Prediction of External Corrosion for Steel Cylinders--2007 Report

Schmoyer, Richard L

Oak Ridge National Laboratory

关键词: Corrosion;    Containment;    Management;    36 Materials Science;    Forecasting;   

DOI  :  10.2172/931115
RP-ID  :  ORNL/TM-2007/227
RP-ID  :  DE-AC05-00OR22725
RP-ID  :  931115

美国|英语

来源: UNT Digital Library

【 摘 要 】

Depleted uranium hexafluoride (DUF{sub 6}) is stored in over 62,000 containment cylinders at the Paducah Gaseous Diffusion Plant (PGDP) in Paducah, Kentucky, and at the Portsmouth Gaseous Diffusion Plant (PORTS) in Portsmouth, Ohio. Over 4,800 of the cylinders at Portsmouth were recently moved there from the East Tennessee Technology Park (ETTP) in Oak Ridge, Tennessee. The cylinders range in age up to 56 years and come in various models, but most are 48-inch diameter 'thin-wall'(312.5 mil) and 'thick-wall' (625 mil) cylinders and 30-inch diameter '30A' (including '30B') cylinders with 1/2-inch (500 mil) walls. Most of the cylinders are carbon steel, and they are subject to corrosion. The United States Department of Energy (DOE) manages the cylinders to maintain them and the DUF{sub 6} they contain. Cylinder management requirements are specified in the System Requirements Document (LMES 1997a), and the activities to fulfill them are specified in the System Engineering Management Plan (LMES 1997b). This report documents activities that address DUF{sub 6} cylinder management requirements involving measuring and forecasting cylinder wall thicknesses. As part of these activities, ultrasonic thickness (UT) measurements are made on samples of cylinders. For each sampled cylinder, multiple measurements are made in an attempt to find, approximately, the minimum wall thickness. Some cylinders have a skirt, which is an extension of the cylinder wall to protect the head (end) and valve. The head/skirt interface crevice is thought to be particularly vulnerable to corrosion, and for some skirted cylinders, in addition to the main body UT measurements, a separate suite of measurements is also made at the head/skirt interface. The main-body and head/skirt minimum thickness data are used to fit models relating minimum thickness to cylinder age, nominal thicknesses, and cylinder functional groups defined in terms of plant site, storage yard, top or bottom row storage positions, etc. These models are then used to compute projections of numbers of cylinders expected to fail various minimum wall thickness criteria. The minimum wall thickness criteria are as follows. For thin-wall cylinders: 0 (breach), 62.5, and 250 mils. For thick-wall cylinders: 0, 62.5, and 500 mils. For 30A cylinders: 0, 62.5, and 100 mils. Each of these criteria triplets are based respectively on (1) loss of DUF{sub 6} (breaching), (2) safe handling and stacking operations, and (3) ANSI N14.1 standards for off-site transport and contents transfer. This report complements and extends previous editions of the cylinder corrosion report by Lyon (1995, 1996, 1997, 1998, 2000), by Schmoyer and Lyon (2001, 2002, 2003), and by Schmoyer (2004). These reports are based on UT data collected in FY03 and before. In this report UT data collected after FY03 but before FY07 is combined with the earlier data, and all of the UT data is inventoried chronologically and by the various functional groups. The UT data is then used to fit models of maximum pit depth and minimum wall thickness, statistical outliers are investigated, and the fitted models are used to extrapolate minimum thickness estimates into the future and in turn to compute projections of numbers of cylinders expected to fail various thickness criteria. A model evaluation is performed comparing UT measurements made after FY05 with model-fitted projections based only on data collected in FY05 and before. As in previous reports, the projections depend on the treatment of outliers.