What Is Cladding in a Heat Exchanger? A Practical Guide to Clad Tubesheets and CRA Overlay
Cladding in a heat exchanger means applying a corrosion-resistant alloy layer to selected heat exchanger surfaces, especially tubesheets, channels, shells, heads, and process-contact faces. The base material provides strength and structure, while the cladding layer protects the surface from corrosion, erosion, galvanic attack, or high-temperature chemical damage.
In shell-and-tube heat exchangers, cladding is most often discussed around the tubesheet. A carbon steel tubesheet may be cladded with stainless steel, duplex, nickel alloy, titanium, copper-nickel, or another corrosion-resistant alloy so the process fluid sees the correct material without making the entire thick tubesheet from expensive alloy.
The practical idea is simple: use economical steel where strength is needed, and use premium alloy only where corrosion resistance is needed.
Short Answer
Heat exchanger cladding is a bonded metallic layer applied to the exchanger’s fluid-contact surface to protect a lower-cost base metal from corrosion or erosion. In many exchangers, the base is carbon steel or low-alloy steel, while the clad layer is stainless steel, duplex stainless, nickel alloy, titanium, copper-nickel, or another corrosion-resistant alloy.
Cladding is common on tubesheets because the tubesheet must be strong, thick, accurately drilled, and corrosion-resistant at the tube-side face. A solid alloy tubesheet can be expensive. A clad tubesheet can deliver the needed surface chemistry at lower cost.
Why Are Heat Exchangers Cladded?
Heat exchangers handle two fluids separated by tubes, plates, or walls. One side may be mild service, while the other side may contain chlorides, acids, seawater, sour gas, cooling water, chemicals, or hot corrosive media. Cladding lets engineers protect only the exposed surface.
The table below explains why cladding is specified. It matters because a heat exchanger cladding decision should follow the fluid service and material compatibility, not just a generic “better material” request.
| Reason for Cladding | What It Solves | Typical Heat Exchanger Area |
|---|---|---|
| Corrosion resistance | Protects carbon steel from aggressive tube-side or shell-side fluids | Tubesheet face, channel, shell, head |
| Tube compatibility | Reduces galvanic corrosion between tube material and tubesheet face | Tubesheet holes and tube-side face |
| Cost reduction | Avoids making thick parts from full solid alloy | Large tubesheets and channels |
| Service life extension | Reduces local corrosion and wastage on expensive components | Existing exchanger repair or upgrade areas |
| Erosion/corrosion protection | Protects inlet zones, impingement areas, and high-velocity surfaces | Channel inlet, nozzle areas, tube-side entrance regions |
| Thermal/chemical resistance | Protects surfaces exposed to hot or chemically aggressive fluids | Process side faces and internal surfaces |
The buyer conclusion: cladding is a targeted material solution. It should be tied to which side of the exchanger sees the aggressive fluid and which surfaces actually need alloy protection.
Where Is Cladding Used in a Heat Exchanger?
Cladding can be used on several heat exchanger components. Tubesheets are the most important example, but they are not the only one. Channels, channel covers, shells, heads, nozzles, and local impingement areas may also be cladded depending on service.
| Component | Why It May Be Cladded | Buyer Note |
|---|---|---|
| Tubesheet face | Tube-side corrosion resistance and compatibility with tube material | Final cladding thickness after drilling/machining is critical |
| Tubesheet holes | Protects tube-to-tubesheet interface from crevice and galvanic corrosion | Tube expansion or welding method affects required clad thickness |
| Channel and channel cover | Protects tube-side fluid containment surfaces | Often matched with tubesheet and tube material |
| Shell or shell-side head | Protects shell-side process fluid surfaces | May be clad plate or weld overlay depending on fabrication route |
| Nozzles and inlet zones | High-velocity flow, turbulence, erosion/corrosion | May need local overlay or upgraded alloy insert |
| Pass partition grooves and gasket faces | Sealing, crevice corrosion, and leakage control | Machining and surface finish must be specified |
The conclusion: cladding must be detailed on the drawing. A buyer should not assume the entire heat exchanger is cladded unless the specification clearly says which faces, holes, grooves, nozzles, and covers are included.
