All castings used are investment castings and only for large size UNP uses sand castings. Investment castings are used to obtain homogeneous and intact lining quality with uniform lining thickness which provides UNP valve a reliable lining quality and long lasting performance. UNP through its stringent design considerations has taken both the aspects of corrosion resistance and mechanical strength. Considering high torques in case of butterly and plug valves UNP decided to use ASTM A890 GR. 4A(CD3MN) duplex material to obtain high MAST (Maximum Allowable Shear Torque) values ensuring intactness of plug and disc shafts even at higher operational torques. For other valves UNP uses trim inserts at higher grade of metal as ASTM A351 GR.CF8.