(2) External. This type of gray spot is caused by external corrosion factors.
The corrosion starts when physical damage (abrasions, nicks, and so forth) to the outer
coatings expose the outer surface of the base metal to the atmosphere. At an
appropriate temperature and relative humidity, corrosion can progress through the base
metal and inner coatings to result in a leaker. This form of corrosion progresses slower
than internal corrosion and should not result in leakers until the expected product shelf
life has been exceeded.
The two types of gray spots can be readily distinguished by probing with a
pointed object, such as a dissecting needle. Cans with internal gray spots
can be easily pierced or have little metal integrity remaining, while those with
external gray spots will retain their structural integrity. However, isolated
reports have been received where external gray spots (when gentle probing is
applied) will make a slight indentation or depression in the base metal but will
not penetrate the interior of the can. This has been observed in cans that
were approaching or exceeded their expected shelf life. Consequently, gray
spot defects will be classified as follows:
Gray spots that leak when probed (Major A defect).
Gray spots with weakened base metal (Major B defect).
Gray spots with no weakening of base metal (Minor defect).
b. Vacuum Defects.
(1) Flipper/loose lid. The lid has a wavy appearance and when the lid is
depressed at one end, the other end will distend (Major A defect).
(2) Paneling. Is the deformation of the can at the bottom corners resulting
from excessive mechanical vacuum during processing. Slight paneling is commonly
found in some bakery type items and is not considered a defect. (Affects double seam
Major B defect; does not affect double seamMinor defect).
(1) Hard swellers. Swelling of the tray pack can which distends the lid
above the double seam (Major A defect).
(2) Soft swellers. Swelling of the tray pack can which distends the lid to the
degree where a 12 inch straight edge, when placed on top of the lid, will rock back and
forth over the distended lid and/or will evidence light under the ends of the straight edge
(Major A defect).
d. Pinhole. A small hole penetrating entirely through the can (Major A defect).