Lean Valemon hits the fast track - Heerema Fabrication Group ...

FIEld dEvElOpmENt
2
One of four roll-ups
of large frames for
the Valemon jacket
at HFG’s Vlissingen
yard.
Lean Valemon
hits the fast track
An impressive example of lean design and fast-track
construction of a major offshore structure is now standing in
133m of water in the Norwegian North Sea. Adrian Cottrill
looks at the technology-stretching jacket at the heart of Statoil’s
NKr20.4 billion valemon field development and the new
lift-installation record it has established.
Every unnecessary kilogramme
of steel in the jacket for Statoil’s
Valemon platform has been
pared away by design and fabrication
contractor Heerema Fabrication Group
(HFG). The vital driver for this crusade
has been the need to keep the structure’s
final weight within the capabilities of the
world’s largest offshore crane vessel and
so enable a record-breaking lift into place
at location.
The 8800 tonne jacket (plus another
800te of temporary rigging) placed on
the seabed at Valemon has also been
built in admirably quick time at HFG’s
yard at Vlissingen in the south of the
Netherlands. ‘It took us just 50 weeks of
fabrication, from cutting our first steel
on 6 June last year to ready for sailaway
on 26 May,’ says Aren Bezuyen, project
manager at the yard.
Pre-production drilling is due to start
at the platform this month. But the main
topside – due to weigh about 10,000te
and being built by Samsung – will not
be lifted on until 2014. By that time four
production wells will have been
pre-drilled through the jacket from
a jackup tender rig that will stand
alongside for the next two years.
Without the intense design effort
put in by in-house design company
HFG Engineering at its Zwijndrecht
headquarters, a more normal jacket to
meet Valemon requirements would likely
have consumed a further 1000te of steel
reckons Cees Spaans, the company’s VP
for technology.
The Valemon jacket is the heaviest ever
to be lift-installed reckons HFG, and by
far the heaviest of the half dozen large
jackets so far built by the company at
Vlissingen. And it is the first large jacket
built by the company for Statoil.
The vessel that lifted it into place on
18 June was Thialf, operated by sister
company Heerema Marine Contractors.
This semisubmersible shares the title of
world’s most powerful crane barge with
rival S7000, operated by Saipem. Each
of these two units sports a pair of main
cranes that provide a maximum tandem
lift capacity of a little over 14,000te.
In the particular configuration needed
for Thialf to lift-install the Valemon
jacket, the HFG team needed to keep
several thousand tonnes below that
for the combined weight of jacket and
temporary rigging hanging off the vessel’s
hooks during the big lift.
Not without considerable effort, and
certainly with one or two periods of some
pain, they have managed to achieve just
that. The company won the 20-month EPC
contract – rumoured to be worth about
$80 million – from Statoil in October
2010. This followed the detail design
contract won in the preceding month.
Earlier competitive FEED studies by
O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2 w w w. o f f s h o r e - e n g i n e e r. c o m

HFG and Aker had already established
lift-installation as the road ahead for the
project.
If a jacket is too heavy for this
approach the main alternative is to skid
it lengthways into the water off a launchbarge.
However, as Cees Spaans points
out, ‘if you can lift-install you should do
so’.
‘Of course, launching is not only an
issue of weight,’ he continues. ‘You need
to have extra strength in the jacket to
undergo the launch, skid rails on your
barge, along with ballast systems and
buoyancy tanks, and favourable weather,
all adding to risk.’
Client Statoil has a long pedigree in
lift-installation of big jackets. Indeed
the company’s man on the job here,
Kjell Arvid Tuen, with the title ‘Statoil
representative, Valemon jacket EPC’ is
very familiar with the concept. He has
been involved with half a dozen such
projects in his 20 years with the oil
company.
Ways to lose weight
For Valemon the sights were always
set on lift-installation, and therefore on
minimum structural weight. Spaans lists
some of the measures adopted to achieve
that at an offshore location where the
100-year design wave has a peak height of
28m. (Under this extreme condition it is
calculated the platform top will displace
about 750mm laterally.)
