The material used to build a shell and tube heat exchanger can have a major impact on corrosion resistance, service life, thermal performance, maintenance requirements, and overall equipment cost.
There is no single material that is right for every industrial application. A material that performs well with one process fluid may corrode rapidly in another. Temperature, pressure, fluid chemistry, velocity, fouling, cleaning methods, and expected equipment life can all influence the decision.
That is why material selection should be considered early when getting a heat exchanger rather than treated as an afterthought once the thermal design has already been established.
Why Heat Exchanger Material Selection Matters
A shell and tube heat exchanger may operate continuously for years while being exposed to elevated temperatures, pressure, corrosive fluids, contaminants, vibration, and repeated thermal cycling.
The materials of construction must be capable of handling those conditions without introducing an unacceptable risk of corrosion, erosion, cracking, leakage, or premature failure.
Choosing the right materials can help:
- Reduce corrosion and erosion
- Extend equipment service life
- Limit unexpected maintenance
- Reduce the risk of tube leaks and cross-contamination
- Support the required design pressure and temperature
- Improve compatibility with cleaning procedures
- Control initial and long-term equipment costs
The lowest-cost material at the time of purchase is not always the lowest-cost option over the life of the equipment.
What Determines the Best Material for a Heat Exchanger?
Material selection begins with understanding the actual operating environment.
Fluid Chemistry
The fluids flowing through the exchanger are one of the biggest factors in material selection. Acids, salts, chlorides, hydrocarbons, process chemicals, treated water, seawater, steam, and other fluids can interact very differently with different metals.
Engineers should consider the complete chemical composition of each fluid, including contaminants and trace compounds that may affect corrosion.
Operating Temperature
Corrosion behavior can change significantly as temperature increases. A material that performs adequately at moderate temperatures may behave differently at elevated operating temperatures.
Temperature also affects material strength and must be evaluated along with the exchanger’s required design conditions.
Operating and Design Pressure
Materials must provide sufficient mechanical strength for the pressure they will experience.
Higher design pressures can influence wall thickness, tube thickness, flange requirements, tubesheet design, and the materials selected for pressure-retaining components.
Flow Velocity
Fluid velocity matters because excessive velocity can contribute to erosion or erosion-corrosion in certain materials and applications.
Very low velocities can create their own problems by allowing solids to settle or deposits to form.
Fouling and Deposits
A fluid that leaves scale, sludge, biological growth, process residue, or other deposits can create localized corrosion conditions beneath those deposits.
Fouling behavior should therefore be evaluated alongside corrosion resistance rather than as an entirely separate issue.
Cleaning Method
Mechanical cleaning, chemical cleaning, clean-in-place procedures, and high-pressure water cleaning can all affect material selection.
A material should be compatible not only with the process fluid, but also with the chemicals and procedures that will be used to clean the exchanger over its operating life.
Common Heat Exchanger Materials of Construction
Shell and tube heat exchangers can be manufactured from numerous metals and alloys depending on the service. Some of the most commonly considered material families include carbon steel, stainless steels, duplex stainless steels, copper alloys, copper-nickel alloys, and high-nickel alloys.
Carbon Steel Heat Exchangers
Carbon steel is commonly used in industrial equipment because it provides good mechanical strength at a relatively economical cost.
It may be suitable for applications where the process fluids and operating environment are not highly corrosive.
Advantages of Carbon Steel
- Relatively economical compared with many specialty alloys
- Widely available
- Strong and familiar to industrial fabricators
- Suitable for many general industrial applications
Potential Limitations
Carbon steel can be vulnerable to corrosion when exposed to certain water conditions, chemicals, acids, oxygenated environments, or other aggressive fluids.
Corrosion allowance, coatings, water treatment, fluid control, or an alternative alloy may be required depending on the service.
Stainless Steel Heat Exchangers
Stainless steel is commonly considered when greater corrosion resistance is needed than carbon steel can provide.
