Corrosion and scale deposition are common flow assurance issues in sour gas wells. Recent studies have shown that scale deposition was derived from metallic corrosion under this condition. No metal is immune to corrosion in all environment. However through monitoring and understanding the environmental conditions that are the cause of corrosion changes to the metal type or development of newly high-performance coating materials to the metals being used can leads to significant reductions in corrosion. A newly developed coating material has shown effective prevention of iron sulfide scale formation under laboratory test conditions. Although these laboratory tests were conducted using conditions such as temperature and pressure from the field it is still very challenging to correlate the lab results to the real field condition since it is difficult to simulate the actual environment and downhole multiphase flow regime in the laboratory.An advanced downhole corrosion and scale monitoring (DCSM) tools has been designed and developed to effectively monitor corrosion and scaling in high temperature sour gas wells. Several exchangeable coated metal coupons can be installed on the tool to evaluate the performance of the coating material. A slick line with a retrievable high-expansion gauge hanger was used to deploy and anchor the DCSM downhole at the desired depth. The tool was retrieved after three months exposure to the reservoir condition for post-laboratory analysis.The retrieved coupons were thoroughly characterized to assess the coating performance and to understand the corrosion and scaling mechanisms. XRD was used to analyze the scale composition of the coupon surface. SEM and EDS analyses were performed to characterize the morphology and mineralogical changes of the coupon surface. Surface profilometer was used to quantify the size and height/depth of the scaled surface or localized corroded area.The results showed that a thin layer (~90 micron in thickness) composed of nickel and sulfur was formed on the surface of the coated coupon after its exposure in the high H2S environment for three months. A slight weight loss of the coated coupon was observed which might due to the combination effects of the reaction of coating material with H2S (weight gain) and abrasion of part of the outer layer from the surface (weight loss). Overall the field testing has demonstrated that this newly developed coating material is able to protect the metal coupon against corrosion and iron sulfide scaling effectively. However the abrasion of the formed surface layer of NiS scale might be a concern for long term field application.The advanced DCSM tool allows direct corrosion and scaling monitoring under downhole conditions. It is recommended that newly developed coating material should be evaluated and qualified under real downhole conditions before any field application.