Page 203 - Pipeline Pigging Technology

Pipeline Pigging Technology

NKK REPORTED INVESTIGATED RESULTS

Metal Loss Number Wall Number Actual Number Percent
%of of Loss Pound Wall Loss Found
Plpewall Locations Found Measured

>40% >40% 4 >40% 1 25
20-40% 1 25
10-20% 1 25
<10% 1 25
20-40% 120 20-40% 81 >40% 3 4
20-40% 47 58
10-20% 28 35
<10% 2 2
No Data* 1 1
10-20% 289 10-20% 195 >40% 0 0
20-40% 24 12
10-20% 1 14 58
<10% 46 24
No Data* 1 1 6
TOTALS 413 280

* These locations were field Inspected prior to the receipt of the pig data. Therefore, a
measurement was not possible for each discrete point indicated by the pig contractor.

Table 3. 1989 NKK data.

is sand blasted to near-white condition, after which the pipe wall is outlined
with a grid and measurements of the pipe wall thickness is taken with
ultrasonic hand-held detectors and pit gauges.
Upon completion of all measurements and inspection, the pipe is recoated
with Carboline 3 76 epoxy phenolic, and retaped with Raychem HTLP-80\
the cathodic protection is reconnected and the pipeline is reburied. Full-
encirclement sleeves are installed where a repair is required.
The data collected from these excavations provides for an opportunity to
make comparisons with the predicted pig reports. Alyeska prioritizes excava-
tions of the pipeline where pipe-wall thinning and operating pressure provide
the least safety margin permitted under the Department of Transportation
Code of Federal Regulations, Part 195.
Most of the reported pig anomalies show minimal wall thinning (less than
20%) which would not require pipeline excavation for some time. These

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