The main causes of creep failure in the pigtails and tubes made of high-temperature Incoloy 800HT and HP-modified alloy materials of two natural gas primary reformers operating at a petrochemical plant complex were studied. Optical emission spectroscopy, high-resolution optical microscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were performed to verify that creep was the prevailing failure mechanism in both cases. Creep was confirmed in both cases by the (massive) presence of intergranular voids (aligned in some cases) at the grain boundaries and cracks originating from the edge and longitudinal to the edge in some areas. Localized overheating due to burner flame impingement most likely accelerated the creep rate deformation for the HP-modified reformer tube material though the material surpassed its design life of 100,000 h. The findings substantiate that high priority should be placed on reformer burner management and ensuring the catalyst in the reformer tubes is packed optimally to avoid downstream flows issues in the outlet pigtails. These measures can serve to mitigate the effects of localized heating that can contribute to the failure of these components.