Thermal, Electrostatic, and Polyester Spray Applications

Thermal, Electrostatic, and Polyester Spray Applications

Quick Answer: Thermal spray (metallizing) melts and propels metal (often zinc, aluminum, or alloys) onto a clean, profiled substrate to form a metallic barrier or sacrificial layer. Electrostatic spray charges coating particles so they wrap toward a grounded workpiece for high transfer efficiency. Polyester spray systems (gel coats, polyester linings/overlays) depend on correct catalyst ratio, thickness, and cure. CIP Level 2 inspects prep, process hold points, film quality, and acceptance tests—not operator art alone.

The Application Equipment blueprint line on thermal, electrostatic, and polyester spray sits in Domain 6 (Coatings and Coating Application, 13%). These methods are “specialty application” territory beyond ordinary airless epoxy spray. Level 2 must recognize process principles, inspector checkpoints, and typical failure modes.

Part A — Thermal Spray (Metallizing)

Process overview for inspectors

Thermal spray (often called metallizing when applied as corrosion protection on steel) heats feedstock—wire, powder, or rod—to a molten or semi-molten state and propels it onto the substrate. On industrial steel structures (bridges, tanks, marine steel, offshore platforms), common consumables include:

Common process families Level 2 should recognize by name (detail depth is awareness/inspection, not metallurgy design):

• Flame spray (wire or powder) — oxygen–fuel flame melts wire/powder; compressed air atomizes and propels particles.
• Arc spray (twin-wire electric arc) — two wires form an arc; compressed air atomizes molten metal. High deposition rates common on large structures.
• Plasma / HVOF / other high-energy processes — more common in specialty shop coatings for wear/high performance; inspect to the invoked procedure when specified.

The deposited layer is built from overlapping solidified particles (splats). It is not a hot-dip galvanized metallurgical coating and is not a conventional liquid paint film. Porosity, oxide content, and bond quality depend heavily on surface prep and spray technique.

Surface preparation needs (critical hold point)

Thermal spray adhesion is mechanical and highly sensitive to contamination and profile:

1. Cleanliness — typically near-white or white-metal abrasive blast cleanliness as specified (commonly SP 10 / NACE No. 2 or SP 5 / NACE No. 1 class requirements when the project demands bare, tightly prepared steel). Mill scale, oil, moisture, and dust destroy bond.
2. Angular profile — grit (angular) blast is preferred over shot peening for metallizing adhesion. Profile depth is usually higher than thin organic coatings—project specs often target a substantial angular roughness (commonly in a multi-mil range defined by the specification/procedure; always use the written value).
3. Timing — coat/metallize before rust-back or recontamination. Thermal spray does not forgive “blast yesterday, spray next week in humid air” without re-prep.
4. Preheat / surface temperature — some procedures require the steel to be warm and dry (above dew point, free of condensation) before spraying.
5. Masking and edges — protect openings, threads, and non-spray zones; feather transitions as specified.

If prep fails, bond tests fail even when spray technique looks professional. Level 2 holds the prep point with the same rigor as immersion-epoxy work.

Spray parameters awareness (what to watch, not invent)

Inspectors do not set gun settings for the contractor, but they verify that procedure parameters in the ITP/WPS/PDS package are followed and logged when required:

Document actual conditions against the approved procedure. Parameter drift is a common root cause of poor adhesion or excessive oxide.

Adhesion and bend-test concepts

Acceptance often combines visual quality, thickness, and mechanical tests:

Bond / adhesion testing (concept)

• Pull-off adhesion (tensile bond) methods may be specified for metallized layers or for sealers over metallizing.
• Values and frequency come from the project specification or referenced standard—do not invent a universal psi number on the exam.
• Failed adhesion with metallizing still stuck to the glue dolly vs steel clean break vs cohesive failure in the metal layer tells different stories (bond to steel vs internal spray quality).

Bend test (concept)

• Sample coupons metallized with production parameters are often bent around a mandrel or to a specified angle.
• Acceptable results typically show the coating adheres without spalling or lifting from the steel (fine cracking may be evaluated per the test criteria).
• Bend tests are process-qualification and production-control tools: they prove the prep + spray combo works before and during the job.

