Cladding Explained: Understanding Its Role and Applications

What is cladding?

Think of cladding like putting a protective coat on a metal surface, but instead of paint, we’re using another metal with special properties. The process involves depositing a layer of filler metal onto a base metal (also called the substrate) to give the surface new characteristics while keeping the structural strength of the base metal underneath.

To understand why we use cladding, imagine you have a large steel structure that needs to resist corrosion. Instead of making the entire structure from expensive corrosion-resistant metal, you can use regular carbon steel and clad just the surface with a corrosion-resistant metal like stainless steel. This gives you the best of both worlds: the strength and cost-effectiveness of carbon steel with the corrosion resistance of stainless steel.

Examples of use

The real beauty of cladding lies in its versatility. You can select different cladding materials based on what properties you need: corrosion resistance, heat resistance, or even special electrical properties. It’s like giving your metal surface a superpower, but only where you need it.

Oil and gas industry

Storage tanks and pipelines face constant exposure to corrosive substances. For example, a crude oil storage tank in Saudi Arabia might need to hold millions of gallons of oil containing corrosive sulfur compounds. Rather than building the entire tank from expensive corrosion-resistant alloys, engineers use carbon steel for structural strength and clad the interior with a 3-5mm layer of stainless steel using submerged arc welding. This cladding protects against corrosion while keeping construction costs manageable.

Chemical processing

Consider pressure vessels in chemical processing plants that need to maintain integrity while handling corrosive materials. Robotic GMAW systems can precisely deposit layers of high alloy material onto carbon steel vessels. The robot’s consistent travel speed and wire feed rate ensure uniform penetration and minimal dilution, creating a high-quality corrosion-resistant layer that protects the underlying structure. This is particularly valuable in areas where manual welding would be difficult, such as the interior curves of vessels or hard-to-reach corners.

Water Treatment

In desalination plants, seawater handling equipment faces constant exposure to chlorides. Consider a large heat exchanger tube sheet made of carbon steel. Automated welding systems can systematically clad the surface with high nickel alloys like Inconel 625. The robot’s precise control allows for overlapping weld beads with consistent 30-40% overlap, creating a continuous corrosion barrier. The automated process maintains exact wire feed speeds and voltage parameters, crucial for achieving the right chemistry in the final deposit.

Offshore

Offshore platforms face particularly challenging conditions where seawater meets hydrocarbons. The risers (pipes that transport oil from the seabed to the platform) experience both internal and external corrosion threats. These components are often manufactured with a carbon steel base and are then clad with Inconel 625 using automated arc welding. This combination provides the necessary strength to handle high pressures while protecting against corrosive fluids.

The cladding process

The cladding process follows a series of key steps that must be executed with precision to achieve optimal results. Each stage plays a critical role in ensuring the quality and reliability of the final protective layer.

1. Surface Preparation: The base metal must be thoroughly cleaned to remove any contaminants that could affect the quality of the cladding. This includes removing rust, scale, oils, and other debris to ensure a clean surface for bonding.
2. Equipment Setup: The welding equipment needs proper setup with corrosion-resistant wire and appropriate shielding gas. The specific settings for voltage and wire feed speed are determined by the materials being used and the application requirements.
3. Preheating: Preheating the base metal helps ensure proper fusion between the base metal and the cladding material. This step is essential for achieving a strong metallurgical bond.
4. Cladding Application: The actual cladding begins with laying down the first layer using a weaving pattern. The welder maintains consistent movement and overlap between passes to ensure complete coverage of the surface.
5. Intermediate Cleaning: Between layers, cleaning is essential to maintain the quality of the cladding. This removes any residue that could affect the next layer’s bonding.
6. Layering and Temperature Control: Additional layers may be added depending on the required thickness and specifications. Temperature control remains important throughout this process to ensure proper fusion and prevent defects. Proper fusion and temperature control can also involve keeping the temperature low. This can be achieved by applying water cooling to the backside and using modified arcs (e.g., EWM React), which ensure focused penetration with low heat input. This approach minimizes excessive mixing of the base material (carbon), typically keeping the base material dilution below 2%. Achieving dilution levels under 1% significantly extends the lifespan of the cladding layer, resulting in substantial financial and environmental savings. However, achieving dilution under 0.6% is impossible due to the carbon content inherent in the wire.
7. Final Inspection: The process concludes with a thorough inspection to verify the quality and completeness of the cladding. This step involves checking for proper coverage and identifying any potential defects.

By adhering to these steps, the cladding process ensures a high-quality protective layer that can withstand rigorous conditions. This meticulous approach not only enhances the structural integrity of the base material but also contributes to improved performance and reliability in its intended application.

Cladding Wire Types

In cladding applications, the choice of wire is crucial to ensure proper bonding and durability. Here are common types of wires specifically used for cladding, not hardfacing:

1. Nickel-based Wires
   • Examples: ERNiCrMo-3, ERNiCu-7
   • Applications: Commonly used for corrosion-resistant cladding in industries such as oil and gas, chemical processing, and marine environments.
2. Stainless Steel Wires
   • Examples: ER309L, ER316L, ER347
   • Applications: Ideal for cladding carbon or low-alloy steels to provide resistance to corrosion and oxidation in high-temperature environments.
3. Aluminum Wires
   • Examples: ER4045, ER5356
   • Applications: Used for cladding aluminum alloys or when weight and corrosion resistance are critical, such as in aerospace and transportation.
4. Inconel Wires
   • Examples: ER625, ER725
   • Applications: These nickel-chromium alloy wires are highly resistant to oxidation and corrosion, making them suitable for cladding in extreme environments, such as offshore and subsea applications.

Each wire type is selected based on the base metal, service conditions, and the desired properties of the cladded surface. Proper wire selection ensures compatibility and optimal performance in the intended application.

Cladding and Robotic Welding

Manual cladding is a labor-intensive and time-consuming process that requires a high level of skill and concentration. Achieving consistent quality across large or complex surfaces is challenging, as human operators are prone to fatigue, variability in technique, and errors. These issues can lead to uneven coverage, poor fusion, and increased rework, compromising the effectiveness of the cladding layer.

Robotic welding, particularly collaborative robot (cobot) welding, addresses these pain points by delivering unparalleled consistency and precision. Robots can maintain uniform movement and overlap, ensuring even coverage and strong bonding throughout the process. Cobots, which are designed to work safely alongside human operators, add flexibility to the process by combining human expertise with robotic accuracy.

Additionally, robotic systems excel in maintaining critical parameters such as temperature, wire feed speed, and travel speed, which are essential for preventing defects. Their ability to handle repetitive tasks without fatigue results in higher productivity and more reliable cladding outcomes, making them an ideal solution for industries demanding superior performance and durability from their materials.