Seawater Corrosion Heat Exchangers: Titanium vs Hastelloy — How to Choose

Seawater is one of the most aggressive coolants in industry. It destroys carbon steel in months, 304 stainless in weeks, and even 316L fails quickly in stagnant or high-temperature conditions. When a heat exchanger is cooled by seawater, material selection is not a cost decision — it is a reliability decision.

Titanium and Hastelloy are the two most common high-performance choices. Both resist chlorides. Both are expensive. But they are not interchangeable. This guide explains how to choose between them based on real operating conditions.

Why seawater destroys heat exchangers

Seawater corrosion is not a single mechanism. It combines:

• Chloride pitting and crevice corrosion — chlorides break down passive films on stainless steels

• Stress corrosion cracking — chlorides plus tensile stress plus temperature above 60°C cracks 304/316

• Galvanic corrosion — dissimilar metals in seawater create strong galvanic cells

• Erosion-corrosion — high velocity strips protective films

• Biofouling — marine organisms create deposits that accelerate under-deposit corrosion

• Hydrogen embrittlement — certain materials absorb hydrogen in cathodic protection systems

The material must resist all of these simultaneously. Titanium and Hastelloy do, but to different degrees and at different costs.

Titanium: the workhorse for seawater cooling

Titanium is the default choice for seawater-cooled heat exchangers. It is used in power plants, desalination, offshore platforms, and marine vessels worldwide.

Why titanium works

• Exceptional chloride resistance — titanium forms a stable TiO₂ passive film that resists chlorides up to very high temperatures

• Excellent erosion resistance — handles velocities up to 10 m/s or more in clean seawater

• Lightweight — about 45% lighter than steel, easier to handle and support

• Good heat transfer — thermal conductivity similar to stainless steel

• Long service life — 20–30 years in seawater is common

Common titanium grades

• Grade 2 (commercially pure) — the standard for seawater cooling. Good corrosion resistance, moderate strength.

• Grade 7 (Pd-stabilized) — better resistance to crevice corrosion in hot, sour, or reducing environments.

• Grade 12 (Ni-Mo stabilized) — improved strength and corrosion resistance at higher temperatures.

For most seawater heat exchangers, Grade 2 is sufficient. Grade 7 is used where crevices, deposits, or reducing conditions are present.

Limitations of titanium

• Temperature limit — titanium is generally limited to about 120–150°C in seawater. Above that, hydriding and corrosion risk increase.

• Fouling — titanium surfaces are prone to biofouling and scaling. Cleaning is required.

• Not for reducing acids — titanium performs poorly in reducing environments (e.g., hydrochloric acid, sulfuric acid at high concentration).

• Hydrogen embrittlement — in cathodic protection systems, titanium can absorb hydrogen and crack. Grade 7 is more resistant.

• Cost — titanium is expensive, though less than Hastelloy.

Best applications for titanium

• Seawater cooling in power plants

• Desalination plants (MSF, MED, RO)

• Offshore oil and gas cooling

• Marine engine cooling

• HVAC cooling with seawater

• Chemical plants using seawater as a utility

Hastelloy: the premium choice for extreme conditions

Hastelloy alloys are nickel-chromium-molybdenum alloys designed for the most corrosive environments. In seawater service, they are used where titanium is not enough.

Why Hastelloy works

• Superior chloride resistance — Hastelloy C276 and C22 resist chlorides at higher temperatures than titanium

• Resists reducing and oxidizing acids — handles mixed acid environments

• Excellent crevice corrosion resistance — better than titanium in tight crevices

• High temperature capability — usable up to 400°C+ in seawater and aggressive chemicals

• Resists pitting and stress corrosion cracking — even in chlorinated seawater

Common Hastelloy grades

• C276 (UNS N10276) — the most common. Excellent resistance to chlorides, acids, and oxidizing/reducing media.

• C22 (UNS N06022) — improved resistance to oxidizing media and pitting.

• C2000 (UNS N06200) — optimized for sulfuric acid and chloride environments.

• B-3 (UNS N10675) — for hydrochloric acid service.

For seawater heat exchangers, C276 is the standard. C22 is used where oxidizing conditions exist.

Limitations of Hastelloy

• Cost — 3–5 times the cost of titanium. Often the most expensive option.

• Availability — longer lead times, fewer suppliers.

• Fabrication — requires careful welding and post-weld cleaning.

• Not always necessary — in clean, cold seawater, titanium performs equally well at lower cost.