Different grades of stainless steel have different chemical compositions and corrosion characteristics, so simply specifying “stainless steel” is generally not enough for a detailed industrial heat exchanger specification.
304 Stainless Steel
304 stainless steel is widely used throughout industrial manufacturing and can provide good corrosion resistance in many relatively mild environments.
316 Stainless Steel
316 stainless steel contains molybdenum, which can provide improved resistance to certain forms of corrosion compared with 304 stainless steel.
However, stainless steel should not automatically be assumed to be corrosion-proof. Chloride concentration, temperature, oxygen content, deposits, and other process conditions can significantly affect performance.
Material grade matters.
The correct stainless steel should be selected based on the actual process environment rather than simply choosing stainless because it is perceived as a premium material.
Duplex Stainless Steel
Duplex stainless steels combine characteristics of austenitic and ferritic stainless steels and may be considered for applications requiring increased strength and enhanced resistance to certain corrosion mechanisms.
These alloys can be useful in challenging industrial environments, but their suitability still depends on fluid chemistry, fabrication requirements, operating temperature, and the specific alloy being considered.
Duplex materials can also cost more than conventional stainless steel, so the potential improvement in service life should be weighed against the increased initial investment.
Copper and Copper-Nickel Alloys
Copper-based alloys have a long history in heat transfer equipment because of their favorable thermal conductivity and performance in certain water services.
Copper-nickel alloys may also be considered in marine and other water-handling applications where appropriate.
Where Copper Alloys Can Make Sense
- Water heating and cooling applications
- Marine environments when the specific alloy is suitable
- Applications where strong thermal conductivity is beneficial
Fluid compatibility must still be carefully evaluated because some chemicals and process environments can aggressively attack copper-based materials.
High-Nickel Alloys
High-nickel alloys may be considered for demanding applications involving aggressive chemicals, elevated temperatures, or corrosion environments that conventional steels cannot adequately handle.
These materials can provide excellent performance in the right application, but they also come with significantly higher material and fabrication costs.
For this reason, specialty alloys are often used strategically rather than automatically constructing every component from the same expensive material.
Does the Entire Heat Exchanger Need to Use the Same Material?
No. One of the advantages of a custom shell and tube heat exchanger is that different components can be evaluated individually.
A heat exchanger may include different materials for:
- Shell
- Tubes
- Tubesheets
- Channels or bonnets
- Baffles
- Flanges
- Supports
- Gaskets
For example, an application might allow carbon steel to be used for certain external or shell-side components while requiring a more corrosion-resistant alloy for the tubes that are directly exposed to an aggressive process fluid.
This type of material optimization is one of the advantages of custom shell and tube heat exchanger manufacturing.
Tube Material Is Especially Important
The tubes provide the primary heat transfer surface and are often among the thinnest pressure-containing components in the exchanger.
Even localized corrosion can eventually penetrate a tube wall and create an internal leak between the shell-side and tube-side fluids.
When selecting tube material, engineers may evaluate:
- Corrosion resistance
- Thermal conductivity
- Tube wall thickness
- Fluid velocity
- Operating pressure
- Temperature
- Fouling tendency
- Mechanical cleaning requirements
- Expected service life
Tube material can therefore have a major impact on both initial exchanger cost and long-term reliability.
Tube Sheet Material and Galvanic Compatibility
The tubesheet supports the tube bundle and creates a pressure boundary between the fluids. Because the tubes are mechanically or metallurgically joined to the tubesheet, compatibility between these components deserves particular attention.
Using dissimilar metals in the presence of a conductive fluid can create conditions for galvanic corrosion.
Material selection should therefore consider the complete assembly rather than selecting individual components in isolation.
Cladding and Other Material Strategies
In some applications, clad materials or other engineered material combinations may allow corrosion-resistant material to be concentrated where it is most needed while using a more economical base material elsewhere.
The appropriate approach depends on design requirements, fabrication methods, applicable codes, and process conditions.
