The Connection Technology of Fire Pipeline

The main points of detailed connection technology of fire pipeline are as follows: 

1. General requirements 
a. If the pipe line for fire hydrant water supply system use hot-dip galvanized steel pipe, welding should not be adopted. If the lining of pipeline system is anti-corrosion, welding connection can be employed, but the pipe welding shall comply with relevant requirements. The pipeline of automatic sprinkler fire extinguisher system (after the alarm valve) cannot adopt welding, and thread, the groove pipe connection or flange connection should be adopted. 

b. If the galvanized steel pipe of the fire hydrant water supply system whose pipe diameter is greater than 100 mm, flange connection or groove connection should be adopted. If the pipe diameter of pipeline of automatic sprinkler system is greater than 100 mm, it is not yet explicitly express that cannot use threaded connections, just requiring that setting flange connections or groove connection point by a certain distance on the pipe whose diameter is greater than 100mm. 

c. If the pipeline of the fire hydrant water supply system and automatic sprinkler system needs use flange, threaded flange is recommended. When welding the flange, secondary galvanizing is advisable. 

d. When pipe diameter of any pipe section needs change, reducing pipe and pipe fittings that meet criteria should be used.Relative connection manner and technology can refer to relevant provisions of the National Civil Building Engineering Design Technical Measures - Water Supply and Drainage. 

2. Groove (clamp) connection
a. The groove fittings (pipe joint) and the steel tube groove depth should comply with the provision of Groove Pipe Joint (CJJ/T156-2001). The maximum working pressure groove tube joint with nominal diameter of DN 250 mm or less is 2.5 MPa. The maximum working pressure groove tube joint with DN nominal diameter of 300 mm or more is 1.6 MPa. 

b. Vibratory places and buried piping should use flexible joint, other places use rigid joint.  When using rigid joint, flexible joint should be set up in every 4 ~ 5 rigid joint. 

3. Threaded connection 
a. The hot-dip galvanized steel pipe or hot-dip galvanized seamless steel tube whose pipe diameter less than DN100 can adopt screw thread connection. When the system adopts both inside and outside wall hot dipped galvanized steel pipe, malleable cast iron threaded pipe fittings (GB3287 ~ 3289) can be used; When the system use internal and external wall hot dipped galvanized seamless steel pipe, forged steel threaded pipe fittings (GB/T14626) can be employed. 

b. If the wall thickness of steel tube is less than the delta < Sch30 (DN 200 mm or higher) or less than the delta < Sch40 (DN < 200 mm), shall not use screw fittings connection. 

c. When the pipeline adopts 55 °taper pipe threads (Rc or R), PTFE with seal screw threaded joint can be used ; When the pipe use 60 °taper pipe threads (NPT), it’s better to adopt  sealant as thread interface sealing; Sealing strip should be imposed on male screw. 

4. Welded or flanged joints 
a. The flange type according to the connection form can be divided into: flat welding flange, double metal welding, butt welding flange, threaded flange, etc. Double metal welded steel pipe is a new type of pipe; Flange choice must conform to the standards of steel pipe flange (GB9112 ~ 9131), steel seamless pipe fittings (GB/T12459), pipe butt welding flange with teflon coated gasket (GB/T13404). 

b. If hot-dip galvanized steel pipe connected by flange, threaded flange should be the choice. If the lining of system pipeline is not anti-corrosion, welding connection can be adopted. Pipe welding shall conform to the Site Equipment, Industrial Pipe Welding Engineering Construction and Acceptance Standard.