The DST Integrity Plan requires the ultrasonic wall thickness measurement of two vertical scans of the tank primary wall from a single riser. The resulting measurements are then used in an extreme value methodology to predict the minimum wall thickness expected for the entire tank. The methodology was developed in previous work by the authors of this report. A component of the methodology is to consider the possible impact of riser differences had multiple risers instead been used. The approach is based on previous analyses of Tank AY-101 which had measurements taken from multiple risers. This report presents estimated maximum wall thickness loss for five DST’s with associated uncertainty estimation and confidence bounds. Several sources of variability are incorporated since the individual sources cannot be separated. These sources include original manufacturing plate thickness and the precision of the measurement process, as well as loss due to corrosion, the actual feature of interest.
Revised: December 10, 2005 |
Published: September 17, 2005