Installation challe
enges - Polarled pipeline
e project
Ins
stallatio
on challe
enges - Polarle
ed pipeliine projject
1. Abstract
A
t
This paperr presents the
T
t techniccal challeng
ges and en
ngineering solutions
a
associated
d with the ssuccessful installation
n of the 36--inch pipeline for the
P
Polarled
piipeline projject. Installlation of the
e Polarled pipeline w
was carried out
b Allseas’’ dynamica
by
ally position
ned pipelayy vessel So
olitaire. The
e main
c
challenges
s that had to
t be overccome during the insta
allation cam
mpaign are
s
summarise
ed below:
•
•
•
•
•
•
Stinge
er setup;
Pipelin
ne initiation
n at Nyham
mna;
Pipela
ay through the Bjørnssundet area
a;
Installation of fou
ur single in
n-line tees and
a one du
ual in-line ttee;
Coatin
ng transitio
on point at 700
7 m water depth;
Laydo
own on the pre-installed foundattion sliding plate (FSP
P) at Aasta
a
Hanstteen.
A compreh
hensive con
ntingency p
procedure was developed for co
oping with the
u
unlikely
scenario of a deep wate
er wet buckle, includiing design and fabriccation
o some un
of
nique equip
pment; a 36-inch isola
ation plug and a 1,00
00 t pipeline
e
r
recovery
to
ool capable
e of launch
hing a dewa
atering pig.
2. Abbrevia
A
ations
A&R
A
C
CWC
F
FSP
F
FSPP
H
HSS
I
ILT
O
OD
P
PE
P
PP
P
PLEM
R
ROV
Abandon
nment and Recovery
Concrete
e Weight Coating
C
Foundattion Sliding
g Plate
Flame S
Spray Polyp
propylene
Heat Shrinkable Slleeve
In-line te
ees
Outside Diameter
hylene
Poly Eth
Poly Pro
opylene
Pipeline End Maniffold
d Vehicle
Remotelly Operated
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 1
Installation challe
enges - Polarled pipeline
e project
3. The
T Pola
arled pipe
eline pro
oject
The Polarle
T
ed pipeline
e project co
omprises o
of a 482 km
m long and 36-inch OD
D gas
t
transmissio
on pipeline
e from the A
Aasta Hanssteen field in the Norw
rwegian Se
ea,
r
reaching
w
water depth
hs of 1,265 m, to the N
Nyhamna p
plant at the
e western ccoast
o Norway.. The Polarrled pipelin
of
ne includess four single
e in-line tee
es assemb
blies
a one du
and
ual in-line ttee assemb
bly, all with
h 12-inch b
branch pipin
ng. The pip
peline
s
system
will transport a dry, rich gas opera
ating in the dense pha
ase, as single
p
phase
gas, with an operating prressure of between 231
2 and 115 barg.
Figure 3.1 – Polarled pipeline
p
overvview
The pipelin
T
ne was laid
d from the N
Nyhamna landfall tow
wards the P
PLEM and
i
initiated
byy means off a shore pu
ull-in opera
ation at the
e landfall. Following
F
i
initiation,
th
he pipeline
e was laid tthrough the
e Bjørnsundet area where
w
the
p
pipelay
wa
as parallel tto existing pipelines with
w tight in
nstallation ttolerances and
p
presence
o unstable
of
e curves with pre-insta
alled tempo
orary coun
nteracts.
The Polarle
T
ed pipeline
e consists o
of pipe secctions with 10 differen
nt combinattions
o wall thicckness (28..9, 30.5, 34
of
4.6 and 37..5 mm), an
nti-corrosion coating (PE
(
a PP) an
and
nd concrete
e weight co
oating thickkness (50 a
and 70 mm
m). In total there
a 21 tran
are
nsitions bettween the various
v
pip
pe sectionss.
The pipelin
T
ne route co
ontains 110
0 curves. T
The radii of the curvess vary betw
ween
1,000 m an
nd 20,000 m. Some o
of the curve
es were un
nstable, the
erefore
counteractts were pre
t
temporary
e-installed.. Polarled ccrosses 28
8 pipelines and
c
cables.
Final laydo
F
own at Aasta Hanstee
en was perrformed using a cut-to
o-length joint for
d
direct
laydo
own onto the pre-insttalled found
dation slidiing plate (F
FSP) using
g an
i
innovative
w ± 1.5 m axial tole
erance in 1,265
1
m wa
ater
laydown cconnector, with
d
depth.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 2
Installation challe
enges - Polarled pipeline
e project
4. Stinger
S
s
setup
Pipelay by means of an S-Lay installation vessel, fro
P
om very shallow to ve
ery
d
deep
water, creates a challenge
e for selectting the op
ptimum stinger
c
configuratio
on.
IIn deep wa
ater, a depa
arture anglle as close
e to verticall as possib
ble is desire
ed in
o
order
to de
ecrease the
e required ttension levvels, resultiing in a sm
maller stinge
er
r
radius.
