1. www.bakerhughes.com/pps
Phone: +1 281-230-7423
Email: Mark.Elliott@bakerhughes.com
Subsea Pre-commissioning of the Nord Stream Pipeline Part 1 and Part 2
By Marco Casirati, Jarleiv Maribu, Nord Stream AG, Zug , Switzerland.
and Daniel Fehnert, John Grover, Baker Hughes, Dubai, UAE.
Reprinted from Oil and Gas Journal May and June 2013

2. Nord Stream natural gas pipeline highlights
need to integrate precommissioning
TRANSPORTATION
Marco Casirati
Jarleiv Maribu
Nord Stream AG
Zug, Switzerland
John Grover
Daniel Fehnert
Baker Hughes PPS
Dubai
As subsea natural gas pipelines get longer and more re-
mote, precommissioning requires increased integration
into the overall project plan. The 1,224-km (760-mile)
twin Nord Stream natural gas pipeline completed precom-
missioning Line 1 in September 2011, ahead of schedule,
and finished Line 2 precommissioning 1 year later. This
first part of the article details the planning, engineering,
and preparation for Nord Stream’s precommissioning,
with the second part addressing relevant field experience
collected during execution.
Nord Stream was the world’s longest-ever single-
section dewatering operation, including the longest travel
distance for tie-in sealing tools. Establishing a concept,
engineering and planning, selecting a main water source
and water treatment regime, and identifying risks were
among the tasks project managers undertook at the
earliest practicable juncture.
Effective dewatering was confirmed by the quick drying
operation which followed. An effective water-treatment con-
cept minimized effects on the environment. Favorable tem-
peratures allowed for quick and effective pressure testing.
The entire process was helped by pigs specifically designed
for the Nord Stream precommissioning. Successful pig track-
ing allowed good control and operational confidence.
Background
Nord Stream consists of two 48-in. OD subsea pipelines
running 1,224 km from Russia to Germany through the Bal-
tic Sea, the world’s longest single-section offshore pipelines.
The pipelines export gas from Vyborg, Russia, crossing the
Gulf of Finland and the Baltic Sea, to a receiving terminal in
Lubmin (near Greifswald), Germany. In addition to crossing
Russia and Germany, the pipelines cross the Exclusive Eco-
nomic Zones (EEZ) of Finland, Sweden, and Denmark (Fig.
1). Each pipeline can ship 84 million standard cu m/day, a
combined 55 billion scm/year.
Pipeline design featured a segmented design-pressure
concept matching the route’s gas pressure profile. Fig. 2
shows the pipelines’ configuration. There are no intermedi-
ate platforms along the route. Pressure testing each of Nord
Stream’s three sections separately required installation of
offshore subsea terminations (start-up and laydown heads)
designed for start-up-abandonment operations and subse-
quent precommissioning, respectively. Hyperbaric tie-ins
subsequently joined the sections at KP 297 and KP 675, cre-
ating a single 1,224-km pipeline.
Saipem served as main contractor for pipelay and pre-
commissioning, with Baker Hughes the precommissioning
subcontractor. As further described below, the design and
construction concept affected precommissioning execution.
Precommissioning concept
The initial precommissioning concept called for water filling
via large-diameter crossovers at the subsea tie-in sites. Sub-
sequently installing high-pressure crossovers would allow
pressure testing, requiring all three sections of the pipeline
to be laid before starting precommissioning.
Since the German area consisted of an almost closed bay
with shallow water and low currents, flooding would have
taken place from Russia to Germany with dewatering in the
opposite direction. This plan required installing a water
winning and injection spread at the Russian landfall and an
air spread at the German landfall.
The concept called for caustic soda (NaOH) and sodium
bisulfite (NaHSO3
) to be used as additives to reduce water
treatment’s environmental impact. Caustic soda would stifle
anaerobic bacteria, with bisulfite acting as an oxygen scaven-
ger. Using caustic soda raised concerns because of the pos-
sibility of precipitation of carbonates and blockage at cross-
overs. Detailed water sampling and analysis were planned to
address these concerns.
All precommissioning on the Nord Stream project needed
to take place as “one-shot” operations that could not be re-
SPECIAL
REPORT
Based on presentation to Deep Offshore Technology (DOT)
International Oil and Gas Conference, Perth, Australia, Nov.
27-29, 2012.

3. peated or reversed without major schedule impacts or ex-
ceeding permit limitations for water disposal.
Nord Stream, Saipem, and Baker Hughes continued to
discuss precommissioning, eventually deciding on an ap-
proach based on intervention at the wet end(s) of each
pipeline section via subsea construction vessel (SCV).
