Custom offshore pipeline repair systems can reduce repair times and costs in Angola. An industry group studied how to adapt existing repair concepts for high-pressure pipelines in Angola's deep waters. They determined that creating a shared repair system for operators would lower costs compared to each operating their own. The system needs to handle a range of pipe sizes and depths up to 3,000 meters, and repair both single-walled and pipe-in-pipe pipelines using remote equipment. Insulation must be restored on repaired sections to prevent hydrates during repairs.

1. JUNE 2, 2014
WORLDWIDE GAS
PROCESSING
US PROCESSING UPDATE
MIDSTREAM
Custom offshore pipeline
repair systems save money
By Suzana Abílio, Stéphane Taxy, Xavier Michel

2. TECHNOLOGY
Based on presentation to Deep Offshore Technology Interna-
tional, Houston, Oct. 22-24, 2013.
TRANSPORTATION
Establishing and operating a custom emergency pipeline-
flowline repair system (PRS) for offshore deepwater
projects can reduce repair times enough to justify the
additional expense.
The Angola Deepwater Consortium (ADC) found that ex-
isting PRS concepts could be adapted with some qualifica-
tion to cope with high pressure and the region’s particular
fluid characteristics and that these concepts could be further
adapted to address pipe-in-pipe (PiP) repair.
The cost of a custom repair system covering 8- to 24-in.
OD pipe might not be effective for a single operator, but shar-
ing the system offers a much improved cost-benefit ratio.
Sonangol EP and DORIS Engineering in 2000 formed
ADC under the guidance of a joint industry project (JIP)
steering committee composed of representatives from BP
Angola, Cabinda Gulf Oil Co. Ltd. (CABGOC), ENI An-
gola, Esso Exploration Angola, Petrobras, and Total E&P
Angola. ADC in 2009 began conceptual studies to screen
and recommend appropriate technologies for an emergency
PRS dedicated to Angola.
The PRS project included three phases:
1. Phase 1 demonstrated that creating a PRS club would
reduce production downtime by having equipment ready for
mobilization in Angola.
2. Phase 2 further investigated the benefits PRS could
provide for Angola and in parallel defined the appropriate
technical solutions to repair single-coated pipes through
successive phases: conceptual, prefront-end engineering de-
sign (pre-FEED), and FEED.
Suzana Abílio
Stéphane Taxy
Xavier Michel
Angola Deepwater Consortium
Luanda
Custom offshore pipeline
repair systems save money
ANGOLA
Atlantic
Ocean
DEEPWATER BLOCKS, GAS EXPORT NETWORK
Soyo
Malongo
Block 31
Block 32
Block 33
Block 34
Block 14
Block 15
Block 16
Block 17
Block 18
Block 1
Block 2
Block 3
Block 4
Block 5
FIG. 1
PIPELINE, FLOWLINE TYPES*
72%
15%4%3%
4%2%
Bundles
Flexible
PiP
Rigid
Rigid DEH
Rigid with liner
*Current and planned.
FIG. 2
2

