Corrosion is the major source of failures and leaks in the oil and gas industry. Internal corrosion has been the most notable contributing factor to pipeline failure. For an extended root cause analysis of the internal corrosion in gas pipelines, a transmission pipe wheel exhibiting significant corrosion scale build-up was taken down after more than 10 years of service. The present investigation aims to analyze the morphologies of the corrosion pits as well as the chemical compositions of the corrosion deposits within. The investigation was carried out by conducting standard failure analysis methods including visual examination, metallurgical examinations using optical microscopy in combination with scanning/transmission electron microscopy (SEM/TEM), thermal gravimetric analysis (TGA) and X-ray Powder Diffraction analysis (XRD). The results revealed that chlorine attack appears to be a major root cause of failure manifested by Akageneite scale build up and consequent tube loss. There is evidence that chlorine penetrated either through and/or underneath the sulfide protective film at the alloy- sulfide interface allowing chlorine ions to become in direct contact with alloy and thus consequent corrosion attack. Moreover, more chlorine and oxyhydroxides were found at the bottom of well close to the reservoir side (associated with moisture presence) suggesting chlorine containing reservoir water might be responsible for pitting and following severe corrosion. It was concluded that the presence of high concentration of chloride might be the main reason of the localized pits. This case study will shed light on root causes of chlorine attack followed with internal corrosion in gas production well.