Cladding vs Weld Overlay vs Lining
In heat exchanger specifications, the words cladding, weld overlay, and lining are sometimes mixed. They can protect similar areas, but they are not identical. The distinction affects bonding, inspection, fabrication, and long-term reliability.
The Heat Exchange Institute has a useful technical sheet on heat exchanger cladding and why cladded materials are used for corrosion, tube compatibility, and cost control: HEI Technical Sheet 137: Heat Exchanger Cladding. Roben Manufacturing also summarizes clad heat exchanger construction and common cladding methods: Clad Heat Exchangers.
| Term | Meaning | Typical Heat Exchanger Use |
|---|---|---|
| Cladding | General term for bonding corrosion-resistant alloy to a base material | Clad plate, clad tubesheets, shells, channels, heads |
| Weld overlay | Depositing CRA weld metal onto a base surface by welding | Tubesheet face, local repair, nozzles, special alloy zones |
| Clad plate | Plate manufactured with alloy layer bonded before fabrication | Shells, heads, channels, large flat or formed sections |
| Lining | A separate protective layer attached or fitted to the inside | Selected lower-pressure or chemical services, depending on design |
| Thermal spray coating | Sprayed metallic or ceramic layer, mostly mechanical bond | Local corrosion/erosion protection where low heat input is needed |
The conclusion: weld overlay is a method of creating cladding. Clad plate is another route. Lining is a different construction approach and may not provide the same fully bonded behavior.
Why Tubesheet Cladding Is So Important
The tubesheet is often thick, expensive, and exposed to aggressive tube-side fluid. It also contains many holes, ligaments, tube expansions, tube welds, and crevice-prone regions. This makes it one of the most critical areas for cladding quality.
| Tubesheet Issue | Why Cladding Helps | Risk If Poorly Specified |
|---|---|---|
| Tube-side corrosion | CRA layer protects the face exposed to process fluid | Base metal corrosion and loss of sealing integrity |
| Galvanic mismatch with tubes | Cladding can match or be compatible with tube alloy | Accelerated attack near tube ends |
| Tube expansion zone | Adequate clad thickness protects the expanded interface | Crevice corrosion or exposure of base metal |
| Tube-to-tubesheet welds | CRA face supports compatible seal or strength welding | Cracking, corrosion, or weld mismatch |
| Machining and drilling | Finished clad thickness must remain after machining | Protective layer becomes too thin or discontinuous |
| Ligament thermal stress | Procedure control reduces cracking around dense hole patterns | Cracks, lack of fusion, or distortion around holes |
The buyer conclusion: tubesheet cladding should be treated as an engineered interface between tubes, process fluid, and pressure-retaining base material. It is not just a cosmetic layer on the face.
Common Cladding Materials
The cladding material should be selected for the fluid side it contacts. Tube-side and shell-side fluids may require different materials. Tube material compatibility also matters because galvanic corrosion can occur where dissimilar materials meet in an electrolyte.
| Cladding Material | Main Benefit | Typical Use |
|---|---|---|
| 304L / 316L stainless steel | General corrosion resistance | Chemical, water, and moderate process service |
| Duplex / super duplex stainless | Chloride resistance and strength | Seawater, offshore, chloride-bearing service |
| Nickel alloys such as Alloy 625 type overlays | High corrosion resistance in aggressive service | Sour, chloride, acid, high-temperature corrosion applications |
| Hastelloy-type nickel alloys | Severe chemical corrosion resistance | Acid and specialty chemical service |
| Monel / copper-nickel | Marine and selected seawater compatibility | Marine exchangers and cooling water service |
| Titanium or zirconium | Excellent resistance in specific aggressive media | Highly corrosive chemical service where compatible |
| Carbide or hardfacing overlay | Erosion and wear resistance | Inlet impingement or slurry-exposed zones |
The conclusion: choose the cladding alloy by corrosion and compatibility data, not by habit. The wrong alloy can fail even if the cladding process is well executed.
How Is Heat Exchanger Cladding Applied?