This approach allowed each section to be completed inde-
pendently of any other sections and Section 1 (closest to
Russia) to be precommissioned earlier in the year while
the sea at the Russian coast remained frozen and while
Section 3 pipelay was still ongoing. This approach signifi-
cantly increased schedule flexibility. The final precom-
missioning concept included:
• Precommissioning spreads onshore in autonomous areas
separate from construction sites used for permanent facilities.
• Precommissioning pigs for the subsea pipeline not tra-
versing the permanent pig traps or permanent valves.
• Flooding, cleaning, and gauging performed offshore
aboard the SCV. All subsea handling was performed by ROV.
• Water treated with sodium bisulfite (NaHSO3
) and ul-
traviolet light (UV) only.
• Pressure test of Sections 1 and 2 from SCV.
• Pressure test of Section 3 from the receiving termi-
nal in Germany (to reduce vessel time and risk from wait-
ing on weather).
• Dewatering the line from Germany with water dis-
charge in Russia, after completing subsea hyperbaric tie-in
at KP 297 and KP 675.
• Drying from Germany to Russia.
• Using nitrogen as a barrier between air and gas during
commissioning of the pipelines.
The flooding, cleaning, gauging, and pressure-testing
spread installed aboard the Saipem vessel Far Samson in-
cluded suction pumps, a water-treatment system, and flood-
z130506OGJsca01
FIG. 1
Source:
NORD STREAM PIPELINE
KP 0
NORWAY
SWEDEN
Vyborg
RUSSIAESTONIA
LATVIA
LITHUANIA
RUSSIA
POLAND
GERMANY
DENMARK
Lubmin near
Greifswald
KP 1,224
KP 675
KP 297
KP = kilometer point
z130506OGJsca02
FIG. 2SECTIONAL NORD STREAM SPECS
KP 0
Design pressure, bar
WT, mm
200
30.9
Section 2
100 177.5
26.8
Section 3
220
34.6
Section 1
KP 1,224
KP 675, water
depth 115 m
KP 297, water
depth 80 m

4. TECHNOLOGY
ter removal and desalination could be
completed in a single pig run. Slugs
of potable water designed to dilute
the residual salt content remaining
on the pipe wall to an acceptable level
separated the first batch of four pigs.
Dry air separated the second batch of
four pigs, designed to pick up water
remaining after the desalination pigs.
Spacing of the pig train allowed the
first four pigs to be received and re-
moved before arrival of the second set
of four pigs.
Constraints
Nord Stream precommissioning in-
cluded the world’s longest offshore
dewatering operation and the world’s
longest sealing tool run. Development
of a pig-tracking system helped ensure
pig integrity along the full pipeline
length and was essential in establish-
ing sites where gauge-plate damage
might occur or pigs might get stuck.
Each 48-in. OD pipeline had an in-
ternal volume of 1.3-million cu m. The
maximum water depth, combined with
losses, required a dewatering pressure
of 29 barg and a very large air-com-
pressor spread in Germany. The large
flooding spread taxed the SCV’s deck
space, accommodations, ROVs, cranes,
and power generators, with the fitting
of all necessary equipment in a man-
ner allowing safe operation requiring
input from specialists.
Most of the Baltic Sea freezes in
winter, limiting the window for off-
shore operations. Water winning and
water disposal could not occur while
the sea was frozen.
Water-treatment planning sought to find the most envi-
ronmentally friendly approach, complying with applicable
international and local regulations while maintaining cor-
rosion protection and minimizing the possible formation
of precipitates inside the pipeline. Strict noise restrictions
required purchasing a custom air-compressor spread to en-
sure compliance.
The large diesel volumes necessary to fuel the compres-
sor spread in Germany required a custom diesel storage and
handling system to receive and distribute 100 cu m/day with
no containment loss. A comprehensive waste-management
system separated, tracked, and managed all waste produced
during project execution.
ing and pressure-test pumps. Pressure-test pumps for Sec-
tion 3 were at the German landfall. Dewatering and drying
occurred at German landfall and included 15 steel water
tanks, each holding 760-cu m. The water receiving facility at
the Russian landfall included a settling pond and a tempo-
rary 20-in. diameter floating discharge line.
The flooding, cleaning, and gauging (FCG) pig train de-
sign ensured that the operation could be completed in a sin-
gle pig run while providing contingency pigs to address wet
buckle scenarios during pipe laying activities. Bidirectional
pigs were back loaded into the subsea test head and installed
on the seabed up to 1 year before the operation.
