Magnetic Particle Procedure DTS-014-MP

For large areas, a grid system helps to ensure proper placement of prods or yokes during magnetic particle inspection.

The magnetizing current should be continuously applied during the entire magnetic particle inspection process, from applying the particles to removing excess particles.

Before starting magnetic particle testing, thoroughly clean the surface to be inspected and surrounding areas to remove any contaminants that might interfere with the examination.

Prod tips can be made of copper, either solid or with a copper electrode, but lead, steel, or aluminum prods can be used when it is important to prevent copper from penetrating the test item.

Magnetizing units equipped with meters should undergo performance and accuracy tests at regular intervals, following the manufacturer's instructions and relevant codes or standards.

The intensity of visible light during magnetic particle inspection must be sufficient for proper viewing of the particles. For white light, the minimum intensity should be 100 foot-candles.

Lower light intensity can be used for field inspections with non-fluorescent particles, but it should be agreed upon by the customer.

For fluorescent magnetic particle inspections, ambient visible light in the darkened area should be minimal, ideally not exceeding two foot-candles.

The process of checking if the surface to be inspected is clean and free from any material that could interfere with the inspection, such as dirt, grease, oil, paint, loose scale, or coatings. It ensures that the magnetic particles can adhere properly to any defects and that indications can be clearly identified.

A field indicator or Gauss meter is used to check for any residual magnetism on the surface. Residual magnetism can interfere with the magnetic particle examination process, so it must be eliminated before the inspection.

Techniques used to remove residual magnetism from a component. This is crucial for ensuring that the magnetic particle examination is accurate. The process ensures that only the magnetism generated for the test is present.

Specific components such as specific detergents, solvents, or cleaning methods used to prepare a surface for magnetic particle testing.

The minimum distance from the area undergoing magnetic particle examination where the surfaces must be free of coatings, dirt, grease, oil, paint, loose scale or other obstructions. It ensures the magnetic particles are not hindered by any obstacles in finding defects.

The act of documenting all inspection results. This is a crucial aspect of the inspection process, as it provides a permanent record of the component's condition.

The technique used to detect surface and near-surface discontinuities in ferromagnetic materials. During this process, a magnetic field is applied to the component, and iron-based particles are applied to the surface. If there are any discontinuities in the surface, the magnetic flux lines will be disrupted, drawing the particles to form a visible indication.

The final step in the magnetic particle inspection process, where any post-inspection surface finishing on the test component must be inspected again. This is necessary to ensure that any potentially new defects introduced during the finishing process are detected.

The magnetic field strength needed for examination is calculated by dividing the ampere-turns by the number of turns in the coil (I = NI/N).

Magnetization is achieved by passing current through the part, creating a circular magnetic field perpendicular to the current flow within the part.

Direct or rectified (half-wave or full-wave) current is used for circular magnetization.

The magnetizing current for circular magnetization should be between 300 amp/inch and 800 amp/inch of the outside diameter.

For non-round parts, the greatest cross-sectional diagonal at a right angle to the current flow is used to determine the 'inches' for calculating the magnetizing current.

If the required current level is unattainable, the maximum available current should be used and the field adequacy verified using a magnetic particle field indicator.

Clamp the contacts to the wall thickness for large parts and non-cylindrical parts, and verify field adequacy using the field indicator.

The magnetizing current for circular magnetization is the same as in 14.2, using the largest distance between two points on the part's circumference as the 'diameter'.

When the conductor passes through the inside of a part and touches an inside wall, the current levels are the same as those specified in paragraph 7.2.1, except that the diameter is calculated by adding the diameter of the central conductor and twice the part's wall thickness.

The effective length of the part that is magnetized is four times the diameter of the central conductor.

The yoke technique is used to detect only surface discontinuities (open to the surface) in the part.

Alternating current yokes are preferred for detecting surface discontinuities in materials thicker than 1/4 inch, compared to direct or permanent magnet yokes with the same lifting power.

The multi-directional technique uses multiple circuits energized rapidly in succession to magnetize the part in different directions, effectively creating a multi-directional magnetic field.

The multi-directional technique can create both circular and longitudinal magnetic fields by using different techniques described in section 12.0.

The multi-directional technique uses high amperage power packs to generate the magnetizing fields.

Linear indications are considered unacceptable if they are evaluated as crater cracks or star cracks exceeding 5/32 inch in length.

Linear indications are unacceptable if they are evaluated as cracks, besides crater or star cracks, regardless of their length.

Linear indications exceeding 1 inch in total length within 12 inches of weld, or 8% of the weld's length (smaller value), are unacceptable.

Rounded indications are unacceptable if the size of an individual pore exceeds 1/8 inch.

Rounded indications are unacceptable if the size of an individual pore exceeds 25% of the thinner wall thickness being joined.

Rounded indications are unacceptable if the distribution of scattered pores exceeds the limits specified in Figure D1 or D2.

Clustered pores that occur in any pass, except the finish pass, are unacceptable if they meet the criteria of 1.3.1 to 1.3.3.

Clustered pores in the finish pass are unacceptable if any of the following conditions are met: cluster diameter exceeds 1/2 inch, aggregate length in 12 inches exceeds 1 inch, or an individual pore within the cluster exceeds 1/16 inch.

Current levels used for magnetic particle inspection typically range from 500 A/inch or lower, with higher currents (up to 800 A/inch) used to inspect for inclusions or low permeability alloys like precipitation hardening steels.

For examining inclusions in precipitation hardening steels, even higher current levels can be used, reaching up to 1000 A/inch.

The central conductor technique uses a conductor placed inside a hollow part (like a cylinder) to generate a magnetic field within the part, enabling the inspection of internal or external surfaces.

The conductor is positioned close to the internal surface of the cylinder for optimal field strength and defect visibility.

For large diameter cylinders, the cylinder is examined in increments, and a magnetic particle field indicator is used to ensure the magnetic field is sufficient for each increment.

The required field strength for the central conductor technique is determined based on the guidelines for a single turn central conductor.

The number of passes the central conductor cable makes through a hollow part affects the overall magnetic field strength, increasing proportionally with each additional pass.

Field adequacy during the central conductor technique is verified using a magnetic particle field indicator, ensuring the magnetic field is sufficient to reveal defects.