 40% corrosion resistance (tested per ASTM G48).

Buyers often ask: *"Should I use C68700, C70600 (CuNi 90/10), or C23000 (red brass)?"*

GNEE recommendation: For seawater, C68700 aluminum brass tube offers the best dezincification resistance per dollar spent. C70600 is overkill for most systems.

Every batch of ASTM B111 C68700 from GNEE undergoes these quality checks:

Chemical analysis (per ASTM E1473) – Confirms Al: 1.5–2.5%, Zn: 19–22%

Microscopic examination (100–500x) – Checks for beta-phase distribution

ASTM G48 dezincification test – 14-day accelerated test, reports depth in mm/year

Hydrostatic test (6.0 MPa minimum) – Verifies no leaks

Eddy current test (ASTM E243) – Scans for pinholes and cracks

Buyers can request a mill certificate (EN 10204 3.1) with all test results. Third-party inspection (SGS, BV, Lloyds) available at extra cost.

GNEE (China) supplies ASTM B111 C68700 seamless tubes in these ranges:

Stock sizes (OD 12–50 mm, wall 2–5 mm) ship in 7–10 days. Custom sizes: 20–25 days.

Q1: Does ASTM B111 C68700 completely stop dezincification?
A: No, but it slows it to less than 0.025 mm per year – safe for 20+ years.
No brass alloy completely stops dezincification. C68700's aluminum addition reduces the rate from 0.25 mm/year (standard brass) to below 0.025 mm/year. A 2.0 mm wall tube loses only 0.5 mm after 20 years. For zero dezincification, choose C70600 copper nickel (no zinc content) – but it costs 70% more.

Q2: How fast does C68700 dezincify in polluted harbor water?
A: 0.04–0.06 mm/year in sulfide-polluted water – still safe for 10–15 years.
GNEE tested C68700 samples from a Chinese harbor with 0.3 ppm H₂S. Dezincification depth was 0.052 mm/year after 3 years. Standard brass failed within 8 months. For heavy pollution, request GNEE's nano-treated C68700 (rate drops to 0.03 mm/year).

Q3: What is the maximum temperature for C68700 to avoid accelerated dezincification?
A: 60°C for continuous operation, 80°C intermittent.
Above 60°C, zinc diffusion accelerates. At 80°C, dezincification rate doubles to 0.05 mm/year. At 100°C, rate triples to 0.075 mm/year. If your seawater exceeds 60°C, switch to C70600 (CuNi 90/10) or use nano-treated C68700 with annual inspections.

Q4: Can I use C68700 for brackish water (river + seawater mix)?
A: Yes – C68700 is excellent for brackish water.
Brackish water has lower chlorides (5,000–15,000 ppm) and varying pH. GNEE supplied C68700 tubes for a Chinese estuary cooling system. After 8 years, dezincification depth was only 0.18 mm. Avoid brackish water with industrial pollution (heavy metals, sulfides) – use nano-treated version.

Q5: How do I inspect installed C68700 tubes for dezincification?
A: Use eddy current testing (ECT) per ASTM E243.
ECT detects wall thinning and localized dezincification without removing tubes. For new systems, inspect at year 5, then every 3–5 years. If average depth exceeds 0.5 mm or deepest pit exceeds 1.0 mm, plan replacement. GNEE offers inspection services for existing customers.

Q6: What wall thickness should I specify for 20-year life?
A: 2.5 mm minimum for seawater, 2.0 mm for freshwater or nano-treated.
Calculation: 20 years × 0.025 mm/year = 0.5 mm loss. Add 1.5 mm for pressure safety and manufacturing tolerance. Total = 2.0 mm. For polluted water (0.05 mm/year), use 2.5 mm. GNEE recommends 2.5 mm for all seawater applications – minimal cost increase for significant safety margin.

Q7: Does C68700 require any post-installation treatment to prevent dezincification?
A: No – the aluminum oxide film forms naturally within 2–4 weeks in seawater.
Do not apply coatings or inhibitors – they block oxide film formation. However, avoid stagnant seawater during startup. Maintain flow >0.5 m/s for the first month to establish a stable film. After film forms, C68700 protects itself.

Q8: How does GNEE guarantee dezincification resistance on shipped tubes?
A: Every batch includes an ASTM G48 test report with the mill certificate.
GNEE's quality control lab runs a 14-day accelerated dezincification test on each heat number. Maximum allowed depth = 0.03 mm/year (GNEE internal standard, stricter than ASTM's 0.05 mm/year). Buyers receive the test report with shipment. If a tube fails in service (proven by third-party lab), GNEE replaces the batch.

Every tube in this lot has passed third-party witnessed inspection per ASTM B111 standard for C68700 alloy. Below are actual photos from customer-onsite inspection, including eddy current testing and dimensional verification.

Inspection items verified:
• Eddy current testing (ECT) – no through-wall defects
• Outer diameter & wall thickness – within ±0.02mm tolerance
• Surface finish & temper (O61) – conforms to ASTM
• Hardness & chemical composition – certified.

After passing inspection, all tubes are packed according to export standards and customer-specific requirements. The packing process is documented below to ensure traceability and damage-free delivery.

Packing steps shown in video & images:
1. Tube cleaning & drying
2. Plastic end caps on both ends
3. VCI anti-rust paper wrapping
4. Bundle strapping with moisture barrier film
5. Plywood wooden case (ISPM-15 compliant) with foam padding
6. Labeling with ASTM grade, lot number, and inspection stamp

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.

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