Dewatering pig train design likewise ensured that wa-
An aerial view of Nord Stream’s German landfall shows the compressor spread, dry-
ers, and both diesel and condensate storage, the diesel to fuel the compressors and
the condensate drawn from the gas stream (Fig. 3). A detailed shot (Fig. 4) shows the
11,400 cu m of on site water storage and some of the more than 1,500 m of steel
pipework.

5. TECHNOLOGY
Compressor, dryer
Precommissioning of the pipelines re-
quired two major equipment spreads,
the FCGT spread offshore and the
compressor spread onshore in Germa-
ny. The FCGT spread provided filtered
and treated seawater to propel the pig
train at 0.5 – 1.0 m/sec, cleaning and
gauging the pipeline while filling it
with water for the pressure test.
The FCGT spread required 10,000
hp of diesel-driven pumping equip-
ment and 750 kw from the SCV’s on-
board generators. Spread installation,
testing, and certification took 7 days,
while the vessel was in port at Nor-
rkoping, Sweden. Spread design used
electrically driven submersible pumps
5 to 20 m below the sea surface to feed
water through the 2-stage filtration
system; primary filtration to 200 µm
and final filtration to 50 µm.
Treating the water with UV and
then metering and treating with sodi-
um bisulfate followed filtration. Twin 6-in. diameter LFH
downlines and 8-in. diameter low-pressure hot stabs boost-
ed pressure through the flooding pumps and injected the
water into subsea test heads. All subsea hose handling and
connection was performed by work-class Innovator ROV
and supported by the vessel crane. The flooding spread con-
sistently achieved flow rates up to 2,500 cu m/hr with no
mechanical downtime.
Compressor spread design and installation focused on
providing dry, oil-free air to push the pig train for dewater-
ing and to subsequently dry the pipeline, with the spread
specifically built for the project. Primary compressors de-
livered 34 barg of air with 34 barg dryers. The 24,000-hp
dewatering spread ensured a minimum free air delivery of
30,000 scf/min injected into the pipeline at ≥ -60° C. dew-
point. The dryers also used active carbon filtration to pre-
vent oil carryover into the pipelines, as required by ISO
8573-1 Class 2.
The compressor spread included central diesel storage of
200 cu m and a distribution system capable of handling 100
cu m/day of diesel. Air spread condensation storage was 100
cu m. Diesel and condensate system design ensured zero
losses to the environment and were approved and certified
by Technischer Überwachungs-Verein (TÜV).
German landfall also included 18,000 sq m of hard stand-
ing, 11,400 cu m of water storage, and more than 1,500 m of
steel pipework (Fig. 3-4).
The Russian landfall area served mainly as a receiving
terminal for precommissioning water. A 6,000-cu m water
storage pond allowed any discolored water from the pipeline
Execution
Nord Stream awarded the precommissioning contract in Au-
gust 2009. A 9-month tendering process allowed sufficient
time to consider multiple concepts before award. Running
this tender concurrently with other project approvals al-
lowed for immediate commencement.
The engineering procedures prepared for precommis-
sioning included 110 documents developed over 18 months,
which required review and approval by both Saipem and
Nord Stream. The 18-month period was necessary not only
to complete the base scope engineering, but also to evaluate
all possible options and changes thoroughly.
Meeting flow and pressure demands while achieving
the strict environmental and noise targets set required a
large percentage of the precommissioning equipment be
procured new for the project. Early award of the precom-
missioning contract afforded 12 months for equipment
building, testing, and delivery. Some vendors did not
meet their delivery schedules, but the 12-month win-
dow allowed sufficient slack for this not to affect the
project’s schedule.
Flooding, cleaning, gauging and pressure testing (FCGT)
took 41 days on Pipeline 1 and 38 days on Pipeline 2. Hav-
ing contingency plans in place for all of the critical equip-
ment and fully testing the inspection spread ashore allowed
for successful FCGT operations.
Dewatering, drying, and nitrogen injection followed
FCGT. Full precommissioning of each line took fewer than
150 days, from commencement of FCGT to completion of
nitrogen injection.
A temporary pig trap installed at the German end of the pipeline launched dewatering
pigs using a 48-in. diameter ball valve. The temporary trap was rated at 50 barg (Fig.
5). Permanent pigging equipment was excluded from pipeline precommissioning to
avoid damage.

6. TECHNOLOGY
to settle and be appropriately disposed.
The20-in.diameter,1,200-mwaterdisposallineconsisted
of 600 m of steel pipe onshore and 600 m of floating HDPE
pipe offshore. Water removed during dewatering was piped
to its permitted discharge site (at a location with a water
depth of more than 5 m) and released back into the sea via a
dedicated diffuser system.
