Metallurgical Analysis of Leaking Tray Packs
Abstract
A metallurgical analysis was performed to determine the cause of leaking tray packs and the origin and development of 'gray spots' which represent potential leak sites. Tray packs are fabricated of tin-free steel (TFS) and are protected with multilayered coatings on both interior and exterior surfaces. Accelerated corrosion tests were carried out in order to monitor the progress of corrosion in a simulated long-term exposure environment. The presence of 'gray spots' on the exterior surface of the tray packs was related to an existing defect in the directly opposite surface of the interior coatings. Microscopic examination, in conjunction with AC impedance measurements, showed that water and aggressive ions contained in the food penetrate into and through interior coatings, through localized defects such as pores and cracks, causing pitting of the TFS which intensifies as a result of the presence of an occluded electrochemical cell at the coating/metal interface. Once the pit has penetrated through the entire thickness of the TFS, a gray spot appears under the exterior clear epoxy coating.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1990
- Accession Number
- ADA223157
Entities
People
- Frank C. Chang
- Kuan S. Lei
- Milton Levy