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If you discover after the facing process that the butts are still not level,
start over, insert the facing tool and repeat the process. When facing
is properly done, pipe alignment has to be checked.
4.3.2 Checking Pipe Alignment and Determining Drag Pressure
When the pipes are properly faced, close in the movable carriage
completely to check whether a potential vertical and horizontal pipe
misalignment is within the tolerance allowed by the applicable welding
standard. If pipe alignment is in order, the welding proper can start.
If the misalignment is outside tolerance, the pipes must be readjusted
in the clamps and, if needed, facing has to be repeated.
When pipe alignment is appropriate, move the carriage apart using the
carriage mover lever; make sure the movable carriage is as far apart
as possible before continuing. Turn the maximum pressure regulator
counter-clockwise as far as it will go to have zero pressure in the hy-
draulic circuit. Then set the carriage mover lever to its close-in posi-
tion while simultaneously turning the maximum pressure regulator
gradually clockwise. Watch the pressure gauge closely to observe at
which pressure level the carriage is "dragged" to start moving. Take
note of this value, preferably on paper, as the drag pressure P
welding operation.
The exact drag pressure depends on various conditions (pipe
size and material, position/altitude of the machine, etc.) and
has to be determined for every welding individually. The
Important
value P
is needed to compute the bead build-up, the heat-
t
ing, and the joining pressures needed for jointing (stages t
t
, and t
in the welding diagram respectively).
2
5
4.3.3 Bead Build-up Stage
Use the welding value tables in the Appendix to look up the joining
pressure (maximum pressure to be applied during bead build-up and
joining) appropriate for your situation. Then set the maximum pressure
regulator to joining pressure plus drag pressure (see Sect. 4.3.2) while
observing the actual pressure shown on the gauge, and move apart
the carriage of the machine. Using the welding value tables, check
that the heating element (heating plate) has the correct temperature
and insert it between the butts, move the carriage in on the heating
plate and press the pipe butts to it at a pressure of P
build-up duration given in the welding value tables in the Appendix
(t
in the diagram above) until the weld bead has properly formed.
1
4.3.4 Heating Stage
After the bead build-up stage (t
pressure must be decreased to below or equal to the level of P
The decreased pressure will then be applied for the entire duration of
the heating stage (t
in the diagram), in which the pipe butts continue
2
to soak heat from the plate. Use the welding value tables in the Ap-
pendix to determine the heat-soaking time (t
pressure (P
+ P
) applicable to your welding situation. To reduce the
2
t
pressure applied to the pipe, use the pressure release valve and observe
the pressure level on the gauge.
Full contact has to be continuously established between the
heating plate and the bead, even with lower pressure. While
heating, if contact between them is lost somewhere along
Important
the circumference, welding has to be aborted and repeated.
12
EN
+ P
1
in the diagram) was completed, the
1
) and the heat-soaking
2
Manual Hydr. 250 User's Manual
for this
t
,
1
for the bead
t
+ P
.
2
t
O . M . I . S . A . S r l
Via Verga 9/11
20845 Sovico (MB), Italy
Version April 2020
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