Cladding method depends on whether the exchanger is new or being repaired, which component needs protection, how large the surface is, and whether a fully bonded alloy layer is required.
| Method | Best Fit | Strength | Limitation |
|---|---|---|---|
| Roll-bonded clad plate | New shells, heads, channels, and flat sections | Uniform clad layer from mill processing | Must be planned before fabrication |
| Explosion-bonded clad plate | Difficult alloy combinations and thick backing materials | Strong bond between dissimilar metals | Requires specialized plate supply and fabrication planning |
| Weld overlay | Tubesheet faces, nozzles, local repair, special alloy areas | Flexible and metallurgically bonded | Dilution, heat input, and distortion must be controlled |
| SAW strip overlay | Large tubesheet or flat overlay areas | Higher productivity than manual welding | Access and procedure control are critical |
| GTAW/GMAW overlay | Smaller or complex areas, repair work | Good control and flexibility | Lower productivity than automated strip overlay |
| Laser cladding | Precision local repair and low heat input overlay | Low dilution and controlled layer | Higher equipment cost and access limitations |
The buyer conclusion: for a new exchanger, clad plate may be the cleanest route for large surfaces. For tubesheet faces, special alloy zones, and repairs, weld overlay is often more flexible. For precision local repair, laser cladding may be worth evaluating.
Clad Tubesheet vs Solid Alloy Tubesheet
A tubesheet can be very thick. Making it entirely from nickel alloy, titanium, duplex, or another expensive alloy may be costly and difficult. Cladding allows the exposed face to be alloy while the backing material provides strength.
| Factor | Clad Tubesheet | Solid Alloy Tubesheet |
|---|---|---|
| Material cost | Lower because premium alloy is only on the surface | Higher because the entire thickness is premium alloy |
| Structural strength | Backing material carries mechanical load | Alloy must provide full structural performance |
| Corrosion resistance | High at cladded surface if thickness and chemistry are controlled | High throughout the full thickness |
| Tube compatibility | Can match tube material at the exposed face | Good if alloy is correctly selected |
| Fabrication complexity | Requires cladding, drilling, tube attachment, and inspection control | Requires full-alloy machining and welding expertise |
| Best fit | Large or thick tubesheets where surface alloy is enough | Small or severe-service designs where full alloy is justified |
The practical conclusion: clad tubesheets are often the best cost-performance compromise, but only when the cladding thickness, tube attachment, and inspection requirements are correctly specified.
Technical Variables Buyers Should Specify
Heat exchanger cladding specifications should define the final usable surface, not only the starting material. Machining, drilling, tube welding, and tube expansion can all affect whether the clad layer actually protects the base metal.
| Variable | Why It Matters | What to Specify |
|---|---|---|
| Minimum finished cladding thickness | Protects against exposing base metal after machining and tube attachment | Final thickness after machining, drilling, and finishing |
| Tube attachment method | Expanded tubes and welded tubes may require different clad thickness and details | Expanded, seal welded, strength welded, or combined method |
| Dilution / chemistry | Weld overlay can mix base metal into the CRA layer | Chemistry or dilution acceptance criteria where critical |
| Bond quality | Lack of bonding can cause delamination or leakage paths | UT, macro checks, bend/shear testing where applicable |
| Porosity and cracks | Defects become corrosion initiation sites | PT, visual, and acceptance criteria |
| Hole finish and ligament quality | Tube holes are high-risk crevice and stress locations | Machining tolerance, surface finish, and inspection around holes |
| Galvanic compatibility | Dissimilar metals in conductive fluid can accelerate corrosion | Material compatibility between tubes, clad face, and fluid |
The conclusion: heat exchanger cladding is not finished when the alloy is deposited. The final drilled, machined, inspected, and tube-attached condition is what determines service reliability.
When Laser Cladding May Be Considered
Laser cladding is not always the first choice for a full-size tubesheet face, but it can be useful for precision local repair, erosion zones, sealing faces, nozzle areas, tube sheet restoration, and components where low dilution and low heat input matter.