Thickness

• Magnetic or other appropriate thickness methods for metallic coatings as specified.
• Check edges, welds, and hard-to-spray faces—thermal spray thins at edges and shadows like any spray process.

Typical thermal-spray defects

Many specifications require a seal coat over thermal spray to close porosity for certain services. Inspect sealer DFT, coverage, and cure separately from the metal layer.

Thermal-spray inspection checklist (Level 2)

1. Confirm consumable type and procedure approval.
2. Verify blast cleanliness and angular profile before first pass.
3. Confirm environmental readiness (dry steel, protected work area).
4. Spot-check technique (distance, angle, overlap) and logged parameters.
5. Measure thickness pattern per ITP.
6. Witness or review bend/adhesion tests as specified.
7. Inspect for spalls, thin areas, contamination.
8. Control sealer application if required.
9. Document lot IDs, operators, and nonconformances.

Part B — Electrostatic Spray Application

Principles

In electrostatic spray, atomized liquid coating (or powder in powder systems—powder detail expands in a later specialty section) receives an electrical charge. The workpiece is grounded. Charged particles are attracted to the grounded surface, improving:

• Transfer efficiency (less paint wasted as overspray)
• Wrap-around on tubulars, wire mesh, and complex shapes
• More uniform coverage on edges in many setups (with limits)

Liquid electrostatic systems may use air spray, air-assisted, or dedicated electrostatic guns. High voltage at the gun and proper grounding of the part and conveyor/rack are fundamental.

Inspection concerns

What CIP Level 2 verifies

1. Specified method is electrostatic when the contract requires it (or allowed alternative is documented).
2. Parts are clean, dry, and profiled/prepared as for any coating system.
3. Grounding practices are in place (visual/continuity checks when the ITP requires).
4. DFT and visual coverage include recesses and Faraday zones, not only flat panels.
5. Touch-up of rack marks and shadow areas is completed.
6. Environmental conditions and flash-off/cure still meet the PDS—electrostatics does not waive recoat windows.

Exam trap: Assuming electrostatic application automatically produces full coverage in deep boxes. Faraday cage limitations are a standard inspection teaching point.

Part C — Polyester Spray Applications

Where polyester spray is used

Polyester resin systems appear in several coating/lining contexts Level 2 should recognize:

• Gel coats on fiberglass-reinforced plastic (FRP) equipment and architectural panels
• Polyester and vinyl-ester linings for chemical secondary containment, tanks, and floors (often with glass flake or fiber reinforcement)
• Repair and overlay systems on concrete or steel when the project specifies polyester chemistry
• Some powder polyesters (shop powder coating—related Domain 6 powder task)

Liquid polyester systems are typically styrene-containing or similarly reactive resins cured by peroxide catalysts (free-radical cure). They are convertible coatings that polymerize after mixing catalyst—not simple solvent-evaporation lacquers.

Cure and film concerns

Polyester spray inspection points

1. Confirm resin type, catalyst type, and mix ratio against PDS and batch tickets.
2. Verify surface prep (steel SP grade/profile or concrete CSP/moisture as specified).
3. Check WFT/DFT build plan and avoid burying holidays in one heroic pass.
4. Inspect for pinholes, voids, dry glass, sags, and soft spots.
5. Confirm cure before immersion or chemical exposure.
6. Document batch numbers—polyester failures often trace to wrong catalyst lots or ratio errors.

Integrating the Three Methods for Domain 6

Common Exam and Field Traps

• Treating thermal spray like paint and skipping high-quality angular blast profile.
• Accepting metallizing without bend or adhesion evidence when the ITP requires it.
• Believing electrostatic wrap eliminates the need to measure DFT in corners.
• Ignoring catalyst ratio documentation on polyester jobs.
• Confusing thermal spray with hot-dip galvanizing (different processes, different defect languages—HDG is a separate Domain 6 cluster).
• Coating over flash-rusted or damp steel “because metallizing is metal.”

Bottom Line: Thermal, Electrostatic, and Polyester Spray

CIP Level 2 owns thermal spray, electrostatic, and polyester spray as specialty application families: know how each deposits film, what prep and process controls matter, which defects appear, and which hold points (profile, ground, catalyst, adhesion/bend, DFT, cure) protect the owner. Method fluency here feeds later tasks on specialty products, linings, and coating inspection defects.