Pig traps
Permanent pig launchers, pig receivers, and all permanent
valves were not included in the precommissioning scope in
an effort to avoid any damage. The temporary pig traps (Fig.
5) designed and built for the project had a 50-barg design
pressure, using a 48-in. ball valve, which allowed for the
individual launching of the dewatering pigs from Germany.
The four FCG pigs, eight dewatering pigs, and the four
sealing tools (inserted in the pipeline by the tie-in operator)
arrived in Russia in batches of four pigs.
Each subsea section termination required a subsea head
that could either receive or launch the FCG pig train and was
designed to be used during the pressure test. Despite their
sizes (48-in. diameter x 25 m), these heads also had to pass
through the firing line on the pipelay vessel.
Design, construction, and testing of the subsea heads
included tight controls and several stages of testing,
validation, and retesting to ensure 100% head integrity
during deployment, flooding, and pressure test operations.
Hot stabs
ROV hot stabs connected the FCGT downlines to the subsea
heads. The three sizes used were:
• 8-in. diameter (low pressure) for flooding.
• 4-in. diameter (high pressure) for pressure testing.
• 1-in. diameter (high pressure) for pressure test instru-
mentation.
Figs. 6 and 7 show the subsea construction vessel’s emer-
gency decoupling system, to be used in a dynamic positioning
runaway or similar unplanned event. A single button would re-
lease all hoses and downwire, which would remain suspended
by buoys pending reconnection.
Inserting the 8-in. and 4-in. hot stabs hydraulically
into balanced T-design receptacles kept friction loss low
and left open the possibility of inserting the stab from
either side of the subsea head. Engineers also developed a
hydraulic hot-stab extractor tool which could push out a
locked stab if necessary.
The project conducted both dry trials and full-scale wet
trials in a Norwegian fjord to confirm the hot stabbing
operation and hose deployment arrangement.
Hoses, coupling
Baker Hughes proposed using lay-flat hoses based on
previous experience working with them on projects in Asia.
Such hoses require far less deck space than hard-wall hoses.
Flooding used two 6-in. LFH supported by steel downwires
and suspended clump weights. During pressurization the
LFH expands, creating an internal bore comparable to an
8-in. diameter hard-wall hose.
A system developed for the project enabled the SCV to
disconnect quickly and safely from the subsea heads in the
event of an emergency such as a dynamic positioning (DP)
run away. The DP controller can release all the hoses and
downwire from the vessel at the push of a single button. The
hoses and downwire remain attached to the subsea heads
and suspended from buoys for subsequent reconnection
(Fig. 6-7). Activation of the disconnect system would shut
down all pumps aboard, while internal check valves ensured
water from the pipeline was not released.
Acknowledgment
The authors wish to make special mention of the Nord
Stream precommissioning team leads for their contributions
to this article: Andrew Turnbull, senior project engineer, and
Giuseppe Lopez, senior project engineer.

7. TECHNOLOGY
Marco Casirati
Jarleiv Maribu
Nord Stream AG
Zug, Switzerland
John Grover
Daniel Fehnert
Baker Hughes PPS
Dubai
As subsea hydrocarbon pipelines have grown in scale, plans
for their precommissioning have been incorporated early in
project development. The Nord Stream natural gas pipeline,
crossing the Baltic Sea from Vyborg, Russia, to Lubmin (near
Greifswald), Germany, successfully used this approach.
Part 1 of this article (OGJ, May 6, 2013, pp. 100) de-
tailed the planning, engineering, and preparation for Nord
Stream’s precommissioning. This second part continues this
discussion before looking at relevant field experience gained
during project execution.
Sealing pigs
All pigs were specifically designed and fabricated for the
Nord Stream project. Nord Stream conducted market sur-
veys and conceptual studies with three different pig vendors,
one of which tested a prototype pig. Tests included pressures
required for initiation, running, restarting forward and re-
verse, and flipping the discs. The resulting recommenda-
tions and proven field experience from earlier projects pro-
vided the basis for the final pig selection. Several concepts
were evaluated but discarded, in-
cluding lightweight pig bodies and
the use of wheels.
During the production and as-
sembly phase, each pig was subject
to extensive quality checks. Before
final delivery, each pig was again
checked and measured to make
certain it was delivered in accor-
dance with specifications.
FCG pigs
Flooding, cleaning, and gauging
(FCG) pig designs required that
they displace the air with water,
ensuring an air content of less
than 0.2% in volume, and pass a
97% nominal internal diameter
gauge plate through the pipeline
without damage. They also had
to be able to remove as much con-
struction debris as possible from
the pipeline.
