Threaded (PT) flange is a non-welded flange that the inner bore is processed into thread, then threaded with the relevant-sized tapered pipe thread. Compared to the welding flange, threaded flange is characterized by the easy installation and maintenance. Alloy steel have sufficient strength, but not easy to weld, so alloy steel flanges could be threaded type. However, to avoid leakage, it is advisable not to use threaded flanges in the event of a sudden temperature change or a temperature above 260 ° C or below -45 ° C.