Best applications for Hastelloy

• Seawater cooling with high temperatures (above 120°C)

• Chlorinated seawater systems

• Offshore platforms with sour service

• Chemical plants with mixed acids and chlorides

• Flue gas desulfurization (FGD) heat exchangers

• Nuclear plant cooling with seawater

Titanium vs Hastelloy: direct comparison

How to choose: a practical decision framework

Choose titanium when:

• Seawater temperature is below 120°C

• Chloride levels are typical (up to 20,000 mg/L)

• Fluid is clean or moderately fouling

• No reducing acids present

• Budget is a concern

• You need fast delivery

Choose Hastelloy when:

• Seawater temperature exceeds 120°C

• Chlorine or hypochlorite is injected

• Crevices are unavoidable

• Reducing acids or mixed acids are present

• Sour service (H₂S) is expected

• You need maximum reliability and service life

• Budget allows

Consider other materials when:

• Super duplex stainless — for moderate chloride, moderate temperature, and cost-sensitive projects. Limited to about 60°C in seawater.

• 6Mo (254 SMO) — better than 316L but not equal to titanium. Limited to about 60–80°C.

• Copper-nickel (CuNi 90/10, 70/30) — good for clean seawater, but erodes at high velocity and is toxic to marine life. Limited to about 2.5 m/s.

• Nickel-aluminum bronze — for pumps and valves, not typically for heat exchanger tubes. 

Design considerations for seawater heat exchangers

Material selection is only part of the solution. Design must support the material:

• Velocity: Maintain 1.5–2.5 m/s for titanium, 1–2 m/s for Hastelloy, to prevent fouling and erosion. Below 1 m/s, biofouling accelerates.

• Crevices: Eliminate or minimize crevices. Use welded joints instead of rolled joints where possible.

• Galvanic isolation: Use insulating gaskets or sleeves between dissimilar metals. Titanium and Hastelloy are cathodic to steel and can accelerate corrosion of adjacent steel components.

• Cleaning: Design for mechanical or chemical cleaning. Titanium and Hastelloy are both prone to biofouling.

• Cathodic protection: If used, ensure it does not cause hydrogen embrittlement of titanium. Grade 7 is more resistant.

• Flow distribution: Avoid dead zones where deposits can form.

• Temperature control: Keep seawater outlet temperature below the material limit. For titanium, stay below 120°C. For Hastelloy, below 400°C.

Cost analysis: upfront vs lifecycle

Titanium heat exchangers cost 2–3 times more than 316L. Hastelloy costs 3–5 times more than titanium. But the cheapest option is not always the lowest lifecycle cost.

Example: A seawater-cooled shell-and-tube exchanger for a power plant.

• 316L: $50,000, fails in 2 years. Replacement cost + downtime = $200,000 over 10 years.

• Titanium: $150,000, lasts 20 years. Lifecycle cost = $150,000 + minimal maintenance.

• Hastelloy: $500,000, lasts 25+ years. Lifecycle cost = $500,000 + minimal maintenance.

In this case, titanium offers the best balance. Hastelloy is only justified if conditions exceed titanium’s limits.

Common mistakes

• Using 316L in seawater because it is “stainless”

• Choosing titanium for high-temperature seawater (above 120°C)

• Choosing Hastelloy for clean, cold seawater where titanium works

• Ignoring velocity and allowing fouling to accelerate corrosion

• Mixing titanium tubes with carbon steel tubesheets without galvanic isolation

• Not accounting for chlorine injection in titanium systems

• Buying on price without checking material certificates and traceability

FAQ

What is the best material for a seawater heat exchanger?
Titanium Grade 2 for most applications below 120°C. Hastelloy C276 for higher temperatures, chlorinated seawater, or aggressive chemical environments.

Can titanium handle chlorinated seawater?
Yes, titanium resists chlorinated seawater well, but chlorine can accelerate biofouling removal and may increase corrosion if residuals are high. Grade 7 is more resistant.

What is the temperature limit for titanium in seawater?
About 120–150°C. Above that, hydriding and corrosion risk increase. Hastelloy is preferred above 120°C.

Is Hastelloy better than titanium for seawater?
Hastelloy is more resistant at higher temperatures and in crevices. But it costs 3–5 times more. Titanium is sufficient for most seawater cooling duties.

Can I use super duplex instead of titanium?
Super duplex is suitable for moderate chloride and temperature (below 60°C). It is not a direct replacement for titanium in hot seawater.

How do I prevent galvanic corrosion in a seawater heat exchanger?
Use insulating gaskets, sleeves, and washers between dissimilar metals. Avoid direct contact between titanium or Hastelloy and carbon steel.

What velocity should I maintain in titanium tubes?
1.5–2.5 m/s to prevent fouling and erosion. Below 1 m/s, biofouling accelerates. Above 3 m/s, erosion may occur in contaminated seawater.