Page 317 - Pipeline Pigging Technology

Pipeline Pigging Technology

overall length of 16-in tool: 2.45m maximum
weight: less than 200kg
maximum measuring speed: 4m/sec
pressure: 150bar
temperature: 5-60°C
measuring range: 300m (without data reduction)
travelling distance: 100km
wall thickness range: up to 40mm
accuracy of remaining wall
thickness measurement: ± 1 mm
corrosion detection: internal and external
circumferential coverage: 40%
axial measurement interval: 2.5mm

The tool is also capable of passing 3D 90° bends, full-bore T-joints and
valves; 10% symmetric and 15% asymmetric diameter reductions can also be
negotiated. TTie system has been designed to provide a field report of results
within 1 hour of retrieval of the tool.
In addition, the RPIT is bi-directional; propulsion disc design provides by-
pass of fluid if this is necessary in the unlikely event that the tool becomes
stuck.
The RPIT can be started by pressure, time, distance or bench-marker, or
any combination of these options. For a delayed start, it travels in a safe and
dormant, energy-saving mode to the section of interest in order either to
measure internal or external corrosion, or both simultaneously.
The on-board memory stores all the data collected. After retrieval of the
tool, a powerful portable desk-top computer is used to process the data;
Fig. 16 shows an example of the results obtained. In practice, colours are
applied to enhance and identify thickness ranges. Results can also be pre-
sented in numerical, statistical or graphic modes for further data analysis. The
16-in RPIT as shown in Fig. 17 has been extensively tested and validated[2] in
Shell's 16-in test loop.

5. RPIT field tests

The 16-in and 20-in RPIT have been used twice offshore[3]. The first
application was a wire-line field test: pending a field test of the 20-in tool, the
opportunity was given to test the 16-in RPIT in open J-tubes on the Dunlin
Alpha platform, located in the northern North Sea. New flowlines were to be
pulled through the J-tubes, which were installed several years ago. High forces
were anticipated on the J-tubes during the flowline pulling operation, and
therefore a thorough integrity check of the tubes was required.
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