How
wever, in sshallow watter departu
ure angles are typicallly low as the
v
vessel
thru
ust is used to keep the sagbend
d strains within limitations. This
r
results
in a shorter sttinger lengtth or a larg
ger radius ((or a combination of b
both).
C
Changing
t stingerr length and
the
d/or radius is an operration that is difficult tto
p
perform
in the field an
nd generallly requiress the vesse
el to make a port call.
M
Minimising
g project co
ost is a sign
nificant drivver, leading
g to an emphasis on
s
setting
up o
one stinger configura
ation for the
e entire pro
oject.
As mention
A
ned above,, a smaller stinger rad
dius allowss for the ten
nsion level to
b reduced
be
d, which ha
as the follo
owing advantages:
• Decre
eased fuel cconsumptio
on, resultin
ng in less e
environmen
ntal impact and
lower project cossts;
• Creatiing shorterr free spanss, consequ
uently less seabed inttervention is
ed which h
has comme
ercial benefits;
require
• Installation of tig
ghter curve radius, wh
hich creates more flexxibility for rroute
optimisation.
However, b
H
by setting a stinger in
n a smaller radius, hig
gher strainss are
i
introduced
, mainly in the overbe
end region. This impa
acts with re
egard to the
a
acceptance
e criteria on which the pipeline is to be insstalled. The
e following key
c
constraints
s were veriffied during
g stinger radius selecttion for the
e Polarled
p
pipeline
insstallation:
•
•
•
•
Local buckling lim
mit state;
Globa
al buckling limit state;
Fatigu
ue limit statte;
Concrrete crushin
ng limit sta
ate.
As a resultt of extensiive enginee
A
ering, a stin
nger config
guration wa
as selected
d
c
consisting
of 140 m le
ength set in combination with a radius in tthe range of
o
2 m to 2
240
220 m, suita
able for insstallation off all pipe prroperties along
a
the ro
oute
f
from
very sshallow to vvery deep water.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 3
Installation challe
enges - Polarled pipeline
e project
Figure 4.1 – Solitaire sstinger during
g Polarled pip
peline installa
ation
IIn addition to the setu
up of the sttinger radiu
us, the elevvation of ro
ollerboxes plays
a significan
nt role in piipeline insttallation. An
n optimal rollerbox
r
elevation se
etup
m
minimises
strains and
d stresses in the pipe
e.
Each rollerrbox is con
E
nstrained byy its design
n load. The
erefore, the
e rollerbox
s
setup
mustt ensure th
hat the load
ds are distrributed as e
evenly as p
possible accross
a rollerboxxes, thereb
all
by decreassing the strresses on the pipe ass well as the
e
l
load
on the
e rollerboxe
es.
Due to the large num
D
mber of diffe
erent pipeliine section
ns and wate
er depth
v
variances,
several se
ensitivity ch
hecks were
e conducted to determ
mine a sing
gle
r
rollerbox
setup suitab
ble for the entire
e
proje
ect.
On Solitairre, the sting
O
ger can be rotated arround the m
main hinge between the
t
h and se
hull
ection 1, the hinge be
etween secctions 1 and
d 2, and the hinge
b
between
se
ections 2 a
and 3. Thiss feature wa
as used to accommodate simple
s
stinger
adjustments during
d
the shore
s
pull--in operatio
ons where tthe water d
depth
a the sting
at
ger main hiinge was o
only 61 m.
5. Pipeline
P
initiation
n at Nyha
amna
5.1. Introd
5
duction
T Polarle
The
ed pipeline
e installatio
on was initia
ated by an onshore p
pull-in operration.
nging and congested
T shore approach is located in a challen
The
d area at th
he live
N
Nyhamna
G Proce
Gas
essing Plan
nt. In additio
on, the high pressure
e Langeled
d
e
export
gas pipeline ru
unning to th
he UK is lo
ocated onlyy 5 m from pipeline ro
oute.
For the pulll-in operattion, a linea
F
ar winch with a capaccity of 500 t was seleccted.
T landfa
The
all, including
g the found
dation for the pull-in w
winch, support blockss
u
under
the p
pull-in wincch/tempora
ary pig laun
ncher and foundation
f
for the pull-in
c
cable
reel, was consttructed prio
or to the arrrival of Sollitaire in th
he field.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 4
Installation challe
enges - Polarled pipeline
e project
A 4-inch diiameter pull-in cable w
with recove
ery rigging was installed on the
p
pipeline
route by a su
upport vesssel prior to the arrivall of Solitairre in the fie
eld.
O arrival of Solitaire
On
e the pull-in
n cable wa
as connecte
ed subsea to the A&R
R
w of Sollitaire by a
wire
an ROV.
Fig
gure 5.1 – Ge
eneral arrang
gement of pull-in winch
The first 2
20 joints of the pipelin
ne were coa
ated with p
polypropyle
ene (PP),
followed by
b concrete
e weight co
oated (CWC
C) pipe join
nts. The fie
eld joint coa
ating
on this secction was m
made with flame spra
ay polyprop
pylene (FSPP) for the
e first
segment and
a heat sh
hrink sleevves (HSS) o
on the CW
WC pipe.
