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Fundamentals of Corrosion
Therefore, covering with the alloy layer is important in decreasing the dissolution of the tin layer.
In carbonated beverages, the potential reversal does not take place; therefore, the steel dissolves preferentially at the defects in the tin layer. Under such
conditions, pitting corrosion sometimes results in perforation. Consequently,
except for fruit cans, almost all tinplate cans are lacquered.
When tinplate is to be used for structural purposes such as roofs, an
alloy of 12 to 25 parts of tin to 88 to 75 parts of lead is frequently used.
This is called terneplate. It is less expensive and more resistant to weather
than a pure tin coating. Terneplate is used for the fuel tanks of automobiles and also in the manufacture of fuel lines, brake lines, and radiators
in automobiles.
8.3.1.4 Lead Coatings
Coatings of lead and its alloy (5 to 10% Sn) protect the steel substrate, especially in industrial areas having an SO x atmosphere. At the time of initial
exposure, pitting occurs on the lead surface; however, the pits are self healed
and then the lead surface is protected by the formation of insoluble lead
sulfate. Little protection is provided by these coatings when in contact with
soil.
Lead coatings are usually applied by either hot dipping or by electrodeposition. When the coating is to be applied by hot dipping, a small percentage
of tin is added to improve the adhesion to the steel plate. If 25% or more of
tin is added, the resultant coating is called terneplate.
Caution: Do not use lead coatings if they will come into contact with drinking water or food products. Lead salts can be formed that are poisonous.
Terneplate. Terneplate is a tin-lead alloy coated sheet steel, and is produced either by hot dipping or electrodeposition. The hot dipping process
with a chloride flux is used to produce most terneplates. The coating layer,
whose electrode potential is more noble than that of the steel substrate,
contains 8 to 16% tin. Because the electrode potential of the coating layer
is more noble than the steel substrate, it is necessary to build a uniform
and dense alloy layer (FeSn 2 ) in order to form a pinhole-free deposit.
Terneplate exhibits excellent corrosion resistance, especially under
wet conditions, excellent weldability and formability, with only small
amounts of corrosion products forming on the surface. A thin nickel
deposit can be applied as an undercoat for the terne layer. Nickel reacts
rapidly with the tin-lead alloy to form a nickel-tin alloy layer. This alloy
layer provides good corrosion resistance and inhibits localized corrosion.
The main application for terneplate is in the production of fuel tanks for
automobiles.
Fundamentals of Corrosion
Therefore, covering with the alloy layer is important in decreasing the dissolution of the tin layer.
In carbonated beverages, the potential reversal does not take place; therefore, the steel dissolves preferentially at the defects in the tin layer. Under such
conditions, pitting corrosion sometimes results in perforation. Consequently,
except for fruit cans, almost all tinplate cans are lacquered.
When tinplate is to be used for structural purposes such as roofs, an
alloy of 12 to 25 parts of tin to 88 to 75 parts of lead is frequently used.
This is called terneplate. It is less expensive and more resistant to weather
than a pure tin coating. Terneplate is used for the fuel tanks of automobiles and also in the manufacture of fuel lines, brake lines, and radiators
in automobiles.
8.3.1.4 Lead Coatings
Coatings of lead and its alloy (5 to 10% Sn) protect the steel substrate, especially in industrial areas having an SO x atmosphere. At the time of initial
exposure, pitting occurs on the lead surface; however, the pits are self healed
and then the lead surface is protected by the formation of insoluble lead
sulfate. Little protection is provided by these coatings when in contact with
soil.
Lead coatings are usually applied by either hot dipping or by electrodeposition. When the coating is to be applied by hot dipping, a small percentage
of tin is added to improve the adhesion to the steel plate. If 25% or more of
tin is added, the resultant coating is called terneplate.
Caution: Do not use lead coatings if they will come into contact with drinking water or food products. Lead salts can be formed that are poisonous.
Terneplate. Terneplate is a tin-lead alloy coated sheet steel, and is produced either by hot dipping or electrodeposition. The hot dipping process
with a chloride flux is used to produce most terneplates. The coating layer,
whose electrode potential is more noble than that of the steel substrate,
contains 8 to 16% tin. Because the electrode potential of the coating layer
is more noble than the steel substrate, it is necessary to build a uniform
and dense alloy layer (FeSn 2 ) in order to form a pinhole-free deposit.
Terneplate exhibits excellent corrosion resistance, especially under
wet conditions, excellent weldability and formability, with only small
amounts of corrosion products forming on the surface. A thin nickel
deposit can be applied as an undercoat for the terne layer. Nickel reacts
rapidly with the tin-lead alloy to form a nickel-tin alloy layer. This alloy
layer provides good corrosion resistance and inhibits localized corrosion.
The main application for terneplate is in the production of fuel tanks for
automobiles.