Environmental Engineering Reference
In-Depth Information
Table 4.5
Some systems and inhibitors used for protection of steel components
Systems
Inhibitors
Waters
:
Potable water
Ca(OH)
2
, polyphosphates, silicates
Seawater
Na-nitrite, na-silicate, NaH
2
PO
4
NaNO
2
Brines
Na-chromate, Na-benzoate, na-nitrite
Recirculating cooling water
Chromate, nitrate, polyphosphates, silicates,
merpholine
Automotive coolants
Nitrite, benzoate, borax, benzotriazole, mercapto-
benzothiazole
Vapor condensates
Morpholine, cyclohexylamine, ammonia, ethylene-
diamine, benzylamine
Acids
:
Sulfuric acid
Phenylacridine, phenylthiourea, mercaptans,
sulfides, aromatic amines, arsenic
Hydrochloric acid
Ethylaniline, quinoline, various amines, phenylthi-
ourea, pyridine
phenylhydrazine, mercapto-
benzothiazole
Phosphoric acid
NaI, thiourea, sulfonated castor oil, As
2
O
3
Oil production
:
Oil field brines
Na-silicate, Na
2
SO
3
, amine acetates, formaldehyde
Primary and secondary recoveries
Imidazoline, various amines
Refining
Imidazoline and derivatives
ter supply and industrial pipelines use of inhibitor is also common, where the
choice is obviously the inexpensive chemicals. Some inhibitors like chromates
and arsenic compounds are toxic, and these cannot be used in potable water
supply or where the effluent might cause pollution problems.
Based on their mechanism of inhibition, the inhibitors may be classified as
1.
Passivators
2.
Cathodic inhibitors
3.
Organic inhibitors, and
4.
Vapor phase inhibitors
However, the demarcation is not always very sharp and more than one mechanism
may be operative in the action of an inhibitor.
Passivators
Passivators or passivating inhibitors or oxidizers, as they are sometimes called,
constitute the most important group of inhibitors for the protection of steel. There
are two types of passivators: oxidizing and nonoxidizing. Chromates, nitrites,
