Clad welding is a process that deposits a layer of one metal onto the surface of a different, less resistant metal to improve its corrosion resistance, wear resistance, or both. The most common application involves bonding a thin layer of corrosion-resistant alloy (stainless steel, nickel alloys, or titanium) onto a carbon steel base. This gives manufacturers the performance of an expensive alloy at a fraction of the cost of building an entire component from that material.
How Clad Welding Works
The basic idea is straightforward: rather than fabricating a pressure vessel, pipe, or reactor entirely from a costly alloy, you build it from affordable carbon steel and then deposit a protective layer where it matters. That protective layer is metallurgically bonded to the base metal, meaning the two materials fuse together at the atomic level rather than simply being glued or pressed together. This bond is what separates clad welding from coatings or linings that can peel or delaminate under stress.
The term “cladding” is broader than welding alone. It covers any method of depositing surface material onto a base metal, including mechanical processes like roll bonding, explosion bonding, and powder metallurgy. “Weld overlay” is the more specific term for cladding that uses fusion welding, where an electric arc or other heat source melts both the filler material and a thin layer of the base metal so they solidify as one. In practice, many people use “clad welding” and “weld overlay” interchangeably.
Common Material Combinations
The filler metal is almost always chosen to be more corrosion-resistant than the base. Carbon steel clad with stainless steel is the classic pairing for chemical processing equipment. For harsher environments, nickel-chromium-molybdenum alloys (like Alloy 625) are deposited onto steel to resist both corrosion and high temperatures. Titanium, zirconium, and tantalum cladding appear in the most aggressive chemical service, where even nickel alloys fall short.
Some combinations require an intermediate “butter” or barrier layer between the base and the final cladding. A good example is cladding carbon steel with a copper-nickel alloy: a pure nickel layer goes down first to act as a compositional bridge, preventing the carbon in the steel from migrating into the final cladding and weakening it. Choosing the right layering strategy is critical because the wrong combination can create brittle zones at the interface.
Arc Welding Methods
Most clad welding in heavy industry uses some form of arc welding. The process choice depends on how large the area is, how fast the job needs to go, and how tightly the chemistry of the deposited layer must be controlled.
For large, flat surfaces like the inside of a pressure vessel, strip cladding is the workhorse. Instead of a round wire electrode, it feeds a wide, flat strip of filler metal into the weld pool. Two main variants exist. Submerged arc strip cladding melts the strip beneath a blanket of granular flux, much like conventional submerged arc welding. It deposits material at rates up to about 75 pounds per hour. Electroslag strip cladding takes a different approach: it melts a flux into a conductive liquid slag, and the welding current passes through that slag rather than striking an arc. Because there is no arc digging into the base metal, less of the base metal melts into the cladding layer. Electroslag strip cladding can reach roughly 115 pounds per hour while keeping dilution rates as low as 8%, compared to 15 to 20% for the submerged arc version.
For smaller or more complex geometries, TIG (gas tungsten arc) welding and MIG (gas metal arc) welding are common. Electronically controlled short-circuit MIG variants are popular because they deliver low heat input and consistent dilution below 20% on the first bead. Specialized TIG variants can push dilution even lower, below 10% in a single layer, which is valuable when the chemistry spec is tight.
Laser Cladding
Laser cladding replaces the electric arc with a focused laser beam. The laser melts a thin layer of the substrate surface while simultaneously melting a stream of metal powder, wire, or strip fed into the beam path. The molten materials fuse into a thin bonding layer with very little mixing between the two metals.
The key advantage is minimal heat input. Because the laser focuses energy so precisely, the surrounding base metal stays relatively cool. This largely eliminates distortion, preserves the mechanical properties of the base material, and avoids the loss of important alloying elements that can evaporate at high temperatures. The clad material also cools rapidly after deposition, producing a fine-grained microstructure that tends to be harder and more uniform than what arc processes achieve.
Laser cladding is also uniquely flexible. Operators can blend two or more metal powders and adjust each powder’s feed rate independently, making it possible to create graded layers where the composition changes gradually from the base to the surface. This is useful for components that need different properties at different depths, such as a hard, wear-resistant surface transitioning smoothly into a tough, ductile core.
Explosion Bonding
Not all cladding involves melting. Explosion bonding is a solid-state process that uses precisely controlled detonations to slam two metal plates together at extreme velocity. The collision strips away surface contaminants and creates a wavy, interlocking interface between the metals, producing a bond that retains the full mechanical and corrosion properties of both layers. No filler metal is involved, and neither plate fully melts.
This process is most commonly used to clad large steel plates with stainless steel, brass, nickel alloys, titanium, zirconium, or tantalum. It excels at joining metals that are difficult or impossible to fusion-weld together because their melting points or thermal expansion rates are too different. The clad plates are then formed and welded into finished equipment like heat exchangers and reactor vessels.
Why Dilution Matters
Dilution is the single most important variable in clad welding quality. It refers to how much of the base metal melts into and mixes with the deposited cladding layer. If too much carbon steel dilutes into a stainless steel overlay, the chromium and molybdenum content of the cladding drops below the threshold needed for corrosion resistance, and the entire point of cladding is lost.
Manufacturers control dilution through process selection, welding parameters, and layering strategy. Lower heat input generally means less base metal melting and lower dilution. When a single layer cannot meet the required chemistry, two or three layers are deposited, with each successive layer having less base metal contamination. Strip cladding processes often achieve the target chemistry in a single pass, which saves significant time and cost compared to multi-layer approaches. For the tightest specifications, electroslag strip cladding and specialized TIG variants offer the lowest dilution rates available.
Inspecting the Finished Clad
A clad layer is only as good as its bond to the base metal. Incomplete fusion, porosity, or cracks at the interface can allow corrosive fluids to reach the unprotected steel underneath, leading to rapid failure. Several inspection methods verify bond integrity without cutting the part open.
Ultrasonic testing is the primary tool. High-frequency sound waves are sent through the clad layer and base metal, and reflections from the interface reveal unbonded areas, porosity, or cracks. Phased array ultrasonic systems, which use multiple elements to steer and focus the sound beam electronically, can detect and size flaws like incomplete fusion and lack of penetration with high confidence. Radiography (industrial X-ray) is also used, though it is less sensitive to certain flaw types, particularly planar defects like lack of fusion that sit parallel to the X-ray beam. In practice, many specifications call for both methods to complement each other’s blind spots.
Where Clad Welding Is Used
Oil and gas is the largest market. Subsea pipelines, pressure vessels, and downhole equipment routinely use carbon steel clad with corrosion-resistant alloys to survive exposure to hydrogen sulfide, carbon dioxide, and chloride-rich brines. Chemical processing plants use clad reactors and heat exchangers to handle acids and caustic solutions. Power generation, pulp and paper, and desalination plants all rely on clad components where the combination of structural strength and surface resistance would otherwise require prohibitively expensive solid alloy construction.
The economic logic is consistent across all these industries: clad welding delivers 80 to 90% of the performance of a solid alloy component at a fraction of the material cost, with a metallurgical bond strong enough to last the full service life of the equipment.