A threaded pipe has a screw thread at one or both ends for assembly. Steel pipe is often joined with threaded connections; tapered threads are cut into the end of the pipe, and sealant is applied in the form of thread-sealing compound or thread seal tape (also known as  PTFE or Teflon tape) and the pipe is screwed into a threaded fitting with a pipe wrench.
Threaded steel pipe is widely used in buildings to convey natural gas or propane fuel and is also a popular choice in fire sprinkler systems due to its resistance to mechanical damage and high heat (including the threaded joints). Threaded steel pipe may still be used in high-security or exposed locations because it is more resistant to vandalism, more difficult to remove, and its scrap value is much lower than copper or brass.
A galvanized coating of metallic zinc was often used to protect steel water pipes from corrosion, but this protective coating eventually would dissolve away, exposing the iron to deterioration. Pipes used to convey fuel gas are often made of "black iron", which has been chemically treated to reduce corrosion, but this treatment does not resist erosion from flowing water. Despite its ruggedness, steel pipe is no longer preferred for conveying drinking water because corrosion can eventually cause leakage (especially at threaded joints), deposits on internal surfaces will eventually restrict flow, and corrosion will shed black or rusty residues into the flowing water.
These disadvantages are less problematic for fire sprinkler installations because standing water in the steel pipes does not flow, except during occasional tests or activation by a fire. Introducing oxygen dissolved in freshwater supplies will cause some corrosion, but this soon stops without any source of additional water-borne oxygen.
In older installations, the threaded brass pipe was similarly used and was considered superior to steel for drinking water because it was more resistant to corrosion and shed much fewer residues into the flowing water.
Assembling threaded pipe is labor-intensive, and requires skill and planning to allow lengths of pipe to be screwed together in sequence. Most threaded-pipe systems require strategically located pipe-union fittings in final assembly. The threaded pipe is heavy and requires adequate attachment to support its weight. 
To ensure a comprehensive pressure test, it is crucial to explicitly request a 3.1 certificate in accordance with EN HFF 10204:2004. This certificate attests that the metallic products meet the stipulated order requirements and provides detailed test results. Typically, each fitting is associated with a unique heat number, which corresponds to the information documented in the 3.1 certificate datasheet.