High strength steel is one of the
measures to keep weight down, he says.
Though not particularly unusual, grades
such as 420 and 460 made a helpful
contribution.
‘The weight of anodes required for
corrosion protection has been reduced
by painting the whole of the jacket,’ he
continues. ‘And the diameter of tubular
members is kept as small as possible, only
ballooning out at end connection nodes
where extra strength is needed to meet
fatigue demands.
‘In addition we have braces that are
flooded so they do not have to resist
hydrostatic collapse.’ This is not normal
practice because buoyant braces lend
themselves to flood detection systems
to indicate fatigue damage, but is an
acceptable trade-off here. Also, ‘instead of
designing in additional strength to meet
demands during the temporary transport
phase at sea, we have dealt with that in
other ways’, says Spaans. For example,
a system of bracing wires to the inner
members dampened any tendency for
them to vibrate in high winds.
Once HMC won the installation
contract, that phase could be designed
specifically around Thialf. One of the
differences from S7000 for example
is that Thialf’s main hook is allowed
underwater, avoiding the need to find
w w w. o f f s h o r e - e n g i n e e r. c o m O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2
courtesy heerema
3
FIEld dEvElOpmENt

FIEld dEvElOpmENt
4
adrian cottrill
adrian cottrill
extra buoyancy to avoid that limitation.
Above all, says Spaans, ‘we worked
steadily towards our weight target by
doing far more than the normal one or
two cycles of engineering to get weight
down. We analysed again and again and
again.’
Both Spaans and Bezuyen speak of
the benefits of having so many aspects
of the whole project within the Heerema
group and the quality of the resulting
interaction between the design and
construction sides. They also underline
the very effective communication with
client Statoil and certifying authority
DNV right from the beginning.
Statoil’s Kjell Arvid Tuen agrees. His
own involvement with the project began
The completed Valemon jacket, loaded on
transport barge at Vlissingen yard quayside
sailed away from the Netherlands early
on the morning of 26 May.
‘We worked steadily towards our
weight target . . . we analysed
again and again and again’
Cees Spaans, HFG
in the very earliest days when the design
basis was being evolved. Then, when
the contract was awarded, Tuen went on
to spend two years in the Netherlands,
starting in HFG’s design offices and
ending with close to four weeks on board
Thialf for the offshore installation.
Clearly he enjoyed the experience.
‘The Dutch and Norwegians have the
same cultural attitudes,’ he says, ‘and
communication has been very effective.
We started working together from day
one of the contract, and that’s one of the
reasons for the success I think.’
Two challenging issues
Certainly the emphasis on lean design,
with maximum input as early as possible,
courtesy heerema
The dominant design factors for HFG at
various points of the jacket are shown
below.
In place – Strength
In place – Fatigue
Accidental – Boat impact
temporary – lift and transport
O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2 w w w. o f f s h o r e - e n g i n e e r. c o m
courtesy heerema

adrian cottrill
paid useful dividends, says Cees Spaans.
However, it did not prevent the design
process going through a couple of painful
periods.
The first of these came during design
of the two mighty trunnion nodes in
the jacket’s lower legs. These huge steel
castings, weighing 110te each, formed the
all-important pivot points when the jacket
was dangling from Thialf’s hooks during
installation offshore and was rotated from
horizontal to vertical.
Built by specialist company Vulcan
Sheffield Forgemasters, they are the
largest cast nodes ever produced. ‘The
challenge of designing these castings was
definitely a little bit underestimated,’
concedes Spaans. ‘In fact in the end it
took us nearly three months instead of
the two or three weeks expected.’
‘The rotating hub is a very tight fit –
with just 3mm of clearance,’ he explains,
‘and the challenge was to prevent it
deforming too much under load.’ There
are also another two smaller cast nodes at
the lift points in the upper legs. Happily
these proved less difficult to design.
Not long after this the designers
encountered another unpleasant surprise.
In autumn last year they discovered that
in their bid to get the thinnest possible
steel wall in the main legs, those legs had
been left too weak to prevent deformation
during the sea journey at two of the main
support points on the grillage aboard the
transport barge.