HALDEN’s related equipment includes laser cladding machine, high-speed laser cladding machine, and pipe hardfacing equipment. For heat exchanger work, access, part rotation, bore geometry, shielding, and inspection are as important as laser power.
Common Buying Mistakes
- Specifying “clad tubesheet” without final thickness. The cladding may be reduced by machining, drilling, or tube attachment, leaving too little corrosion-resistant alloy in service.
- Ignoring tube-to-tubesheet compatibility. A cladding alloy that does not match the tube material or fluid environment can create galvanic corrosion or crevice corrosion near tube ends.
- Confusing lining, cladding, and weld overlay. This can lead to the wrong bond type, wrong inspection plan, or a construction method that does not fit exchanger duty.
- Choosing alloy only by name. A stainless or nickel overlay can still fail if the actual fluid chemistry, temperature, chlorides, or cleaning chemicals are not considered.
- Ignoring dilution in weld overlay. Excessive mixing with base metal can reduce corrosion resistance, especially for nickel alloy and stainless overlays.
- Not specifying inspection around tube holes. Defects around holes and ligaments can create leak paths, corrosion cells, or tube joint failures.
- Assuming cladding replaces all corrosion design thinking. Poor gasket design, dead zones, crevices, or wrong cleaning procedures can still cause corrosion even with a good clad layer.
Buyer Checklist
- Which side of the exchanger needs cladding? Tube side and shell side may see different fluids, temperatures, and corrosion mechanisms.
- Which parts are cladded? Tubesheet face, holes, channel, channel cover, shell, head, nozzles, and inlet zones should be listed clearly on the drawing.
- What tube material will be used? Tube material affects galvanic compatibility and the best cladding alloy for the tubesheet face.
- How will tubes be attached? Expanded-only, seal-welded, and strength-welded tube joints can require different clad thickness and machining details.
- What minimum final cladding thickness is required? Finished thickness after machining and drilling is what protects the base metal in service.
- How will dilution or chemistry be verified for weld overlay? Dilution can reduce corrosion resistance if the final surface chemistry is not controlled.
- What inspection will be performed after cladding and drilling? Visual, PT, UT, thickness, and dimensional checks may all be needed depending on service risk.
- Is this new fabrication or repair? New exchangers may use clad plate, while repair may require weld overlay, local laser cladding, or another field-friendly method.
- What cleaning chemicals and operating upsets are expected? Cleaning agents, shutdown conditions, and upset chemistry can be more aggressive than normal operation.
What to Send for a Heat Exchanger Cladding Quote
A useful quotation requires details about both sides of the exchanger and the tube-to-tubesheet design. A vague request for “cladded tubesheet” is not enough.
| Information to Send | Why It Matters |
|---|---|
| Heat exchanger type and drawing | Shows tubesheet, channel, shell, head, nozzle, and pass partition details |
| Tube-side and shell-side fluids | Determines corrosion mechanism and alloy choice |
| Operating temperature and pressure | Affects alloy selection, fabrication route, and inspection risk |
| Base material and tube material | Controls compatibility, weldability, and galvanic risk |
| Required cladding alloy | Defines corrosion resistance, cost, and fabrication method |
| Minimum finished cladding thickness | Prevents loss of protection after machining, drilling, and finishing |
| Tube attachment method | Determines hole details, clad thickness, and tube joint inspection |
| Inspection and code requirements | Defines NDT, documentation, and acceptance criteria |
This information lets the supplier recommend clad plate, weld overlay, laser cladding, or another cladding route based on the exchanger’s actual service conditions.
Final Recommendation
Cladding in a heat exchanger is the application of a corrosion-resistant or wear-resistant metallic layer to the surfaces that need protection, especially tubesheets, channels, shells, and heads. It allows an economical base material to provide strength while a premium alloy protects the fluid-contact surface.
For buyers, the critical details are material compatibility, cladded area, tube attachment method, final thickness, dilution, inspection, and machining quality. A well-specified clad tubesheet can reduce cost and extend exchanger life. A vague cladding requirement can leave the most vulnerable area, the tube-to-tubesheet interface, exposed to corrosion and leakage risk.
