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[Heberto Calderon]

How to Use ASTM E125 Reference Photographs for Magnetic Particle Testing of Ferrous Castings

Magnetic particle testing (MPT) is a nondestructive method for detecting surface and subsurface discontinuities in ferrous materials. It involves applying a magnetic field to the material and observing the patterns of magnetic particles that accumulate on the surface where discontinuities are present.

However, interpreting the magnetic particle indications can be challenging, especially for complex or irregular shapes of castings. That's why ASTM International has developed a collection of reference photographs that cover types and degrees of discontinuities occurring in steel castings and other types of ferrous castings detectable by the dry powder MPT method.

The reference photographs are intended to assist in the classification of those discontinuities revealed in ferrous castings subjected to MPT. They are also intended to be used for purposes of comparison with the magnetic particle indications observed on actual castings.

In this article, we will explain how to use the ASTM E125 reference photographs for MPT of ferrous castings, and what are the benefits and limitations of this standard.

What are the ASTM E125 reference photographs?

The ASTM E125 reference photographs are a set of 29 black-and-white photographs that show typical magnetic particle indications for various types of discontinuities found in ferrous castings. The photographs are numbered from E125-1 to E125-29, and each photograph is identified with a letter designation that corresponds to the type of discontinuity shown.

The types of discontinuities covered by the reference photographs are listed and described in Table 1 of the standard. They include cracks, shrinkage, gas porosity, sand inclusions, slag inclusions, hot tears, cold shuts, laps, seams, and others.

The reference photographs represent magnetic particle indications as found on production steel castings. They represent the actual size of the indications and the procedure followed was in accordance with ASTM E709 Guide for Magnetic Particle Testing. The peak magnetizing current employed was from 600 to 800 A and prod spacing from 4 to 10 in.

The white line indications as illustrated in most of the photographs were obtained by painting the casting area with a slurry of lamp-black in kerosene, gasoline, or alcohol. A gray magnetic powder was then used. The result was a white indication under normal photographic methods.

The black line indications resulted from applying red magnetic powder to the casting surface and photographing the magnetic particle indications.

How to use the ASTM E125 reference photographs?

The ASTM E125 reference photographs are intended to be used as follows:

• First, perform MPT on the ferrous casting according to ASTM E709 or other applicable standards.

• Second, compare the magnetic particle indications observed on the casting with those shown in the reference photographs.

• Third, identify the type and degree of discontinuity based on the letter designation and description given in Table 1 of ASTM E125.

• Fourth, evaluate the acceptability or rejectability of the casting based on the applicable acceptance criteria or specifications.

The reference photographs are not intended to be used as a substitute for engineering knowledge, experience, or judgment. They are also not intended to define or limit the meaning of any word or term used in product specifications dealing with MPT.

What are the benefits and limitations of using ASTM E125 reference photographs?

Some of the benefits of using ASTM E125 reference photographs are:

• They provide a visual aid for classifying and comparing magnetic particle indications for different types of discontinuities.

• They help reduce ambiguity and inconsistency in interpreting MPT results.

• They facilitate communication and documentation of MPT findings among inspectors, engineers, customers, and suppliers.

Some of the limitations of using ASTM E125 reference photographs are:

• They do not cover all possible types, shapes, sizes, locations, orientations, or combinations of discontinuities that may occur in ferrous castings.

• They do not provide quantitative measurements or acceptance criteria for evaluating magnetic particle indications.

• They do not account for variations in MPT techniques, equipment, materials 51082c0ec5