5.2. Installlation eng
5
gineering c
challenges
s
T
This
sectio
on highlightts the technical issue
es faced du
uring the de
etailed
e
engineerin
g in order to achieve a safe, co
ost effective
e and robusst pipeline
s
shore
pull--in operatio
on in a cong
gested are
ea.
5.2.1. P
Pull-in ana
alysis
Comprehensive analyses were performed
C
d for the pu
ull-in operation to spe
ecify
t minimu
the
um required
d pull-in force for the winch, the
e minimum required p
pull-in
c
cable
lengtth and the minimum rrequired So
olitaire top
p tension to
o be applie
ed
d
during
eacch pull-in sttep. This in
n order to maintain
m
the
e shape off the catena
ary
m
meeting
the limit state criteria and
a the corrresponding
g strains in
n the pipelin
ne
d
during
the pull-in ope
eration. The
e analysess consisted of:
• Calculation of top and botto
om tension
ns and stra
ains in the p
pipeline
catena
ary;
n
• Calculation of the required winch forcce by taking
g upper bo
ound friction
ne and seabed;
factorss between the pipelin
• Calculation of pipeline stab
bility after rreleasing th
he pull-in winch
w
by
adoptiing lower b
bound axial friction factors.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 5
Installation challe
enges - Polarled pipeline
e project
The resultts of the ab
bove analysses are pre
esented in Table 5.1 below.
T
Table 5.1 - Su
ummary of pu
ull-in analysiss
M
Maximum lay tension
S
Stand-off position
M
Maximum pipe length to b
be pulled over seabed up to tie-in
M
Maximum botttom tension
R
Required tenssion capacityy of the winch
h
[t]
[m]
[m]
[t]
[t]
112
2
670
0
368
8
86
6
334
4
• The m
maximum pull-in winch
h tension w
which was experience
ed at Nyha
amna
was approximate
ely 300 t. T
This value was
w 10% le
ess than th
he calculate
ed
pull-in tension.
Flange loa
ad analysis
s
5.2.2. F
T pull-in head wass connected
The
d to the pip
peline via a flange asssembly,
p
preventing
e pull-in he
ead by a pig launcherr. In
hot work ffor replacement of the
over
o
order
to faccilitate passsage of the
e flange asssembly through the ffiring line, o
t stingerr and onto the
the
t seabed
d, a cocoon
n-shaped rollerguide
r
was designed.
To design the cocoon
T
n, the axiall loads, ben
nding mom
ments and ssupport
r
reactions
a
applied to tthe flange w
were separrately calcu
ulated. The
e flange wa
as
m
modelled
a
as a stiff se
ection and the offset b
between th
he flange and pipeline
e was
t
taken
into account. T
The analysis was repe
eated for each individ
dual rollerbox
a the ma
and
aximum axxial tension and bendiing momen
nt were con
nsidered ass the
b
basis
for th
he cocoon design.
Figure 5
5.2 – Genera
al arrangeme
ent of pull-in h
head assemb
bly
5.2.3. H
Holdback clamp des
sign
A
After
comp
pletion of th
he pull-in o
operation, the intention was to re
elease the pulli winch ass soon as tthe pull-in h
in
head reach
hed the tarrget box.
The Polarle
T
ed pipeline
e was route
ed in such a way that immediate
ely after the
e
p
pull-in
operation the p
pipeline layy on a veryy steep slop
pe of 14 de
egrees follo
owed
b a long ccurve on a free span. Hence, there was a risk of the pipeline sliding
by
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 6
Installation challe
enges - Polarled pipeline
e project
after releassing the pu
a
ull-in tensio
on due to te
ension fluctuations ass result of
v
vessel
dyn
namics and
d the installation in a ccurve.
A holdbackk clamp wa
as designed and mou
unted on the pipeline close to th
he
p
pull-in
head, secured
d to an anchor point constructed
c
d at the landfall by
d
dedicated
rigging, ass shown in Figure 5.3. After layin
ng approximately 2 km of
p
pipe,
for which the an
nalysis sho
owed that the pipeline
e stability criteria
c
were
e
s
satisfied
du
uring norm
mal pipelay operation, the tension in the pu
ull-in cable was
s
slowly
redu
uced to zerro and the pull-in cab
ble was discconnected from the p
pull-in
h
head.
Figure 5
5.3 – Onshorre hold-back clamp
6. Pipeline
P
installattion challlenges
6 Pipela
6.1.
ay through
h the Bjørn
rnsundet a
area
Pipelay in tthe nearsh
P
hore section
n of the Po
olarled routte, the so-ccalled
B
Bjørnsunde
et area, is considered
d to be one
e of the mo
ost challeng
ging pipelin
ne
i
installation
n operationss ever atte
empted.
