What Is Thermal Spray Coating?

Thermal spray coating is a surface protection process in which molten or semi-molten metal particles are sprayed onto a prepared steel substrate using a high-energy heat source. The two primary types used in the oil and gas industry are Thermally Sprayed Aluminum (TSA) and Thermally Sprayed Zinc (TSZ). These coatings provide long-term corrosion protection for carbon steel components exposed to marine, high-temperature, or aggressive atmospheric environments.

Thermal spray coatings work as sacrificial anodes (like galvanizing) but can be applied to any size component and withstand much higher temperatures than organic coatings such as epoxy or polyurethane.

Parameter	TSA (Aluminum)	TSZ (Zinc)	85/15 Zn-Al
Wire material	99.5% aluminum	99.9% zinc	85% Zn / 15% Al alloy
Coating thickness	150-350 microns	100-250 microns	150-300 microns
Max service temp	500°C+	250°C	300°C
Corrosion rate	Very low	Low-moderate	Low
Marine splash zone	Excellent	Good	Excellent
Immersed seawater	Excellent (with sealant)	Fair	Good
Application standard	ISO 2063, NORSOK M-501	ISO 2063	ISO 2063, AWS C2.23
Typical use	Offshore platforms, risers	Atmospheric steel	Marine structures

Application Process

The most common thermal spray method for corrosion protection is twin-wire electric arc spraying:

1. Surface preparation: Abrasive blasting to Sa 3 (white metal) per ISO 8501-1, surface profile 75-125 microns
2. Arc spraying: Two metal wires are fed into a spray gun where an electric arc melts the wire tips. Compressed air atomizes the molten metal and propels the droplets onto the steel surface at high velocity
3. Sealant application: A thin organic sealant (typically silicone or epoxy-based) is applied to fill the porosity of the sprayed coating
4. Topcoat (optional): Epoxy or polyurethane topcoat for additional barrier protection and color coding

The resulting coating is a dense, layered structure of flattened metal particles (splats) with 3-10% porosity. The sealant penetrates this porosity to create a continuous barrier.

Key Applications

TSA is the preferred thermal spray coating for:

• Offshore platform structural steel (splash zone, atmospheric zone)
• Subsea risers and caissons
• Flare stacks and high-temperature equipment (above the 80-110°C limit of organic coatings)
• Components that cannot be hot-dip galvanized due to size or distortion risk

TSZ is generally limited to atmospheric-exposure steelwork where temperatures remain below 250°C and the corrosion environment is less aggressive than marine immersion.

Common Mistake

Failing to seal a thermal spray coating after application is a frequent quality issue. Unsealed TSA or TSZ coatings have open porosity that allows moisture and salt to reach the steel substrate, dramatically reducing coating life. NORSOK M-501 System 1 (TSA) requires a sealant coat immediately after spraying, followed by one or two topcoats. Always verify that the sealant step is included in the coating procedure specification.

Standards

Standard	Scope
ISO 2063	Thermal spray metallic coatings
NORSOK M-501	Surface preparation and protective coating (TSA System 1)
AWS C2.23	Thermal spray coatings for corrosion protection
SSPC-CS 23.00	Metallic thermal spray coatings

Thermal spray coatings are part of a broader family of pipe and steel protection systems used across the oil and gas industry.

Read the full guide to pipe coatings