API 570 EXAM STUDY GUIDE [MODULE 2 : PART 6] ATMOSPHERIC CORROSION


ATMOSPHERIC CORROSION
(API 570 EXAM STUDY GUIDE)

API 571 : 4.3.2 Atmospheric Corrosion

This is a common damage mechanism which happens to all the structural steel items exposed to atmosphere in our house and in industrial environment, which are not protected by surface coatings. API 571 does not gives a very in-depth analysis of this damage mechanism. It occurs every where and proper surface coating is the only way to prevent it.

Moist environment is one of the reasons for galvanic corrosion, this way atmospheric corrosion overlaps with atmospheric corrosion.

Description of Damage

Occurs from moisture associated with atmospheric conditions
Marine environments and moist polluted industrial environments with airborne contaminants are most severe

Affected Materials

CS, LAS and copper alloyed aluminum

Critical Factors

Physical location (Industrial, Marine, Local)
Moisture (Humidity)
Designs that trap moisture
Cooling tower mist
Presence of salts, sulfur compounds and dirt


Corrosivity:
Marine environments: 20mpy (mpy: Mills Per Year; corrosion rate)
Industrial environments that contain acids or sulfur compounds that can form acids: 5 to 10mpy
Inland locations: 1-3mpy
Dry rural environments: <1mpy
Corrosion increases with temperature up to 121deg.C [250 Deg.F], after that not of any effect. This condition is not for insulated lines.
Chlorides, H2S, flyash all accelerates corrosion
Bird turds accelerate corrosion
bird pooping on businessman car cartoon vector
BIRD TURD; Refer Shutterstock for this image

Affected Units or Equipment

Piping and equipment with operating temperature sufficiently low.
Piping that rests on pipe supports are prone to atmospheric corrosion
Bimetallic connections such as copper to aluminum electrical connections.

Appearance or Morphology of Damage

General or localized depends upon whether or not the moisture is trapped.
Metal loss may not be visually evident.

Prevention/Mitigation

Surface preparation and proper coating application

Inspection and Monitoring

VT and UT techniques

Related Mechanisms

Corrosion Under Insulation (CUI)


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