Thermal Spray Coating Application Presented by: Dean Hooks, Thermion

Scope This webinar defines thermal spray coating (TSC) and provides an overview of its application and uses

Introduction This webinar will review the procedures for the application of metallic thermal spray coatings (TSCs) of aluminum, zinc, and their alloys and composites for the corrosion protection of steel Required equipment, application procedures, and in-process quality control (QC) checkpoints will be discussed

What is Thermal Spray? Thermal spraying is a group of processes in which the thermal-spray feedstock material is heated, atomized, and propelled by a conveying gas stream and deposited to form a layer of thermal spray coating (TSC) on a prepared substrate. The process is also sometimes called metallizing. We will be referring to the term TSC through out this presentation.

Thermal Spray Coating (TSC) Materials Aluminum, zinc, and their alloys in the form of powder or wire heated to a plastic or molten state The metals used for corrosion protection are aluminum, zinc, and their alloys in the form of a powder or wire. The thermal spray gun generates the necessary heat by using combustible gases (“flame-spray”) or an electric arc. As the materials are heated, they are changed to a plastic or molten state, atomized, confined, and accelerated by a compressed gas stream to the substrate. The particles strike the substrate, flatten, and form thin platelets (splats) that conform and adhere to the irregularities of the prepared substrate and to each other. Other metals may be sprayed as well. Steel has been sprayed on worn shafts to refurbish them.

How do TSCs Protect Steel? Sealed: Good barrier protection Unsealed: Galvanic (sacrificial) protection Aluminum, zinc, and their alloys provide both barrier and galvanic protection; Zinc’s greater chemical activity provides greater galvanic protection than aluminum. Aluminum’s lower chemical activity, adherent oxide film, and higher wear and temperature resistance as compared to zinc, provides longer term protection along with high-temperature and abrasion/wear resistance. Sealed TSCs provide good barrier protection to steel isolating it from aggressive environments. Unsealed TSCs provide galvanic (sacrificial) protection to steel; as TSC pores become filled with their corrosion products, they provide barrier protection. When zinc is alloyed with aluminum, the zinc-rich spray material forms an effective corrosion-resistant coating, having the attributes of both elemental components. The wire made of 85% zinc and 15% aluminum (85/15 Zn/Al) alloy and pseudo aluminum and zinc (Al-Zn) alloy, produced by arc spraying Al and Zn wires, can be used to maximize their alloy performance over their individual performance. It seems to provide the best protection to steel in atmospheric service while aluminum seems to provide the best protection to steel in immersion service.

Special Properties Very good resistance to high temperatures, sunlight, and weathering Good application properties: adhesion to metals, film build, edge retention, and transfer efficiency Good impact and abrasion resistance Attacked by acids or alkalis unless topcoated Because TSCs are 100% metal, they are resistant to many severe environments that will degrade coatings with organic binders. TSCs can be seal-coated and top coated for even longer protection or to provide a different appearance.

Environmental Advantages No volatile organic compounds (VOCs) to cause air pollution (100% solids) No hazardous air pollutants (HAPs) Limited overspray into surrounding areas Using 100% solids thermal spray coatings presents none of the air pollution problems found with solvent-based liquid coatings. Overspray difficulties are limited as well. The terms VOCs and HAPs are used frequently through out the industry.

Economic Advantages Long-term protection (40+ years) of steel structures resulting in low life-cycle costs (costs per year) Reduced rework for original coating defects Reduced maintenance over coating life

SSPC-CS 23.00/AWS C2.23/NACE No. 12 A procedure for the application of metallic thermal spray coating (TSCs) of aluminum, zinc, and their alloys and composites for the corrosion protection of steel Required equipment, application procedures, and in-process quality control (QC) checkpoints are specified

SSPC-CS 23.00/AWS C2.23/NACE No. 12 Currently being revised Publication date expected in June 2016

SSPC-QP 6 Qualifies contractors who apply thermal spray coatings

Safety Issues The basic precautions for thermal spraying are essentially the same as for welding and cutting Information on safety can be found in: ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes NFPA 58, Standard for the Storage and Handling of Liquefied Petroleum Gases The basic precautions for thermal spraying are essentially the same as for welding and cutting. Information on safety can be found in the Safety Chapter in AWS Thermal Spraying: Practice, Theory, and Application; ANSI Z49.1, Safety in Welding, Cutting; and Allied Processes; and NFPA 58 Standard for the Storage and Handling of Liquefied Petroleum Gases. Safety precautions can also be found in the manufacturer’s equipment technical instructions and manuals and the feedstock material safety data sheet (MSDS). Potential thermal spraying hazards include exposure to vapors, dust, fumes, gases, noise (from the spray gun), and arc ultraviolet (UV) radiation. Additionally, improperly used thermal spray equipment can create potential fire and explosion hazards from the fuel and carrier gases and a potential electrical shock hazard from the electrical and electronic equipment and charged wire spools. To minimize hazards, proper safety precautions must be followed. Operators should comply with the procedures in the safety references, the manufacturer’s technical manuals, and the material safety data sheets. AWS is an abbreviation for the American Welding Society, who has developed numerous welding standards as well as this joint standard for Thermal Spray.

