FERRITE TESTING

Ferrite Testing in NDT (Non-Destructive Testing)

Overview

Ferrite testing is a Non-Destructive Testing (NDT) method used to measure the ferrite content in austenitic and duplex stainless steels. The test helps ensure that the material has the right balance of austenite and ferrite to maintain mechanical properties, corrosion resistance, and weld integrity.

Why is Ferrite Testing Important?

1. Corrosion Resistance: Ferrite content affects resistance to stress corrosion cracking and pitting corrosion.
2. Mechanical Properties: Ensures toughness and ductility in stainless steels.
3. Weld Quality: Helps prevent hot cracking in welds.
4. Standard Compliance: Meets industry standards such as ASTM A800, AWS D1.6, and ISO 8249.

Testing Methods

1. Magnetic Induction Method (Ferritscope)
   • Uses a handheld probe to measure ferrite content based on magnetic permeability.
   • Provides quick, non-destructive, and accurate results.
   • Common in field inspections and production monitoring.
2. Metallographic (Microscopic) Examination
   • Requires cutting a sample and preparing a polished cross-section.
   • Ferrite is measured using image analysis software or manual point counting.
   • More precise but destructive and time-consuming.
3. Chemical Analysis (Electrolytic)
   • Involves dissolving a sample in an electrolyte and measuring ferrite phase content.
   • Less common due to complexity.

Typical Ferrite Content Ranges

• Austenitic Stainless Steels (e.g., 304, 316): 3% – 10% Ferrite
• Duplex Stainless Steels (e.g., 2205, 2507): 30% – 70% Ferrite

Ferrite Number (FN) vs. Volume %

• Ferrite content is often expressed as a Ferrite Number (FN) rather than a percentage.
• FN is measured using a Ferritscope and can be converted to volume % using correlation charts.

Common Applications

• Weld Inspection in Pipelines, Pressure Vessels, and Heat Exchangers
• Aerospace and Nuclear Industry Components
• Chemical and Petrochemical Plants
• Cryogenic Equipment