The area, characteris
T
c
sed by a wide range o
of water de
epths and ffrequent
c
changes
in
n seabed gradient, cre
eated man
ny challenges during both
b
the
d
detailed
insstallation engineering
e
g and execcution phasses of the p
project.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 7
Installation challe
enges - Polarled pipeline
e project
Figure 6.1 – Overview off Polarled pip
peline route in
n Bjørnsunde
et area
Combinatio
C
on of the lim
mitations p
presented b
below were
e associate
ed with pipe
elay
i the Bjørn
in
nsundet arrea:
• The firrst 14 km of
o the pipelline route – through th
he Bjørnsu
undet area – is
restriccted by the existing La
angeled No
orth pipelin
ne and Orm
men Lange
e
pipelin
nes and ca
ables togeth
her with the
e topograp
phy of the fjord,
fj
resultting in
limited
d manoeuvvrability for the pipelayy vessel du
ue to the tight installa
ation
toleran
nces.
• The stteep slope at the land
dfall resultss in a rapid
d increase in the tension
level. Increasing
g the top tension has a direct efffect on the bottom ten
nsion,
which must be kkept as low as feasible
e for curve
e stability and on-botto
om
mprehensivve approacch was nee
eded during
g
roughness analyyses. A com
ay analysis in order to
o optimise tthe require
ed tension llevel which
h
pipela
satisfie
ed the limitt state crite
eria of pipe
eline installation and tto provide
proper input for the
t counteracts desig
gn.
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 8
Installation challe
enges - Polarled pipeline
e project
Figure 6.2 – Slope at landfall locattion
• There were 8 tig
ght radius ccurves in th
he Bjørnsun
ndet area ffor which th
he
laterall seabed frriction was insufficient to provide
e on-bottom
m stability of the
pipelin
ne so the curves
c
were
e unstable. According
gly, counte
eracts had tto be
installe
ed within th
he narrow corridor. In
nstallation of the pipe
eline next to
o the
counte
eracts wass very difficcult at locattions where
e the countteracts werre
installe
ed inside the lay corrridor, conse
equently fu
urther reducing the lay
corrido
or.
Figure 6.3
3 – Pipelay next to counte
eract
• In the Bjørnsund
det area the
ere are larg
ge lateral in
nclinationss and an
extrem
mely uneve
en seabed resulting in
n a large nu
umber of frree spans;
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 9
Installation challe
enges - Polarled pipeline
e project
• Pipelin
ne wall thicckness tran
nsitions in the
t Bjørnsu
undet area
a required
chang
ges in the te
ension leve
el in order to maintain
n the pipeliine catenary as
require
ed as per tthe installa
ation speciffication. Du
ue to the ch
hanges in tthe
bottom
m tension a
and the varrying latera
al stability of
o the pipelline on the
seabe
ed, the curvve stability assessme
ent was con
nverted to a more
compllicated ana
alysis.
• The Polarled
P
pip
peline insta
alled in the Bjørnsund
det area wa
as very stifff due
to a w
wall thicknesss of 37.5 mm (in add
dition to the concrete
e weight
coatin
ng). Installa
ation of succh a rigid pipe with co
onstraints, ssuch as lon
ng
pans, tight curve radiii laying next to countteracts and
d a narrow
free sp
laying corridor, g
generated a significan
nt number of challeng
ges. These
e
were d
dealt with b
both during
g the engin
neering pha
ase to asse
ess the
behavviour of the catenary a
and during the execu
ution phase
e with regard to
the acccurately co
ontrolling b
barge posittion and ten
nsion.
• In add
dition to the
e pipeline in
nstallation challengess discussed above, th
he
Polarle
ed pipeline
e was route
ed through no loading
g zones in the
Bjørnssundet area, due to p
proximity off the Lange
eled pipelin
ne and sevveral
other ssubsea pip
pelines and
d umbilicalss over the ffirst 14 km. An overview
of the pipeline ro
oute in the Bjørnsund
det area is sshown in F
Figure 6.1.
Solitaiire has the
e capacity tto store ap
pproximately 10 km off 36-inch pipe
p
where
e the length
h of the pip
peline throu
ugh the Bjø
ørnsundet a
area was
14 km
m. This wou
uld mean th
hat after layying 10 km
m of pipe, th
he pipeline
would need to be
e laid down
n and the vessel
v
wou
uld have to sail to a
g pipe.
loading area for restocking
er to avoid
d the laydow
wn operatio
on, which w
would intro
oduce safetty
In orde
risks and
a consum
me operational time, research w
was perform
med to iden
ntify
areas in the Bjørrnsundet area where pipe loadin
ng would b
be allowed.. The
assessment wass performed
n the requirements in
ndicated in
d based on
ence 1 and
d three loca
ations were
e considere
ed to be accceptable
Refere
loading zones, allowing
a
pip
pelay to continue thro
oughout the
e first 14 km
m
withou
ut having to
o temporarrily lay dow
wn the pipe.
