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Special Report

Stress cracking ConCluSion
Stress cracking can be attributed It is not surprising that coatings can
to surface movement, aging, absorp- suffer from premature failure and/or
tion and desorption of moisture, ther- exhibit defects that may or may not result
mal cycling, and general lack of flexi- in failure. It is not generally straightforward
bility of the coating. The thicker the to establish the reason for the failure of a
paint film, the greater is the possibi- coating due to the many potential factors
that may be involved. These could include
formulation, surface preparation, applica-
Fig. 40: Solvent popping tion, drying & curing times and condi-
soon after application can be seen tions, and environmental exposure, with
causing solvent popping in Figure-40. more than one contributing factor often
being involved.
Prevention methods
Use correct coating specifications Failures and defects can manifest
and materials, and ensure correct appli- themselves at various times in the life of a
cation techniques and environmental coating. Prior to application, they can take
conditions. the form of settlement and skinning, dur-
Fig. 42: Stress cracking
ing application as runs and sags, shortly
Staining lity that cracking may occur. It often after application as solvent popping and
It can happen when contacted with occurs around welds and changes in orange peel, and during service as blis-
a solid or liquid that imparts a discolora- section. Figure-42 illustrates paint tering and rust spotting. To determine the
cause and mechanism of coating failure,
all possible contributory factors must be
evaluated together with a detailed history
from the time of application to the time the
failure was first noted. Many coating fail-
ures require further evaluation and analy-
sis to be carried out by a qualified chemist,
engineer, or coating specialist, often using
specialized laboratory equipment.

ReFeRenCeS
1. Fontana M.G, Green N.D, Corrosion
Engineering (1967) McGraw-Hill
Book Co.
2. Pludek, V.R. Design and Corrosion
Control, (1977), The Macmillan
Press Ltd.
3. Coatings for Material Protection,
Edited by Makhlouf, A.S.H., Wood-
Fig. 41: Staining head Publishing (2014).
tion or stain to the coating. Figure-41 coating with visible cracks, which 4. B. Fitzsimons and T. Parry, Fitz’s
shows such discoloration of a coating may penetrate down to the substrate, Atlas 2 of Coating Defects, MPI Group.
system due to staining. due to stress cracking. 5. Kenneth B. Tator, ASM Handbook
Volume 5B: Protective Organic
Prevention methods Prevention methods Coatings, USA, 2015.
Avoid contact with solids and Use correct coating systems, appli- 6. Schweitzer, P.A., ‘Corrosion of Lin-
liquids that are prone to cause staining, cation techniques, and dry-film thick- ings & Coatings’, Corrosion Engi-
or use dark-coloured coatings where any nesses, or use a more flexible coating neering Handbook, Second Edition,
staining would not be so apparent. system. CRC Press.

Chemical Weekly June 24, 2025 181

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