STAGES OF RUST AND CORROSION
A.1 As an aid in evaluating rust damage and planning rust repair actions, rust shall be classified into four
A.1.1 Stage 1 Red, black, or white corrosion deposits on surface accompanied by minor etching
and pitting. Base metal is sound.
A.1.2 Stage 2 Powered granular and scaled condition resulting in erosion of material from the
surface. Base metal is sound.
A.1.3 Stage 3 Surface condition and corrosion deposits are similar to Stage 2, except that metal
in the corroded areas is unsound and small pinholes may be present.
A.1.4 Stage 4 Corrosions have advanced to a point where the surface has been penetrated. No
metal remains at point of severest corrosion. There are rust holes in the surface area, or metal is
completely missing along the edge.
A.2. Exterior surfaces of units with areas of Stage 1 or Stage 2 rust shall be blasted, cleaned, treated,
primed and painted. Units with areas of Stage 3 or Stage 4 rust shall be repaired, cleaned, treated, primed
and painted in those areas or should have assemblies replaced with new assemblies if repair is not
A.3. Any evidence of corrosion on working surfaces of close tolerance parts is not acceptable. Pitting or
surface deterioration in the area of any seal or gasket is not acceptable if it affects the proper functioning
and/or proper performance of the applicable component.