3. 3. The third phase began in April
2012, following the recommendations
of Phase 2 to complete a PRS FEED
document package, investigate PiP re-
pair feasibility, and reach an agreement
establishing a PRS club in Angola.
The PRS study covered uninsulated
(water and gas injection), wet insu-
lated, and pipe-in-pipe flowlines and
pipelines. This article focuses on pipe-
in-pipe repair feasibility via the diver-
less on-bottom spool repair method,
cutting the pipeline and installing a
spool using dedicated repair connectors.
Angola network
Since Angola’s first deepwater developments in the late
1990s, its pipeline network has grown to 2,618 km
(about 1,625 miles), with additional growth expected for
several years. Analysis of JIP-collected data yielded the
following details:
• Water depth, 20-2,200 m.
• Maximum design pressure, 555 bar.
• 1,524 km of 4-20 in. OD single-coated rigid pipeline
installed or soon to be installed in water depths greater than
200 m.
• 403 km of PiP lines installed or soon to be installed
(representing 15% of all production lines).
• An 836-km gas export network (Fig. 1).
The operators agreed not to consider bundles and flexi-
bles but to focus the JIP on rigid and pipe-in-pipe technolo-
gies. These are the most common flowline types in Angolan
deep waters.
Table 1 provides the typical size of each pipeline type.
Production duty centers on three main OD: 8, 10, and 12-
in., with 6-in. included in the case of
well jumpers. A wider variety of sizes
makes up the gas export network.
Fig. 3 shows how much of each
pipeline diameter each operator runs
in Angola. Each color represents one
oil company. The appearance of most
companies across Fig. 3’s spectrum
suggests the synergies available joint-
ly to address PRS. The JIP focused on
8-24 in. OD pipelines, which make up
94% of the lines off Angola.
Wet insulated flowlines
A conceptual study helped select the
most suitable method for repairing
wet insulated flowlines and any other
single-coated pipe. The PRS’s recom-
mended approach centers on full-sub-
sea, diverless deepwater repair, using one of two techniques:
• Integrity clamp. Repair with an integrity clamp will
take place on minor localized damage provided the pipeline
is not leaking when, for example, the flowline has been hit
but not ruptured by a dropped object. This method rein-
forces pipeline structural integrity to prevent a leak caused
by propagation of the damage.
• Repair with spool. Replacing the damaged section of
the line on-bottom with a spool allows repair of major dam-
age (e.g., rupture with leak). The repair spool can be either
straight or shaped, depending on the characteristics of the
section to be replaced. Before connector installation, a re-
motely operated vehicle (ROV) must prepare the sealing sur-
face on the outside of the installed flowline to ensure a suit-
able surface for the seal.
Some operators have internal guidelines dictating that
ANGOLA OFFSHORE DEEPWATER GAS PIPELINES Table 1
4 5 6 8 10 12 14 16 18 20 22 24
––––––––––––––––––––– Diameter, in.*––––––––––––––––––––
Production Wet insulated O X X X
PiP X X X
Oil export X X X
Gas lift O O X X X
Uninsulated Gas injection X X X X
Gas export X X X X X X X X X
Water injection X X X X
Service O X X X
Test O O O X X
*X, found on existing projects in Angola; O assumption or typical data foreseen for future project in Angola
PIPE-IN-PIPE CHARACTERISTICS Table 2
Concept Swaged PiP; quad joints, insulated sleeve
Length 10 km
Diameters 9-in., 11-in. OD
Design temperature 70° C.
U-value 0.6 w/sq m.K
100
90
80
70
60
50
40
30
20
10
0
Length,%
Diameter, in.
6 8 10 12 14 16 18 20 22 24
A B C D E F G
FIG. 3BLOCK SHAREHOLDER PIPE DISTRIBUTION
3

4. TECHNOLOGY
straight of shaped spools, so as not to limit the number of
potential installation vessels. These concerns prompted the
JIP to recommend horizontal orientation despite the prac-
tices of certain operators.
The JIP decided that repair operations should be per-
formed with intervention vessels already typically available
in Angola conducting routine inspection, maintenance, and
repair (IMR). The minimum vessel required for an emergen-
cy pipeline repair would be a multipurpose vessel with a
crane rated at 70 tonnes.
Characteristics specific to Angola affected PRS design, re-
sulting in a gap between the available technology—primar-
ily focused on post-hurricane pipeline repair in the Gulf of
Mexico—and the technology that was required.
Water depth
The deepest producing Angolan field is at 2,100-m water
depth (Block 31). But to ensure compatibility with possible
future ultradeep water developments, PRS equipment should
be qualified for use in water as deep as 3,000 m.
The JIP considered minimum water depths of 200 m,
with repair of sections less than 200 m deep benefitting from
diver assistance. Some PRS equipment, however, such as lift-
ing frames, could support shallow-water repair operations to
ease diver handling of large pipelines.
Soil data
Angola deepwater offshore soils consist mostly of very soft,
highly plastic, clay. The JIP ensured that dedicated founda-
tions can be developed to cope with these soils, which have
a particularly low shear stress.
H-frames with foldable mudmats, and other PRS compact
equipment, should remain within a 12-m × 8-m footprint to
fit the deck of the IMR vessel. Potential ship-to-ship trans-
fers in wave heights of 1.5 m suggest the need to keep the
weight of such equipment lighter than 25 tonnes.
Qualification
Connectors for some Angolan flowlines have to withstand
pressures exceeding 5,500 psi and sour service, again re-
quiring development and qualifica-
tion of repair components beyond
what was previously available. The JIP
is preparing a dedicated specification
for connector qualification in accor-
dance with industry standards such
as DNV RP F113, API 6A, API 17D,
and ISO 21329.
Thermal insulation
The repaired section of a production
flowline is unlikely to meet design in-
sulation specification for U-value and
cooldown time. Insulation on the re-
the spool-repair connection be vertical rather than horizon-
tal. The JIP screened different repair methods considering
both vertical and horizontal connections with various types
of deepwater repair connectors.
Under considerations of cost and technical maturity, the
PRS design’s effect on installation vessel size and capabil-
ity emerged as the main selection criterion. The presence of
deepwater pipelines in Angola with OD greater than 20 in.
required compromise on system design.
The JIP concluded that PRS design should be as com-
pact as possible, with the combined ability to install either
Repair spool
RESTORATION, CATEGORY B PIP
Annulus
Annulus seal connector Annulus seal connector
PiP
flowline
Wet-insulated
flowline connector
Wet-insulated
flowline connector
Annulus
PiP
flowline
FIG. 6
PIPE-IN-PIPE DESIGNS
Category A – Swaged J-lay
Category B – Long continuous annulus
Pipe section 24-48 m
Centralizers Failure
Inner pipe
Inner pipe
Pipe section, several km
FIG. 5
PRODUCTION FLOWLINE TYPES
PiP 53%
Rigid 25%
Bundles 9%
Flexible 7%
Rigid DEH
6%
FIG. 4
4

