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Butt Welding in Brief

HDPE and MDPE pipe and fittings are butt welded by selecting the appropriate temperature, pressure and time cycle, according to the type of the material, and wall thickness to be welded. The most common  temperature is:

210'C ±10'C

The above value is also dependant on wall thickness, therefore for accurate temperature set-up, we suggest reference to the following graphic:

Preparation of the machine
  1. Connect the plugs to the power supply
  2. Select the correct temperature on the heating mirror
  3. If required, fit the inserts of the diameter to be welded into the machine

 

Positioning pipes into the machine
  1. Open the pivoting clamps of the machine
  2. Position the pipes into the machine taking care to leave enough space for the insertion of the facing tool
  3. Check pipe alignment
  4. clean ends of pipe

 

Facing operation
  1. Open the moveable trolleys of the machine
  2. fit the facing tool between the two ends of pipe to be faced, by means of lowering the facing tool
  3. Start the facing tool engine
  4. Bring the pipe ends towards the facing tool by means of acting on the hydraulic control unit keeping a pressure a little higher than the inertial pressure
  5. When enough shavings from both sides will appear continuous and homogeneous the facing operation is completed
  6. Proceed to take away the pipes ends from the facing tool and switch off the facing tool engine
  7. Before carrying out further operation remove all the shavings from the pipes and the machine avoiding to dirty the faced pipes ends

 

Inertial pressure measurement
  1. Bring the pressure to zero, checking the pressure guage
  2. Achieve the inertial pressure (value of pressure needed in order to allow the trolleys to move) note the value of inertial pressure read on the pressure guage

 

Welding Cycle

The welding cycle is divided in 5 + 1 different phases

 

Phase
  1. Bead formation t1
  2. Heating up t2
  3. Change over t3
  4. Bringing up to pressure t4
  5. Cooling down under pressure t5
  6. Cooling down out of the machine t6

The above graphic shows all the phases:
t1 = Time requested for the bead formation with the specified wall thickness
t2 = Time requested for the continual heating
t3 = Time requested for the change over
t4 = Time requested for brining up to pressure
t5 = Time requested for cooling down
P2 = Pressure during the continual heating

P1 = Pressure during the bead formation and the cooling down, this value is the result of the following formula:

 
Pipe section (cm2) x Material thrust coefficient (Kg/cm2) = bar
Total machine cylinder section (cm2)

 

Bead formation t1
  1. Lowering the heating mirror by acting the selector taking care that the temperature of the surfaces is the one selected
  2. bring the pressure in order to have the bead formation as per attached table, this operation must be done with the true welding pressure value: (Inertial pressure + P1)
  3. Check the bead formation wall thickness according to the welding table

 

Heating up t2
  1. After bead formation bring the pressure to zero and proceed to the heating time at pressure P2

 

Change over t3
  1. Once the heating time has elapsed at pressure P2 open the trolleys and after removing the heating mirror close the trolleys and put in contact the two pipes

 

Bringing up to pressure t4
  1. Achieve the true welding pressure value: (Inertial pressure + P1) by checking the pressure guage. This operation must be done according to the time indicated in the welding tables

 

Cooling down t5
  1. Maintaining the true welding pressure value (Inertial pressure + P1) keep such situation for all the cooling time indicated into the welding table, taking care that the pressure will not decrease too much
  2. Once the cooling time has elapsed, bring the pressure to zero
  3. Take away the pipes welded and leave them for the time t6 indicated on the welding tables.

 

Weld Bead Inspection     Welding Fittings    

images and data courtesy of ITS

  
 
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