1. General requirements
(1) When the pipes of the fire hydrant water supply system adopt hot-dip galvanized steel pipes with inner and outer walls, welding should not be used. When the system pipeline adopts a non-corrosion inner wall, it can be welded, but the welding of the pipeline should meet the relevant requirements. The pipes of the automatic sprinkler system (referring to after the alarm valve) cannot be welded but should be connected by threaded, grooved pipe joints or flanges.
(2) Galvanized steel pipes with a pipe diameter > 100mm in the fire hydrant water supply system shall be flanged or grooved. The automatic sprinkler system pipe diameter > 100mm does not specify that the threaded connection cannot be used. It is only required that the pipe section with a pipe diameter ≥ 100mm should be equipped with a flange connection or a groove connection point at a certain distance.
(3) For fire hydrant water supply systems and automatic sprinkler system pipes, it is recommended to use threaded flanges when flange connections are used, and secondary galvanizing should be performed when welded flanges are used.
(4) When the diameter of any pipe section needs to be changed, standard reducing pipe joints and fittings should be used.
(5) For the connection method and related technical requirements of fire-fighting pipelines, please refer to the relevant regulations in “Technical Measures for Design of Civil Construction Engineering – Water Supply and Drainage”.
2. Groove (clamp) connection
(1) Grooved connectors (pipe joints) and steel pipe groove depths shall comply with the provisions of “Grooved Pipe Joints” (CJJ/T156-2001). The working pressure of grooved pipe joints with a nominal diameter DN≤250mm is 2.5MPa, and the working pressure of grooved pipe joints with a nominal diameter DN≥300mm is 1.6MPa.
(2) Flexible joints should be used in places with vibration and buried pipelines, and steel joints should be used in other places. When steel joints are used, a flexible joint should be installed every 4 to 5 steel joints.
3. Screw connection
(1) In the system, the inner and outer wall hot-dip galvanized steel pipes or inner and outer wall hot-dip galvanized seamless steel pipes with pipe diameters < DN100 can be threaded. When the system uses hot-dip galvanized steel pipes with inner and outer walls, the pipe fittings can use forged cast iron threaded pipe fittings (GB3287~3289); when the system uses hot-dip galvanized seamless steel pipes with inner and outer walls, the pipe fittings can use forged steel threaded pipe fittings (GB/T14626 ).
(2) If the wall thickness of the steel pipe is less than δ<Sch30 (DN≥200mm) or the wall thickness is less than δ<Sch40 (DN<200mm), threaded connectors shall not be used for the connection.
(3) When the pipe adopts 55° tapered pipe thread (Rc or R), the threaded joint can be sealed with PTFE tape; when the pipe adopts 60° tapered pipe thread (NPT), it is advisable to use sealant as the seal of the threaded joint; The sealing tape shall be applied on the male thread.
(4) Threaded joints shall not be used for pipes with a pipe diameter > DN50, and single reducing joints shall be used at pipe diameter reduction.
4. Welding or flange joints
(1) Flange types can be divided into flat welding flange, bimetal welding, butt welding flange, and threaded flange according to the connection form. Bimetal welded steel pipe is a new type of pipe, and the flange selection must comply with steel pipe flanges (GB9112-9131), steel butt-welded seamless pipe fittings (GB/T12459), and pipe flanges covered with PTFE Gasket (GB/T13404) standard.
(2) If the hot-dip galvanized steel pipe is connected by a flange, a threaded flange should be used. When the system pipeline adopts a non-corrosion inner wall pipeline, it can be connected by welding. Pipeline welding shall comply with the “Code for Construction and Acceptance of Field Equipment and Industrial Pipeline Welding Engineering”.
Post time: Jun-05-2023