The selected design was a con-
ventional bidirectional pig with
four guiding discs, three sealing
TRANSPORTATION
Growth in pipeline scale prompts
early precommissioning planning
A pig tracking vessel followed each pig train, checking smart gauge and pig positions from
launch to receipt (Fig. 1).

8. TECHNOLOGY
discs, and one gauge plate on each pig. All pigs also car-
ried magnets and were designed to carry a transponder for
tracking. One pig carried a smart gauge plate through each
pipeline section.
Dewatering pigs
Dewatering pigs were to separate the desalination slugs and
remove as much water as possible before starting the dry-
ing operation. These pigs had to perform over the 1,224-km
(760-mile) full length of the pipeline, a dewatering length
that had never been done before. Careful selection of pig
dimensions ensured the discs did not wear out (stiff discs)
during the distance or lose contact with the pipe wall (soft
discs) because of aquaplaning. The discs needed to have cor-
rect hardness, wear properties, flexibility, and contact forces
with the pipe wall.
The selected dewatering pig was also bidirectional with
four guiding discs and four sealing discs. All pigs carried
rare-earth magnets for local pig tracking and were designed
to carry a transponder for global pig tracking.
Sealing tools
Sealing tools used during hyperbaric tie-ins prevent water in
the welding area. A minimum of one tool on each side of the
weld is required. To provide a sufficient level of protection
with respect to pressure variations (tidal variations, atmo-
spheric pressure variations), the sealing tool must be able to
hold a certain pressure without any movement.
This tool is a further development of the traditional
spheres used in earlier projects. It contains two sealing ele-
ments (tires) mounted on a bidirectional pig with guiding
discs to achieve long-distance wear resistance after comple-
tion of the tie-in. Nord Stream sealing tools’ nominal de-
signed break-loose pressure was 1.5 bar. The tools also had
to be capable of travelling up to 675 km for removal after
weld completion. A total of four tools were used.
Smart gauge
The third pig in each of the FCG pig trains carried a smart
gauge plate to identify any gauge plate damage and assist in
locating pipeline defects. The system, once activated, could
be interrogated either subsea while travelling through the
pipeline, or when at rest in the receivers. The smart gauge
records the first damage event and communicates the time
of event through the pipe wall when interrogated without
physically removing the pigs from the head.
Pig tracking
Accurate pig tracking is essential to confirm the location of
the pigs when launched, received, and in transit. It provides
increased operational confidence and was required on the
Nord Stream project to divert any discolored water in front
of each pig into the settling pond.
Acoustic transponders provided global pig tracking when
the pig train was moving or stationary. The magnets, includ-
ed in all bidirectional pigs, provided the local pig tracking
when passing magnetic pig detectors. All FCG pigs and Pigs
1-3 of the dewatering train included active acoustic tran-
sponders. These allowed each pig to be individually identi-
fied and its distance from the pig tracking vessel calculated.
The duration of the pig runs and the time between the
subsea deployments in the laydown heads and the actual
run required a long battery life and a delayed start mecha-
nism. Acoustic transponders provided an excellent solution
because they only emit an acoustic signal when requested
and can be left in sleep mode for more than a year before use.
In addition to the active acoustic transponders, magnets
activated detectors subsea and onshore to confirm the pas-
sage of each of the pigs out of the launchers and into the re-
ceivers on each section. A pig tracking vessel followed each
pig train, checking both the smart gauge and pig position
from launch to receipt on the FCG, sealing tools, and dewa-
tering pigs (Fig. 1).
Velocity Pipeline
FIG. 2PROFILES

9. TECHNOLOGY
• In preparation for the precom-
missioning operations, over a peri-
od of about 2 years, to test and se-
lect the most appropriate treatment
and obtain the discharge approval
by the agencies.
• During precommissioning, in
particular during the FCG opera-
tions and during the dewatering of
the pipelines, to monitor and docu-
ment the results of the selected and
approved treatment approach.
Seawater treatment has a two-
fold objective in terms of pipeline
integrity: avoiding oxygen-induced
corrosion (OIC) and minimizing
the risk of microbiologically in-
duced corrosion (MIC). Adding
oxygen-depleting agents to the sea-
water (oxygen scavengers, typically
sodium hydrogen sulfite) meets the
first objective.
The offshore industry uses several
different methods for MIC control, ranging from strong bio-
cides, to the inhibition of bacterial activity by pH control of
seawater, to ultraviolet (UV) light. Nord Stream chose not
to use biocides, and pH control had to be carefully evalu-
ated for possible carbonate precipitate formation, which
could prove problematic for pigs travelling during the de-
watering phases.
