Page 348 - Pipeline Pigging Technology

Bi-directional ultrasonic pigging

been confirmed, as shown in photos 1 and 2. Figs 4-6 show the inspection
results using the internal, natural corrosion sample (shown in Photo 3, which
was 6mm deep, 41 Omm circumference and 20mm long) which was generated
on the girth weld.

Overview of inspection work

Inspection period: September, 1988.

Pigging operation: A launcher/receiver was temporarily set at the shore
end of the pipeline. On the PLEM, a tanker was moored and a flexible hose
connected to the tanker from the PLEM.
Initially, the pig was launched into the pipeline from the shore to the PLEM,
propelled by seawater injected from a brine pump installed on the shore; the
seawater was drained into the oil hold of the tanker. Upon arrival at the PLEM,
the pig was returned to the shore by means of a cargo pump mounted on the
tanker, and recovered in the launcher/receiver. The seawater was then
drained into a crude-oil tank on the shore.

Profile pig: A profile pig with the same outside diameter as that of the
inspection pig was provided with an aluminium fin in the equivalent location
of the ultrasonic transducer ring. After its passage through the pipeline, the
profile pig was examined to investigate any deformation of the fin and the
state of disc abrasion; it was confirmed that there was no obstruction to the
subsequent safe passage of the inspection pig. Photo 4 shows the bi-direc-
tional profile pig.

Ultrasonic inspection pig: Following confirmation by the profile pig that
there was no obstruction in the pipeline to the safe passage of the inspection
pig, the inspection pig was launched to examine the condition of the inside
wall of the pipeline. The travel speed during inspection averaged 0.24m/sec;
photo 5 shows the ultrasonic inspection pig.

Site review: Immediately following inspection by the ultrasonic pig, data
analysis was undertaken, firstly by analyzing the data from a calibration
section (comprising an artificially-corroded test pipe installed downstream of
the launcher/receiver), followed by validating the accuracy of the data
acquired from the pipeline under observation. Data analysis was conducted
and observed on site.
After detailed data analysis, a final report was delivered to the client
approximately one month after completion of the pig inspection.

329