5. TECHNOLOGY
Insulation restoration
Thermal insulation in a Category B PiP system could typi-
cally be lost over 1-2 km in the event of a failure. PiP flowline
design provides insulation with a U value of 0.5-2 w/sq m-K.
If damage occurs, the annulus is flooded and its thermal
properties are lost, allowing hydrates to form during cool
down or shutdown before repairs can be executed.
The PiP insulation, combined with strict, precise operat-
paired section, however, must be suffi-
cient not to compromise the operation
of the flowline.
Pipe-in-pipe feasibility
Fig. 2 showed rigid single-coated pipe
to make up the majority of lines in
the Angolan pipeline network. For
production lines alone, however, PiP’s
proportion grows to 53%, with rigid
single-coated lines dropping to 25%.
The increasing use of pipe-in-pipe
technology in Angola prompted ADC
to conduct further investigation on
their repairs.
Conceptual study
Repairing PiP lines requires restoring
mechanical integrity while also
guaranteeing insulation properties
similar to the original. PiP damage
includes flooding its annulus with
seawater, which destroys the dry
insulation material and exposes the
annulus to corrosion.
Fig. 5 highlights the specifics of
the two main categories of PiP tech-
nology: swaged J-lay and long con-
tinuous annulus.
• Swaged J-lay (Category A).
PiP segment preparation typically
occurs onshore. Deforming the
outer pipe and welding it to the
inner pipe seals the annulus at the
end of each segment. Flooding thus
affects one annulus compartment (in
blue), while the other compartments
remain watertight (in green).
• Long, continuous annulus
(Category B). The annulus consists
of long, continuous sections without
compartments.
The JIP focused on repairing
Category A PiP systems. Category
B poses greater integrity issues
stemming from the combined loss of
thermal and mechanical integrity and the susceptibility
to corrosion of the bare steel annulus.
Fig. 6 shows the JIP’s recommended approach to restoring
mechanical integrity for PiP Category B, using a combination
of the connector for wet insulated flowlines with a newly
developed annulus seal connector.
CATEGORY A PIP REPAIR
3. Cut and remove field joint sleeve
4. Prepare exposed inner pipe section for connector
5. Install connector
6. Install spool piece, insulation dog house
1. Lift pipeline*
2. Cut field joints next to the swaged connection
*Photo: Total E&P Angola
Cavity fill with
open-cell
foam or gel
Connector
insulation
cover
Connector
insulation
cover Existing
coated
pipeline
Existing
coated
pipeline
Pipeline
Repair spool
Connector set Connector set
Pipeline
Coated
repair spool
FIG. 7
5

