ACFMP for inspection for ferromagnetic material.pptx

This is one of the NDT method used to detect surface bracking defect.

1. ACFM 2009 1 What is ACFM? ACFM is an Electromagnetic inspection technique providing one pass inspection It has a high tolerance to lift off It requires no electrical contact, so can be used through coatings Provides crack detection and sizing (length and depth) Does not rely on operator calibration

2. ACFM 2009 2 Application Areas Inspection of a wide range of materials including carbon steels, stainless steels, duplex, super duplex, titanium, inconel and aluminium General Weld Inspection Thread Inspection High Temperature Applications ‘In Air’ and subsea

3. ACFM 2009 3 ACFM ACFM is a ‘ current perturbation’ technique It is significantly different to conventional eddy current testing methods It works by making quantitative measurements of magnetic field disturbances which arise when an electric current is disturbed by the presence of a surface breaking crack

4. ACFM 2009 4 ACFM Theory A magnetic field is generated by coils carrying a 5 kHz AC current, over a metallic component containing fatigue cracks in the weld

5. ACFM 2009 5 ACFM Theory The field generation coils induce a current across the surface of the metal plate, perpendicular to the magnetic field. This is shown in orange

6. ACFM 2009 6 ACFM Theory The flow of current, induced by the magnetic field, is disturbed by a surface breaking defect. Some of the current is forced away from the surface as it flows underneath the defect. This reduces the strength of the magnetic field in the middle of the defect (shown in blue). Some of the current flows around the ends of the defect - the increased current density strengthens the magnetic field at the ends (shown in red)

7. ACFM 2009 7 ACFM Theory Current flowing around the ends of the defect, causing increased current density

8. ACFM 2009 8 ACFM Theory A rotating current produces a magnetic field, perpendicular to the rotation. As the current is forced to flow around the ends of the defect, it has a slight rotation to its motion, as shown on the left. It rotates clockwise at one end of the crack, producing a negative vertical field and anti-clockwise at the other end - this produces a positive vertical field; this can be seen as the red and blue areas on the diagram to the right

9. ACFM 2009 9 Typical ACFM Defect Indication The butterfly plot does not require uniform speed of probe movement

10. ACFM 2009 10 Inspection through coatings ACFM does not require the removal of paint coatings. Standard probes can operate through non-conductive coatings up to 5mm thick. This provides large cost savings compared to conventional inspection methods. (Magnetic Particle Testing or Penetrant Testing).

11. ACFM 2009 11 Limitations of ‘standard’ ACFM Should only be used for surface breaking cracks Sizing models available for some materials but not all - new ones being developed all the time Sizing models are based on planar cracks and so will not work on complex branched cracks Scanning with simple probes is in expected direction of cracking. Transverse cracks should still be detected but can’t be sized without another scan

12. ACFM 2009 12 Defect Depth Sizing Is based on theoretical models Removes need to calibrate equipment on site Based on sizing of semi elliptical defects – typical of fatigue cracking Originally based on models for thin skin materials but can be modified to consider other materials. Solutions are available for some non-magnetic materials

13. ACFM 2009 13 TSC AMIGO Portable ACFM Instrument

14. ACFM 2009 14 Standard Weld Probe

15. ACFM 2009 15 Pencil Probes

16. ACFM 2009 16 ASTM Standard Practice - 2003

17. ACFM 2009 17 New ACFMT ASME Standard ASME V Article 15 ACFM Technique (ACFMT)