Hope you mean porosity in carbon steel and not pourisity because I don’t think any thing like that exist in carbon steel.
If you mean porosity in carbon steel, the following tests can be carried out to determine porosity in carbon steel.
(1) Ultrasonic Testing: a non destructive test that enables typical metal (Carbon steel) faults like cracks, blow holes and inclusions to be detected and located. It works through the same mechanism of echo sounding device in ships . Information revealed can be viewed on a CRT (cathode ray tube).
(2) Radiographic Techniques : examples of this techniques are X-ray and Gamma ray techniques.They can also be used in detecting and locating porosity in metals.
(3) Dye- penetrant testing: this test is suited only to the detection of various types of surface defects like grinding and fatigue cracks,porosity and lack of joint welds.