Field ResearchApril 2026· 12 min read
Thermal Behaviour and Substrate Response During High-Power CW Laser Ablation Coating Removal on Structural Steel
Petr Yurchenko
Director, Laser Blasting LLC | Laser Blasting Limited
Practitioner field paper — drawn from multi-year commercial CW LACR operations. Not peer-reviewed academic research.
Abstract
Field-measured thermal characterisation of high-power continuous wave (CW) laser ablation coating removal (LACR) on structural steel is presented, drawn from multiple years of commercial infrastructure operations. A two-phase thermal model is proposed and field-validated: Phase 1 (active coating removal, 160–230°C / 320–446°F with a 70°C / 126°F edge-to-centre differential on hollow sections) and Phase 2 (post-removal bare metal with correct technique, 70–90°C / 158–194°F, dissipating to ambient within seconds).
Introduction
Laser ablation coating removal (LACR) is an emerging surface preparation technology increasingly deployed on bridges, marine structures, industrial platforms, and heritage assets. Unlike conventional abrasive blasting or chemical stripping, LACR operates through photonic energy interaction with coating materials, producing minimal secondary waste and enabling precision surface treatment depth control.
A fundamental distinction exists between pulsed and continuous wave (CW) laser operation that has significant implications for thermal behaviour on infrastructure steel. Pulsed lasers deliver energy in discrete high-intensity bursts with inter-pulse intervals during which the substrate surface cools. CW fiber lasers deliver energy continuously — the beam traverses the substrate surface at a controlled speed, depositing energy across a moving interaction zone with no cooling intervals between pulses.
Despite growing commercial deployment of high-power CW laser systems at 1–4kW on infrastructure, published operational data from field practitioners remains sparse. This creates a critical gap in the thermal characterisation of CW operation on aged, thick coating systems on real structural profiles.
Two-Phase Thermal Model
A two-phase thermal model is proposed to describe LACR operations on structural steel:
Phase 1 — Active Coating Removal: The paint system absorbs and converts laser energy, generating significant localised substrate heating. Phase 1 temperatures of 160–230°C (320–446°F) were recorded on the test hollow section. Edge zones reached 230°C (446°F); centre face 160°C (320°F). Without correct technique, edge zones on thin-geometry structural sections readily exceeded 200°C (392°F).
Phase 2 — Post-Removal Bare Metal: Following successful coating removal with correct technique (SSRT), instantaneous peak temperatures on bare steel were 70–90°C (158–194°F), measured immediately after laser passage. The thermal pulse dissipated to near-ambient within seconds.
Thermal Differential — Hollow Steel Sections
The 70°C (126°F) differential between edge and centre zones of hollow steel sections is attributed to geometry-dependent heat dissipation. At the corner edge of a hollow section, the substrate mass available for lateral thermal conduction is constrained in two dimensions simultaneously. At the centre flat face, identical energy input distributes across an unrestricted thermal mass.
This finding has direct operational implications for the substantial infrastructure asset base incorporating hollow sections, RHS, SHS, angles, and channel profiles as primary structural members.
Paint Color and Pigment Absorptivity
Field observations revealed a consistent pattern: dark-colored and black paint systems were notably easier to remove than white, yellow, or bright-colored systems under identical laser parameters.
Black and dark-colored paints are pigmented primarily with carbon black — an amorphous carbon compound that absorbs all wavelengths including 1064nm. Carbon black achieves minimum absorbance of 80 percent throughout 400–1,400nm wavelength range.
White and bright-colored paints are pigmented primarily with titanium dioxide (TiO₂) which achieves hiding power through scattering and reflection rather than absorption — reducing energy coupling at 1064nm and requiring greater laser energy input.
The inverse relationship between removal ease and fire hazard is operationally significant: black paint is easiest to remove but presents the highest ignition risk; white paint is hardest to remove but presents lower fire hazard.
Sequential Section Rotation Technique (SSRT)
The Sequential Section Rotation Technique (SSRT) was developed and validated through field operations on structural steel in corrosion-sensitive environments. The technique is patent-pending.
SSRT maintains Phase 2 substrate temperatures within the 70–90°C (158–194°F) envelope throughout extended operations on structural steel — regardless of total working area, coating thermal resistance, or structural profile complexity. The technique is adaptive to field conditions: the operator calibrates to the substrate in real time using visual and thermal feedback.
Metallurgical Context
Structural steel yield strength begins to reduce measurably above approximately 200°C (392°F) under sustained loading, with significant strength loss above 550°C (1022°F).
Strain aging — the principal time-dependent metallurgical degradation mechanism for structural steels — requires sustained temperatures of 150–370°C (302–698°F) for 1–5 hours to produce measurable property changes. The transient thermal pulse produced by LACR, dissipating to near-ambient within seconds, is categorically insufficient in duration to induce strain aging effects, regardless of peak temperature reached.
No evidence of a metallurgically significant heat affected zone or strain aging was observed under the measurement and operational conditions described in this study.
Conclusions
1. Field measurement across multiple commercial project sites validates a two-phase thermal model: Phase 1 (160–230°C with 70°C edge/centre differential on hollow sections) and Phase 2 (70–90°C instantaneous peak, ambient within seconds). Phase 2 temperatures are well within safe limits for structural steel integrity and coating reapplication requirements.
2. Edge zones of hollow steel sections reached 230°C during Phase 1 — approaching metallurgical concern — while centre faces were 160°C. This 70°C differential is attributable to constrained two-dimensional heat dissipation geometry.
3. The Sequential Section Rotation Technique (SSRT) was validated on 410UB I-beam structural steel in a coastal environment, substantially mitigating post-ablation oxidation.
4. Bare rust removal produced temperatures consistently below 80–100°C. CW LACR exhibits absorptivity-driven self-limiting behaviour — the laser is more active on contaminated surfaces than clean steel.
5. No evidence of a metallurgically significant HAZ was observed. The transient thermal pulse is categorically insufficient in duration to induce strain aging or metallurgical degradation.
Disclaimer: This is a practitioner field paper based on observations from commercial CW LACR operations. Findings are not derived from controlled laboratory testing. Substrate conditions, coating systems, and environmental factors varied across project sites. These observations are intended as a practitioner contribution to the evidence base, complementary to laboratory research rather than a substitute for it.
Author disclosure: Petr Yurchenko is Director of Laser Blasting LLC (Tennessee, USA) and Laser Blasting Limited (Auckland, New Zealand). The SSRT methodology and ThermaLog instrument referenced in this paper are patent-pending. No external funding was received.