Page 220 - Pipeline Pigging Technology

Ethylene pipeline cleaning

encountered, attributable to the restrictive tees. A summary of the inspection
runs is presented in Fig.6.

Recommissioning

Pipeline recommissioning commenced on day 24. Pigging was complete
on 20th May, leaving 8 days for leak checking and maintenance work. On day
23, the pipeline pressure was increased to 2300kPa (330psi), and ethylene
vapour was introduced at 23,000kg/hr. Venting took place at BV10 (north
end) to maintain pressure in the pipeline. The vent stream was analyzed by
portable gas chromatograph to detect the ethylene/nitrogen interface. It took
28 hours for the interface to reach the north end of the pipeline. At this point,
the vent stream was flared until product-quality ethylene was detected. This
took an additional four hours. Flaring was then stopped and the line was
allowed to pressure-up to operating pressures. The pipeline was put back into
service on 12th June, 30 days after shutdown operations began.

PROJECT RESULTS

Pipeline capacity

Calculations from pressure-drop readings taken after the pipeline was put
back into service revealed that the pipeline capacity had been restored to
I60,000kg/hr (an increase of 26%). This was confirmed in August, when
pipeline flows reached 157,000kg/hr without maximum operating pressure
limits being exceeded. Fig.7 lists friction factor ratios before and after
cleaning.

Pipeline integrity

Results from the inspection revealed only five reportable defects (more
than 20% metal loss) along the entire 180-km (110-mile) pipeline. The
maximum depth reported was 34% metal loss. Novacorp performed an
engineering critical assessment on the data, and determined that no immedi-
ate repairs were required. AGEC will excavate, inspect and recoat these
defects over the next two years.

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