The only solution at this stage was
to add local strengthening. Just over
40 ring stiffeners were welded inside
the 3.5m diameter lower legs at the two
affected points. This brought the triple
inconveniences of about 60te of extra
steel weight, a large amount of planning,
and ‘a tremendous lot of hours needed
to weld them in’. However, ‘that’s all
part of the EPC risk’, observes Spaans
philosophically.
A further area of challenge for both
designers and fabricators was the grillage
and sea-fastening for the journey to the
offshore location. The demanding North
Sea environment to be designed for (a
maximum wave height of nearly 11m
during sea transport) meant high loads
and large reactions between barge and
jacket. It was difficult to find an example
‘It took us just fifty weeks
of fabrication, from
cutting our first steel to
being ready for sailaway.’
Aren Bezuyen, HFG
from a different project and ‘that was a
challenge we solved together with HMC’,
says Spaans.
‘What did go very well was the whole
certification process,’ he notes. ‘I thought
the main challenge would be to meet
fatigue criteria with DNV, not least
because when different organisations do
the same analysis, they are bound to use
different kinds of software.’
However, the verification process with
DNV went amazingly smoothly, he says.
‘This was a lot to do with them being
involved early.’
Boat impact and foundations
Designing against boat impact is clearly
another area where HFG is proud of its
efforts. ‘This generated a very interesting
technical discussion,’ notes Spaans.
The criteria for Valemon are unusually
high. Because the platform sits in a
shipping lane it could potentially be hit
by vessels as big as a large supply boat
weighing up to 7500te and moving at up
to 5 knots. In addition, a vessel like that
can have more complicated aspects to its
shape, such as a bulb at the bow, which
influence the way it could penetrate a
platform.
In more standard locations, the
One of the two
huge trunnion
nodes cast
by Vulcan
Sheffield
Forgemasters.
requirements are based on a 5000te
vessel moving at up to 4 knots. All this
translates into Valemon having to cater
for 35MJ of impact energy. This figure is
close to three times what is more usually
called for.
‘In general, you want the jacket to be as
open as possible to minimise wave load,’
Spaans points out. ‘But in the area where
a boat could impact (between about 12m
above and below water level) members
need to be more closely packed to prevent
a boat penetrating too far into the jacket.
‘Industry guidelines are based simply
on impact energy and point load,’ he says.
‘They don’t look at the physical shape of
the boat, nor where you can enter or what
you can hit.’
‘So we engaged in a more probabalistic
approach to define the real challenge and
find the right balance. We went through
a question and answer process, asking
ourselves just how far a boat could
penetrate into the body of the jacket.’
To do this, HFG engaged in ‘a very
sophisticated study’ jointly with Dutch
research organisation TNO which has
done considerable work in this field. At
the same time Statoil undertook a similar
study through Trondheim’s University of
Science & Technology. > overleaf
All rigged up in the yard: huge slings in place round one of the pair of trunnion nodes
that provide vital pivot points for rotation. The sling is made of steel rope of nearly
300mm diameter and over 6500te breaking strength.
w w w. o f f s h o r e - e n g i n e e r. c o m O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2
adrian cottrill
5
FIEld dEvElOpmENt

FIEld dEvElOpmENt
8
courtesy heerema
the valemon field
the valemon gas and condensate
accumulation, a 1985 discovery 160km
off the coast from Bergen, has estimated
recoverable reserves equivalent to
210 million barrels of oil. development
is currently priced at NKr20.4 billion by
operator Statoil and its partners petoro,
Centrica and Enterprise.
the valemon platform is designed to
In the platform’s foundations one
novelty is the inclusion of cages of 16mm
steel reinforcing bar within the annulus
of grout that connects each pile to its
sleeve once it has been driven. This is
part of the latest DNV codes on grouted
connections.
