36” above ground pipeline repair
Overview
A 36” pipeline header system had significant internal
erosion/corrosion at the 6’oclock position with a minimum
remaining wall thickness of 3mm. It was estimated that the
annual erosion/corrosion rate was determined as 3mm per
year. The length of pipeline requiring repair was 150
meters which contained 15 saddle supports, 4 of which
were welded. The client required a qualification test of the
proposed repair solution, on site, prior to installation of the
actual repair.
Pipeline Specification:
Design Pressure : 29 bar
Design Temperature : 820C
Repair lifetime: 4 years
Installation Procedure
A detailed installation procedure was developed for
application of this repair solution
Qualification Test
The Client required a qualification test of the proposed
repair solution prior to installation of the actual repair. The
qualification test replicated the geometry and the worst
case defect conditions of the actual pipeline i.e. a 35 mm
wide through wall axial slot located at the 6 o’clock
position. The axial length of the slot was that of the pipe
test spool. The acceptance criterion for the qualification
test was that the repair solution had to survive a test
pressure of 35 bar. This qualification test would replicate a
‘worst case scenario’ of the actual repair.
Proposed Solution
Repair Design
The repair design was performed according to ISO/TS
24817. Due to pipeline diameter and severity of the
erosion/corrosion the repair design was split into two
calculations. The first calculation was to ensure the leak
sealing capability of the repair. This part of the repair
solution involved 14 layers of Technowrap 2KTM in the form
of a patch repair located between the 5 o’clock to 7 o’clock
position. The second calculation was to ensure that the
strength of the damaged pipeline was returned to its
original value. This part of the solution involved 4 layers of
Technowrap 2KTM in the form of a fully circumferential wrap
on top of the patch encapsulating the pipeline.
Fig 1: Test spool prior to repair application
The installation of the repair for the qualification test
followed the detailed installation procedure. The first step
was to prepare the outer surface of the test spool by grit
blasting
Fig 3: Application of patch layer
Fig 2: Photograph of test spool after grit blasting and prior to
repair application
The test spool was wrapped by Walker Technical
Supervisors under the scrutiny of the client as shown in the
following photographs.
Fig 4: Fully circumferential wrap installed
The repair was then left to cure until the quality checks had
determined that the test piece could be pressure tested.
The hydrotest was performed with the pressure raised in 5
bar increments until the composite repair failed at 37 bar.
Quality checks
Visual Inspection remarks
(e.g. Bare fibres, voids,
smoothed ends etc)
None of note
Repair thickness (mm)
15.66 minimum
Repair axial extent (total)
(m)
150
Cure assessment (Barcol
hardness of DSC T
measurement
55
Table 1: Quality check results
Fig 6: test piece failing at 37 bar
This failure pressure met the qualification test acceptance
criterion of 35 bar. On successful completion of the
hydrotest the client approved the repair of 150 metres of
the 36 inch pipeline.
Proposed Solution
Fig 5: Inspection and quality check of wrap
Installation procedure of the composite repair , as
demonstrated on the test spool, was approved by the client
and produced for site installation . To compliment the repair
application procedure, a detailed lifting plan of the pipeline
over the supports was created to ensure complete
encapsulation of the pipeline. Additional requirements of
applying the repair on all areas of the pipework included
where the pipe work was resting on the pipe supports.
The work was planned to be completed in 50 days. The
actual time to complete the 150 meters was in fact 38 days.
This was due to the effectiveness of the installation
methodology and the quality and competency of the Walker
Technical Supervisors on the job.
A pictorial sequence of the repair application follows
Fig 8: Pipeline repair application
Fig 7: Pipeline surface preparation
Fig 9: Pipework sitting on one of the supports
Fig 10: Lowering of repaired pipe onto supports
Fig 12: The completed repair
Challenges
Walker Technical overcame challenges associated with the
project co-ordination and planning associated with a job of
this scale. Perhaps the greatest challenge being lifting the
pipeline from the various supports so that the repair could
be applied continuously along the required 150 meter
length.
Fig 11: Repair application of lifted pipeline