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Rust Prevention

September 23, 2011

 

All types of material viz. steel, cast iron, aluminum, stainless alloys, concrete etc. needs to be protected from corrosion, rust bloom, blistering and de-lamination. Corrosion control and rust prevention is an important feature for keeping the quality of this structures intact. Rust formation is the deterioration of a material, because of its reaction with the environment. This disintegration process can be due to chemical oxidation, atmospheric affects, galvanic couple reaction etc. Atmospheric corrosion accounts for more failures on both a tonnage and cost basis than any other type of environmental corrosion.

Tremendous amount of material in tanks, columns, ships, marine structures, pipelines…..are exposed to the atmosphere and attacked by “oxygen and water”. High humidity is one of the main reason leading to corrosion of metal structures.

High humidity can allow blooming or flash rust between the time surface preparation for painting and coating is carried out and when the coating is applied, which may result in premature coating failure. This problem can occur on any surface but is most common when there is a large continuous surface as in the interiors of storage tanks, process piping and reaction vessels. In these circumstances, the practical logistics of coating operation prevent the immediate coating of the surface after cleaning.

While the surface is waiting for the coating to be carried out, small reductions in surface temperature or small increase in the humidity of the surrounding air can result in condensation, which causes immediate corrosion and negates the entire exercise.

General Recommendation:

Whatever the surface to be coated, from the preparation of the surface to the application of the first coat, the surface is subject to environmental factors. The term “Hold the Blast” is commonly used and refers to the prevention of rust bloom from forming between the blasting and coating cycles. This is essential to avoid coating failures.

General rules have been established which attempt to meet the specifications set by NACE and SSPC to maintain a 5°C differential between the air dew point and the surface to be coated in case of metals, and complete removal of dampness and moisture in the case of a non-metal like concrete.

To avoid the above problem of corrosion, dehumidifier can be used to remove enough moisture from the air at the surface so that the air dew point is lowered sufficiently for the metal.

TDS Solution:

TDS provides desiccant based dehumidifiers along with other accessories and technical manpower to provide the desired humidity level. The desiccant based dehumidifier removes moisture from the air by chemical attraction rather than condensation and helps in rust prevention. Dehumidification is used 24 hours per day until all the blasting and lining application is complete.

Dehumidifier takes moist air from outside environment, and feed dry air to the interior of the structure where coating is to be carried out. The dry air prevents condensation and high relative humidity at the surface.

 
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