Page 204 - Pipeline Pigging Technology

Corrosion inspection of the Trans-Alaska pipeline

NKK REPORTED INVESTIGATED RESULTS

Metal Loss Number Wall Number Actual Number Percent
%of of Loss Found Wall Loss Found
Pipewall Locations Found Measured

>40% >40% 5 >40% 1 20
20-40% 2 40
10-20% 0 0
<10% 0 0
No Data* 2 40
20-40% 210 20-40% 109 >40% 2 2
20-40% 36 33
10-20% 21 19
<10% 2 2
No Data* 48 44
10-20% 686 10-20% 283 >40% 0 0
20-40% 20 7
10-20% 79 28
<10% 36 13
No Data* 148 52
TOTALS 901 397

* 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 4.1990 NKK data.

anomalies are monitored at each pig run for changes and are used for
comparison of pig repeatability and accuracy. Of the data collected from
actual field excavations, Tables 3 and 4 reflect the results compared to NKK
pig reported corrosion anomalies.
These results are preliminary, as the data is still being reviewed and
analyzed; however, some general conclusions on the corrosion status of the
Alyeska pipeline can be made.

CONCLUSIONS

1. All Alyeska pipeline corrosion is external and occurs in buried pipe.
2. Corrosion has been most prevalent in areas that tend to be wet.

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