ASTM G46 Examination and Evaluation of Pitting Corrosion

ASTM G46 – Examination and Evaluation of Pitting Corrosion

ASTM G46 is a widely recognized standard that provides guidelines for the examination and evaluation of pitting corrosion on metallic materials. Pitting is a highly localized form of corrosion that can cause significant structural damage despite minimal overall material loss. ASTM G46 establishes systematic procedures for identifying, measuring, and reporting pitting damage to ensure consistent and reliable assessment.

Purpose of ASTM G46

The primary objective of ASTM G46 is to:

• Detect and characterize pitting corrosion
• Measure pit depth and distribution
• Evaluate the severity of the localized attack
• Provide standardized reporting methods

The standard does not describe how to perform corrosion exposure tests but focuses on post-exposure examination and evaluation.

Importance of Pitting Evaluation

Pitting corrosion can lead to:

• Leakage in pressure vessels and pipelines
• Reduced load-bearing capacity
• Crack initiation and propagation
• Premature component failure

Since pits can penetrate deeply into the material while appearing small at the surface, accurate evaluation is critical for determining serviceability and safety.

Examination Methods Under ASTM G46

ASTM G46 outlines several techniques for assessing pitting corrosion:

1. Visual Examination

An initial inspection is performed to identify visible pits and the general surface condition. Surface cleaning may be required to remove corrosion products before evaluation.

2. Optical Microscopy

Low- and high-magnification microscopy is used to examine pit morphology, distribution, and density.

3. Pit Depth Measurement

Pit depth is one of the most icriticalparameters. Measurement techniques include:

• Depth micrometers
• Metallographic cross-sectioning
• Focus variation microscopy
• Profilometry

The maximum pit depth is often used to assess severity.

4. Metallographic Cross-Sectioning

Samples may be sectioned and polished to examine pit shape, penetration depth, and possible crack initiation at the pit base.

Key Parameters Evaluated

ASTM G46 focuses on quantifying:

• Maximum pit depth
• Average pit depth
• Pit density (number of pits per unit area)
• Pit morphology (shape and growth pattern)
• Distribution across the surface

These parameters help determine the potential impact on structural integrity.

Reporting Requirements

A complete ASTM G46 evaluation report typically includes:

• Description of material and exposure conditions
• Surface preparation methods
• Measurement techniques used
• Maximum and average pit depth
• Photographic documentation
• Observations on pit distribution and morphology

Standardized reporting ensures consistency and comparability between evaluations.

Applications

ASTM G46 is commonly applied in:

• Oil and gas pipelines
• Marine components
• Chemical processing equipment
• Stainless steel and alloy performance testing
• Post-service failure investigations

It is often used in conjunction with corrosion-exposure standards, such as ASTM G48.

Limitations

While ASTM G46 provides detailed evaluation procedures, it:

• Does not specify corrosion testing conditions
• Requires proper surface preparation
• May require destructive sample sectioning
• Relies on accurate measurement techniques

Careful execution is essential to avoid measurement errors.

Conclusion

ASTM G46 is a standardized method of examining and evaluating pitting corrosion in metals. By accurately measuring the depth, density, and morphology of the pits, engineers can assess the severity of localized corrosion and inform decisions on material performance and preventive measures. The proper use of this standard is a critical factor in the reliability and safety of structures.

Why Choose Infinita Lab for ASTM G46?

With Infinita Lab (www.infinitalab.com), you are guaranteed a Nationwide Network of Accredited Laboratories spread across the USA, the best Consultants from around the world, Convenient Sample Pick-Up and Delivery, and Fast Turnaround Time. 

Our team understands the stakes and subtleties of every test. Whether you’re validating a new Product, de-risking a prototype, or navigating complex compliance requirements, our specialists guide the process with rigor and clarity.  

Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090  to learn more about our services and how we can support you. Request a Quote