What are the specifications for fire-fighting steel pipe construction

1. General Requirements for Fire-fighting Steel Pipes

(1) When using hot-dip galvanized fire-fighting steel pipes with inner and outer walls for fire hydrant water supply systems, welding should not be used. When using non-corrosion-resistant steel pipes with inner walls, welding connections are permissible, but welding of fire-fighting steel pipes must meet relevant requirements. For automatic sprinkler systems (after the alarm valve), fire-fighting steel pipes cannot be welded; threaded, grooved pipe joints, or flange connections should be used.

(2) For galvanized fire-fighting steel pipes with a diameter > 100mm in fire hydrant water supply systems, flange or grooved connections should be used. For automatic sprinkler systems with a diameter > 100mm, threaded connections are not explicitly prohibited; only flange or grooved connection points are required at certain intervals on pipe sections with a diameter ≥ 100mm.

(3) When using flange connections between fire hydrant water supply systems and automatic sprinkler systems, threaded flanges are recommended; when using welded flanges, secondary galvanizing is required.

(4) When the diameter of any section of fire-fighting steel pipe needs to be changed, standard reducing fittings and pipe joints should be used.

(5) For relevant connection methods and technical requirements of fire-fighting steel pipes, please refer to the relevant provisions in "National Civil Building Engineering Design Technical Measures - Water Supply and Drainage".

2. Grooved (Clamped) Connection of Fire-fighting Steel Pipes

(1) The groove depth of grooved connectors (pipe joints) and fire-fighting steel pipes should 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 for buried pipelines. Rigid joints are preferred in other places. When using rigid joints, a flexible joint should be installed every 4 to 5 rigid joints.

3. Threaded Connections of Firefighting Steel Pipes

(1) Threaded connections can be used for both internally and externally hot-dip galvanized firefighting steel pipes with a diameter <DN100 or for seamless internally and externally hot-dip galvanized firefighting steel pipes in the system. When the system uses internally and externally hot-dip galvanized firefighting steel pipes, forged cast iron threaded fittings (GB3287~3289) can be used; when the system uses internally and externally hot-dip galvanized seamless firefighting steel pipes, forged steel threaded fittings (GB/T14626) can be used.

(2) Threaded connections are not permitted for firefighting steel pipes with a wall thickness less than δ<Sch30 (DN≥200mm) or less than δ<Sch40 (DN<200mm).

(3) When the pipe uses a 55° tapered pipe thread (Rc or R), the threaded joint can be sealed with PTFE tape; when the pipe uses a 60° tapered pipe thread (NPT), sealant should be used as the sealant for the threaded joint; the sealant should be applied to the male thread. (4) Pipes with a diameter > DN50 shall not use threaded unions. Single-piece reducers shall be used at pipe diameter changes.

4. Welding or Flange Joints for Firefighting Steel Pipes

(1) Flange types can be classified according to connection method: flat-welded flanges, bimetallic welded flanges, butt-welded flanges, and threaded flanges. Bimetallic welded firefighting steel pipes are a new type of steel pipe. Flange selection must comply with the standards for steel pipe flanges (GB9112～9131), steel butt-welded seamless pipe fittings (GB/T12459), and PTFE-coated gaskets for pipe flanges (GB/T13404).

(2) If hot-dip galvanized firefighting steel pipes are connected by flanges, threaded flanges should be selected. When the system pipeline uses non-corrosion-resistant steel pipes on the inner wall, welding connections are permitted. Pipeline welding shall comply with the "Code for Construction and Acceptance of Welding Engineering for On-site Equipment and Industrial Pipelines".