
Overlay welding is one of the technologies used in the manufacturing of pressure vessels for the process industry. This method allows to construct the highly corrosion resistant pressure vessel with ordinary materials. In this article, West Welding’s welding expert, Esa Ristiluoma, explains the significance and application of overlay welding, particularly in demanding process industry applications.
Overlay welding in a nutshell
In overlay welding, a layer of corrosion-resistant material is welded onto the selected base material of the pressure vessel. This process makes the pressure vessel corrosion-resistant, enabling it to withstand harsh conditions.
“There are two different welding methods. The first is traditional submerged arc welding, identified by the process code 122. The second is electro slag welding, identified by the process code 122 ESW. In the 122 ESW process, the mixing of the base material with the weld material is lower, and the output of the weld material is higher than in traditional submerged arc overlay welding,” explains Ristiluoma.
Overlay welding is particularly important in industries like oil, mining, and chemical, where equipment are constantly exposed to corrosion. Corrosion can be caused by abrasion, chemical attacks, high pressures, and temperatures. However, this is not a surface treatment but a welding process where the coating becomes an integral part of the equipment.

Overlay welding of a heat exchanger flange with a 60 x 0.5mm welding strip.
Overlay welding vs. surface treatment
Compared to many other surface treatments, the advantage of overlay welding is mechanical durability. Overlay welding withstands high temperatures, corrosive chemicals, and mechanical stress. The purpose of the surface treatment is not to withstand the internal load factors. “In overlay welding, the weld material is permanently bonded to the base material, making it a superior choice when long-term durability is required,” Ristiluoma emphasizes.
The materials used are carefully selected based on the application and requirements of the equipment. A typical combination is 309L for the first layer and 316L for the second.
“Commonly, In the first layer, known as the buffer layer, we use 309L filler material because it mixes with the base material and ensures that the overlay meets all the requirements. The second layer is 316L if the goal is to achieve a final overlay similar to 316L stainless steel,” Ristiluoma clarifies.
This multi-layered approach ensures that the pressure vessels can withstand both corrosion and mechanical stress.
The best choice for high-pressure equipment
In West Welding’s projects, overlay welding has been used particularly in high-pressure and thick-walled vessels in the oil and mining industries. “Overlay welding is well suited for high-pressure and thick-walled equipment, where it performs the best. It doesn’t make sense to use special material such as Inconel 625 throughout the entire structure, but only at the areas where it’s needed” says Ristiluoma.
Carbon steel acts as the load-bearing pressure shell of the equipment, while the overlay protects it from corrosion and chemical exposure. This creates a cost-effective solution, as special materials are only used where they are truly needed.

A sample piece of the overlay welding. The image shows how the welding materials are bonded.
Overlay welding in practice
Overlay welding is a precision-driven, multi-stage process that requires thorough cleaning and adherence to correct welding procedures. First, the material to be welded has to be carefully cleaned, after which the welding is carried out similarly to submerged arc welding. The first layer, called buffer layer, ensures the bonding of the base material and the overlay, and the second layer provides the final corrosion resistance.
“The first pass, the buffer layer, partially mixes with the base material, and the second layer is welded on top of this. This ensures that the final overlay meets the requirements and withstands the conditions imposed by the substances of the equipment,” Ristiluoma highlights.
West Welding’s overlay welding – a reliable choice
Overlay welding is a crucial solution when the material of the equipment is required to withstand both mechanical and chemical stresses. A cost-effective solution is to use carbon steel as the pressure shell and coat it with a chemically resistant material.
“For example, in one of our current projects, heat exchanger components, including the shell and solid flange, are overlayed with a 60 x 0.5 mm weld strip, using 309L in the buffer layer and 316L in the top layer. This ensures that the equipment components are resistant to both chemical and mechanical stresses,” describes Ristiluoma.
According to Ristiluoma, overlay welding can significantly extend the service life of pressure vessels and improve their safety. It is an advanced technology in the manufacturing of pressure vessels, especially in conditions where high pressure and corrosion are major challenges.
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