How to Read a Thermographic Survey Report

The Structure of a Thermographic Report

A professionally produced thermographic survey report contains several distinct sections. Understanding what each section contains and what it means allows you to act on the findings correctly — and respond appropriately to your insurer or maintenance team.

Most insurance-compliant thermographic reports follow a standard structure: executive summary, survey conditions, findings by location, severity classification, recommendations, and appendices containing all thermal and visible images. Here is how to read each section.

Survey Conditions — Why They Matter

The first section of a credible report documents the conditions under which the survey was conducted: ambient temperature, date and time, equipment load at time of survey, and the thermographer's qualifications.

Load conditions are critical. SANS 10142-1 and insurance underwriter requirements specify that surveys be conducted at or above 40% of rated load. A survey conducted at low load will miss fault signatures that only become visible at normal operating current. If your report does not document load conditions, or if the load at time of survey was below 40%, the findings may be incomplete and the report may not satisfy insurance requirements.

Understanding ΔT — the Core Measurement

ΔT (delta T) is the temperature difference between the suspect component and a reference. The reference is typically either an identical component under similar load conditions, or the ambient background temperature. ΔT is the primary metric used to classify severity — not absolute temperature.

Why ΔT rather than absolute temperature? A component at 80°C in a 75°C ambient environment may be operating normally. The same component at 80°C in a 20°C ambient environment is a serious finding. Absolute temperature without context is meaningless. ΔT provides that context.

The P1–P4 Severity Classification

Most professional thermographic reports classify findings using a four-tier severity scale, referenced against NETA MTS (Maintenance Testing Specification) criteria, supplemented by thermographer judgement as described in the survey methodology. An additional Escalation Flag (ES) is applied where active burning, charring, or smoke is observed — this designation is condition-triggered and overrides ΔT thresholds entirely.

Note that these ΔT thresholds are guidelines, not absolute rules. A qualified thermographer applies engineering judgement to each finding — a ΔT of 12°C on a critical process drive may warrant P2 classification given the consequence of failure, while the same ΔT on a non-critical circuit may correctly be classified P3. The ES flag operates entirely outside the ΔT framework and is applied on observed condition alone.

Reading the Thermal Images

Each finding in a professional report is documented with two images: a visible light photograph showing the physical location of the component, and a thermal image showing the temperature distribution. Reading both together is essential for understanding the finding.

• Colour scale — every thermal image has a colour scale bar showing the temperature range represented. The hottest areas are typically shown in white or yellow; cool areas in blue or purple. The scale is calibrated to the measurement range, so the colours mean different things in different images.
• Spot measurements — the thermographer will have placed measurement spots on the hottest point of the finding and on the reference. These are labelled in the image and the temperature values are reported in the findings table.
• Isotherms — some reports use isotherms (lines connecting points of equal temperature) to show the extent of a hot zone. A concentrated hot spot indicates a localised fault; a distributed hot zone may indicate overloading across a broader area.

What to Do With the Report

A thermographic report is a maintenance document. Its value depends entirely on what you do with the findings.

• ES findings — immediate isolation and intervention. Do not defer pending a maintenance window or management approval. Document the event, the time of observation, and the isolation action taken.
• P1 findings — treat as immediate safety issues. Isolate and repair as soon as safely possible. Thermographic re-inspection is mandatory after repair to confirm resolution. Document corrective action with photographs and date.
• P2 findings — schedule corrective action urgently. Thermographic re-inspection is required post-repair. In practice, many P2 findings are addressed during the same planned shutdown used for P1 repairs.
• P3 findings — include in the next planned maintenance shutdown within 30 days. Re-inspect following repair. Track these findings and verify they have not progressed to P2 at the next survey.
• P4 findings — note and monitor. These are early indicators that should be tracked over successive surveys. A P4 finding that becomes P3 at the next inspection signals an accelerating fault that needs prompt attention.

Providing the Report to Your Insurer

When submitting a thermographic report to your insurer or broker, include the complete report and any documentation of corrective actions taken in response to P1 and P2 findings. Insurers are not only checking that a survey was conducted — they are assessing whether the facility has responded appropriately to the findings. A report showing P1 findings with no evidence of corrective action may work against you at renewal.