Inspection Techniques – Advantages and Disadvantages

The advantages and disadvantages of each type of inspection are described in table (1.1 Visual Inspection), (1.2 Dye Penetrant Inspection), (1.3 Magnetic Particle Inspection), (1.4 Ultrasonic Inspection), (1.5 Eddy Current Inspection), (1.6 Radiographic X-Ray Inspection). These should be studied by personnel who are about to make the inspection on an area that is not covered in a specific instruction (manufacturer’s manual, etc.). The information given in this table is for information only and not as a guide to be used on the daily inspection activities. Always the manufacturer technical manuals will be followed.

Inspection Illustrations

Usually inspection illustrations are given by the Original Equipment Manufacturer (OEM) in the engine manuals and other publications to cover each part of the engine that needs inspection. Areas of inspected parts or assemblies are indexed on the Illustrated Parts Catalog, or other illustrated manuals. Each illustration shown the location of the area to be inspected, type of inspection, the method of performing the inspection such as type of dye penetrant to be used, etc. The technical manuals also indicate the preparation of the part as cleaning, paint removal, etc., before the part is to be inspected. When a particular type of inspection has been completed, reference is made to the next step of inspection. For example, if an FPI has been performed, it may be necessary to confirm any suspected or visible defect by visual inspection.

Radiographic Inspection (X-RAY)

Is used to show internal and external structural details of all types of parts and materials. It is used for inspection of structures inaccessible or unsatisfactory for the application of other NDT methods. It is accomplished by passing the X-Ray or Gamma-Ray through the part being tested to expose a radiographic film. The processed film shows the structural details of the part. Interpretation of the radiographic film will indicate defects or damage.

Eddy Current Inspection

Is a method suitable for the inspection of surface or near surface defects of most metals and to separate metals and alloys and their heat treat condition. It can be applied to parts or assemblies where the suspected detected area is accessible to contact by the eddy current probe. The inspection is performed by inducting eddy currents into a part and electronically observing variations in the induced field. The character of observed field change is interpreted to determine the nature of defect condition.

Ultrasonic Inspection

Is a method suitable for the inspection of surface or subsurface defects of most metals, ceramics, and plastics. The inspection is accomplished by beaming high frequency sound wave through the part and viewing the response pattern on an oscilloscope (cathode ray) tube. By examine the variations of a given response pattern, discontinuities, flaws, or boundary conditions are detected.

Magnetic Particle Inspection – MPI

Is used to indicate surface or near surface defects in ferro magnetic parts. This inspection is performed by inducting a magnetic field into the part and applying a dry powder or liquid suspension of iron oxide particles. Local magnetic poles are formed by defects so that may be seen and evaluated by color contrast under a “black light”.

Dye Penetrant Inspection – FPI

Is used to detect cracks and discontinuities open to the surface which can not be seen by visual inspection. Dye penetrant inspection can be used on most engine parts accessible for this application. The inspection is performed by applying a liquid which penetrates into surface defects. Excessive penetrant liquid is removed and suitable developers applied to draw the penetrant from the surface defects so that visual indications are obtained by color contrast of the penetrant under the influence of a “black light”.

Visual Inspection

Is the most common form of inspection and consists of examining the area with the eyes, and with the help of magnifying glass, borescope, light source, etc.

Type of Inspection

The type of inspection can be classified into two major categories: 1. The non-destructive inspection, and 2. The destructive inspection The most common types of non-destructive inspection in aircraft engine and industrial are: 1. Visual Inspection 2. Dye Penetrat Inspection - FPI 3. Magnetic Particle Inspection - MPI 4. Ultrasonic Inspection 5. Eddy Current Inspection 6. Radiographic Inspection ( X – Ray )

Inspector Attitudes

The good inspector is not the inspector that accepts everything or the inspector that rejects everything. The good inspector is the inspector who considers himself a real working member of the team. The good inspector is the inspector who has the skills and knowledge and confidence to assure that a product is acceptable to specifications. The good inspector is the inspector who has gained the confidence of the people he works with and those people know that when he rejects a part, the part is not acceptable and when he accepts a part the part is not reject. He is able to apply his skills and knowledge to the specifications and make sound judgements.