History of Thermal Spray in Pressure Vessels Thermal Spray Coatings have been utilized in pressure vessels for 25 years in Western Canada Traditionally, a band aid system, due to the oxy-acetylene applications and poor mechanical characteristics Typical alloys applied, aluminum and stainless steel!
Past Seven - Ten Years… Oil & Gas Twin Wire Arc and High Velocity Oxygen Fuel coatings have been utilized in amine contactors, waste heat boilers, exchanger tubesheets. Alloy of choice…. Hastelloy C-276! Manual and Automated applications
HVOF on Exchanger Tubesheets
HVOF in Amine Contactor
TWA on Exchanger Tubesheets
Past 10+ Years… Pulp & Paper High Velocity Oxygen Fuel coatings have been utilized in Black Liquor Recovery Boilers on firewall tubes to stop corrosion/washing issues Alloy of choice…Inconel 625! Power Boiler I.D. Fans and Tungsten Carbide! Manual and Automated Applications!
HVOF in Recovery Boiler!
Power Boiler HVOF Application
Life of Coatings…? History has shown that TWA and HVOF applications have a very low failure rate if chosen properly. Not a Band Aid system anymore. Why has there been no failure….? Mechanical properties of coatings and application methods. These choices encourage the proper coating system for the applicable environment. For example.. Stopping Hydrogen Blistering in Oil & Gas Environments…stop the corrosion attack at the coating before it gets to the substrate!
Life of Coatings…? Inconel 625 in the Recovery Boiler has proven highly corrosion and wear resistant in both TWA and HVOF forms. 1997, 1998, 1999 & 2000. Applications occurred at pulp mills in Western Canada. To date there has been no failure of these coating systems. Coating thickness does not change during life of coating.
Future of Thermal Spray? Depending on the application… All thermal spray coating applications must be chosen carefully to ensure that the mechanical characteristics of the coating meet the physical characteristics of the vessel! If this is not done, the perception that thermal spray coatings are a Band Aid system, becomes apparent.
Welding in Pressure Vessels? Who thought that a pressure containing piece of equipment could be welded in after final hydrotesting? New Technologies and ASME Section IX allow hardsurfacing technologies to occur especially utilizing the new technology of PTA (Plasma Transferred Arc Welding)
PTA Process Description
Valve Spools with T.C.
Cavitation Resistance Pulp and Paper Industry utilized Eccentric Reducers in almost every facet of piping requirements. Applications of Stellite 6 in eccentric reducers have improved the life of the piping by a factor of 4 – 6 times. In some cases, Inconel 625 has been utilized to reduce cavitation and improve corrosion resistance. Best of all, smooth overlay surfaces!
Finishing of PTA Overlays! In some cases, the piping has been ground (32 – 64 Ra) in the first 6 to reduce any further turbulent flow. Faces of flanges have been ground clean to ensure wear/corrosion resistant alloys are present right to the seal face.
Ground Surfaces on any Component
Down Stream Piping Sand at high velocities provides an amazing wear pattern on down stream piping elbows and pups. Wear resistant Tungsten Carbide overlays have been applied to dramatically extend the life of these components. Customer in Dawson Creek, BC, losing a section of pipe in a particular application once every 30 days. The system has been in place for 135 days to date. Non Destructive testing indicates no loss of wall thickness of pipe to date!
Valve Tube Overlaid with Tungsten Carbide
Conclusion Thermal Spray coatings and PTA welded overlays can be utilized in pressure vessel applications as long as they are chosen correctly and applied correctly! Approved procedures and experienced personnel are critical to each application in each situation! Amine Contactors, Recovery Boilers, Exchanger Tubesheets, Pressure Piping, the applications are endless and the technology is at your fingertips!