Page 453 - Pipeline Pigging Technology

Pipeline Pigging Technology

IDENTIFYING PIPELINE INTEGRITY PROJECTS

The economic risk assessment essentially provides a ranking of pipeline
segments according to the potential effect of a failure on our business: the first
step in reaching our primary goal. The next step is to develop pipeline
integrity projects that will reduce the economic risk by lowering the probabil-
ity of failures caused by deterioration of structural integrity. Some of the
guidelines for approval of projects in the programme are:

1. Projects to prevent outages on pipelines with a known integrity
problem that would otherwise cause recurring failures must be
included in the programme.
2. Priority for action is indicated by first addressing unacceptable safety
risks and then by the ranking of economic risk.
3. Cost of an individual project ^ 50% of the estimated outage conse-
quences.
4. Annual programme cost should be approximately 1-2% of operating
and maintenance costs.

Fig.9 provides a summary of the projects either completed in, or planned
for, the years 1988 to 1990 inclusive. It is noteworthy that 55% of the
programme expenditures have been on projects to assess the condition of
pipelines anticipated to have developing structural integrity problems but
with no history of failures or observed damage. 72% of the total expenditure
was aimed at reducing the risks associated with external corrosion.

External corrosion projects

At the present time, external corrosion is the largest component (approxi-
mately 80%) of the estimated outage probability for pipelines with the highest
estimated economic risk. The two pipelines with known external corrosion
(Table 2) were, or will be, re-inspected using an "advanced" in-line inspection
(ILI) system. The approach of using in-line inspection and analysis in prefer-
ence to hydrostatic testing, as described in an earlier paper[5], has proven
satisfactory and is continuing.
The three pipelines with anticipated problems were identified solely on
the basis of the estimated risk. "Conventional" ILI systems were used on two
of the lines and an "advance" ILI system was used on the other line. External
corrosion of varying severity and extent was found on each of these pipelines

434