I. Connecting Malleable Cast Iron Pipe Fittings
Features: Hard but more brittle than ductile iron, commonly used for threaded connections.
A.Connection Method:
Thread Sealing
B.Steps:
Wrap raw tape or apply sealant (such as pipe thread sealant) to the fitting threads.
Use a pipe wrench to tighten the fitting onto the external threads of the ductile iron pipe.
Applicable: Low-pressure pipelines (DN ≤ 100mm) (water, gas)
C.Key Points:
Avoid overtightening, which may cause cracking.
A flexible joint may be required for easy maintenance.
D.Flange Conversion
A flange is cast on one end of the malleable cast iron fitting and connected to the ductile iron pipe flange using bolts.
Application: Disassembly required for pump room instrument branches, etc.
II. Grooved Pipe Fittings (Clamp Connection)
Structure: Prefabricated grooves on both ends of the fitting, secured with rubber seals and clamps.
Connection Process:
Pipe End Grooving: Use a groover to press a standard groove into the end of the ductile iron pipe.
Seal Installation: Insert a C-shaped EPDM rubber ring into the pipe end.
Butt Fittings: Align the grooved fitting with the pipe.
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III. Welded Pipe Fitting Connections
A.Application Scenarios:
Special Operating Conditions (High Temperature and High Pressure)
Renovation and Repair of Flange-Unavailable Connections
B.Welding Process:
Groove Preparation: Mill a 30° V-groove on the pipe fitting and end
Preheating: Oxyacetylene flame heated to 250-300°C
C.Welding:
Welding Material: ENi-CI nickel-based electrode (AWS A5.15)
Interpass Temperature Control: ≤150°C
D.Post-Weld Treatment:
Asbestos Felt Wrap, Slow Cooling (Cooling Rate ≤50°C/h)
100% Radiographic Inspection
Risk Warning: The heat-affected zone (HAZ) can reach a hardness of HB350 and requires annealing to prevent brittle cracking
Ⅳ. Valve and Pipe Connections
A. Flange Valve
Direct Connection: The valve flange is bolted to the ductile iron pipe flange.
B. Threaded Valves
Connect via malleable cast iron male and female threaded fittings.
Note: Install a double union joint before the valve to facilitate maintenance.
C. Welded Valves
Use socket welding or butt welding for special operating conditions.
Remove valve trim before welding to prevent heat damage.
D. Grooved Valves
Commonly used in fire protection systems, use clamp connections similar to grooved fittings.
A support bracket must be installed downstream of the valve.
Learn more: China malleable cast iron pipe fittings; malleable iron pipe fittings.