In manufacturing, we all realize how important it is to follow the correct sequence of operations on every part.  At American Testing Services, we perform two types of common surface inspection processes – Magnetic Particle and Liquid Penetrant.  These processes are executed to several different prime specifications, such as General Electric, Rolls Royce, Hartzell Propeller, Lockheed Martin, and Honeywell, just to name a few.  The inspection techniques are typically based on ASTM specifications, with each prime’s own little nuances.

Both magnetic particle and liquid penetrant inspections should be performed BEFORE any special coatings are applied to parts.  We receive calls all the time because a customer missed the inspection process on the print.  In effort to raise awareness of the proper sequence of events and surface preparations, here are the specific requirements for each method in accordance with ASTM standards:

ASTM E1444 Standard Practice for Magnetic Particle Inspection

Examination Sequence – Perform magnetic particle examination after all operations which might cause or reveal discontinuities.   Such operations include, but are not limited to, forging, heat treating, electroplating, forming, welding, grinding, straightening, machining, and proof loading.

Perform magnetic particle examination prior to shot peening (to provide a beneficial compressive layer) and prior to applying protective finishes such as priming, painting, plating, or other coatings.  Examination is required prior to all non-electroplated coatings.  Electroplated surfaces with a final plating thickness of between 0.0008 inches and 0.0050 inches shall be examined both before and after electroplating, or grinding, or both, of electroplated surfaces.  Electroplated surfaces with a final plating thickness of 0.0050 inches or greater shall be examined before electroplating.

ASTM E1417 Standard Practice for Liquid Penetrant Testing

Examination Sequence – Final penetrant examination shall be performed after completion of all operations that could cause surface-connected discontinuities or operations that could expose discontinuities not previously open to the surface.  Such operations include, but are not limited to, grinding, welding, straightening, machining, and heat treating.

Final penetrant examination may be performed prior to treatments that can smear the surface but not by themselves cause surface discontinuities.  Such treatments include, but are not limited to, vapor blasting, deburring, sanding, buffing, sandblasting, lapping, and peening.  Performance of final penetrant examination after such surface treatments requires that etching be performed unless otherwise agreed on between the cognizant engineering organization and the inspection facility.

All coatings and other surface conditions, such as paint, plating, corrosion, etc. shall be removed from the area to be examined prior to penetrant examination.  The penetrant examination shall precede any surface finish, such as anodize, except for in-service parts that may be examined without removing anodize.