Storage Tank Integrity And Materials Evaluation PDF Download

Radioactive supernate, salt, and/or sludge wastes (i.e., high level wastes) are confined in 49 underground storage tanks at the Savannah River Site (SRS). The waste is transported between tanks within and between the F and H area tank farms and other facilities on site via underground and a limited number of aboveground transfer lines. The Department of Energy - Savannah River Operations Office (DOE-SR) performed a comprehensive assessment of the structural integrity program for the Tank Farm waste transfer system at the SRS. This document addresses the following issues raised during the DOE assessment: (1) Inspections of failed or replaced transfer lines indicated that the wall thickness of some core and jacket piping is less than nominal; (2) No corrosion allowance is utilized in the transfer line structural qualification calculations. No basis for neglecting corrosion was provided in the calculations; (3) Wall loss due to erosion is not addressed in the transfer line structural qualification calculations; and (4) No basis is provided for neglecting intergranular stress corrosion cracking in the transfer line structural qualification calculations. The common theme in most of these issues is the need to assess the potential for occurrence of material degradation of the transfer line piping. The approach used to resolve these issues involved: (1) Review the design and specifications utilized to construct and fabricate the piping system; (2) Review degradation mechanisms for stainless steel and carbon steel and determine their relevance to the transfer line piping; (3) Review the transfer piping inspection data; (4) Life estimation calculations for the transfer lines; and (5) A Fitness-For-Service evaluation for one of the transfer line jackets. The evaluation concluded that the transfer line system piping has performed well for over fifty years. Although there have been instances of failures of the stainless steel core pipe during off-normal service, no significant degradation is anticipated during normal operations for the planned service life. General corrosion of stainless steel in high level waste environments was shown to be insignificant (i.e., little or no wall loss is expected for a time on the order of 180 years or more). Erosion is also not expected to limit the life of the pipes due to the low usage of the transfer lines and low fluid velocity during transfers. Quality controls on the material (e.g., corrosion evaluation testing) and procedures/specifications that limit contact with chloride bearing materials or liquids minimize the potential for the occurrence of stress corrosion cracking of the core pipe. General corrosion of the carbon steel jacket is not expected to be significant for a reasonable intended service life (e.g., on the order of 170 years). However, the carbon steel jackets are expected to continue to fail in local areas due to pitting corrosion. Life prediction estimates project that a significant increase in the number of jacket failures (i.e., through-wall penetrations) may occur after an additional 30 to 60 years of service life (i.e., between 2035 and 2065). A Fitness-For-Service evaluation was performed for a recently inspected jacket that showed evidence of pitting within a locally thinned area. The evaluation concluded that the line is still able to perform its intended function and can remain in service.