The jacket stands on a group of four
84in diameter piles at the base of each of
its four main legs. These piles are driven
59m into the medium seabed soil at this
site.
produce about 85,000boe/d. the bulk of
reserves – about 80% – take the form
of natural gas, with the remainder as
condensate and natural gas liquids.
two years of pre-drilling is due to start this
month to provide four of the 11 production
wells currently planned, using a jackup tender
rig standing alongside the jacket and the small
wellhead module placed on it. there will also
be two injection wells – one for drill cuttings
and the other for produced water.
Design codes now require steel bar reinforcement in the grout
annulus in the pile to sleeve connection.
Wellhead module
To cater for the pre-drilling operations due to
run for two years from July until the platform’s
main topside arrives, the Valemon jacket carries
a wellhead module which will later be partly
integrated into the main topsides. This has
also been designed and built by HFG in just six
months, fabricating at a smaller yard near its main
Vlissingen site.
Athough relatively small, at 190te, 25m long
and just 3m high, it was also not without its
challenges. Rapid action had to be taken last
October when Statoil called for the design to be
completely changed: from two-deck to single
deck. Also, to enable adjustments when the main
topside arrives in two years, it is fixed by some
2000 bolts because of the ban on hot work once
drilling has started.
In mid-2014 the topside being built
by Samsung, and likely to weigh about
10,000te, will be lifted on. the completed
platform is due onstream by the end of
that year. It will be able to treat gas and
condensate from future discoveries in the
area as well as valemon itself.
the installation is classed as ‘not
normally manned’ once drilling is
completed, although it will have 40 cabins
of accommodation. It will be remotely
The move to add rebar cages to the
grout follows a certain amount of
trouble with foundations in the offshore
wind sector, perhaps too economically
designed. There are reports of grout
‘crunching’ and tube damage. In effect the
addition of rebar cages turns the grout
layer into straightforward reinforced
concrete.
In the yard
Summarising the jacket construction
work at Vlissingen, HFG project manager
Aren Bezuyen describes the rapid pace
of early procurement on this fast-track
project as ‘especially necessary with
certain specialist suppliers like Vulcan
Sheffield Forgemasters for the highlydemanding
cast nodes’. He also outlines
the weight uncertainties and puzzles
confronted as fabrication proceeded. ‘We
did as much work as possible at ground
level, building the jacket in four main
parts which could be rolled up,’ says
Bezuyen. The heaviest lifts at height were
two 400te leg base sections. Late delivery
in certain areas meant that ‘we had to
do more work at height than we’d hoped.
For example we were not able to get all
the risers and caissons in place before
roll-up.’
Another delaying factor, he adds,
was the information provided by HMC,
controlled from the Kvitebjorn platform
11km away, which will also supply power by
cable. Kvitebjorn will also be the recipient
of valemon’s condensate via a new pipeline
between the two, with onward transport
through the existing network to mongstad
refinery.
the main flow of rich gas from valemon
will go through a new 27km pipe to connect
with an existing line and then be transported
onward to Heimdal.
One of the main support points on the transport barge. Ring
stiffeners had to be added inside the jacket legs at two such points.
themselves wrestling with a jacket that
was bringing Thialf to the limits of its
capacity. But after less than a year of
physical construction work, all was ready
by mid-May for the completed jacket to
start moving from the yard. In a two-part
operation the combination of jacket,
support grillage and temporary
attachments (a total load of 10,790te) was
first moved 35m sideways by load-out
subcontractor Mammoet on a massive
wheeled array of 400 axles. > overleaf
In the drive to minimise steel weight, jacket
braces only balloon out in diameter at their
ends to meet fatigue requirements at nodes.
O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2 w w w. o f f s h o r e - e n g i n e e r. c o m
adrian cottrill adrian cottrill

FIEld dEvElOpmENt
10
courtesy woldcam as, anette westgård
‘Effective
communication a
major reason for
project success’
Kyell Arvid Tuen,
Statoil
Then it was moved 160m forwards
onto the barge which would take it to
location. Total rolling time was about
five hours. Next came ten days of fixing
sea-fastenings, guy-lines to braces and
suchlike, leading up to sailaway of barge
and cargo early on 26 May.
