How to Select the Right Tube Material
for Your Heat Exchanger

Introduction — Why Tube Material Is the Most Critical Decision

In a shell-and-tube heat exchanger, the tube bundle accounts for the majority of capital cost, virtually all of the maintenance expenditure and almost every corrosion-related failure. Getting the tube material right at the specification stage is therefore not a detail — it is the most consequential engineering decision in the entire heat exchanger design process.

The challenge is that no single tube material excels across all parameters simultaneously. Admiralty Brass offers outstanding dezincification resistance at low cost but fails in highly polluted or high-velocity seawater. 90/10 Cupro-Nickel handles most seawater conditions reliably but falls short where H₂S is present. Titanium Grade 2 performs in virtually every environment but at a material cost 8–12× that of brass. Stainless steel is the chemical industry default but pits rapidly in chloride-rich cooling water.

This guide provides a systematic framework for selecting the correct tube material based on fluid type, temperature, velocity, chloride content, H₂S levels and budget — with the complete international standard reference for each material.

Key Factors Governing Tube Material Selection

Every heat exchanger tube selection decision should begin by systematically evaluating these seven parameters for both the tube-side and shell-side fluids:

• 1. Fluid chemistry — tube side: Fresh water, brackish water, seawater, brine, acid, alkali, hydrocarbon, steam condensate? Chloride content (ppm)? H₂S (ppm)? Ammonia (ppm)? Dissolved oxygen (ppb)?
• 2. Fluid chemistry — shell side: Same analysis for the shell-side fluid — particularly important for tube materials susceptible to external stress corrosion cracking (SCC).
• 3. Temperature — tube side and shell side: Inlet and outlet temperatures of both streams. Maximum tube wall temperature. Low-temperature (cryogenic) service requirements.
• 4. Flow velocity — tube side: Critical parameter for copper alloys. Below minimum velocity → biofouling and silt deposition. Above maximum → erosion-corrosion. Each alloy has an optimal velocity window.
• 5. Pressure — design and operating: Higher pressures require thicker walls. TEMA standards define minimum wall thickness requirements by material and tube OD.
• 6. Thermal performance requirements: Thermal conductivity of tube material affects the overall heat transfer coefficient U — higher conductivity = thinner walls permissible = more tubes in same shell = lower cost.
• 7. Service life and maintenance philosophy: What is the acceptable maintenance interval? Is retubing cost included in lifecycle analysis? What is the cost of unplanned downtime?

The Seven Major Tube Materials Compared

Admiralty Brass C44300 — The Traditional Workhorse

Admiralty Brass C44300 (Cu 70%, Zn 29%, As 0.04%) has been the global standard for power plant condenser tubing since the early 20th century. Its combination of dezincification resistance (due to arsenic inhibition), good thermal conductivity (~150 W/m·K) and low cost made it the first choice for coal and oil-fired power station condensers worldwide.

Also available as: C44400 (Antimonial — Sb inhibitor) and C44500 (Phosphorised — P inhibitor) where arsenic is restricted by environmental regulations.

• Optimal tube-side velocity: 0.9 – 2.4 m/s (freshwater); 0.9 – 1.8 m/s (seawater)
• Max chloride tolerance: ~500 ppm Cl⁻ in cooling water (above this, consider Aluminium Brass or CuNi)
• H₂S tolerance: Poor — even trace H₂S (>0.01 ppm) causes rapid film breakdown and pitting
• Max temperature — tube side: 200°C continuous
• Typical BWG wall thickness: 18 BWG (1.24 mm) to 14 BWG (2.11 mm) per ASTM B111
• U-tube service: Excellent — specified per ASTM B395

Primary Standards: ASTM B111 C44300 ASTM B395 C44300 EN 12449 CW706R BS 2871 Part 3 CZ111 JIS H3300 C4430 DIN 1785 CuZn28Sn1As IS 1545 ISO 274

Aluminium Brass C68700 — The Upgraded Brass Option

Aluminium Brass C68700 (Cu 76%, Zn 22%, Al 2%, As 0.04%) is a step up from Admiralty Brass, offering significantly improved erosion-corrosion resistance due to the formation of a more protective Al₂O₃-enriched surface film. It handles higher cooling water velocities and slightly higher chloride concentrations before film breakdown occurs.

