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Pitting and crevice corrosion

October 3, 2025
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Pitting and crevice corrosion are the most dangerous forms of localized corrosion and can lead to sudden failures of industrial equipment. This article provides an overview of these two destructive phenomena, their similarities and differences, and effective prevention and control strategies.

Part One: Bites

1.1 Definition and main features

Pitting is a type of localized corrosion in which small, deep holes form on the surface of a metal:

  • The diameter of the hole is usually smaller than its depth.

  • rapid vertical growth

  • The disease is difficult to diagnose in the early stages.

  • Increased risk of sudden failure

1.2 Mechanism of cavity formation

  • Start with surface defects (stains and scratches).

  • Microelectrochemical cell formation

  • Self-reinforcing process due to the acidic conditions in the cavity.

  • The main role of chloride and bromide ions

1.3 Factors influencing pitting corrosion

  • Environment     : presence of corrosive ions (Cl⁻, Br⁻)

  • Materials     : Stainless steel (especially 300 series) is more vulnerable.

  • Temperature     : High temperatures are an aggravating factor.

  • Electrochemical potential     : greater than the cavity potential

Part Two: Crack Erosion

2.1 Definition and founding conditions

Crevice corrosion occurs in the space between two surfaces:

  • Washers, screws and accessories

  • Freedom for design or assembly

  • Minimum required gap width (~0.1 mm)

2.2 Electrochemical mechanism

  • The oxygen content in space is gradually decreasing.

  • Formation of oxygen concentration cells

  • Acidification of the crack environment

  • Active dissolution of metal in the anode zone

2.3 Sensitive materials and environments

  • austenitic stainless steel

  • aluminum alloys

  • Marine and chemical environment

  • stagnant water with low oxygen content

Part 3: Comparison of     pitting     and crevice corrosion

3.1 Important similarities

  • The nature of localization and self-expansion

  • An ionic environment (electrolyte) is required

  • The role of local environmental acidity

  • Similar effects of halide ions

3.2 Key differences

Special feature Bites Crack erosion
Starting position free surface Restricted area
Attack ions required necessary This is not always the case.
Initial speed fast progressive
diagnosis It is very difficult relatively easy

Part Four: Diagnostic and Evaluation Methods

4.1 Optical and microscopic methods

4.2 Electrochemical methods

4.3 Standardized tests

  • ASTM G48 (Testing of Stainless Steel Voids)

  • ASTM G78 (Standard Corrosion Rating)

  • ISO 11463 (Determination of cavitation resistance)

Diaphragm pumpsSection 5. Prevention and control strategies

5.1 Selection of suitable materials

  • Use stainless steel with high molybdenum content (316, 317).

  • Nickel alloys such as   Hastelloy   and Inconel

  • Titanium and its alloys in aggressive environments

5.2 Design draft

  • Remove unnecessary spaces

  • Use continuous welded joints instead of mechanical connections.

  • Designed for    complete drainage

  • Avoid stagnant areas.

5.3 Protection methods

  • Full coverage

  • cathodic protection

  • Use corrosion inhibitors

  • Environmental control (cooling, deionization)

Part 6: Examples of industrial companies

6.1 Malfunction of the heat exchanger tube

  • A cavity that forms on the side of the body

  • Accumulation     of chlorides     in stagnant zones

  • Solution: Use an alloy with a high molybdenum content.

6.2 Problems of flange connections in shipbuilding

6.3 Corrosion of chemical storage tanks

  • Cavitation in steam pipes

  • Solutions: Interior coatings and water quality monitoring

Section 7 Technical standards and recommendations

7.1 Design standards

  • ASME B31.3 Piping Systems

  • API 570 Pipe Inspection

  • NACE SP0178 Protection of the marine environment

7.2 Review procedure

  • Regular checks of UT and RT

  • electrochemical monitoring

  • Non-destructive testing (NDT)

7.3 Calculation of the remaining service life

  • Assessment of the growth rate of rooms

  • Advanced   corrosion modeling

  • Risk and reliability analysis

Finally

Due to their localized and progressive nature, pitting and crevice corrosion pose a serious threat to the safety of industrial facilities. Understanding the mechanisms and differences between these two types of corrosion is the first step toward developing effective prevention systems.

A combination of materials science solutions, advanced design, and monitoring software can     reduce the risk of these phenomena. Remember that preventing corrosion and cracking early on is more effective and cost-effective than repairing them after failure.

Implementing a comprehensive corrosion protection program, including proper material selection, thoughtful design, effective coatings, and regular inspections, helps avoid repair costs and production downtime. Investments in this area not only increase safety but also ensure long-term productivity and profitability.