Corrosion Should Drive Material Decisions Early
Repeated corrosion problems are often a sign that the operating environment and metallurgy need to be reviewed together.
Simply duplicating the material used in an old exchanger can reproduce the same failure mechanism in the replacement unit.
If an existing exchanger has experienced pitting, tube thinning, repeated leaks, under-deposit corrosion, or other recurring damage, the cause should be investigated before specifying replacement materials.
Our guide to preventing corrosion in shell and tube heat exchangers explains several of the corrosion mechanisms that can affect exchanger service life.
Do More Expensive Materials Always Mean a Better Heat Exchanger?
No.
Using the most expensive alloy available does not automatically create the best design.
A good heat exchanger specification balances:
- Process compatibility
- Mechanical strength
- Corrosion resistance
- Thermal performance
- Fabrication requirements
- Maintenance expectations
- Availability
- Initial cost
- Expected service life
The goal is to select materials that are appropriate for the actual application without adding unnecessary cost or compromising reliability.
Heat Exchanger Materials and ASME Requirements
Material selection for pressure equipment must also account for applicable design and construction requirements.
The ASME Boiler and Pressure Vessel Code includes material specifications and material property information used in the design and fabrication of pressure vessels and related equipment.
ASME Section II covers ferrous materials, nonferrous materials, welding materials, and material properties used throughout the Boiler and Pressure Vessel Code.
More information is available through the official ASME Boiler and Pressure Vessel Code resources.
Information Your Manufacturer Needs Before Selecting Materials
If the correct material has not already been specified, provide your heat exchanger manufacturer with as much operating information as possible.
Important information may include:
- Complete shell-side fluid composition
- Complete tube-side fluid composition
- Contaminants and solids
- Chloride or salt concentrations when applicable
- Operating temperatures
- Design temperatures
- Operating pressure
- Design pressure
- Flow rates
- Expected fluid velocity
- Known corrosion history
- Fouling or scaling concerns
- Cleaning chemicals and procedures
- Previous tube or shell failures
- Required design life
The more information available during the design process, the better the manufacturer can evaluate suitable material options.
Should You Use the Same Material as the Existing Heat Exchanger?
Not necessarily.
If an existing exchanger has provided reliable service for many years under unchanged operating conditions, its original materials can provide useful information for a replacement design.
However, blindly duplicating the old metallurgy is not always the best approach.
Process conditions may have changed. Fluid chemistry may be different. Production rates may have increased. Cleaning chemicals may have changed. A recurring failure may also indicate that the existing material was never ideal for the service.
A replacement project creates an opportunity to evaluate whether material upgrades could improve reliability or equipment life.
Material Selection Is Part of the Complete Heat Exchanger Design
Heat exchanger materials cannot be selected independently from the rest of the equipment.
Material choice interacts with:
- Tube diameter and wall thickness
- Tube layout and pitch
- Shell thickness
- Pressure and temperature ratings
- Thermal expansion
- Tube-to-tubesheet joints
- Welding procedures
- Cleaning access
- Corrosion allowance
- Applicable construction codes
For industrial applications, these factors should be evaluated as one complete system rather than a collection of unrelated specifications.
Custom Heat Exchanger Materials for Industrial Applications
KAM Thermal Equipment is a custom shell and tube manufacturer specializing in heat exchangers for industrial applications.
Our team evaluates process requirements, pressure, temperature, fluids, corrosion concerns, maintenance requirements, and fabrication considerations when developing equipment for demanding operating environments.
As a fourth-generation fabricator of specialized industrial products, KAM Thermal Equipment has been designing and manufacturing heat transfer equipment since 1906.
Need Help Selecting Materials for Your Heat Exchanger?
If you are specifying a new shell and tube heat exchanger or replacing equipment that has experienced corrosion or premature failure, KAM Thermal can review the operating conditions and help evaluate appropriate materials for the application.
Call KAM Thermal Equipment at (631) 348-4880 to discuss your heat exchanger requirements.