Figure 6.4 – Schematic of drop
d
cone ob
bject and accceptable load
ding zone
T 2016
OPT
Sam
man Dabighi – Arne Foss
se
5, 2016
Febrruary 24 & 25
Page 10
Installation challe
enges - Polarled pipeline
e project
6.2. Pipela
6
ay along th
he route
6.2.1. A&R restrricted area
as
A
Along
the rroute, seve
eral restrictted zones w
were identiified where
e A&R
o
operations
could not be perform
med for the
e following rreasons:
• In orde
er to ensurre a one-tim
me touchdo
own of the Polarled p
pipeline ove
er
existin
ng subsea assets, a special
s
wea
ather windo
ow was de
efined in ord
der to
guarantee eitherr a safe passsage of th
he subsea assets or a
an
donment att a sufficien
nt length be
efore the crossing.
c
aband
• During
g the installlation of a curve, the pipelay ve
essel does not follow the
design
n route. Co
onsequentlyy, in case of
o any requ
uired abandonment, the
t
pipelin
ne will not be
b laid dow
wn on the d
designed ro
oute. In case survey data
are no
ot available
e for such locations, these areass have to b
be defined as a
restriccted area fo
or pipeline abandonm
ment.
In thesse areas, temporary
t
pipeline ab
bandonmen
nt had to b
be avoided..
Therefore, for ea
ach of the iidentified zzones, a we
eather wind
dow was
define
ed and used
d as a guid
deline to en
nsure sufficcient pipe ccould be la
aid to
pass tthe zone prrior to aban
ndonment.
Figure 6.5 – Schem
matic of barge
e track at currve installatio
on
6.2.2. Critical crrossings
The Polarle
T
ed pipeline
e route crossses a tota
al of 28 pipe
elines, ME
EG lines and
u
umbilicals,
which werre covered by rock du
umping prio
or to pipela
ay to preve
ent
a damag
any
ges. The piipelay corrridor was re
educed from ±10 m to
o ±1 m at these
c
crossing
lo
ocations in order to m
minimise the
e amount o
of rock dum
mping required.
Several of the crosse
S
ed pipeliness and cable
es are loca
ated close to each oth
her.
I order to hit all target boxes, p
In
pipelay had
d to be veryy accurate and was
by two RO
c
controlled
OVs. Figure
e 6.6 showss one of the
e most critical crossin
ngs
a
along
the Polarled
P
route.
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e project
Figure 6.6 – Typical critical crrossing along
g Polarled rou
ute
6.2.3. Coating trransition p
point at 70
00 m waterr depth
At the transsition from concrete w
A
weight coa
ated pipe to
o polypropyylene coate
ed
p
pipe,
Solita
aire’s tensioners had to hold the
e PP coate
ed pipe with
h the full
c
catenary
frrom the vesssel to the seabed co
onsisting off concrete weight coa
ated
p
pipe.
The tensions during tthis operation with the
T
e least favo
ourable wa
ave and wind
d
direction
w
were analyssed to be:
• Static tension: 32
27 t
• Dynam
mic tension
n at Hs 4 m
m: 438 t
The above
T
e tensions a
are spread over the vvessel’s thrree tension
ners, which
h
r
results
in th
he followin
ng:
• Static tension: 109 t/tensioner
• Dynam
mic tension
n at Hs 4m: 146 t/tenssioner
The tensioner pads p
T
play a signiificant role in translating the tensioner cap
pacity
ntify the re
t holding ccapacity. A slip test w
to
was perform
med to iden
equired squ
ueeze
p
pressure
o
of the tensio
oners and to verify th
he maximum
m holding ccapacity off
e
each
tensio
oner. The slip
s test esstablished tthat, with a single ten
nsioner usin
ng
h
hard
pads a holding ccapacity off 300 t coulld be achie
eved and 3
325 t with soft
p
pads.
Therefore it could be concluded
T
d that this o
operation ccould be exxecuted safely
w either hard padss or soft pads because the tension levels would
with
w
not reach
r
s levels. In order to
slip
o decrease
e the risk off pipeline sslippage, a decision was
w
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Installation challe
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e project
made to usse hard pads for the cconcrete co
m
oated pipe, which wo
ould be rep
placed
b soft pad
by
ds prior to rreaching th
he coating transition p
point.
7. Installati
I
ion of in--line tees
s
7.1. Generral descrip
ption
Along the P
A
Polarled pipeline routte, four single tees an
nd one dua
al in-line tee
e
(
(ILTs)
need
ded to be installed fo
or future tie-ins. Table
e 7.1 presents an ove
erview
o the weig
of
ght of the structures.
Table 7.1 – Weightt of inline stru
uctures
Inline Tee
Weight [t]
[-]
Dry
Subm
merged
Dual
38
18
S
Single
20
10
Figure 7.1 – Co
onfiguration o
of single and dual ILTs
IInstallation
n tolerances of the ILT
Ts were ±6
6.1 m and ± 1 m in lon
ngitudinal a
and
directions respective
t
transverse
ely. The rolll tolerance
e of the ILT
Ts was ±15
5
d
degrees.
Any in-line structure that
A
t
is to be installed from an S-lay installa
ation vesse
el
m
must
be de
esigned so that it fits through the tensione
ers and can
n travel ove
er the
s
stinger
whiile the overrbend straiins remain acceptable
e. This is a common issue
w
when
insta
alling in-line
e structuress in S-mod
de and wass addressed during th
he
d
detailed
de
esign phase.
