Met-L-Chek® provides lab services exclusively for Aerospace customers to evaluate in use materials for compliance with the ASTM E-1444 (Magnetic) and ASTM E-1417 (Penetrant) Guidelines for re-use.
This test measures the settling volume of magnetic particles present in a user’s sample to determine if the bath particle concentration is within the ASTM E-1444/ASTM E-709 standard requirement ranges. Particle concentrations outside of the range of 0.1 to 0.4 mL in a 100 mL bath sample for fluorescent particles and 1.2 – 2.4 mL in a 100 mL sample for non-fluorescent particles shall not be used. If the particle concentration is low, a sufficient amount of particles can be added to obtain the desired concentration; if the particle content is high, a sufficient amount of bath suspension fluid can be added to obtain the desired concentration.
Wet Particle Contamination
This test determines if the wet magnetic particles in the bath are contaminated. Examination of the sample under both UV-A and visible light for separation, striations or discoloration bands may indicate contamination. When the total volume of the contaminants, including bands or striations, exceeds 30 % of the total settled volume of magnetic particles and the contaminants, the bath must be adjusted or replaced. Clouding or fluorescence of the material which occludes view of the centrifuge tube measurements between 5 ml and 25 ml, indicate the bath must be replaced before further use.
When excess oil contamination is present, it causes magnetic particles to congeal and hinders the bath’s wetting ability and may also cause a blue fluorescence background that can hinder discontinuity detection. When water contaminates an oil bath, particle coagulation occurs.
Several devices can demonstrate the sensitivity of wet-method particles and can be used to verify particle performance. These devices contain permanent magnetization and are independent of the magnetizing system. In the Mag-Chek method, a sample of the user’s solution is applied to an encoded magnetic strip card that generates magnetic gradients and displays the number of indications that can be observed. These gradients are used to grade the magnetic particle performance on the basis of the weakest visible indication.
This test determines the kinematic viscosity of the bath suspension fluid by measuring the time for the liquid to flow under gravity through a calibrated glass capillary viscometer. Viscosity is important because the magnetic particles must move and collect at the leakage field of a discontinuity to form a visible indication. Interference with this movement impacts the sensitivity of the penetrant test. If viscosity of the bath suspension fluid exceeds 3.0cSt @100°F, the bath must be discarded and refilled with fresh suspension.
This test evaluates the fluorescence of the bath suspension fluid by comparing its’ relative fluorescence versus the AMS-2641 fluorescence standard. If the fluorescence of the bath suspension fluid exceeds that of the AMS-2641 standard, the bath must be discarded and refilled with fresh suspension.
Frequently Asked Questions