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How to Do Magnetic Particle Testing as per ASTM E709 & E1444

Magnetic Particle Testing (MPT), also known as Magnetic Particle Inspection (MPI), is an essential non-destructive testing (NDT) method used to detect surface and near-surface flaws in ferromagnetic materials such as iron, nickel, and cobalt alloys. Industries like automotive, aerospace, oil and gas, and manufacturing extensively use this method due to its effectiveness in ensuring the quality and integrity of components.

Steps to Start Magnetic Particle Testing

Before beginning Magnetic Particle Testing, a detailed procedure must be prepared. This procedure should include both essential and non-essential parameters related to the test. The procedure will outline factors such as:

• MPI techniques
• Selection of powders and light requirements
• Medium and current calculations
• Equipment to be used
• Testing sequence
• Personnel qualifications

The MPI procedure should be drafted by an NDT Level II professional and approved by an NDT Level III in Magnetic Particle Testing.

Differences Between ASTM E709 and ASTM E1444

Both ASTM E709 and ASTM E1444 are internationally recognized standards issued by the American Society for Testing and Materials(ASTM). They are widely adopted in industries performing MPI. Here's a breakdown:

• ASTM E709: This is the primary standard for Magnetic Particle Testing, providing guidelines for performing MPI on materials like steel, iron, and alloys. It covers the methodology and techniques but does not specify acceptance criteria.
• ASTM E1444: This standard is more specific to the aerospace industry, outlining the minimum requirements for performing MPI and ensuring quality in high-precision fields like aerospace. It is recommended to use in conjunction with ASTM E709.

Scope of Magnetic Particle Testing

Both ASTM E709 and ASTM E1444 cover techniques for dry and wet magnetic particle inspection and apply to materials like blooms, billets, castings, forged products, and weld joints. The testing can be used in both raw and semi-processed materials, as well as for in-service inspections of plants and structures.

• ASTM E709: Serves as a guide to prepare MPI procedures, techniques, and customer-specific evaluation.
• ASTM E1444: Specifies the minimum standards for aerospace-related MPI testing and addresses critical quality control requirements.

Personnel Qualifications

To perform MPI testing, inspectors must hold proper certification, such as those recommended by ASNT (American Society for Nondestructive Testing) under practices like SNT-TC-1A, ANSI, CP189, or NAS410 for aerospace. Certification should be according to recognized standards, ensuring the inspector has the necessary skills and experience.

Magnetic Particle Testing Techniques

The two main MPI techniques are:

1. Dry Powder Technique: Dry magnetic particles are used to detect surface flaws.
2. Wet Powder Technique: Wet magnetic particles (suspended in a liquid) are applied for higher sensitivity and are effective for detecting more subtle surface flaws.

Magnetic Field Generation

To detect flaws in ferromagnetic materials, a magnetic field must be introduced into the component. Different techniques for magnetization include:

• Permanent magnets (e.g., permanent magnet yokes)
• Electromagnetic yokes
• Head shot
• Central conductor
• Cable wrap
• Solenoid
• Coil shot
• Prod technique

The field strength should be adequate to detect flaws but not so strong that it causes excessive flux leakage or makes flaw identification difficult.

Fluorescent vs. Non-Fluorescent Techniques

• Fluorescent Magnetic Particles: These are used in dark environments and are more sensitive. They glow under UV light, making flaws easier to identify.
• Non-Fluorescent Magnetic Particles: Typically used for field testing or in situations where the test site cannot be darkened. These are cost-effective but less sensitive than fluorescent particles.

Flaws Detected by Magnetic Particle Testing

MPI is effective for detecting surface and near-surface defects, such as:

• Cracks
• Porosity
• Inclusions
• Weld defects

These flaws must be aligned or close to the direction of the magnetic flux. Surface flaws are indicated by sharp, well-defined patterns, while subsurface flaws produce broader, less distinct indications.

Equipment Selection

Selecting the right MPI equipment is crucial to ensuring accurate results. Some key factors include:

• Permanent Magnetic Yokes: Ideal for environments where electricity is unavailable or a spark hazard is present (e.g., refineries).
• Electromagnetic Yokes and Other Power Tools: These require electrical power but are more versatile in terms of testing capacity.

Conclusion

Magnetic Particle Testing (MPI) is a critical non-destructive testing method that helps detect surface and near-surface defects in ferromagnetic materials. By adhering to established procedures such as ASTM E709 and ASTM E1444, industries can ensure the quality, safety, and integrity of their components. Proper equipment, techniques, and qualified personnel are key to achieving accurate and reliable results in MPI testing.