Ndt-magnetic-particle-lab - Final 2.docx

LAB PRACTICUM AND THEORY In Magnetic Particle Examination, electric prods or a magnetic yoke are used to polarize or magnetize a portion of the test specimen. If there are any breaks in this magnetized portion of the test specimen a new north and south pole are created. The lines of force used to polarize/magnetize the specimen are called flux lines. Discontinuities and cracks cause the flux lines to move around the flaw and possibly out of the material. When they leave the material it is known as flux leakage. Magnetic particles are attracted to this flux leakage revealing the flaw. Magnetic particle examination takes advantage of this phenomenon in ferromagnetic materials to find flaws close to the surface (typically max of 1/4” depth) when the flaw provides good obstruction to flux lines. For this lab we used the ASTM E1444-01 standard. First, you demagnetize the part to be examined and make sure it is clean and free of contaminants. Then you decide on an orientation for the magnetic yokes and make sure the yokes are no more than 6” to 8” apart. The yokes are then applied. At the same time as the yoke application (Active shot) the dry magnetic particle developer is applied in a light, uniform, dust-like coating. As mentioned above these particles are attracted to the flux leakage in the part. After the powder is applied and before the yoke is removed or turned off, excess powder is removed with a dry air current. This air current should not be strong enough to disturb the particles held by flux leakage. Now the part can be evaluated and indications are recorded with written description or photography. These steps are repeated in a second position 90 degrees from the first to ensure no defects were missed. After testing the specimen is degaussed to eliminate residual magnetic fields and cleaned to ensure all particles and developer are removed from the surface.

EQUIPMENT LIST      

Test specimens: Structural Component/ Weld Test/ Elbow. Magnaflux powder: 3A Black, Part No-01-1748-81 An adjustable magnetizing yoke: Magnaflux Corp, Model: Y-6, 115V.-60 HZ-6 A. Safety glass Safety boots Hand broom

DATA ANALYSIS Table 1 below shows all results of the defects, location and magnetic field direction Table 1: Results from Magnetic Particle Testing Specimen

Defect ID W1

#1 – Weld Test W2 #2 – Structural Component

S1 S2 E1

#3 - Elbow

E2 E3

Defect Location Welding joint (Top side) Welding Joint (Bottom side Left end (Top side) Right end (Bottom side The nameplate Left end (Top side) Right end (Bottom side)

Magnetic Field Direction Horizontal Horizontal Vertical Vertical Circular Circular Circular

Specimen #1: Weld Test Top Side

Figure 1: Defect in welding joint – W1

Figure 2: Defect in welding joint – W1

Bottom Side

Figure 3: Defect in welding joint - W2

Figure 4: Defect in bottom welding joint

Figure 5: Defect in bottom welding joint

With the weld test specimen, no defects were observed with the yoke in the longitudinal magnetism orientation on either side. When the yoke was placed in the circumferential orientation (AKA perpendicular to the weld) many near surface discontinuities were found on top side and bottom side. However, as possible to observe in the figures, it was found that the defects were not with the plates of steel themselves but where the plates met the weld. On the top side, in figure 1 and 2 you can observe the magnetic particles were attracted to the area where the bad weld meets the metal plate. These defects may have been caused by lack of weld fusion. This can also be observed on the bottom side at figures, 3 and 4, where the weld does appear to be better done, but a small amount of flux leakage still occurs where the weld meets the plate indicating small cracks which can reduce the usability of the part and are therefore nonconformances. The weld quality on the second side is of much higher quality than the weld on top side. On bottom side, at Figure 5 the test results were inconclusive because welding slag attracted the metal particles. In order to correct this further pre-cleaning may be necessary to eliminate the slag from the surface and thus giving the opportunity of relevant results.

Specimen #2: Structural Component The specimen is part of metal which has been tested by magnetic particle examination. The part has four big holes, three small holes and two semi-circular holes at the end as shown in figure 6. While during magnetic testing, two defects have been observed on the part. One defect at the left hand side near the semi-circular hole, other at the right hand side of the part near the side edge of the part.

Figure 6: Structural component Source: Original (Patel)

DEFECTS The first defect at the left hand side of the corner is shown in figure 7. It shows the small crack around 12 mm long which may cause due to stress induced in it while it has been cut. It may have been caused due to impact on the side and between the cutting tools. It is major defect which may reduce the usability part due to the cracks in it.it is non-conformance.

The second defect at the right hand side corner near the side edge is shown in figure 8. It shows the small crack around 10 mm long which may cause due to presence of microstructural cracks.it is to be major defect which may cause failure to and which can reduce the safety of part because of this crack. It is non-conformance.

Figure 7: Defect at left hand side semi-circular hole – S1 Source: Original (Patel)

Figure 8: Defect at right hand side near side edge – S2 Source: Original (Patel)

False Indication

False indications are shown in figure 9. The magnaflux powder shows at the two sides of the corner side edges. This may be the reasons that the probe was held too much causing the large particles to extend from the magnetic flux lines, or it’s caused due to the flux leakage at the side of the part while it magnetized by turning 90 degrees.

Figure 9: False indications Source: Original (Patel)

Specimen #3: Elbow The part is an elbow of plumbing pipe made from metal as shown in Figure 10. There are so many rusts and slags on the outside of the elbow, especially on the both ends. Magnetic particle testing was carried out on the top side and bottom side with two orientation of magnetic field (horizontal and circumferential)

Figure 10: elbow specimen

Defects There is no indication of defect when the part was applied in circumferential orientation of magnetic field. There are 3 defects appeared when the horizontal direction of magnetic field was applied to the elbow. The first one is shown in Figure 11, the particles were attracted around the name plate which indicate minor cracks or openings around the nameplate.

Figure 11: Defect at the nameplate – S1 The second defect is at the right end of the top side as show in Figure 12. The particles were attracted to concave areas of the slag which indicate porous defects or fracture.

Figure 12: Defect at right end of top side – S2

The third defect is on the right end of the bottom side. There are many particles appeared on the welded joint, and the particles were distributed non-uniform. The welding condition is deteriorated, there are so many porous indications.

Figure 13: Defect at the right end of bottom side – S3

Identification of Error Sources The false indication in the specimen #2 shown in Figure 9 is probably caused by holding the probe too much causing the large particles to extend from the magnetic flux lines. The indication in Figure 5 is not clear, there so many particles covering a large area, this is because the developer was applied too much. One very minor other thing we noticed was that when we turned the magnetic yoke off the dust collected on the yoke fell on anything within the vicinity of it. After making note of this we were careful to only turn off the yoke away from the test specimen area.

Conclusion After completing the magnetic particle examination and following all the proper procedures, the results attained were as expected. As Indicated in the data analysis the procedure which we followed proved the theory as we observed in the defects by using the ASTM standard.