Page 295 - Pipeline Pigging Technology

Pipeline Pigging Technology

Fig. 5 is a schematic of the tool as it passes a dent. In most cases, a dent is
recorded on one or two lead sensors and one or two trail sensors. Fig.5-A
shows an actual dent as recorded by the tool; the numbers at the bottom of
the chart give the dent in inches of penetration by feet of longitudinal area
covered; in this case, O.Tin penetration by 3ft. The second set of figures that
are in parenthesis give the associated ovality in inches of penetration at the
maximum deflection over the number of feet affected longitudinally; the
ovality here is 1.4in by 25ft.
Fig.6 is a schematic of how the tool reacts to a buckle. An actual case study
of a pipeline buckle is included later in this paper. Fig.6-A shows how the tool
recorded a buckle. The number at the bottom of this log indicates the buckle
feature has a maximum penetration of 2.1 in over 1ft. Associated ovality is
3.0in over 11ft. This particular defect was in a 40-in crude oil pipeline, and has
now been removed.
Fig.7 is a schematic of how the tool reacts to a wrinkle. As with the buckle,
a case study is included in a later part of this paper.
Fig.8 shows how the Vetco log detects a bulge. An actual bulge is displayed
on the log in Fig.8-A. A dent with associated bulge is the first stage of pipeline
buckling. If the area depicted is being affected by dynamic forces, then a
buckle will probably form at this location.
Figs 9 and 9-A shows pipeline ovality from a side view and end view. Ovality
generally covers a much larger area than is depicted here, but these drawings
are designed to show tool function. As shown in previous log examples,
nearly all pipeline physical changes are accompanied by some form and
degree of ovality. Fig.9-B shows two areas of ovality that occur in the same
area.

CASE STUDY 1

The first defect we would like to look at is the buckle in a 40-in pipeline.
Buckles are usually the most restrictive mechanical anomaly, and under API
should be removed. Fig. 10 shows the D/S information on the buckle as being
1.8in over 3ft; the associated ovality is 2.5in over 15ft. It is interesting to note
that in this log example, the slope channel has deviated a maximum of 10ft
starting 25ft upstream of the buckle. Also, a bulge can be seen that is a
common factor in buckling. After the buckle was uncovered by the operator
for repair, it was found that the tool-recorded data matched the actual defect
almost exactly. In this case, the pipeline operator used the D/S data and
reports to make several necessary repairs.

276