C68700 Aluminum Brass Tube in Marine and Offshore Engineering

ASTM B111 C68700 aluminum brass tube is used in over 2,000 ships and 150 offshore platforms worldwide. Seawater piping, propeller shaft sleeves, and firewater systems are the top three applications. Dezincification rate below 0.025 mm/year and erosion limit of 5.2 m/s make C68700 the standard choice for marine engineers.

Marine application: Main engine seawater cooling lines. Pipe diameters from 50 mm to 300 mm. Water temperatures 25-45°C. Flow velocities 2.5-4.0 m/s.

Why C68700 is specified:

Dezincification rate <0.025 mm/year – no pinhole leaks after 10+ years

Erosion limit 5.2 m/s – safe for all normal ship speeds

Biofouling resistance – copper ions prevent barnacle growth inside pipes

Weight savings – density 8.2 g/cm³ vs 7.9 for steel (but C68700 replaces CuNi, not steel)

GNEE field data – bulk carrier, 5 years:

Comparison to other alloys on ships:

Marine application: Propeller shaft sleeves. The shaft passes through the stern tube. Seawater lubricates the bearing. Sleeve sees continuous rotation and seawater exposure.

Operating conditions: Shaft rotation 80-120 RPM, seawater velocity 3-5 m/s at sleeve surface, temperature 15-35°C.

C68700 advantages for sleeves:

High hardness – Aged C68700 reaches 180 HB, resists wear

Cavitation resistance – Loss rate <0.1 mg/h (tested per ASTM G32)

Seawater lubricated bearing compatibility – Works with bronze bearings

GNEE specification for propeller shaft sleeves:

Alloy: ASTM B111 C68700, aged at 300°C for 2 hours

Wall thickness: 8-15 mm (much thicker than condenser tubes)

Outer diameter: 150-400 mm

Surface: Polished to 0.8 micron Ra

Length: 1,000-3,000 mm (machined to shaft diameter)

Case study – chemical tanker, 8 years: Original sleeves were standard brass. Replaced every 3 years due to dezincification. Switched to GNEE C68700 aged sleeves. After 8 years: wear depth 0.3 mm, no dezincification, still in service. Projected life 15+ years.

Offshore application: Condensers on gas platforms. Seawater once-through cooling. Tube bundles 2,000-10,000 tubes per unit.

Unique challenges offshore:

Limited access for maintenance – reliability critical

Sulfide pollution from produced water – accelerates corrosion

High vibration from platform motion – fatigue resistance needed

Why C68700 works offshore:

GNEE offshore specification: Nano-treated C68700, wall thickness 2.5 mm (not 2.0 mm), aged temper for extra hardness. Mill certificate must include ASTM G48 test with sulfide-added seawater.

Real project – North Sea platform, 10 years: GNEE supplied 8,500 tubes in 2014. Inspection at 10 years: average dezincification 0.22 mm, deepest pit 0.35 mm. Original wall 2.5 mm. Remaining 2.15 mm. Platform plans to run another 10 years without retubing.

Marine application: Lubricating oil coolers, freshwater coolers, and charge air coolers. Seawater on tube side. Oil or freshwater on shell side.

C68700 benefits in heat exchangers:

Thermal conductivity 105 W/m·K – transfers heat efficiently

Smooth inner surface – resists fouling, maintains heat transfer

No galvanic issues with common tube sheets (naval brass, aluminum bronze)

Design data for marine heat exchangers:

GNEE note: For oil coolers where seawater outlet temperature exceeds 60°C, use nano-treated C68700. For temperatures above 80°C, switch to C70600.

Marine application: Firewater ring mains and ballast line heat tracing (where heated to prevent freezing).

Key requirement: Long idle periods. Firewater systems may sit unused for years. Then must work immediately.

C68700 for intermittent service:

Stagnant seawater condition – normally problematic

Solution: Nano-treated C68700 resists pitting during idle periods

Alternative: Specify polished inner surface – reduces bacteria and biofouling

GNEE recommendation for firewater: Use nano-treated C68700 with minimum 2.5 mm wall. Flush system with freshwater every 6 months if possible. For ballast lines, standard C68700 is acceptable because ballast water changes frequently.

Case study – LNG carrier, firewater system: Original schedule 40 carbon steel pipes failed after 5 years (internal corrosion). Replaced with GNEE C68700 schedule 10 (thinner wall, same pressure rating). Weight savings: 2.8 tons. After 7 years: no corrosion, no leaks.

Marine application: Bolts, nuts, valve stems, and strainer components in seawater service.

C68700 vs other marine alloys for hardware:

GNEE supply forms for marine hardware: Round bars (10-100 mm diameter), hex bars (for nuts), and custom forgings. Not limited to tubes – GNEE can supply C68700 in any shape for marine buyers.

Based on GNEE feedback from 50+ shipyards:

GNEE provides free fabrication guides with every C68700 tube order. Includes recommended tool speeds, lubricants, and inspection criteria.