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Installation challe
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e project
Figure
e 7.2 – Schem
matic overvie
ew of tension
ner envelope
7.2. Rotati
tion mitiga
ation
A
Although
ro
otation of the
t pipeline
e is not pro
oblematic fo
or normal p
pipelay,
m
maintaining
g the verticcality of the
e in-line strructure on tthe seabed
d is alwayss a
c
concern.
A
Any unexpe
ected large angles willl result in an
a increase
ed duration
n of
t future ssubsea tie--in operatio
the
ons and will require modification
m
ns to the tie
e-in
e
equipment
t.
According to the theo
A
ory describ
bed in Refe
erence 2, piipelines tha
at are subjected
t residual curvature during pipeline installlation tend
to
d to rotate while
w
trave
eling
t
through
the
e sagbend. The seve
erity of the rotation
r
inccreases witth the level of
b
bending
strain introdu
uced in the
e overbend
d and the suspended pipeline length
i the sagb
in
bend. The rotation
r
ca
an howeverr be counte
eracted effe
ectively by
a
applying
an
n external moment to
o the system
m.
A common
nly applied measure to ensure vvertical insttallation of in-line
is to conne
s
structures
ect a buoya
ancy modu
ule via a yo
oke on top o
of the pipe
eline.
I the pipe and thus yyoke rotates, an up-rig
If
ghting mom
ment is cre
eated and this
r
reduces
the rotation to
t an acceptable ang
gle.
The anti-ro
T
otation arra
angement ffor the Pola
arled pipeline (see Fig
gure 7.3)
c
consisted
o
of an 8 m long yoke w
with an 8 t buoyancy for the sing
gle ILTs, and
11 t of buo
oyancy per yoke for th
he dual ILT
T, as follow
ws:
• One arrangemen
a
nt at appro
oximately 275 m in fro
ont of the centre
c
of the
ILT.
• One arrangemen
a
nt at appro
oximately 75 m behind
d the centrre of the ILT
T.
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Installation challe
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Figure 7.3
3 – Anti-rotatiion arrangem
ment
The anti-ro
T
otation arra
angement a
as describe
ed above g
generated tthe followin
ng asi
installed
co
onditions p
presented in
n Table 7.2
2.
Table 7
7.2- ILT rotatiions on seab
bed [deg]
ILT
An
nalysed
Acttual
Dual
Victoriia
Zidane
n
Kristin
Drauge
en
1.4
-0.11
1.7
-1.71
-0.18
+2.08
-1.17
Figure 7.4 – In-lin
ne double tee
e assembly including anti-rotation arra
angements
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7.3. Installation of dual
d
ILT
T dual IL
The
LT length w
was greate
er than the distance between two
o tensioners
a therefo
and
ore, it was necessaryy to open tw
wo tensioners simulta
aneously,
r
resulting
in
n the pipelin
ne being held by one
e tensioner only.
Figu
ure 7.5 – Passage of dual ILT through tensioners
Due to the tension levvels (staticc tension off 186 t and
D
d dynamic ttension of 286
2 t
a Hs of 3 m),
at
m it was already
a
known that S
Solitaire wo
ould have ssufficient
c
capacity
to
o hold the P
Polarled pip
peline with only one ttensioner.
However, iin order to minimise tthe risk of p
H
pipe slippa
age, some safety
s
were taken
m
measures
n.
The major safeguard was to continuously monitor th
T
he tension levels
l
durin
ng
t transfe
the
er of the dual ILT to th
he beadsta
all, the weld
ding of the dual ILT to
o the
p
pipe
string and before
e opening the tension
ners.
IIn case of any indicattion of an increase in the tensio
on, an A&R
R head wou
uld be
i
introduced
to the system to tran
nsfer loadss from the tensioners to the A&R
R
w
winch
and accordinglly increase
e the cumulative holdiing capacitty.
H
However,
d
during the actual installation of tthe dual IL
LT, it was fo
ound that the
t
t
tension
wa
as well belo
ow the sing
gle tensione
er capacityy and there
efore installation
o an A&R head was not require
of
ed.
8. Laydown
L
n onto th
he FSP att Aasta H
Hansteen
n
8.1. Generral descrip
8
ption
T Polarle
The
ed laydown
n operation
n was the d
deepest 36
6-inch pipeline laydow
wn
o
operation
e
ever perforrmed by an
ny pipelay ccontractor. The waterr depth at tthe
l
laydown
ta
arget box w
was 1,265 m
m. The layd
down operration at Aa
asta Hanste
een
s
started
at a
approximattely 7.5 km
m before the
e laydown location in a water de
epth
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Installation challe
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e project
of 1170 m, where the
o
e first transsponder wa
as attached
d to the pip
peline and tthe
t
transponde
er location relative to the laydow
wn target box
b was me
easured ussing
t LBL array. This to
the
o calculate the remain
ning pipelin
ne length a
and to
d
determine
the length required fo
or the cut-tto-length jo
oint.
