Usually casting defects of ductile iron includes macro-defects such as sand inclusion, air holes, shrinkage or shrinkage cavity, sand inclusion and micro-defects such as unqualified nodularity rate and extremely large grain size, among others. There are three inspection methods normally followed in ductile iron casting: visual inspection, ultrasonic test, and magnetic powder test.

Visual Inspection:
Visual inspection is the heaviest of works: they require lots of grinding works. Generally, visual inspection is expected to meet the below-mentioned requirements:

• No welding treatment, no cracks, no slag inclusion or no sand.
• No air holes or sand holes. There are different allowable amounts and sizes for the air and sand holes which you can find online. Various casting may demand different requirements:
• No mismatch defects or cold flake
• No impression or scratch due to machining

You can easily identify between sand holes and air holes during visual inspection. Air holes usually contain inside surfaces that are smooth and have regular shapes. Sand holes, whereas, have irregular shapes, sand residues and dirt inside. When it comes to air holes, as they’re shallow, their sizes could be measured and checked whether they’re allowable by the inspector. Except for the sand residues, most of them will deepen the damage caused to the castings; therefore, they must be repaired or grinded before acceptance.

Further, the sandblasting is to be checked. In the case of inadequate sandblasting, there will be rough surface quality or it’ll even leave the oxide skin. This is fixed by sandblasting again or be grinded another time.

Magnetic Particle (Powder) Inspection:
This is a type of NDT testing. The testing most recommended for ductile iron castings is the florescent magnetic particle testing. Both the dry magnetic particle as well as water base magnetic flaw detection ink is right for inspection to SG iron. As the surface smoothness can affect inspection results largely, you need to grind the surfaces for the improvement of the inspection sensitivity. Usually, the casting head areas easily contain defects or flaws.

Ultrasonic Testing:
This testing method can inspect not an only sand hole and air holes, but also inspect the cracks, slag inclusion, and various material defects. However, if you compare this with the forged, cast steel or welding parts, the ultrasonic testing to SG iron castings is quite difficult as the result requires skillful and meticulous identification. The reason is ductile iron contains more complex structures on the inside. Some structures may result in faulty judgments, and furthermore, the surface quality can affect the accuracy levels of inspection results.