Equipment and piping made of metallic materials of construction are susceptible to electrochemical corrosion as a result of external influences. Particularly susceptible to atmospheric corrosion are insulated piping and equipment. Water, contaminated with aggressive components, may penetrate through defects in the insulation jacketing and migrate through the insulation material to the metal surface. At the hot metal surface water will evaporate, leaving the corrosion components behind. After concentrating for some years, the corrosive deposits are likely to cause more or less severe corrosion depending on the type of material.
Atmospheric corrosion in petrochemical plants is generally electrochemical in nature. In order for this type of corrosion to occur, an electrolyte (i.e. moisture) must be present. Aggressive components which are present in insulation material or get there via the cover sheeting can migrate to the surface of insulated equipment or pipe via ingress of moisture acting as a vehicle. This paper describes the different forms of atmospheric corrosion.