Figurre 8.1 - Impre
ession of pipeline and layydown conne
ector landing on the FSP
The laydow
T
wn operatio
on was perrformed byy means of a so-called
d collet
c
connector,
designed and fabrica
ated by Fre
eudenberg
g (Vector C
Co.), locked
d onto
a special la
aydown joint. The layydown conn
nector had a total length of 6.3 m, a
m
maximum
d
diameter of
o 1920 mm
m and a dryy weight of 24.5 t.
Figure 8.2 - Layydown conne
ector and layd
down joint
8
8.2.
Shroud design
n
A compreh
hensive ana
alysis was performed
d for the de
esign of the
e protection
n
s
shroud,
wh
hich would compensa
ate the effe
ect of rollerbox loads o
on the systtem,
c
caused
by the large o
offset betw
ween the bo
ottom of the
e pipeline and
a the bo
ottom
o the laydo
of
own conne
ector, and ffacilitate sm
mooth passsage of the
e laydown
c
connector
over the sttinger and firing line d
during both
h the laydown operatiion
a a pote
and
ential contin
ngency reccovery.
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Installation challe
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e project
Figurre 8.3 - Laydo
own shroud
Several de
S
esign limitations were taken into
o account w
which are ssummarised
d
b
below:
• The la
arge weightt of the layydown conn
nector and shroud asssembly at the
end off the pipe string
s
would
d lead to in
ncreased sstresses at the connection
betwe
een the pipe
eline and the connecctor. Thereffore, the lim
mitation of the
weight of the shrroud was a
an importan
nt considerration in the
e design.
Additio
onally, afte
er completio
on of the la
aydown op
peration, the shroud w
would
be rem
moved from
m the laydo
own connecctor and re
ecovered by a separa
ate
ROV vvessel. Inccreasing the
e weight off the shroud would ha
ave a direcct
impacct on this op
peration.
hroud would experien
nce a large
e reaction fforce from the rollerbo
oxes
• The sh
and th
herefore req
quire sufficcient streng
gth. The strengthenin
ng of the sh
hroud
was achieved byy increasing
g the thickness of the
e plates. Ass discusse
ed
above
e, optimisattion betwee
en weight a
and strength was an issue due to
the ressulting high
h stress on
n the pipe.
• Mountting of the shroud ove
er the pipeline and laydown con
nnector wa
as
also cconsidered a constrain
nt. In Solita
aire’s bead
dstall there
e is a space
e of
neral, rollerguides ca
an be
approxximately 5 m between the rollerrs so in gen
easily installed. However,
H
d
due to the dimensions of the co
onnector, th
he
shroud
d had a len
ngth of app
proximatelyy 9 m and ttherefore th
he decision
n was
made to design a four-partt shroud. The modified four-partt shroud de
esign
onsiderablyy and, as a conseque
ence,
improvved the insstallation effficiency co
limited
d the opera
ational time
e.
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Installation challe
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e project
• Severral lift pointss had to be
e installed on the shro
oud for easse of recovvery
by an ROV vesssel.
8.3. Cut-tto-length m
8
measurem
ment
C
Common
p
practice forr measuring
g the cut-to
o-length for hitting a ttarget box is to
u surveyy equipmen
use
nt such as transponde
ers in an L
LBL array. T
The distancce
b
between
th
he transpon
nders and centre of th
he target b
box can be calculated
d
u
using
the a
array. In ad
ddition, durring the fina
al approach the exact length of each
p
pipe
joint iss measured by laser and, accorrdingly, the
e required length for the
c
cut-to-leng
gth joint is calculated.
c
Figure 8.4 - Cut to leng
gth measurem
ment using survey equipm
ment
On the Pollarled proje
O
ect, the abo
ove method
dology had
d some ope
erational rissks
d to the following:
due
• A veryy tight longitudinal tolerance of ±
±1.5 m, considering a suspende
ed
pipe le
ength of 3,800 m (312
2 pipe jointts), needed
d to be acccounted forr.
• Althou
ugh the LBL array is a
an accurate
e survey syystem, som
me tolerancces
had to
o be taken into account.
• Joint length mea
asurement errors as small
s
as 5 mm per joiint would re
esult
arget box.
in missing the ta
onmental fa
actors such
h as tempe
erature cha
anges, seab
bed slopess, and
• Enviro
possib
ble curves in the final pipeline approach ne
eeded to be
b accounte
ed
for.
Hence, in o
H
order to en
nsure the la
aydown con
nnector of the Polarle
ed pipeline
e
l
landing
on the pre-insstalled FSP
P within the
e specified
d longitudin
nal tolerancces,
t decisio
the
on was mad
de to perfo
orm an intermediate A
A&R operattion
a
approxima
tely 150 m before the
e FSP, usin
ng the avaiilable A&R
R head. Thiss
e
enabled
a final checkk of the rela
ative position and the
e required length of th
he
c
cut-to-leng
gth joint.
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Installation challe
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8
8.4.
