27 July 2008

Protective Coatings and Paints -01 Introduction

INTRODUCTION
The main purpose of painting on facilities is to protect them from deterioration. These structures comprise a vital resource in the integrity, safety and continuous production of facilities. They must be kept in a state of operational readiness by efficient use of the limited funds available for this purpose. Unfortunately, these facilities are frequently subject to environments and uses that accelerate their natural deterioration and require costly repairs and maintenance.
Metals corrode in aggressive soil, industrial or chemical atmospheres, or immersion environments; woods swell, warp, and crack during weathering; concrete and masonry structures crack and spall in severe environments; and organic polymeric materials suffer degradation in sunlight. To adequately meet the challenges of protecting constructed facilities, it is necessary to have a general understanding of the common ways in which materials deteriorate and make it able to control.


TYPE of MATERIAL DETERIORATION
Deterioration of Metal :
Commonly name as Corrosion. Metals corrode because they exist in chemically unstable states. Thus, iron ore is a corrosion product in its natural, stable state. Energy must be used in blast furnaces to reduce iron to its metallic state. Iron and steel products are then slowly oxidized by corrosion to their previous stable lower energy states. at least four conditions must be present for corrosion to occur:
a) Anodic areas where corrosion occurs
b) Cathodic areas where the metal is protected
c) An electrolyte (conductive medium such as soil or water)
d) A metallic path between the anode and cathode
In atmospheric corrosion, surface moisture and contamination serve as the electrolyte. Dissimilar metals are
anodic and cathodic to each other; also, the same metal components have anodic and cathodic areas because of slight chemical or physical differences.

Deterioration of Wood

The lead causes of deterioration of wood are effects of ultraviolet light, and swelling and contracting. These adversely affect the physical properties of the wood.

Deterioration of Concrete

The main cause of concrete deterioration is moisture and electrolyte penetration. This may result in deterioration of the concrete itself or in corrosion of reinforcing steel which causes spalling of the concrete.

..next Design Consideration

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