• Optimal tube-side velocity: 1.2 – 3.0 m/s (seawater) — significantly higher than Admiralty Brass
• Max chloride tolerance: ~700 ppm Cl⁻ in cooling water
• H₂S tolerance: Poor — same sensitivity as Admiralty Brass
• Thermal conductivity: ~120 W/m·K (lower than Admiralty Brass — compensate with thinner walls or more tubes)
• Typical use: Power plant condensers with higher velocity cooling water; coastal power stations where velocity exceeds 2 m/s

Primary Standards: ASTM B111 C68700 ASTM B395 C68700 EN 12449 CW702R BS 2871 Part 3 CZ110 JIS H3300 C6870 DIN 1785 CuZn20Al2As

90/10 Cupro-Nickel C70600 — Best-Value Marine Tube

90/10 Cupro-Nickel C70600 (Cu 88.6%, Ni 10%, Fe 1.4%, Mn 1.0%) is the marine industry's go-to tube material for most seawater service applications. The addition of iron and manganese creates a complex, self-repairing oxide film that is far more resistant to seawater than any copper-zinc or copper-zinc-tin alloy. It combines excellent corrosion resistance with moderate thermal conductivity and reasonable material cost — making it the best-value option for a wide range of marine and offshore applications.

• Optimal tube-side velocity: 1.5 – 3.5 m/s in seawater — handles high-velocity conditions
• Max chloride tolerance: Full seawater (35,000 ppm Cl⁻ equivalent) — unlimited in clean seawater
• H₂S tolerance: Moderate — tolerates up to ~0.1 ppm H₂S; above this, use 70/30 CuNi or Titanium
• Thermal conductivity: ~40 W/m·K (lower than brass — compensate with tube count)
• Max temperature: 260°C continuous
• Biofouling resistance: Excellent — copper's natural antifouling reduces marine growth on tube surfaces

Primary Standards: ASTM B111 C70600 ASTM B395 C70600 ASTM B543 C70600 (welded) EN 12449 CW352H BS 2871 Part 3 CN102 JIS H3300 C7060 DIN 17664 CuNi10Fe1Mn IS 1545

70/30 Cupro-Nickel C71500 — High-Performance Marine & Power

70/30 Cupro-Nickel C71500 (Cu 68.5%, Ni 30%, Fe 0.5–1.0%, Mn 1.0%) is the premium seawater tube alloy in the copper-nickel family. Its higher nickel content gives it superior performance over C70600 in the most aggressive marine environments — highly polluted harbour waters, high-velocity conditions, warm seawater above 30°C, and environments where H₂S may be present.

• Optimal tube-side velocity: 1.5 – 4.0 m/s in seawater
• H₂S tolerance: Good — tolerates up to ~0.5 ppm H₂S before film breakdown; best CuNi for polluted seawater
• Thermal conductivity: ~29 W/m·K (lower than C70600 — requires engineering compensation)
• Max temperature: 300°C continuous
• Cost premium over C70600: ~25–40% higher per kg — justify only where C70600 has proven insufficient

Primary Standards: ASTM B111 C71500 ASTM B395 C71500 EN 12449 CW354H BS 2871 Part 3 CN107 JIS H3300 C7150 DIN 17664 CuNi30Mn1Fe

Titanium Grade 2 (UNS R50400) — The Premium Long-Life Choice

Titanium Grade 2 is the universal tube material — it performs in seawater, brine, hypochlorite solutions, organic acids, alkalis, H₂S-saturated environments and virtually every industrial cooling medium except dry chlorine gas and hot concentrated HF acid. Its selection is driven by extreme corrosion requirements, very long service life targets (>25 years) or where retubing is impractical.

• Seawater resistance: Perfect — no known velocity limit or chloride concentration limit
• H₂S resistance: Excellent — immune to sulphide attack that destroys copper alloys
• Thermal conductivity: 16 W/m·K — lowest of all tube materials; requires more surface area to achieve same heat transfer as brass or copper alloy tubes
• Density: 4.51 g/cm³ — lightest metallic tube material; allows more tubes per bundle for equivalent tube-side pressure drop
• Cost: 8–12× Admiralty Brass per kg; justified by 25–30 year maintenance-free service life in severe environments
• Crevice corrosion: Immune below 80°C; above 80°C in highly concentrated chloride solutions, use Grade 12 or ASTM Grade 7 (Pd-stabilised)

Primary Standards: ASTM B338 Grade 2 (seamless and welded Ti tubes for condensers) ASTM B265 Grade 2 (Ti sheet/plate — tube sheets) ASTM B381 Grade 2 (Ti forgings — channel covers, bonnets) EN 10216-5 JIS H4631

Stainless Steel SS 316L & SS 304 — Industrial Default

SS 316L (ASTM A213 Grade TP316L / A249) and SS 304 (ASTM A213 Grade TP304) are the default tube materials for chemical process coolers where the cooling medium is fresh water, industrial water or steam condensate — not seawater. Their key limitation is susceptibility to chloride-induced pitting and crevice corrosion in stagnant conditions above ~200 ppm Cl⁻.

