Corrosion is in essence a statistical effect governed by a number of variables. microscopic variations in a surface tend to cause different forms of corrosion and also variations in the corrosion rate over either a wide or small area (pitting). In these areas the simple assumption that corrosion rate is uniform across an area is unlikely to be accurate, and sample thickness measurements are unlikely to be representative of the whole component.The corrosion effect on the operability and serviceability of bottom plates of a steel aboveground storage tank, the effect which is considered to be a serious threat to the tank structural integrity. In this study the data of the analysis are collected as a readings of thickness through all the area of the tank bottom, processed statically and shows that the critical thickness profile represented by an averaged value for thickness could be reliably taken to consideration for further analysis through finite element when the COV is less than 10%, The finite element analysis result concise with the results of basic design limits.