FY19 Status of the Full Circumference Examination of the Inner Container Closure Weld Region for Selected 3013 DE Containers

Abstract

One of the main focus areas of the 3013 Surveillance Program is a thorough evaluation of the inner container closure weld region (ICCWR) opened for destructive examination (DE). As part of the protocol to investigate the corrosion in the ICCWR a laser confocal microscope (LCM) is used to perform close visual examination of the surface and measurements of corrosion features on the surface. In FY17, DE containers from FY13 through FY16 were evaluated to select candidates for a full circumference analysis of the ICCWR. In FY18, the selected DE containers for full circumference evaluation (FCE) were processed according to the ICCWR protocol and LCM data collection was completed for the full circumference only for FY15 DE07. In FY19 the remaining DE containers were completed.The ICCWR protocol was completed as follows: (1) the FCE containers were sectioned into quarters and the weld removed to access the ICCWR; (2) a series of images of the ICCWR full circumference were taken using a stereo microscope and assembled into panoramic views; (3) SEM/EDS analysis performed on selected sections showed what is most likely corrosion products on the surface and chlorides randomly dispersed; (4) the presence of chlorides was also confirmed with ion chromatography of citric acid washes, in which FY15 DE07 and FY16 DE05 showed a significant amount of chlorides with FY15 DE08 showing the less amount of chlorides; (5) dye penetrant examination was performed on the interior and exterior surfaces of all the sidewall sections but reveled no relevant indication of surface-breaking defects, (6) finally, as described above, the full circumference examination of the ICCWR by LCM was completed.The three ICCWRs show general and localized corrosion on the surface. However, FY15 DE08 show more areas with agglomerated pits in Zones 2 and 3 than the other two DEs. The major suspect corrosion events were observed for FY15 DE07 on Sections C1 and C2 and for FY15 DE08 on Section C2. These events correspond to suspect cracks or crack-like features identified with a unique name to easily refer to each feature. FY15 DE07 shows a crack-like feature, identified as Acrux, in Section C1 and three features 07/25/2019

Status of the Full Circumference Examination of the Inner Container Closure Weld Region for Selected 3013 DE Container

“…The FCE containers were sectioned into quarters and the weld removed from each section as described in previous reports [4][5][6]. However, the current nomenclature for the quarter sections follows a clockwise direction starting from the weld overlap (defined as 0°) when facing the interior of the inner container lid as shown in Figure 1.…”

“…Dye penetrant examination was performed on the interior and exterior surfaces of the sidewall sections of the FCE containers. The method utilized for the dye penetrant test is described in details in reference [4]. The test was performed by a Penetrant Inspector -Level III.…”

“…Sample preparation for LCM included (1) cutting 1/4 sections (A, B, C and D) into 1/8 sections of the container lid to reduce the curvature of each sidewall piece to be scanned and to fit the sample in the sample holder box (LCM box); (2) cleaning the samples from corrosion products using 2.0 M nitric acid solution and sonication for 60 min at 60°C; (3) mounting each 1/8 section into the LCM box minimizing tilt as much as possible. Detailed sample preparation is described in previous report [4].…”

“…A protocol to investigate the corrosion in the ICCWR was developed to characterize the type of corrosion (i.e., mechanisms), the extent of corrosion (percentage of area and depth of attack) and the variables impacting this corrosion (chloride concentration and metallurgical condition) [2,3]. Figure 1 shows an overview of the protocol for the examination of the ICCWR, which includes some updated steps from the original version [4]. The steps include (1) the sectioning of the inner container lid into easily handled pieces and weld removal, (2) low-magnification imaging of the entire circumference of the ICCWR, (3) surface analysis of selected pieces using Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS), (4) chemical analysis of selected pieces using wet chemistry techniques, (5) dye penetrant examination of exterior surfaces, (6) further sectioning of selected pieces into 1/8 can sections in preparation for LCM analysis, (7) cleaning selected pieces for removing corrosion products using nitric acid, (8) surface depth profiling and high-magnification imaging of the cleaned pieces with identified corroded areas within the ICCWR using LCM, and (9) serial metallography of pieces as necessary.…”

“…As part of the ICCWR examination protocol, a Keyence 3D laser confocal microscope (LCM) model VK-X110 is used to perform close visual examination of the surface at the ICCWR and surface profile measurements for pit depths or other corrosion features on the surface. Initial analysis of selected DE containers using the LCM revealed several challenges for acquiring, processing and interpreting the data [4,5]. These challenges include topography of the ICCWR sample, surface features, and the amount of surface area for collecting data at high magnification conditions.…”