The three alternative treatments of natural seawater in-
vestigated were doses of:
• Oxygen scavenger (OS).
• OS and pH control with caustic soda (NaOH).
• OS and biocide (Gluteraldehyde), for comparison pur-
poses only.
Natural seawater (without any treatment) acted as the
control.
The 2009-10 testing program, in cooperation with Finn-
ish company Ramboll OY, included:
• Seasonal seawater sampling and analysis at sites in-
tended for water uptake (KP297 and KP675), and at a site
representing KP0.
• Bench-scale laboratory tests.
• Pilot plant-scale tests for precipitation potential of treat-
ment option.
• Laboratory-scale medium and long-term corrosion
tests (LCT), reproducing anticipated conditions inside the
pipelines and various residence times of the treated seawater
in the lines (between 1 and 10 months).
• Full-scale testing (FST), whereby sections of pipeline
were filled with treated and non-treated seawater, deployed
subsea and left on the sea bottom for 6-12 months (Fig 3).
Seawaters collected at KP0 underwent FST and LCT, with
Tracking the interface between water and air by plotting
the velocity as measured at the discharge outlet in Russia
provided an additional way of tracking the dewatering train.
The water column in front of this pig (Fig. 2) will produce an
outlet flow and velocity proportional to the pipeline profile
(height of liquid column).
The interface pig will always be at the last plotted position
on the velocity graph. Comparing it with the pipeline profile
shows the pig’s location. This method is accurate as long as
the pig train is in a reasonably good condition so that little
or no air bypasses the pigs. The velocity graph slowly trend-
ing away from the pipeline profile shows the pig train losing
sealing integrity due to large amounts of air bypassing the
pigs. This method may also be used for pig train quality con-
trol as it progresses through the pipeline. The information
received helps engineers at the receiving end better prepare
for what to expect; air in front of train, two-phase flow, etc.
Water treatment selection
Given the volumes involved, seawater was the only practi-
cal option as a water source. Seawater had to be adequate-
ly treated before injection into the pipelines, satisfying two
conflicting requirements: line integrity (protecting the inner
surfaces of the pipelines) and compliance with international
and local environmental standards for the direct discharge
of precommissioning waters back into the sea.
Testing of the treatment approach and specifications to
the maximum possible extent in laboratory and field tests
occurred before submittal to the environmental agencies for
water discharge permits. Nord Stream carried out studies on
precommissioning water in two distinct phases:
Nord Stream precommissioning included full-scale testing, during which sections of
pipeline were filled with treated and non-treated seawater, deployed subsea, and left on
the sea bottom for 6 and 12 months (Fig. 3).

10. TECHNOLOGY
limits of 65 db (day) and 55 db
(night) at the closest dwelling. The
local marina was within 500 m of the
compressor spread. Sound-proofing
all supplied equipment to 76 db at 7
m ensured noise emission limits were
met without any additional special
sound barrier.
Results
The subsea heads, hot stabs, and pig
tracking system worked flawlessly
during FCGT operations. All FCG pigs
performed as expected and no dam-
age was observed. The water filtration,
additive system, and pumping spread
operated consistently at or above their
specified duty levels.
Air content confirmed to be well
within the Det Norske Veritas (DNV)
requirement of less than 0.2% demon-
strated the flooding operation’s suc-
cess. A final cleaning run removed
less than 2 kg of construction debris
in each section. Iron oxide and small
amounts of sand and some red-col-
ored dust were also removed.
Gauging plates confirmed the in-
ternal diameter to be within design
requirements. Out of six smart gauge
runs, one gave a damage indication
(which proved to be false). Acceptance
of pressure test operations occurred after only hours of pres-
sure stabilization before the mandatory 24-hr holding pe-
riod. The accompanying table shows a summary of the pres-
sure test data for Pipeline 1. Pipeline 2 had similar results.
Favorable spring weather conditions, with temperatures
similar at the surface and at the bottom of the Baltic Sea,
were one of the main reasons for the quick and successful
pressure test.
Dewatering
Temporary onshore pig traps, together with a temporary 48-
in. diameter valve, resulted in smooth and controlled de-
watering. This made it easier to control the operation and
to keep water and air separated during launching of the pig
train. Pig 4 provided a perfect barrier between desalination
water and the air.
The compressor spread and dryers, as well as all support
systems, met or exceeded their specified duties during the
operation. Air injections ceased as planned when the dewa-
tering pig train had travelled 60% of the pipeline length,
with remaining pig travel driven by the expanding air. This
saved fuel and minimized depressurization requirements af-
results then factored for seawater at KP297 and KP675
using scientific judgment based on detailed knowledge of
the physical-chemical characteristics of the water at the
three locations.
