Evaluate the Likelihood of Metal Developing Localized Corrosion

Pitting corrosion is a localized form of corrosion that leads to the creation of small holes or “pits” in the metal. This form of corrosion is mainly found on passive metals. Passive metals and alloys, such as aluminum, titanium and stainless steel owe their corrosion resistance to a thin oxide layer on the surface with a thickness of only a few nanometers. The corrosion initiating process starts with a local break-down of the passive layer. Local corrosive attack can be initiated on stainless steels, for example, by chloride ions. Fig.1 shows the most significant phases of this corrosion phenomenon on stainless steel.

 

CAUSES OF PITTING CORROSION

The most common pitting corrosion causes are:

 

  • Cracks in protective coating
  • Scratches, scuffs & small chips
  • Non-uniform stress
  • Defective metal substrate
  • Turbulent fluid flow
  • Non-uniform protective coating
  • Chemical attack on protective coating

 

EVALUATION OF PITTING CORROSION

EILAB conducts various tests for the determination of the resistance of stainless steels and related alloys to pitting corrosion when exposed to chloride environments.

 

An immersion test or weight loss method is the best option. They involve preparing metal sample and immersing in a solution. After a few hours / days it can be removed so the corrosion rate can be calculated. You can observe the pits and pit depth under a microscope and make the necessary calculations.

 

Pitting Corrosion Test Specification : There are several standards which provide guidance for electrochemical pitting tests of stainless steels and the most popular ones are:

 

  • ASTM G48 – Standard Test Method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution.

Method A—Ferric chloride pitting test.
Method C—Critical pitting temperature test for nickel-base and chromium-bearing alloys.
Method E—Critical pitting temperature test for stainless steels.

 

  • ASTM  G46 – Standard Recommended Practice for examination and evaluation of pitting corrosion.

OUR CORE SERVICES INCLUDE:

Inspection, testing and endorsement services for various industries

Conventional and Advance NDT Services


Asset Integrity Management and Field Inspection Services


Post-Weld Heat Treatment (PWHT) Services


Mechanical and Welding Qualification Testing


Metallurgical Failure Investigation


Corrosion Investigation and Testing


Analytical Chemical Testing


Rope Access for inspection at heights and "Normally difficult to Access" locations.


Our services are indispensable for the process owners and help them decide the course of action related to their materials, equipment, components for qualification and continued usage through our core services.

OVER THREE DECADES OF PROFESSIONAL EXCELLENCE

Analytical and Technical Laboratory in the Middle East having Metallurgy, Mechanical Testing, Chemical Testing,
NDT, Marine Survey, Field Inspection, Asset Integrity Services and PWHT facilities all under one roof that employs over 100 professionals. And Versatile Integrated Quality Management System and International Approvals.

Our pool of talent includes Engineers, Inspectors, Accountants, Finance Experts and Technicians.