<p>Infrared thermography with a narrow-band filter centered near 3.9 micrometers was applied during normal operation to inspect steam methane reformer tubes through the flame. The thermal images revealed characteristic patterns associated with oxide scale, hot bands at a common elevation, and burner misalignment with localized flame impingement. Scale-affected areas showed higher apparent temperature than adjacent cleaner metal, including a representative contrast of 78&#xa0;°C between collocated spots, which is consistent with the higher emissivity of oxidized surfaces. Quantitative interpretation accounted for emissivity and reflected apparent temperature, and a representative line profile agreed closely with plant instrumentation, which supports the reliability of the measurements when measurement practice is followed. For each image, we paired spot readings with temperature line profiles across the tube surface and with statistics from clearly defined regions of interest to convert qualitative observation into quantitative evidence for maintenance decisions. From an operational perspective, these contrasts provide direct triggers for burner tuning, prioritized tube inspection during planned outages, and closer monitoring of locations where scaling can conceal developing hot spots. The study demonstrates practical diagnostic value while also making explicit the sensitivities of the method to surface condition, view geometry, and gas-path effects. A program for broader validation across different furnaces and firing conditions, together with automated image interpretation and integration into plant decision workflows, is proposed.</p>