certain liquid environments. Thisp henomenon is known as environmental
stress cracking or stress corrosion cracking.
Other factors in the atmosphere that cause corrosionordegradationofthe
coating are UV light,t emperature, oxygen, ozone,p ollutants, and wind.
Types of failures caused by these factors are:
1. Chalking. UV light,m oisture, oxygen, and chemicals degrade the
coating resulting in chalk. This may be corrected by providing an
additional top coat of material with proper UV inhibitor.
2. Color fading or color change. Thismay be caused by chalk on the
surface or by breakdown of the colored pigments. Pigments can be
decomposed or degradedb yU Vlight or reaction with chemicals.
3. Blistering. Blisteringm ay be caused by:
a. Inadequater elease of solvent during botha pplication and
drying of the coating system.
b. Moisture vapor that passes through the film and condenses at a
point of low adhesion.
c. Poor surface preparation.
d. Poor adhesiono ft he coatingt ot he substrateo rp oor
intercoat adhesion.
e. Ac oatw ithint he paints ystem that is notr esistant to
the environment.
f. Application of arelatively fast drying coating over arelatively
porous surface.
g. Failures because of chemical or solvent attack. When acoating
is not resistant to its chemical or solvent environment, there is
apparent disintegrationoft he film.
4. Erosion, coating worn away.Loss of coating because of inadequate
erosion protection.P rovide material with greater resistance
to erosion.
7.13.9M aintenance of the Coating
Any paintjob, even if properly done,does not last forever.Withinthe first six
monthsoryear after application, spots, inadvertent misses, or weak spots in
the coating system can be detectedbysimple visual inspection. Athorough
inspection and repair should be donea tthis time.
Over ap eriod of time, the coating willb reak downa nd deteriorate as a
result of the effect of the environment. Scheduled inspections should he
made to determine the extent and rate of the coating breakdown. Spot
touchupr epairs houldb em adea tl ocalized areaso ff ailureb efore
deteriorationoft he entire coated surfaceh as taken place.
Extensive costs of total surfacep reparation (such as completeb last
cleaning removalo fa ll oldc oating)c an be avoidedi fa“planned
Corrosion of Linings and Coatings
484
CAT8247—CHAPTER 7—17/10/2006—15:04—TRGANESH—XMLM ODEL B–pp. 403–485
stress cracking or stress corrosion cracking.
Other factors in the atmosphere that cause corrosionordegradationofthe
coating are UV light,t emperature, oxygen, ozone,p ollutants, and wind.
Types of failures caused by these factors are:
1. Chalking. UV light,m oisture, oxygen, and chemicals degrade the
coating resulting in chalk. This may be corrected by providing an
additional top coat of material with proper UV inhibitor.
2. Color fading or color change. Thismay be caused by chalk on the
surface or by breakdown of the colored pigments. Pigments can be
decomposed or degradedb yU Vlight or reaction with chemicals.
3. Blistering. Blisteringm ay be caused by:
a. Inadequater elease of solvent during botha pplication and
drying of the coating system.
b. Moisture vapor that passes through the film and condenses at a
point of low adhesion.
c. Poor surface preparation.
d. Poor adhesiono ft he coatingt ot he substrateo rp oor
intercoat adhesion.
e. Ac oatw ithint he paints ystem that is notr esistant to
the environment.
f. Application of arelatively fast drying coating over arelatively
porous surface.
g. Failures because of chemical or solvent attack. When acoating
is not resistant to its chemical or solvent environment, there is
apparent disintegrationoft he film.
4. Erosion, coating worn away.Loss of coating because of inadequate
erosion protection.P rovide material with greater resistance
to erosion.
7.13.9M aintenance of the Coating
Any paintjob, even if properly done,does not last forever.Withinthe first six
monthsoryear after application, spots, inadvertent misses, or weak spots in
the coating system can be detectedbysimple visual inspection. Athorough
inspection and repair should be donea tthis time.
Over ap eriod of time, the coating willb reak downa nd deteriorate as a
result of the effect of the environment. Scheduled inspections should he
made to determine the extent and rate of the coating breakdown. Spot
touchupr epairs houldb em adea tl ocalized areaso ff ailureb efore
deteriorationoft he entire coated surfaceh as taken place.
Extensive costs of total surfacep reparation (such as completeb last
cleaning removalo fa ll oldc oating)c an be avoidedi fa“planned
Corrosion of Linings and Coatings
484
CAT8247—CHAPTER 7—17/10/2006—15:04—TRGANESH—XMLM ODEL B–pp. 403–485