Why Is ASTM B111 C68700 the Preferred Choice for Power Plant Condensers?

Power plant condensers are the backbone of thermal cycle efficiency. A single tube failure can force an unplanned outage, costing a 500MW plant over $500,000 per day in lost revenue. For decades, ASTM B111 C68700 has been the industry standard for seawater-cooled power plant condensers. But why?

This article explains the technical and economic reasons why C68700 aluminum brass tube dominates this application - and when you might consider alternatives.

For technical specifications, visit our [ASTM B111 C68700] . For other power plant alloy options, see our [ASTM B111 heat exchanger tubes]  page.

Power plant condensers operate under unique conditions that push tube materials to their limits.

C68700 tube corrosion resistance addresses the two biggest challenges: erosion from high velocity and corrosion from seawater.

Velocity is the #1 killer of condenser tubes. Pure copper tubes fail within months at 2 m/s in seawater. ASTM B111 C68700 thrives at these velocities.

Why C68700 wins: The aluminum content (1.8-2.5%) forms a hard, durable aluminum oxide film that resists erosion far better than the copper oxide film on pure copper or admiralty brass.

However, there is a catch: C68700 requires minimum flow of approximately 1 m/s to maintain this protective film. Below this threshold, the film breaks down and pitting begins.

This is the most common debate in condenser material selection. Both are excellent alloys, but they serve different niches.

Selection guide for power plants:

Clean seawater, stable operation → C68700 (best value)

Polluted or variable water quality → C70600 (safer choice)

Low-flow or stagnant conditions → C70600 (C68700 requires minimum flow)

Budget-constrained project → C68700

Lifecycle cost priority → C70600 (longer life, less maintenance)

Real-world practice: Many coastal power plants use C68700 in the main condenser and C70600 in auxiliary coolers that may see lower flow or polluted water.

Proper design prevents many failure modes. If you are specifying a new condenser or retubing, consider these factors.

Plant profile: 800MW coal-fired plant, once-through seawater cooling, clean open ocean intake.

Tube specification: 19.05mm OD × 1.245mm wall (5/8" × 18 BWG), ASTM B111 C68700, O61 temper.

Operating conditions: Velocity 1.8-2.2 m/s, seawater temperature 10-30°C, pH 7.8-8.2.

Maintenance practices:

Sponge ball cleaning twice per day

Eddy current testing every 3 years

Water chemistry monitored continuously

Annual visual inspection during outages

Results after 22 years:

Average wall loss: 0.15-0.25 mm (12-20% of original)

Less than 2% of tubes plugged

No stress corrosion cracking observed

Projected remaining life: 5-8 more years

Key takeaway: With proper design, operation, and maintenance, C68700 aluminum brass tube achieved nearly 30 years of total service life.

1. Why is C68700 called "arsenical aluminum brass"?

The name describes its three key alloying elements. "Arsenical" refers to the 0.02-0.06% arsenic added specifically to prevent dezincification (selective leaching of zinc). "Aluminum" refers to the 1.8-2.5% aluminum that forms the protective oxide film for erosion resistance. "Brass" indicates it is a copper-zinc base alloy (approximately 77.5% copper, 20.5% zinc). Together, these three additions make ASTM B111 C68700 uniquely suited for seawater condenser service.

2. Can C68700 be used in nuclear power plant condensers?

Yes, C68700 is widely used in nuclear power plant condensers, both for pressurized water reactors (PWR) and boiling water reactors (BWR). However, nuclear applications require additional quality assurance: (1) full material traceability from melt to finished tube, (2) certified mill test reports (MTRs) for each heat lot, (3) third-party inspection, (4) compliance with ASME Section III if required. The main difference from fossil plants is that nuclear plants typically have stricter water chemistry control, which actually benefits C68700 tube life.

3. What is the typical cost difference between C68700 and C70600 for a power plant condenser?

C70600 (90/10 Copper-Nickel) typically costs 50-100% more than C68700 for the same tube size and quantity. For a large power plant condenser requiring 50,000 tubes, the difference can be $500,000 to $1,000,000. This is why ASTM B111 C68700 remains the default choice for clean seawater applications - the cost savings are substantial. However, if water quality is marginal, the additional cost of C70600 may be justified by longer life and reduced maintenance. Always perform a lifecycle cost analysis.

4. How does C68700 handle chlorinated seawater for biofouling control?

C68700 can tolerate up to 0.5 ppm residual chlorine without significant corrosion. This is sufficient for intermittent chlorination (1-2 hours per day) to control biofouling. Above 0.5 ppm, or with continuous chlorination, the protective aluminum oxide film can be damaged, leading to accelerated corrosion. Best practice: use intermittent chlorination (not continuous), monitor residual chlorine levels, and alternate with other biofouling control methods (sponge balls, ultrasonic, or copper ion dosing).

5. What is the maximum tube length available for C68700 power plant condensers?

Seamless C68700 tubes can be produced in lengths up to 30 meters (approximately 100 feet) depending on the manufacturer's mill capabilities. For longer condensers, tubes are typically joined with welded intermediate butt joints (allowed by ASTM B111 but not common) or the condenser is designed with a divided waterbox. Most large power plant condensers use tube lengths of 10-20 meters (33-66 feet). Always confirm maximum length with your supplier before finalizing design.

6. Can I retrofit an existing C70600 condenser with C68700 tubes?

Yes, but you must evaluate the operating conditions first. If the original C70600 condenser was chosen due to polluted or low-flow water, switching to ASTM B111 C68700 could result in rapid failure. However, if the original choice was simply conservative and the actual water quality is clean seawater with good velocity, C68700 will perform well and save significant cost. Key retrofit steps: (1) analyze 12 months of water quality data, (2) measure actual flow velocities, (3) inspect existing tubes for failure modes, (4) consult a materials engineer.

7. How does thermal conductivity affect condenser performance with C68700?

C68700 has lower thermal conductivity (approx. 120 W/m·K) than C12200 (380 W/m·K) or C70600 (50 W/m·K? Let me check). Actually, C70600 has about 40-50 W/m·K - lower than C68700. So C68700 actually has better thermal conductivity than C70600 (120 vs 45 W/m·K). This means a C68700 condenser requires less surface area (fewer tubes) than a C70600 condenser for the same heat duty. For power plants, this is an advantage - C68700 provides good corrosion resistance AND better heat transfer than copper-nickel.

8. What is the recommended wall thickness for new C68700 power plant condensers?

18 BWG (1.245 mm or 0.049 inches) is the industry standard for most power plant condensers. This provides adequate corrosion allowance for 15-25 years of service. For plants with aggressive water (higher velocity, sand, or slightly polluted conditions), specify 16 BWG (1.651 mm or 0.065 inches) for additional corrosion allowance. For very clean, well-controlled conditions, some plants use 20 BWG (0.889 mm) to reduce cost, but this reduces life expectancy. We recommend 18 BWG as the best balance of cost and longevity.

9. Can C68700 tubes be used with titanium tubesheets?

Yes, but galvanic corrosion is a concern. Titanium is much more noble (cathodic) than C68700 aluminum brass. In seawater, the titanium tubesheet will cathodically protect the C68700 tubes - meaning the tubes will corrode preferentially at the tube-to-tubesheet joint. Mitigation methods: (1) coat the titanium tubesheet with an insulating layer, (2) use non-conductive tube end sleeves, (3) maintain very clean water to minimize galvanic current, (4) accept that tube ends may corrode faster and plan for earlier retubing. For new designs, use a C68700 or copper-nickel tubesheet instead.

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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