Compare the spatial pattern

A sun-facing region that differs from a shaded face raises a different question from a sharply localized mark around a heat-producing part. A runoff-shaped stain points toward transport or chemical contact. Compare the same coating under similar lighting, because shadows and camera processing can create apparent colour boundaries. Include the timing of any cleaning or nearby process exposure rather than assuming every new dark patch is a hot spot.

Seek independent evidence

Existing temperature records, protective events and changes in nearby materials may help, provided their location and timing correspond to the mark. A measurement of present temperature cannot reconstruct an unknown past excursion. Conversely, a normal reading after equipment has stopped does not exclude an earlier event. Qualified assessment should separate the coating condition from the condition of any insulation, seals or internal parts potentially affected by heat.

If the colour boundary follows a sun shadow rather than the outline of a heat-producing component, solar exposure deserves consideration. If another independent indicator aligns with the component outline, the thermal hypothesis gains a different basis. Neither pattern establishes a temperature value.

Decide what needs further assessment

Ask whether the evidence supports a thermal investigation, materials compatibility review or finish-aging assessment. If overheating remains plausible, cleaning or repainting should not erase the physical indicators before the reviewer defines the scope. No maximum permissible temperature or MARSTON thermal capability is established by this page. A return-to-service decision needs the actual equipment limits and an understanding of the affected function, not a colour-based judgment.