PITTING CORROSION

 PITTING CORROSION.

Learn about (Types of pitting corrosion) and where do they appear.

1. One of the most dangerous types of localized corrosion that can cause sudden failure of equipment.

2. Why is Pitting Corrosion considered difficult to detect and dangerous?

3. What are the different types and how to recognize them?

4. Learn how to protect equipment from this sneaky type of corrosion!

5. A part of the Corrosion Control course

 Presented by Engineering Skills Academy

Series 6 | Post (14)

A. Pitting Corrosion:

It is a severe positional corrosion that attacks the metal surface consisting of small or deep pits, while the rest of the surface remains visibly intact.

The danger lies in that it can penetrate a metal wall quickly causing a leak or explosion, even with a small metal block missing.

B. Why is it happening?

1. It often begins with fine imperfections in the paint or metal surface.

2. Accelerates in environments containing chloride or acidic center.

3. Feeds on micro-variations in surface electrochemical voltage.

C. Common Types of Pitting Corrosion:

1. Narrow, Deep Pits

- Pits are very tight but they are very deep.

2. Shallow, Wide Pits

– Holes are shallow but wide.

3. Elliptical Pits 

– A regular oval shaped.

4. Vertical Grain Attack

– Eat along the grains vertically.

5. Subsurface Pits

– Holes beneath the surface are not easily seen.

6. Undercutting Pits

– Starts small and then expands below the roof.

7. Horizontal Grain Attack 

– Eat along the grains horizontally.

D. Where is it commonly seen?

1. Seawater or Cooling water systems containing Chloride.

2. Pressure Vessels and Heat Exchanges

3. Stainless Steel equipment in wet and salty environments.

E. Ways to cope:

1. Chloride resistant materials like Duplex or Super Duplex.

2. Application of high quality protective coating.

3. Taking control of the chemistry of the waist

(pH - oxygen - salts content)

4. Periodical check using

a. Eddy Current 

b. Ultrasonic Testing

To discover the hidden pitfalls.

Pitting Corrosion

Effect is just devastating