LOCAL HEAD LOSS IN PLASTIC PIPELINE JOINT WELDED BY ...

J. Melichar, J. Háková, J. Veselský, L. Michlík
Fig. 3. Test section of the test loop, location of pressure taps and pressure-difference sensors; S – pipe jointing point, 1, 2, 3 – pressure
taps.
Obr. 3. Experimentální úsek potrubní trasy, umístění odběrů tlaků a snímačů tlakové diference; S – spoj potrubí, 1, 2, 3 – odběry
statického tlaku.
The horizontal test section of the test loop is
composed of the proper metering pipe length (pipeline
joint between pressure taps 2 and 3) with sufficient
straight pipeline length before (l2S ≈ 5.1d) and
behind the jointing point (lS3 ≈ 10.13d), where the
influence of jointing point on flow pattern is anticipated.
In front of this measuring section there is a
straight pipeline with the corresponding length (l12
= l2S + lS3 = l23 – b = 15.23d). The inner projection
of the butt weld with length b ≈ 0.08d in the pipeline
joint affects the flow in particular behind the
jointing point, where the head loss occurs at relatively
long pipeline length. The losses in a pipeline
before and behind the butt weld or more precisely
the lengths, which we can assume to have significant
influence on flow pattern, depend on the type
of element, its geometric parameters, pipeline wall
roughness and the Reynolds number value. Skalička
(1985) showed that the flow pattern could be sometimes
affected on the distance of 50d behind the
element projection that evokes the head loss. However,
for location of static pressure taps in relation
to measured element there are no any universal
recommendations. With reference to the butt weld
302
geometry and used pipeline material (βPP-H is nontransparent)
the above-mentioned distances between
static pressure taps and examined jointing
point were used. Static pressure taps at a pipeline
cross-section (metering locations) in the experimental
pipeline were made of four pipeline side inlets
that were evenly placed. Fig. 4 shows the detailed
arrangement.
The static pressure differences, ∆p12, between the
cross-section 1 and 2 and ∆p23 between the crosssection
2 and 3 were measured with the use of calibrated
differential pressure sensors with range 0 –
–16 kPa/4 – 20 mA. The estimated accuracy of
pressure difference measurements is up to 0.25 % of
a measuring range. The flow rate, Q, was measured
using magnetic flow meter of type MQI 99
SMART. The accuracy 0.5 % of measured flow rate
was guaranteed within the range of 10 to 100 %
of Qmax. The mercury thermometer was used to
measure the water temperature. The analogue output
signals from the magnetic flow meter and the
differential manometers were compiled by A/D
converter UDAQ – 1208 and transmitted and stored
into PC using program for UDAQ – 1208 proces-