Any of the aboved efects can result in undercutting. After the corrosive
penetrates to the substrate, corrosion will proceed to extend under the film
areas that have not been penetrated or have not failed. Some linings are
more resistant than others to undercutting or underfilm corrosion. Usually,
if the lininge xhibits good adhesive properties, and if the primer coat is
chemically-resistant to the corrosive environment, underfilmcorrosion will
be greatly retarded.
In addition, at ank lining mustn ot impart any impurities to the material
contained within it. The application is af ailure if any taste, smell, color,o r
otherc ontamination is imparted to the product, even if the lining is intact.
Such contaminationc an be caused by the extraction of impurities from the
lining, leading to blisteringb etween coats to the metal.
If the liningi su nsuited to the service,c omplete failure may occurb y
softening, dissolution, and finally completedisintegration of the lining. This
typeofproblem is prevalent between the interphase and bottomofthe tank.
At the bottomofthe tank and throughout the liquidphase,penetration is of
great concern.
The vapor phase of the tank is subject to corrosion from concentrated
vapors mixed with any oxygenpresent and can cause extensive corrosion.
4.10 SpecificL iquidL inings
Mostl iquid-applied liningm aterials are capableo fb eing formulated to
meet requirements for specifica pplications. Corrosion data referring to
the suitability of al iningm aterial for as pecific corrodent indicates that a
formulation is available to meet these conditions. Because all formulations
may not be suitable, the manufacturer must be checked as to the suitability of
his formulation.T he most common linings are discussed.
4.10.1P henolics
Synthetic phenolic resins were developed and commercialized in the early
1900s by Leo Bakeland.
2
The reduction of phenola nd formaldehyde
produces ap roduct that formsah ighly cross-linked, three-dimensional
product when cured. The resins have found use in various applications in
the lining industry because of theire xcellent heat resistance, chemical
resistance, and electrical properties. Theyalso offer good adhesion to many
substrates and have good compatibility with other polymers.
Phenolic resins have two basic classifications: resoles and novalaks.
Resoles, or heat reactive resins, are made usinga ne xcess of formaldehyde
and ab ase catalyst. The polymer that is produced has reactive methylol
groups that form at hermoset structure when heat is applied.
Novalaks are made using an excess of phenol and an acid catalyst.
Reaction occurs by the protonation of formaldehyde,
3
andthe intermediate
Corrosion of Linings and Coatings
84
CAT8247—CHAPTER 4—17/10/2006—14:33—SRIDHAR—XML MODEL B–pp. 69–174
penetrates to the substrate, corrosion will proceed to extend under the film
areas that have not been penetrated or have not failed. Some linings are
more resistant than others to undercutting or underfilm corrosion. Usually,
if the lininge xhibits good adhesive properties, and if the primer coat is
chemically-resistant to the corrosive environment, underfilmcorrosion will
be greatly retarded.
In addition, at ank lining mustn ot impart any impurities to the material
contained within it. The application is af ailure if any taste, smell, color,o r
otherc ontamination is imparted to the product, even if the lining is intact.
Such contaminationc an be caused by the extraction of impurities from the
lining, leading to blisteringb etween coats to the metal.
If the liningi su nsuited to the service,c omplete failure may occurb y
softening, dissolution, and finally completedisintegration of the lining. This
typeofproblem is prevalent between the interphase and bottomofthe tank.
At the bottomofthe tank and throughout the liquidphase,penetration is of
great concern.
The vapor phase of the tank is subject to corrosion from concentrated
vapors mixed with any oxygenpresent and can cause extensive corrosion.
4.10 SpecificL iquidL inings
Mostl iquid-applied liningm aterials are capableo fb eing formulated to
meet requirements for specifica pplications. Corrosion data referring to
the suitability of al iningm aterial for as pecific corrodent indicates that a
formulation is available to meet these conditions. Because all formulations
may not be suitable, the manufacturer must be checked as to the suitability of
his formulation.T he most common linings are discussed.
4.10.1P henolics
Synthetic phenolic resins were developed and commercialized in the early
1900s by Leo Bakeland.
2
The reduction of phenola nd formaldehyde
produces ap roduct that formsah ighly cross-linked, three-dimensional
product when cured. The resins have found use in various applications in
the lining industry because of theire xcellent heat resistance, chemical
resistance, and electrical properties. Theyalso offer good adhesion to many
substrates and have good compatibility with other polymers.
Phenolic resins have two basic classifications: resoles and novalaks.
Resoles, or heat reactive resins, are made usinga ne xcess of formaldehyde
and ab ase catalyst. The polymer that is produced has reactive methylol
groups that form at hermoset structure when heat is applied.
Novalaks are made using an excess of phenol and an acid catalyst.
Reaction occurs by the protonation of formaldehyde,
3
andthe intermediate
Corrosion of Linings and Coatings
84
CAT8247—CHAPTER 4—17/10/2006—14:33—SRIDHAR—XML MODEL B–pp. 69–174