High velocity thermal spraying is emerging as a viable alternative to welding for maintaining major industrial components. Image courtesy of CandyRetriever via Shutterstock.
Process vessels and industrial boilers provide essential manufacturing infrastructure in many heavy industries, including oil and gas, pulp and paper, chemicals, and waste management. However, the media processed within these vessels are often corrosive in nature. For example, in amine processing equipment, carbon steel surfaces can be attacked by water vapor condensation and carbonic acid formation. Additionally, these components are often exposed to high temperatures and heavy use, which can lead to erosion and stress cracking.
Maintaining asset integrity is essential to ensure the safety and reliability of critical equipment is not compromised. However, addressing corrosion and metal wastage often results in significant repair and replacement costs. Moreover, the cost of shutting down equipment, especially for unplanned repairs, can cost companies billions of dollars in lost production costs. According to a Siemens report, unplanned downtime represents 11% of annual sales for Fortune 500 companies, resulting in losses of approximately $1.5 trillion.(i)
Traditionally, welding has been employed to address corrosion issues, but this high temperature process can place extra stress on equipment and typically requires pre- and post-weld heat treatment. High Velocity Thermal Spray (HVTS) has emerged as an innovative alternative solution that provides faster and equally durable in-situ corrosion mitigation for process vessels and boilers.
Advantages and disadvantages of welding and thermal spraying
Corrosion eventually leads to metal wastage and loss of shell thickness, which must be identified as soon as possible to prevent minimum corrosion tolerances from being exceeded. Welding is often used as a common solution to repair equipment that is not beyond repair. In this process, wall thickness is rebuilt using a corrosion resistant alloy (CRA), which also improves pressure retention.
However, overheating during the welding process can put significant stress on the thin vessel, causing shrinkage of approximately 1%. For a 5-meter diameter column, this can result in a significant distortion of 50 mm. Additionally, welding is a time-consuming process that can add weeks to repairs to critical equipment. Simply removing and reinstalling the support rings and downcomers can double the time a welding project takes, and can be further complicated by the skill of the welder.
But most importantly, weld overlay repairs do not address the root of the problem, which will eventually corrode in the same way as the material underneath. Repairs to process vessels and boilers using this method must be repeated every few years, resulting in significant asset downtime and financial loss.
Thermal spray technology has been used to apply CRA since the 1980s, but welding has been preferred to solve corrosion issues because the thermal spray process itself increases the permeability of the resulting coating. However, the latest iterations of thermal spray equipment have innovated to eliminate these deficiencies, instead applying the coating through a high-speed process that creates an impermeable barrier.
Latest High Velocity Thermal Spray Solutions
High Velocity Thermal Spray (HVTS) uses specific processes and chemicals to prevent coating particles from oxidizing in flight and forming permeation paths during deposition. This process allows the coating to be applied within a few days, significantly reducing turnaround time compared to welding and placing no additional thermal stress on the equipment. While HVTS alone will not improve the structural integrity of the equipment, if the vessel has not passed Fitness for Service (FFS) testing, it can be applied after welding to prevent corrosive media from attacking the substrate, significantly extending the life of the equipment.
This technology pioneered by IGS is already seeing application across a variety of industries. In 2011, IGS partnered with a gas plant in Qatar to remediate severe pitting corrosion in their gas processing equipment. A January 2023 inspection, several years after the application of HVTS, found that the protected vessel was still in good condition.
Another HVTS success story can be found in Switzerland, where a waste-to-energy plant was experiencing hearth corrosion. The plant provides electricity to over 44,000 homes and steam and hot water to local plants. IGS was contracted to apply HVTS cladding over a welded overlay that was showing early signs of accelerated degradation. After 10 months of operation, the IGS thermal spray showed no defects and the HVTS solution was reapplied to other areas of the Alloy 625 that were showing signs of wear and degradation. Six years later, the IGS HVTS cladding continues to protect the waterwall from high-temperature molten salt corrosion.
In its latest form, high velocity thermal spray has become a reliable method for protecting industrial equipment from erosion and corrosion, offering significant advantages over welding in terms of speed of application, alloy compatibility, life span, field deployment, time to return to service and commercial return. IGS has developed HVTS for application on high pressure, high temperature equipment.
To learn more about HVTS and other IGS solutions, download your free report below.
(i) https://assets.new.siemens.com/siemens/assets/api/uuid:3d606495-dbe0-43e4-80b1-d04e27ada920/dics-b10153-00-7600truecostofdowntime2022-144.pdf