The “no treatment” option was ruled out based
on possible long residence time in the pipeline. The
combination of OS dosage and pH control using NaOH
gave no advantage over OS dosage, except for the planned
2-4 month residence time of the seawater in the pipelines
during precommissioning.
Pilot scale precipitation tests showed that calcium car-
bonate precipitates inside the pipelines could add to the
project’s risk because of the resulting amounts of sludge to
be moved along the pipelines during dewatering.
Nord Stream selected the OS-only option for treatment of
seawater, adding UV light treatment before filling the pipe-
lines with water as an extra safety contingency. Compara-
tively high numbers of sulfate-reducing bacteria (SRB) in the
seawater sampled at KP297 and KP675 during spring and
summer prompted the UV usage. SRB can lead to MIC.
Noise
The German landfall site has stringent noise emission
PRESSURE TEST DATA, PIPELINE 1 Table 1
Test Volume Pressure
Length, Volume, pressure, Pressurization added, Stabilization drop during
km cu m barg duration, hr cu m period, hr test period, %
Section 1 297 310,098 248 36:33 4,823 2 0.048
Section 2 378 394,670 226 53:16 5,772 4 0.035
Section 3 548 572,167 201 40:68 7,596 6 0.102
Injection pressure
Back pressure
Pig speed
Air injection shut off
once pigs reach
~60% (734 km)
35
30
25
20
15
10
5
0
0 200 400 600 800 1,000 1,200
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Pressure,barg
Length, km
Pigspeed,m/sec
DEWATERING PRESSURE, PIG VELOCITY FIG. 4

11. TECHNOLOGY
Drying removed 4.5 cu m of water, based on dew point
readings and air volume, corresponding to a water film
thickness of 1 µm on the pipe wall and demonstrating the
best dewatering results ever achieved. Recorded gas dew-
point levels confirmed dryness post-commissioning.
Nitrogen
Avoiding explosive mixtures in the pipeline during gas fill
(as set out by DNV OS-F101) required an inert gas as a
barrier between the air and the natural gas in the pipeline.
Nitrogen packing differed between Lines 1 and 2. Line 1
was completely filled from Germany with 99.9% pure ni-
trogen. Line 2 was partially filled from Russia (gas filling
end) using a 99.9% pure nitrogen batch equal to 10% of the
pipeline volume.
The mixing zone between air and nitrogen measured
about 1.5 km for both pipelines. The mixing zone between
nitrogen and gas was 2-3 km. Maintaining the interface ve-
locity above the critical minimum was an important compo-
nent of obtaining these results.
Water treatment
The SCV with seawater injection pumps installed carried
out treatment of seawater, pumping precommissioning
water into the pipelines at KP297 and KP675. Water treat-
ment included:
• Filtration through 200 µm and 50 µm cartridge filters.
• Online injection of the oxygen scavenger (OS), a com-
ter receipt of the pig train at the Russian end.
The pig-tracking vessel followed the different pigs all the
way to the Russian coast. The two sets of sealing tools (one
set from KP 297 and one from KP 675) arrived first, then
the dewatering train. Diverting the water in front of each
pig to the settling pond required accurate pig tracking. Fig.
4 shows the dewatering pressure and pig velocity, with Fig.
2 showing additional details with respect to pipeline profile
and pig velocity.
Receipt of the pig train included checking the desalina-
tion water’s chloride content. Analysis demonstrated final
chloride content was well below the specified 200-ppm lim-
it. Water volume in front of the swabbing pigs was small.
Experience from Pipeline 1 (little water) allowed the flow in
front of the swabbing pigs to be routed through the silencers
for Pipeline 2.
The amount of water in front of the swabbing pigs mea-
sured less than 1 cu m. This was due to good pigs, internal
coating, and smooth operations. The discharge control valve
only operated once, toward the end of dewatering to main-
tain maximum 1 m/sec velocity.
The desalination pigs showed little wear after travelling
1,224 km. The swabbing pigs showed more wear, but still
maintained sealing integrity, indicating that they had been
running mostly dry and confirming the results. Drying
Pipeline 1 took 18 days, including a 24-hr soak period. The
soak period confirmed an atmospheric water dewpoint of
less than -35° C., allowing Pipeline 2 to be dried to less than
-35° C. without a soak period.