• Seawater service: Not recommended for extended service — pitting occurs at tube-to-tubesheet joints and in stagnant zones during shutdown
• Freshwater and DM water: Excellent — the most common choice for steam surface condensers with deaerated condensate
• Chemical compatibility: Wide — organic acids, alkalis, solvents (check chloride content of each)
• H₂S tolerance: Moderate — 316L better than 304; hydrogen sulphide stress cracking (HSSC) risk at elevated partial pressures in sour service
• Max temperature — 316L: 870°C oxidising; 425°C continuous in reducing
• Advantage: Widely available, extensive ASME/TEMA design data, low initial cost for non-corrosive service

Primary Standards: ASTM A213 TP304/316L ASTM A249 TP316L (welded) EN 10216-5 JIS G3463

Copper C12200 — Freshwater & HVAC Applications

Copper C12200 DHP is used in HVAC condensers, chillers, domestic hot water heaters and process coolers where the tube-side fluid is clean freshwater, deaerated water or refrigerant. Its outstanding thermal conductivity (~339 W/m·K — highest of all tube materials) allows thinner walls, more compact bundles and higher U values than any alloy.

Primary Standards: ASTM B111 C12200 ASTM B359 C12200 (integral-fin tube) EN 12449 Cu-DHP BS 2871 Part 1 C106 JIS H3300 C1220

Master Comparison Table — All Materials Side by Side

Complete Standards Reference — ASTM, EN, BS, JIS, DIN

Quick Decision Guide by Application Type

TEMA Standards & Heat Exchanger Design

The Tubular Exchanger Manufacturers Association (TEMA) publishes standards that govern the mechanical design, fabrication and materials of shell-and-tube heat exchangers worldwide. TEMA standards define three classes:

• TEMA Class R: Severe requirements — refinery, chemical processing and offshore applications
• TEMA Class C: Commercial and general process applications
• TEMA Class B: Chemical process industry — intermediate between R and C

TEMA specifies minimum wall thickness for copper alloy tubes at 0.65 mm for 19 mm OD tubes in Class C and 0.71 mm for Class B and R. For tube sheet design with copper alloy tubes, TEMA references ASME Section VIII Division 1 for pressure calculations, with material allowable stresses taken from ASME II Part D for the specific UNS alloy.

When ordering copper alloy condenser tubes, always specify:

1. UNS grade (e.g. C44300, C70600)
2. Applicable standard (e.g. ASTM B111)
3. Tube OD (e.g. 19.05 mm / ¾ inch)
4. Wall thickness in BWG or mm (e.g. 18 BWG = 1.245 mm)
5. Length (e.g. 6096 mm / 20 ft)
6. Temper/condition (e.g. O61 annealed or H55 light drawn)
7. Test requirements (e.g. hydrostatic per ASTM B111, eddy current per ASTM E243)
8. TEMA class (R, B or C)

Frequently Asked Questions

Why is Admiralty Brass being replaced by CuNi in new power plant designs?

As coastal and nuclear power plant cooling water quality deteriorates due to industrial discharge and algal blooms, Admiralty Brass C44300 is increasingly failing prematurely due to H₂S attack and high-velocity erosion. New-build specifications now increasingly default to 90/10 CuNi C70600 as the standard first choice, with Admiralty Brass retained only for inland freshwater stations with clean, low-velocity cooling water.

What is the minimum tube-side velocity to prevent biofouling in seawater?

A minimum tube-side seawater velocity of approximately 1.0 m/s is required to prevent silt settlement and biological fouling in copper alloy tubes. Below 0.9 m/s, stagnant zones form, accelerating under-deposit corrosion. Copper alloy's natural biocidal copper ion release helps — but velocity must still be maintained above the minimum threshold, particularly during partial-load operation.

Can Melta Alloys supply ASTM B111 tubes with eddy current test reports?

Yes — Melta Alloys supplies all copper alloy condenser and heat exchanger tubes per ASTM B111, BS 2871, JIS H3300 and EN 12449 with hydrostatic test certificates and eddy current test reports per ASTM E243. Full EN 10204 Type 3.1 MTCs, chemical analysis certificates, dimensional reports and TEMA compliance statements are available.