6. TECHNOLOGY
tion would be limited to a manageable length. No unsolvable
problems were seen in applying on-bottom cut and repair to
an insulated spool in a manner similar to that used for wet
insulated flowlines. Repair would require development of a
few additional tools, but neither feasibility nor qualification
would be problematic.
Table 2 shows specifications of the dry-insulated PiP
flowline used as the study’s basis.
Repair objectives
When a Category A PiP is damaged, it results in at most 48
m of flooded section. Given this relatively short length, the
optimum solution would be to replace the entire damaged
section with an insulated spool, restoring original PiP insu-
lation performance. This approach also solves corrosion is-
sues, as long as cathodic protection and electrical continuity
are installed for the tie-in section.
The line’s mechanical integrity must also be restored.
Connections between spool and PiP must be as resistant as
any other section of the PiP to avoid weak points in the line.
Fig. 7 shows the six steps of a typical swaged J-Lay (Cat-
egory A) PiP pipe repair and its completed configuration.
Connector selection
The JIP considered two concepts for the repair connector.
Fig. 8 shows the selected base case concept, which allows
the use of the same connector technology already available
in PRS equipment for the repair of wet insulated flowlines.
Once the damaged section of the pipe-in-pipe is cut, the
now exposed inner pipe section can accommodate the con-
nector. The operator must first cut the damaged section at
the outer pipe swaged connection to avoid additional dam-
age, relying on a compact cut-to-fit connector to join the
spool and the inner pipe.
This concept seems realistic at feasibility stage, but a con-
tingency case study may be necessary if the connector size
increases during development. Cutting the damaged section
upstream from the swaged connection and using the end
preparation tool for removing the required outer pipe length
in addition to the sleeve would provide the additional ex-
posed length if needed.
The JIP weighed the benefits of the base case connector
against those of an alternative concept, which gripped the
outer pipe instead of the inner pipe (Fig. 9).
The alternative’s only benefit was the lack of restriction
on the length of exposed inner pipe needed to accommo-
date the connector. It would, however, require the design
and qualification of a new type of connector. Since the
PRS study was attempting to standardize equipment be-
tween wet insulated flowlines and PiP flowlines, it chose
the base case concept.
Repair operations would be similar to those executed on rig-
id pipe from IMR vessels, with only minor cost increases associ-
ated with adding equipment if planned sufficiently in advance.
ing procedures validated by extensive flow assurance engi-
neering, makes restoring thermal integrity difficult. Degra-
dation of the thermal insulation will most likely invalidate
the system’s standard operating procedures.
Re-evaluation of operating procedures based on degrad-
ed insulation would require emergency, labor intensive, re-
running of flow assurance studies, including transient cal-
culations. It would also create a number of practical issues
regarding training of staff, managing the change, etc.
The JIP considered burying the PiP at a minimum depth
of 1.5 m from its top among the options for restoring insu-
lation of its flooded annulus. Though less than satisfactory
for inspection purposes, burial with a trenching tool should
provide the most efficient thermal insulation. Cool-down
performance would be close to PiP initial specification.
Soil conductivity is a key parameter in thermal perfor-
mance predictions. Burying the PiP at 1.5 m from its top in
soil with 1.2 w/m-K conductivity yields a U value of about 4
w/sq m-K or lower.
Burying a pipe-in-pipe, however, is not sufficient to re-
cover initial pipe-in-pipe insulation values. The operator
must also modify field operating procedures (i.e. combined
early depressurization and dead oil circulation).
Swaged J-Lay
The JIP sought to detail repair procedures further for Cat-
egory A (swaged J-Lay), for which the loss of thermal insula-
OUTER PIPE GRIP, ALTERNATE CASE
Collet, clamp, or grip
and seal connector
Outer pipe
Inner pipeSpool
Grip Seal
FIG. 9
INNER PIPE GRIP, BASE CASE
Collet, clamp, or grip
and seal connector
L required
Outer pipe
Inner pipe
Spool
Grip Seal
FIG. 8
6

7. TECHNOLOGY
Acknowledgment
ADC thanks the JIP participants, their steering committee
members, and subject matter experts for their continued
support and advice and for permission to publish this ar-
ticle. ADC also thanks AS Connector, Oceaneering, and Oil
States Industries for their support.
The authors
Suzana Abílio (suzana.abilio@sonangol.co.ao) is a project
engineer at Sonangol EP, Luanda. She is attached to the subsea
department, supervising installation of equipment and structures
on the seabed and providing technical and economic analysis
during subsea project approvals. She holds a BS (2009) in
petroleum engineering from the University of Tulsa and an
MS (2014) in energy and markets from the French Institute of
Petroleum’s IFP School, Rueil-Malmaison.
Stéphane Taxy (taxy.s@doriseng.com) is technical manager
subsea and production at DORIS Engineering with 17 years
of experience in the oil and gas industry. He has worked as
a process and flow assurance engineer developing numerous
offshore deepwater oil and gas projects. Taxy currently manages
projects for the Angolan Deepwater Consortium to share
industrial approaches in Angola with deepwater operators.
Xavier Michel (michel.x@doriseng.com) is senior pipeline
engineer at DORIS Engineering with 11 years of experience in
the oil and gas industry. He has been involved in the pipeline-
flowline repair system project since its first phase and is now
responsible for coordination of technical matters.
Eprinted and posted with permission to DORIS Engineering from Oil & Gas Journal
June 2 © 2014 PennWell Corporation
ANGOLA DEEPWATER CONSORTIUM
A.D.C.
ADC c/o DORIS Engineering
58A rue du Dessous des Berges
75013 Paris – France
e-mail : adc@doriseng.com
) +33.1.44.06.10.00
7