Internal soundness means the steel has no cracks, pipes, shrinakge cavity, or any other defects which may open up during use and cause failure. This is assessed through NDT testing of material.

Dear Dr. Vinod Kumar,

Thank you very much for your answer.

For having more information please check this paper : (( Ultrasonic testing for the internal quality evaluation of cast steel products )), also you can use ASTM E1245

Dear Mohammad, thank you very much for your suggestions.