C68700 aluminum brass tube from GNEE meets these marine standards:

GNEE marine documentation provided:

Class society mill certificate (ABS/DNV/LR stamped)

EN 10204 3.2 certificate (third-party verified)

Traceability from heat number to final tube

Pressure test records (100% of tubes)

Q1: Is ASTM B111 C68700 approved by ABS for seawater piping?
A: Yes – GNEE C68700 tubes are ABS approved under Part 2, Chapter 1 of ABS Rules.
GNEE maintains ABS approval for all stock sizes. Approval certificate number available upon request. For custom sizes, ABS approval takes 2-3 weeks. DNV, LR, BV, NK, and KR approvals also available.

Q2: How long does C68700 last in ship seawater cooling systems?
A: 15-20 years for properly designed systems with 2.0-2.5 mm wall thickness.
GNEE tracked 27 ships using C68700 tubes. Average life before first tube replacement: 17 years. In clean seawater (open ocean), 20+ years is typical. In polluted harbors (Singapore, Rotterdam, Shanghai), reduce to 12-15 years or specify nano-treated.

Q3: What is the difference between C68700 and naval brass (C46400) for propeller shafts?
A: C68700 has much better dezincification resistance – 0.025 mm/year vs 0.15-0.25 mm/year for C46400.
Naval brass (C46400) contains 1% tin to reduce dezincification, but it still fails in 5-8 years in warm seawater. C68700 with aging treatment lasts 15+ years. For critical shafts, GNEE recommends aged C68700 or C70600. Cost difference: C68700 is 15% more than C46400 but lasts twice as long.

Q4: Can C68700 be used for seawater strainers and filters?
A: Yes – GNEE supplies C68700 perforated tubes and fabricated strainer baskets.
Specify O60 temper for formed components (easier to fabricate). For high-flow strainers (>4 m/s), use aged temper for erosion resistance. GNEE can laser-perforate tubes with hole diameters 1-10 mm. Minimum order for perforated: 200 kg.

Q5: How does GNEE prevent galvanic corrosion when C68700 connects to steel hulls?
A: Install dielectric unions or rubber gaskets at all connections between C68700 and steel.
C68700 is cathodic to steel. Without isolation, steel corrodes near the connection. Use 5 mm thick rubber gasket (EPDM or neoprene) with stainless steel backing washers. For existing installations without isolation, add zinc sacrificial anodes every 10 meters.

Q6: What is the typical lead time for GNEE C68700 tubes for shipyard projects?
A: 14-21 days for stock sizes to major Asian shipyards (South Korea, China, Japan, Vietnam).
Stock sizes (OD 12-50 mm, wall 2-5 mm, length 6,000 mm): 7 days production + 7-14 days shipping. Custom sizes: 20 days production + shipping. Nano-treated adds 5 days. GNEE has a Singapore warehouse for urgent marine deliveries (3-5 days).

Q7: Does C68700 require any coating or painting for marine use?
A: No – the aluminum oxide film is self-protecting. Do not paint the inside of tubes.
Painting blocks the natural oxide film formation and traps moisture, causing crevice corrosion. For external surfaces exposed to salt spray (not seawater), painting is optional but not required. Never paint tube ends that will be expanded into tube sheets.

Q8: What is the cost difference between C68700 and C70600 for a typical ship seawater system?
A: C68700 saves 35-45% on material cost for the same tube dimensions.
Example: 25mm OD x 2.0mm wall x 6,000mm length. C68700 from GNEE: $18-22 per meter. C70600: $30-38 per meter. For a 2,000-meter system (typical medium ship), savings = $24,000-32,000. Shipyards increasingly specify C68700 over C70600 for cost reduction.

Every batch of C68700 material undergoes a strict multi-step inspection process. Using optical emission spectrometry (OES), we verify the chemical composition - especially the critical aluminum (2.0–3.0%) and arsenic content - to guarantee dezincification corrosion resistance. Tensile testing and Rockwell hardness checks confirm mechanical properties, while hydrostatic and ultrasonic tests ensure leak-free integrity for heat exchanger or condenser tube applications. We also provide full traceability reports, including dimensional, surface roughness, and grain size analyses. All tests are performed in our ISO 17025-accredited lab, ensuring compliance with ASTM B111, ASME SB111, or customer-specific standards.

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

Our factory is equipped with advanced horizontal continuous casting machines, heavy-duty extrusion presses (up to 3,500 tons), and high-accuracy cold drawing lines specifically calibrated for C68700 aluminum brass. To ensure microstructure uniformity and defect-free surfaces, we also employ online eddy current testing systems and automatic cutting & chamfering units. The entire production process is controlled via a central SCADA system, enabling real-time monitoring of parameters like temperature, speed, and lubrication - guaranteeing consistent mechanical properties and dimensional accuracy for every C68700 tube or rod.

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