Pass
sage throu
ugh the ten
nsioner
For the layydown operration, the tension ha
F
ad to be tra
ansferred frrom the
t
tensioners
to the A&R
R winch an
nd the tenssioners had
d to be ope
ened in orde
er to
a
allow
for th
he laydown
n connectorr to pass th
hrough.
However, w
H
with tensioners in the
e open position, the p
pipe string ccan be lifte
ed off
t rollerbo
the
oxes due to
o its stiffne
ess and the
e shape of the catena
ary. The de
eep
w
water
sectiion of the 36-inch
3
Polarled pipeline had a wall thickn
ness of
3
34.6
mm, w
which can be conside
ered to be a very stiff pipe. In orrder to mod
del
t lift off, sseveral analyses werre performe
the
ed using F
FE software
e. The
m
maximum
cclearance between th
he pipe botttom and th
he rollers ju
ust before the
was calcu
t
tensioners
ulated to be
e maximum
m 10 cm.
A geometryy check wa
as performed and it w
was concluded that no
o clashing
w
would
occu
ur during th
he passage
e of the layydown conn
nector thro
ough the
t
tensioners
.
8.5. Stinge
8
er tip clearance
A
Allseas’
pip
pelay insta
allation philosophy is b
based on m
maintaining
g a separattion
o at least 0.3 m betw
of
ween the piipeline and
d the stinge
er tip at all times. Durring
l
laydown
an
nd/or any abandonme
a
ent and reccovery ope
eration, half the OD size of
p
pipe
is to b
be added to
o the above
e mentione
ed criterion
n in order to
o model the
e
c
cable
in the
e laydown analysis in
n a correct manner. Therefore,
T
t keep the
to
e
s
stinger
tip clearance during the passage of
o the large
e OD laydo
own connecctor,
t tension
the
n level wou
uld have to be increassed prior to
o the laydown connecctor
l
leaving
the
e stinger.
H
However,
ffor this layd
down, the stinger
s
tip clearance was achievved by rota
ating
t stingerr downward
the
d when the
e connectorr had reach
hed rollerbox no. 7, while
w
m
maintaining
g the same
e tension.
Figure 8.5 - Impression of
o stinger rotation during laydown ope
eration
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Installation challe
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8 Final laydown and
8.6.
a
recove
ery of the laydown rrigging
Following tthe landing
F
g of the laydown joint in the forkk on the FS
SP the laydown
c
connector
was only 0
0.5 m off ta
arget.
F
Figure
8.6 - A
As-installed p
position on th
he FSP
The Polarle
T
ed pipeline
e laydown w
was performed using a 500 t rig
gging set. This
T
r
rigging
wass to be discconnected by an ROV
V. In orderr to preventt this heavyy
r
rigging
hitting the FSP, after confirmation of the succcessful laydown, Soliitaire
m
moved
aste
ern toward
ds the FSP while retrieving the A
A&R cable. When the
e
R
ROV
cut th
he sacrificia
al sling, it was
w ensure
ed that the A&R was in a vertica
al
p
position
an
nd without any
a slack, preventing
g the rigging to drop on
o the FSP
P.
F
Figure 8.7 – R
Recovery of Solitaire
S
A&R cable
9. Conclus
C
ions
IInstallation
n of the reccord-breaking Polarled
d pipeline w
was complleted in a ssingle
s
season
witthout encou
untering an
ny major co
ontingencie
es or safetty issues. S
Some
c
challenges
s were enco
ountered, a
and overco
ome, during
g the installation
e
engineerin
g and execcution phasses.
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Installation challe
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e project
Allseas devveloped methodologiies, as brie
A
efly describ
bed in this p
paper, in order
t successsfully installl the Polarlled pipeline
to
e, one of th
he toughesst subsea
p
pipeline
pro
ojects everr carried ou
ut, in a watter depth never
n
beforre reached with
t
this
the pip
pe diameter.
The main ffactors con
T
ntributing to
o the succe
ess of the p
pipeline insstallation were:
w
• Develo
opment of a well-plan
nned installlation strattegy, which
h reduced tthe
producction time and lowere
ed the overrall cost;
• Effective commu
unication w
with all partiies involved in finding
g the best
ons, while taking
t
into account sa
afety, operrational cosst and
solutio
installa
ation sched
dule;
• Implem
menting co
omprehenssive risk asssessmentss with all pa
arties involved
and th
he proper u
utilisation o
of risk mitigation mana
agement in
n order to
achievve the high
hest safety class for th
his project..
10.
Ackno
owledgm
ments
The authorrs on behalf of Allsea
T
as and Stattoil would liike to thank all the
c
companies
s involved iin the proje
ect for theirr contributio
on to the success
s
of the
P
Polarled
prroject.
11. Referen
nces
1- DNV-R
RP-F107, 2
2010, Riskk assessme
ent of pipeline protecttion
2- Endal,G., Ness, O.B., Verle
ey, R., Holte, K., Rem
mseth, S., ““Behaviourr of
Offsho
ore Pipeline
es Subjectted to Residual Curva
ature Durin
ng Laying”,
Paperr, 1995 OM
MAE - Volum
me V.
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