Altogether HFG’s Valemon jacket
project has notched up half a million
manhours. A fifth of that was divided
equally between engineering and
management. Another fifth was by
subcontractors.
The remaining 300,000 manhours
went to fabrication in the Vlissingen
yard.
Statoil’s Tuen sums it up. ‘The big goal
right from the start was of course to make
the jacket liftable,’ he says, ‘and in my
mind HFG has done a very good job, both
technically and commercially.’
He has sympathy with HFG over the
difficult stages it had to overcome. ‘It’s
always good to finish as much analysis
as possible before you order steel. But it’s
also important to work as fast as possible.
I think HFG did as well as they could.
They had to finish by a certain date, so
they had to order the steel in the way they
did.’
As to value for money, Tuen reckons
‘Valemon is more or less the best we’ve
had. This was helped by our timing in
the market, but also by the fact that
HFG wanted to show Statoil they were a
professional jacket EPC contractor.
‘It’s the first they have ever built for us,
and now we have no doubt that they can
do it.’
Statoil’s vice president for Valemon,
Bjørn Laastad, notes: ‘We are very
pleased with this delivery from Heerema
Fabrication Group, which is a new
supplier to Statoil for steel jackets of this
size.’
As the bright yellow jacket sailed away
in the pale dawn light on 26 May, both
the designers and the builders in HFG
could reflect on a good job done. They had
derived all the in-house advantages they
could in integrating the engineering and
fabrication processes, placed
fruitful emphasis on constructability,
and been greatly aided by effective
communication with their client Statoil
and partners. OE
Lift-installation’s
latest benchmark
After two weeks of waiting on
weather, Thialf could at last get to
work on the Valemon jacket.
O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2 w w w. o f f s h o r e - e n g i n e e r. c o m

w w w. o f f s h o r e - e n g i n e e r. c o m O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2
courtesy woldcam as, anette westgård
courtesy heerema
All the careful planning and
refinement of the Valemon jacket
design finally paid off on 18 June
when the structure’s record-breaking
offshore lift-installation was completed.
At 03.00 hours, the base of the 160m high
steel frame finally touched the seabed, on
target and perfectly upright.
The sequence had started with vessel
operator HMC first bringing the transport
barge into position at the stern of Thialf.
Then, with the twin cranes hooked to the
jacket’s pre-installed lifting slings, the
transport barge could be slowly ballasted
lower in the water, sea fastenings cut and
the jacket raised above its deck.
Once the free-floating cargo barge had
been towed away, the bottom end of the
jacket could be steadily lowered into the
water, with the structure just as steadily
rotating from horizontal to vertical as it
went.
The procedure did however suffer a late
interruption when a mechanical problem
stopped one of the main cranes and
caused the whole lift operation to halt.
At that point the jacket had been fully
rotated but still had another 7m to go to
reach the seabed 133m below water. So
the last stage of set-down was achieved by
a combination of booming down the crane
and ballasting of Thialf.
Thirteen days later, HMC had stabbed,
driven and grouted all 16 foundation piles
and finished with the small lifts of five
caissons and the 190te wellhead module.
On 1 July the vessel was able to sail away
from a highly demanding job well done
for client Statoil.
Waiting on weather
The immediate run-up to this, the world’s
heaviest lift-installation, had been a stark
contrast to all that activity. Before they
were at last able to swing into action,
the team onboard Thialf had to sit out a
frustrating 15 days of inactivity, waiting
on weather and hoping for sea conditions
to calm down enough for them to start the
delicate jacket lift.
When that window did open, says HMC
project manager Carol Granneman, ‘the
weather was excellent. It was very quiet,
with seas of less than half a metre and
hardly any wind, and that helped us a lot.’
The total load on the hooks of Thialf’s
11
FIEld dEvElOpmENt

FIEld dEvElOpmENt
12
twin cranes as the jacket rose off its
transport barge was 9600te. This included
some 800te of temporary equipment such
as spreader bars and slings.
