[ Casting ]
[ Casting ]
Radiograph film interpretation by a Level III Radiographer . Photo : InspecTech Corp ., Milwaukee , WI .
of a casting . The appearance of the general condition is the first thing to look at . Does the casting have visual defects and if so , what size are they ? Do they meet the general criteria needed that are called out on the castings VT acceptance criteria ? Visual testing is often performed using only one ’ s eyes . Magnifiers , bore scopes , and mirrors all can assist . Where high-specification work is being inspected , the report form and the endorsements contained in it are key . One of the most common standards to perform visual testing on sand castings is SCRATA comparator plates . This is a series of photographic plates with some acceptable and some unacceptable images . It is a simple inspection practice employing ASTM A802 . This standard has four quality levels to work within . Each of these levels works with a set of tactile plates with different defect classifications and the severity of those defects . Investment castings have tighter requirements to comply with , such as ASTM A997 with many quality levels .
Magnetic Particle Testing ( MT ): surface technique and slightly sub-surface technique Magnetic particle testing is very commonly applied to high-specification projects . It is an extremely sensitive method of NDT which can be done both wet and dry . MPT can only be performed on ferromagnetic materials . It shows the location of linear defects very well .
Rounded defects do not show up as easily due to how the magnetic field travels past the indications . A side benefit of MT is that if there are slightly sub-surface defects , they will show up during the examination .
Liquid Penetrant Testing ( PT ): surface technique The flexibility of liquid penetrant testing makes it a versatile technique which can be applied in the lab or in the field easily . It is a simple NDT method but very powerful . It can be performed as a
“ Contract review , inspection , and material testing are crucial to ensure all criteria are met .”
water-washable format or an extremely sensitive solvent method . There is a fluorescent technique that is also very sensitive that is inspected in the dark with a black light . Liquid penetrant is generally used for testing on nonmagnetic materials . A word of caution when processing high alloy castings with PT : with nickel-based alloys specifically , grain boundary effects and false indications can be present . When in the presence of inexperienced source inspection personnel , these issues might be determined to be rejectable . Also , broad areas of pigmentation where there is a haze of penetrant that may not have been completely washed off require that the process be cleaned and repeated .
Radiographic Testing ( RT ): volumetric technique Radiographic testing is a wellaccepted method . It directs source radiation through the casting of interest and images are exposed on the film . The film has many quality indicators ( IQI ’ s ) to ensure that the x-ray films meet all the appropriate specifications . Radiography has numerous different standards made of reference radiographs with many different defects and conditions highlighted for acceptance . Most of these standards have levels of acceptance that are used to depict porosity such as shrinkage categories , tears and cracks , and other anomalies . Reference radiographs which are put out by many agencies such as ASTM and EN / ISO offer at times subjectivity due to many of the defects that are exposed .
Ultrasonic Evaluation ( UT ): volumetric technique Being a volumetric method , UT offers a strong and accurate technique to see defects and items of interest within the casting . There are many engineering firms and OEMs that specify UT over RT as they feel it is more accurate
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