Ketos ring

Ketos Ring: The Quantitative Calibration Standard in MPI

The Ketos Ring, often referred to as a Test Ring or AS 5282 Ring (based on the standard that defines it), is a crucial, quantitative calibration and performance verification standard used in Magnetic Particle Inspection (MPI). Unlike the Pie Gauge, which is qualitative and confirms only the presence and direction of a magnetic field, the Ketos Ring is used to verify the actual circular magnetization level and the overall sensitivity of an MPI system (usually a wet bench unit)

Design and Function

The Ketos Ring is a precisely manufactured steel component with known properties and dimensions.

• Material: It is typically made from a known, low-carbon steel (like AISI 1018 or Ketos-grade steel, giving it its name) to ensure consistent magnetic properties.

• Dimensions: It has a specific diameter and thickness (commonly 1.375 inches in diameter).

• Artificial Flaws: The ring contains 10 to 12 through-holes (non-ferromagnetic drilled holes) of a specific size arranged in a circular pattern near the circumference.

Principle of Operation

1. Magnetization: The Ketos Ring is magnetized by placing it on a central conductor (a copper rod or cable) and passing a controlled electric current through the conductor. This induces a circular magnetic field within the ring itself.

2. Particle Application: Wet fluorescent magnetic particles are applied to the ring while the current is flowing.

3. Indication: The magnetic flux lines are distorted by the subsurface holes, causing flux leakage at the surface, which attracts the magnetic particles. Indications appear as bright rings around the hole locations.

Importance in MPI Calibration

The Ketos Ring is an essential tool for formal, quantitative system checks:

• System Performance Check: It provides a reliable, repeatable method to check the overall performance of the MPI bench, including the magnetization power source, the wet bath concentration, and the UV light intensity—all in one test.

• Current Standardization: It allows inspectors to establish and standardize the correct amperage required to achieve a specified magnetic field strength for a given component size.

• Auditing and Compliance: Because its results are quantitative (a number of holes visible), the Ketos Ring is widely used to meet the stringent calibration requirements of industry standards (e.g., ASME, API, and military specifications) and is often required as part of the daily or shift-start performance check.