Thialf has lifted heavier loads than this
a number of times in the past. Largest of
these to date has been the 11,800te topside
for the Shearwater platform in the UK
North Sea, placed in 2000.
But a large jacket is a rather different
proposition. It may not be as susceptible
to wind forces as a big topside, but it does
call for the delicate and complicated task
of rotating from horizontal to vertical
once it has been raised from the transport
barge.
That lift-off is just as delicate, governed
by the relative motion between crane
vessel and the transport barge brought
beneath its cranes. ‘Every lift has its own
limits,’ says Granneman, ‘and this one
had probably the most stringent limits we
have seen.’
Valemon called for sea conditions
below 2m significant wave height. ‘In the
event we experienced no more than half
that,’ he says. ‘That put us well within
crane limits, still with spare capacity left.’
The movement at crane tips was probably
less than 100mm.
Weather during the preceding 15 days
of standby time was poor rather than
dramatically bad as Thialf waited on
location and the jacket stood off about
5km. ‘The most exciting part of the day
was the weather forecaster’s presentation
on what he expected for the next week,’
says Granneman.
‘We had one instance where we thought
the lift could be possible and got ourselves
ready,’ he continues. ‘But actual
Slowly rotating, the lower end
of the jacket descends into the
water. Right: Landed on the
seabed, the jacket awaits the
first of the 16 foundation piles
in foreground to be stabbed
and driven. Below: Hooking
up in a calm sea for a
record-breaking lift.
conditions turned out a little worse than
expected and we had to postpone. You
can’t do anything about the weather.’
When a viable five-day window did
come into view HMC could at
last spring into action.
Once the jacket had
been landed on the seabed,
foundation work went faster
than expected. About a day
was trimmed from the nineday
schedule for driving with
the big Menck MHU 2100
underwater hammer and
grouting the skirt piles.
Installation of the wellhead
module also went well.
‘Our colleagues at Heerema
Fabrication Group did a
terrific job in aligning all
those boltholes for connecting to the
jacket,’ Granneman remarks.
The ‘in-house’ combination of all
aspects from design to installation of the
Valemon jacket – divided between sister
companies HFG and HMC – bore fruit
right from the start.
Once Thialf was chosen as installation
vessel, the jacket design could be tailored
even more precisely. One difference
from rival vessel S7000 is that the blocks
of Thialf’s main cranes are allowed
underwater, even if that does mean a
substantial job of cleaning and greasing
afterwards. In the procedure chosen, one
block went about 30m underwater.
As for the two large trunnion nodes
that proved such a headache to design,
‘the jacket turned very smoothly’, says
Granneman. He also mentions that
because the planned operation was so
close to Thialf’s limits, the option was
kept open to place counterweights on the
very top of the jacket to modify the load
distribution between the two cranes. In
the end that was not called
for.
‘Small things can have
a great impact on the
whole operation,’ says
Granneman. He quotes
the example of a flooding
pipe whose position could
interfere with the piledriving
hammer. ‘We just
adjusted our work method
a little to allow that pipe to
stay there.’ Similarly it was
agreed that guide pins on
the top of the jacket could be
included in the lift and be a
helpful influence on centre of gravity.
Valemon has taken jacket
lift-installation procedures another
impressive step forward with completion
of this lump sum contract from Statoil,
rumoured to be worth about E150 million.
There may not be any more big jacket
lift-installation operations coming up
this year, but clearly the technique will
continue to be seen on some impressively
heavy structures. Right now, Statoil’s
representative through the whole
Valemon jacket EPC – Kjell Arvid Tuen –
is moving to the Dagny project.
Dagny, says Tuen, ‘has a heavier
topside, so the jacket is even closer to
the maximum lift capacity of the two big
crane vessels in the market. We are just
about to take a decision on whether we
should choose lift-installation or bargelaunch
for Dagny.’ OE
O F F S H O R E E N G I N E E R | a u g u s t 2 0 1 2 w w w. o f f s h o r e - e n g i n e e r. c o m
courtesy heerema
courtesy heerema
courtesy woldcam as, anette westgård