Almost all precommissioning water was eventually discharged directly into the sea. Discolored water in front of each pig was cap-
tured, diverted to a water settlement pond, and settled for a minimum of 24 hr before being discharged. All water discharged to sea
was clean (Fig. 5).

12. TECHNOLOGY
Eprinted and posted with permission to Baker Hughes Inc from Oil & Gas Journal
May 6 and June 3 © 2013 PennWell Corporation
The calculated killing rates for anaerobic bacteria were
generally in line with expectations. Results and observa-
tions confirmed water treatment achieved project targets.
Measurements found no measurable impact on the marine
environment at the discharge site and pipeline integrity
was confirmed.
Environmental
The water treatment program allowed discharge of almost all
water directly into the sea. Discolored water in front of each
pig was captured and settled before discharge. Water stored
in the settlement pond was discharged to sea through filters
after no less than 24 hr. All water discharged to sea was clean
and contained no oxygen.
Discharge occurred 600 m offshore through a diffuser
nozzle to ensure rapid oxygenation of the water. Any oxygen
levels greater than 7 ppm were well within the 100-m from
the diffuser required by regulations. Fig. 5 shows discolored
water as sampled during operations.
A third party monitored noise in Germany. The compres-
sor spread complied fully with the project’s stringent noise
limits. Sound proofing all individual units also improved
the working environment for operational personnel and im-
proved safety as normal verbal communication was possible
within the compressor spread.
mercial solution of sodium bisulfite and iron-based catalyst.
• UV-light treatment.
A fully equipped laboratory aboard the SCV obtained
the key analytical parameters of seawater for control of the
treatment operations. Daily adjustments to metered OS dos-
es matched the measured oxygen concentrations of filtered
seawater. The results of the test program set the OS dose rate
at its stoichiometric value, 6.5 mg OS/mg O2.
Dissolved oxygen concentrations in the filtered seawater
were generally at saturation values of 12.5-15.0 mg/l. Over-
saturation also occurred at times. The potential environ-
mental impact of oxygen-depleted water at the discharge lo-
cation received particular attention. A special water diffuser
was designed and installed to achieve a high re-oxygenation
effect in the immediate proximity of the discharge point, a
requirement of the water discharge permit released by the
Russian authorities. Field measurements carried out during
dewatering confirmed the effectiveness of the diffuser.
A UV treatment unit also installed on the precommis-
sioning vessel had a design killing-rate of more than 99%
of the initial bacteria count at effective UV dosages of 40-60
millijoule/sq cm. Bacteriological analysis was carried out in
the laboratory aboard the SCV during the FCG operations
for both total anaerobic and total aerobic bacteria before and
after the UV package.
The authors
Marco Casirati (marco.casirati@nord-stream.
com) is project manager for Nord Stream AG in
charge of precommissioning, commissioning,
gas-in, and shore approach at the Russian land-
fall, with overall responsibility for the concept,
design, and performance of operations. He has
held this position since October 2008. He has
also served as project director for engineering, procurement,
construction, and installation (EPCI) on the Dolphin Sea Lines
and Export Pipelines and has managed other projects, such as
the Libya Gas Transmission System (GreenStream) and the off-
shore section of Blue Stream. Casirati holds a PhD in aeronauti-
cal engineering from the Polytechnic University of Milan, Italy.
Jarleiv Maribu (jarleiv.maribu@nord-stream.com)
is an advisor with Nord Stream AG on engineer-
ing, precommissioning, and commissioning mat-
ters. Maribu has been in this role since October
2008. He has also served as responsible man-
ager for precommissioning concepts, planning,
and execution of all pipeline systems with Statoil,
Norway. Maribu holds an MS in mechanical engineering from
the Norwegian Technical University, Trondheim.
Daniel Fehnert (Daniel.Fehnert@bakerhughes.
com) is Eastern hemisphere operations manager
with Baker Hughes Process & Pipeline Services,
based in Dubai. He has 19 years of experience
in providing process and pipeline commission-
ing and precommissioning services around the
world and was the Baker Hughes project man-
ager on Nord Stream. Fehnert is a PMI, PMP certified project
manager and holds a first-class engineering degree from the
University of Newcastle upon Tyne, UK.
John Grover (John.Grover@bakerhughes.com) is
with Baker Hughes Process & Pipeline Services
as director–Eastern hemisphere, overseeing all
pipeline precommissioning operations performed
in Europe, Africa, CIS, Russia, Middle East, Far
East, and Australia. Grover is based in Dubai
and has been in this role since July 2010 and
with Baker Hughes since 2005. He has also served as manager
at the PII pipeline inspection business of GE Energy. Grover
holds a higher national certificate in electronic engineering from
Norwich City College.