Safety Issues Potential thermal spraying hazards include: Exposure to vapors, dust, fumes, gases, noise (from the spray gun), and arc ultraviolet (UV) radiation

Single Wire - Flame Spray

Thermal Flame Spray Coatings Single wire fed into spray gun Acetylene/oxygen flame melts wire Compressed air blows melted metal onto surface Flame spray metallizing employs an oxygen-acetylene generated flame to melt a spool-driven wire (as it exits the spray gun). Once the wire is melted, compressed air atomizes the molten metal wire and blows it onto the surface. The spray fan is only approximately 2 inches (6 cm) wide, and the spray distance is typically maintained at 5-8 inches (13-20 cm), making flame spray application very labor intensive (and oftentimes cost-prohibitive) for large projects. Flame spray can be economical for metallizing small areas and for repairing/rebuilding metal components subject to cavitation erosion.

Typical TSC Wire Flame-Spray Components Spray Head (also referred to as a spray gun or pistol) Fuel Gas, Oxygen, and Air Wire and Feed Unit System Controls (gas and wire)

Typical TSC Wire Flame-Spray Components

TSC Wire Caddy and Control The caddy holds the metal (i.e., wire feedstock) for application. A control system is used to adjust the wire feed rate.

Wire Flame-Spray Head

TSC 3/16-inch Zinc Wire Here is 3/16-in. size zinc wire on a spool on the caddy.

Thermal Spray Coating System Requirements

Thermal Spray Application Process Coating thickness should be attained in several overlapping passes Acceptability should be confirmed by tensile adhesion testing Bend Test Cut Test

TSC Wire Flame-Spray

Twin Wire Arc Spray

Typical Arc Spray Installation In the arc-wire process, two consumable wire electrodes that are insulated from each other automatically advance to meet at a point in an atomizing gas stream. A powerful electrical current is applied across the wires starts an arc that melts the tips of the wire electrodes. An atomizing gas stream, usually compressed air, is directed into the arc zone, shearing off molten droplets that form the atomized spray. Wire electrodes are fed through wire guides and into the contact tips. The atomizing nozzle conducts the compressed air and directs it across the arc zone. Insulated power cables connect the gun to the DC power source. Arc guns also include mechanisms for feeding the wire at a controlled rate. Contact tips are sized for a particular wire diameter. A trigger switch on the gun controls the wire feed, compressed air supply, and electric power.

Electric Arc Thermal Spraying in Progress The operator is using an arc spray gun to apply a TSC to a steel beam in a shop. The wire feedstock is contained in the two drums in the foreground and fed to the gun through the wheel wire drivers on top.

Arc Spray Application Note that the applicator is wearing personal protective equipment (PPE) which includes hood; gloves; protective clothing; eye shield; air-supplied respirator) for safety purposes. What other PPE might be worn that you do not see? How about hearing protection because the spraying process can be noisy.

Thermal Spraying onto Blast Cleaned Steel Using thermal spray offers an excellent combination of properties for many different service environments, as well as reduced environmental and safety concerns and a long service life despite a higher initial installation cost. The British Standards Institution code of practice for corrosion protection of steel specifies that only TSCs give protection greater than 20 years to first maintenance for the 19 industrial and marine environments they consider and that only sealed, sprayed aluminum or zinc gives such protection in sea water immersion or splash zones.

Thermal Spraying onto Blast Cleaned Steel Using thermal spray offers an excellent combination of properties for many different service environments, as well as reduced environmental and safety concerns and a long service life despite a higher initial installation cost. The British Standards Institution code of practice for corrosion protection of steel specifies that only TSCs give protection greater than 20 years to first maintenance for the 19 industrial and marine environments they consider and that only sealed, sprayed aluminum or zinc gives such protection in sea water immersion or splash zones.

Bend Test 180 degree bend on a Mandrel Qualitative, testing proper surface preparation, equipment setup, and spray parameters Mandrel diameter for threshold of cracking depends on substrate and coating thickness

Bend Test Passes On the bend radius, there is no cracking or spalling, or only minor cracking that cannot be lifted from the substrate with a knife blade Fails Coating cracks with lifting from the substrate

Bend Test

Cut Test A procedure to identify areas of metallized coating that are poorly adhering Involves impacting the coating with blow from a hammer to a masonry chisel Any disbonding or peel of the coating is considered a failure

Cut Test

Cut Test- Pass

Cut Test- Fail

Thermal Spray Repair Defined as less than 1 square foot area Mark nonconforming area Repair the nonconforming area Feather the damaged area to achieve an 2-3 inch overlap Apply the TSC to the newly prepared surface, and overlap the existing TSC to the extent of the feathered edge so the overlap is a consistent thickness

TSC on Highway Structure Holding Signs TSCs are used on some highway sign supports because of their excellent weathering properties. They are also resistant to de-icing with road salts.

TSC on Piling in Immersion Service Steel pilings are subjected to a severe marine environment, as well as impact and abrasion damage.

TSC Applied to Girders for Atmospheric Service There is a history of aluminum and zinc TSC corrosion protection for structural steel work: buildings, bridges, towers, radio and TV antenna masts, steel gantry structures, high-power search radar aerials, overhead walkways, railroad overhead line support columns, electrification masts, tower cranes, traffic island posts, and street and bridge railings.

Thermal-Spray Coated Components of Industrial Structure Industrial components can be shop-sprayed and stored as shown until ready for use. Sealed TSC coatings have a greatly improved impact resistance. Storage and shipping does not require padding or blocking.

Questions?