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Technology

High Velocity Thermal Spray (HVTS) Technology

Onsite Thermal Spray Coating Technology

Metal wastage from erosion and corrosion can lead to expensive unscheduled downtime, costly repair or replacement of equipment, and potentially unsafe working conditions. With over 30-years’ experience and several million square feet of successful applications worldwide, IGS is the preeminent, most experienced provider of onsite and in-shop erosion- and corrosion-resistant thermal spray coatings in the world. The Company’s unmatched experience and continuous devotion to research and development have led the industry’s advancements in materials, application processes, and job site execution standards. IGS uses highly advanced High Velocity Thermal Spray (HVTS) equipment and proprietary materials customized to the attacking environment. Consequently, IGS can deliver erosion and corrosion resistant coatings that resist wastage, cracking, and delamination in areas where other thermal spray coatings have failed. The result is extended run time, increased reliability, longer service life, and greater return on investment of mission critical equipment.

Corrosion and Erosion of Critical Industrial Equipment

Critical industrial equipment is susceptible to internal corrosion and erosion. Design considerations generally anticipate the service requirements and allowances are built into alloy selection, equipment design and acceptable metal loss due to corrosive and abrasive wear. In addition to equipment shell design considerations, corrosion abatement is frequently addressed through the employment of passive barriers such as paints, or through the use of more active control measures such as cathodic protection systems or injection of corrosion inhibitors.

Notwithstanding the above considerations, it is not uncommon for erosive and corrosive metal loss to exceed expectations. The loss can be local or expansive in scope. It may be manifest in uniform thinning or localized pitting. In many cases, shell pressure boundaries are compromised not explicitly through thickness or weight loss of the shell, but rather in the weakening of shell walls through intergranular or transgranular cracking. Other corrosion mechanisms are hydrogen permeation with shell blistering, or, in selective high temperature conditions, carburization and metal dusting.

Where materials are generally resistant to attack from corrosive species, occasionally the introduction of a tertiary factor can initiate corrosion. A common example of this is with stress corrosion cracking (SCC), or in H²S environments, sulfide stress cracking (SSC). In these systems, a combination of a susceptible material, a corrosive media and a stress component cause material failure that would not have otherwise occurred if any one of the three factors were removed.

High Velocity Thermal Spray Technology

The application of metal alloy coatings by thermal spray methods has long been employed in component repair, increasing the wear resistance of components and to some degree, in corrosion mitigation. A coating is formed from the successive deposition of layers or splats formed from individual coating droplets. These splats are discrete and as such the coating does not have a homogenous structure.

The application of thermal sprayed aluminium (TSA) coatings is commonly employed to protect the external surfaces of pipelines and vessels from atmospheric and marine corrosion. This technique uses a twin wire arc spray (TWAS) apparatus to apply a thin layer of sacrificial aluminium to a carbon steel surface. The material is resistant to corrosion from oxidation or chloride attack and cathodically protects the substrate material. This ensures that the substrate material is protected, even if exposed through a non-continuous coating layer.

As TSA coatings and the substrate they protect are not subject to immediate failure given breakthrough in coating continuity, the TWAS process is fit for purpose. In more aggressive environments where the only effective alloys for protecting substrate materials are nobler, such as those found in the nickel-chromium and nickel-copper based super-alloy family, such discontinuity cannot be tolerated. A corrosion path to the substrate would lead to a corrosion layer between the coating and the substrate. Should a TWAS process be used to apply a coating of these super alloys, the coating droplets sprayed toward the substrate material undergo in-flight oxidation due to their elevated temperatures and presence of atmospheric oxygen. Consequently, coating droplets form splats with interstitial oxide bands and some porosity. These oxide bands are generally thick and as they form in a rapid turbulent reaction sequence, are themselves porous and fractured. As such, aside from instances of porosity, oxide films provide an effective ionic corrosion path to the base metal from corrosive bad actors in the process media.

As a first step in the mitigation of this corrosion path, High Velocity Thermal Spray coatings are employed. These are characterized by a high velocity stream of finely divided droplets. The resulting coating has an order of magnitude finer composition and denser microstructure. The HVTS process, although producing a finer microstructure than TWAS, still has significant oxide structure due to the high particle temperatures experienced in the application process. As these structures still present a corrosion path, albeit a longer and more tortuous one, a means of reducing in-flight oxidation is required. This is achieved through selective alloy modification to suppress oxide formation. These improved materials are able to effectively close down any corrosion path through the coating to the substrate material.

IGS HVTS Advantages

  • Preeminent, most experienced on-site thermal spray provider in the world
  • Ability to respond to emergencies within 24 hours
  • Rigorous project safety program
  • Industry-leading quality control
  • Extensive selection of customized materials and application processes
  • Project management excellence
  • Technical, engineering-based approach that customizes coating solutions
  • Unique multi-service offering with automated and hand-applied weld overlay, mechanical services, and extended life filtration
  • Global responsivenesson several continents.