Pipelines transporting gaseous and liquid products are installed all over the world. While in general steel pipelines are considered to be a safe method to transport large quantities of oil, gas and other products, they are also prone to deterioration over time. This process may result in volumetric corrosion defects. Intelligent inline inspection (ILI) programs offer the possibility to receive an accurate description of the pipeline condition. The results of the inspection have to be analyzed with regards to economic and safety aspects for the entire transporting system. This analysis is based on available inspection and pipeline data and has to be carried out under different aspects and regulations, e.g. legal requirements, regional standards and internal operator regulations. This paper presents results based on high resolution ultrasonic inspection (UT) data. We will describe and enlighten major advantages of the assessment method RSTRENG case 1 (Riverbottom) which was developed for high resolution wall thickness data of corrosion anomalies. Furthermore, this paper will discuss limitations of the method, e.g. inspection data with reduced signal to noise ratio, typically caused by debris, wax or reduced coupling conditions. The authors will present a general approach to improve the reliability of the assessment results. The findings are compared to a representative amount of high quality field verifications.