In a fired heater, the tubes carry the process load, and how well their steel surface absorbs radiant heat sets how much fuel the burners need. A high emissivity coating for steel heater tubes and heat exchangers turns a reflective, oxidizing metal surface into one that absorbs radiant heat efficiently and resists scaling.
Q: What Does a High Emissivity Coating Do on Steel Tubes?
A: It Improves Radiant Heat Absorption and Protects the Steel Surface
Most heat reaches a furnace tube as radiation from the flame and hot refractory. A surface’s ability to absorb that radiation tracks its emissivity, so bare or partly reflective steel absorbs less of the available heat. A high-emissivity coating improves absorption, so more energy reaches the process for the same firing.
The coating also shields the steel. Incure’s catalog describes both steel grades as resisting oxidation and scaling at high temperatures, and that matters because oxidation is often what thins tube walls over time.
Incure offers two grades for steel in its Epo-Weld™ HECC line:
- Epo-Weld™ HECC-618: an emissivity coating for carbon and stainless steel, designed for heating tubes and exchangers.
- Epo-Weld™ HECC-627: an ultra-high-temperature emissivity coating for steel alloys in extreme environments, rated by Incure to 2,400°F, for high-temperature process vessels and stacks.
HECC-618 vs. HECC-627
| HECC-618 | HECC-627 | |
|---|---|---|
| Target substrate | Carbon and stainless steel | Steel alloys in extreme environments |
| Stated temperature rating | Not specified in the catalog | Up to 2,400°F |
| Viscosity | 2,000–3,000 cps | 3,000–4,000 cps |
| Flexural / tensile shear | 1,100 / 300 PSI | 1,100 / 300 PSI |
| Cure | 1 hr at 200°F | 1 hr at 200°F |
| Typical parts | Heating tubes, heat exchangers | Process vessels, stacks |
The practical difference is the operating envelope. HECC-618 is the general grade for carbon and stainless steel tubes and exchangers. HECC-627 is the step up when the steel runs in the hottest zones or in severe thermal stress, where its 2,400°F rating gives the margin.
Choosing Between Them
- Start with metal temperature, not flame temperature. The coating sees the tube surface temperature. If the surface approaches the upper end of what carbon or stainless steel equipment normally sees, plan on HECC-627.
- Match the part type. Incure points HECC-618 at heating tubes and exchangers and HECC-627 at process vessels and stacks.
- Consider film build. HECC-627’s higher viscosity builds a heavier coat per pass; HECC-618’s lower viscosity spreads more easily over long tube runs.
- Plan the cure. Both grades list 1 hour at 200°F. In the field, that usually means a controlled first heat-up, or a heat source applied to the coated section before full service.
Email Us with the tube or vessel alloy, surface temperature and furnace atmosphere to confirm the right grade.
Surface Preparation on Steel
Emissivity coatings bond only as well as the surface allows. Loose mill scale, rust and combustion deposits must come off first, or the coating will flake off with them. Degrease after cleaning, and coat promptly before fresh rust forms. Incure’s guide on how to apply high-emissive ceramic coating to metal substrate surfaces covers preparation and film control in more detail.
Pay particular attention to welds, supports and tube bends. These areas see the most thermal stress and are where a thin or missed coating first lets oxidation back in.
Inspecting Coated Tubes at Each Turnaround
A coating on furnace tubes earns its keep over years, so plan for inspection during planned shutdowns rather than waiting for a problem. Walk the radiant section looking for three things: bare or discolored patches where the coating has worn through, flaking near welds and supports, and deposits building up on the coated surface.
Keep a simple record of where defects appear. Repeated wear in the same zone usually points to a local cause, such as flame impingement, a hot spot or mechanical rubbing at a support, rather than a coating problem. Touch up damaged areas with the original grade and complete its 1 hour at 200°F cure before the heater returns to full firing.
Track operating data alongside the visual checks. Comparing fuel use and tube-skin readings at similar throughput before and after coating gives the clearest picture of what the coating is delivering.
Where These Grades Fit
- Fired heater and furnace tubes in refining, chemical and process plants.
- Heat exchanger surfaces exposed to radiant heat or combustion gases.
- Process vessels and exhaust stacks in high-temperature service (HECC-627).
For refractory, ceramic-fiber and non-ferrous surfaces, Incure’s other HECC grades apply instead, compared in its overview of Epo-Weld™ HECC coatings by substrate and service temperature.
Final Thoughts
A high emissivity coating for steel heater tubes and heat exchangers improves how the steel takes in radiant heat and helps protect it from oxidation and scale. Incure’s Epo-Weld™ HECC-618 covers carbon and stainless steel tubes and exchangers. HECC-627 handles steel alloys in extreme service up to 2,400°F. Contact Our Team to choose a grade for your heater.
Visit www.incurelab.com for more information.