Heat-Resistant Coatings up to 600°C — Silicone vs Organic for Stacks, Exhausts, Furnaces, and CUI in Thai Industry

Equipment that runs hot — stacks, exhaust pipe, furnaces, steam lines, process vessels — destroys ordinary anti-corrosion paint quickly: the resin burns, peels, yellows, and cracks, and the steel then rusts. Ordinary coatings are designed for room temperature, not surfaces at 300-600°C.

Hot service requires heat-resistant coatings, with resin and thickness matched to the actual surface temperature band — and you must watch out for the most dangerous trap of all: CUI, the invisible corrosion under insulation. This article summarizes how to choose the right system.

1. Choose the Resin by Temperature Band

The key is the maximum surface temperature actually reached (not the surrounding air temperature):

Wrong band = the coating burns/peels within weeks. Spec from the equipment's maximum operating + cyclic temperature.

2. Heat Curing

Many heat-resistant silicone coatings must first reach ~200-260°C to fully cross-link:

flowchart TD
  A[Prep Sa 2.5-3
ISO 8501-1] --> B[Apply silicone-Al
thin DFT 25-50 micron/coat]
  B --> C[Film still green
not truly hardened]
  C --> D[Equipment first runs
surface reaches ~200-260°C]
  D --> E[Silicone cross-links
film truly hardens]
  C -.caution.-> F[Before cure: no
water/chemicals/impact]

• Before curing the film is still soft and easily scraped — watch during transport/installation
• In real service the film cures itself once the equipment runs — but plan protection during the wait
• DFT must be thin (usually 25-50 micron/coat) — a film too thick cracks during heat-cool cycling

3. The Most Dangerous Trap — CUI

CUI (Corrosion Under Insulation) is rust beneath thermal insulation, occurring when water penetrates the insulation of pipe/vessels in the risk temperature band:

• Risk band ~ -4°C to 175°C — water sits against warm steel, accelerating rust
• Invisible from outside — you must remove insulation to find it → usually discovered only after a leak/rupture
• Prevent with a dedicated CUI coating (e.g. inert multipolymer matrix) per NACE SP0198 / CINI

Don't use ordinary heat-resistant paint under insulation — insulated pipe in the CUI temperature band must specify a dedicated CUI system.

4. Surface Prep + DFT — Why It's Strict

Heat-resistant coatings adhere harder than normal paint because of constant thermal expansion-contraction:

• Specify blast Sa 2.5 to Sa 3 (near-white to white metal) per ISO 8501-1 — see our surface preparation Sa 2.5 guide
• Profile to the maker's spec (heat-resistant coatings are often profile-sensitive)
• Keep DFT thin — too thick = cracking on thermal cycling
• Don't use ordinary primer under heat-resistant paint (it will burn) — use only a compatible heat-resistant primer

5. Heat-Resistant Coating Spec Checklist

1. Specify max operating + cyclic surface temperature — match the resin band (200/400/600°C)
2. Separate insulated vs bare work — insulated → CUI system, bare → silicone-Al
3. Surface prep Sa 2.5-3 + profile to the maker's spec
4. Keep DFT thin to spec — do not over-apply
5. Plan the heat cure + protect the film before curing (water/chemicals/impact)
6. Primer must be heat-resistant and compatible — never use ordinary primer
7. Record the ITP — temperature/DFT/profile for hand-over

We supply and coordinate heat-resistant coating systems for stacks, exhaust pipe, and furnaces, and CUI systems for insulated pipe/vessels — selecting resin by the actual temperature band, specifying surface prep and DFT so the film survives thermal cycling, with an ITP for hand-over.

Talk to our engineering team to match a heat-resistant system to your temperature and service conditions — call 02-096-2118 or LINE OA @sahawatt1988.

Summary

• Choose resin by actual surface temperature: ~200°C (silicone-acrylic) · 400-600°C (silicone-aluminium) · >600°C (ceramic/thermal spray)
• Silicone coatings need a first heat cure ~200-260°C — before curing the film is soft, handle with care
• CUI = invisible rust under insulation (-4 to 175°C band) — insulated pipe needs a dedicated CUI system, not ordinary heat-resistant paint
• Surface prep Sa 2.5-3 + thin DFT because thermal cycling cracks thick films
• Reference standards: ASTM D2485, NACE SP0198, CINI, ISO 12944-9

Heat-resistant coating is not "fireproof paint" — choose by actual surface temperature and separate insulated work correctly, or it fails both ways.