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www.bakerhughes.com/pps Phone: +1 281-230-7423 Email: [email protected] 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

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Page 1: OGJ Nordstream

www.bakerhughes.com/ppsPhone: +1 281-230-7423Email: [email protected]

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

Page 2: OGJ Nordstream

Nord Stream natural gas pipeline highlights need to integrate precommissioning

TRANSPORTATION

Marco Casirati Jarleiv MaribuNord Stream AGZug, Switzerland

John Grover Daniel FehnertBaker Hughes PPSDubai

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.

BackgroundNord 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 (NaHSO

3) 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-

SPECIALREPORT

Based on presentation to Deep Offshore Technology (DOT) International Oil and Gas Conference, Perth, Australia, Nov. 27-29, 2012.

Page 3: OGJ Nordstream

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-

z13

05

06

OG

Jsca

01

FIG. 1

Source:

NORD STREAM PIPELINE

KP 0

NORWAY

SWEDEN

Vyborg

RUSSIAESTONIA

LATVIA

LITHUANIA

RUSSIA

POLANDGERMANY

DENMARK

Lubmin nearGreifswald

KP 1,224

KP 675

KP 297

KP = kilometer point

z13

05

06

OG

Jsca

02

FIG. 2SECTIONAL NORD STREAM SPECS

KP 0

Design pressure, barWT, mm

20030.9

Section 2

100 177.526.8

Section 3

22034.6

Section 1

KP 1,224

KP 675, waterdepth 115 m

KP 297, waterdepth 80 m

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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.

ConstraintsNord 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.

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TECHNOLOGY

Compressor, dryerPrecommissioning 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

ExecutionNord 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 f low 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.

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TECHNOLOGY

to settle and be appropriately disposed.The 20-in. diameter, 1,200-m water disposal line consisted

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 trapsPermanent 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 stabsROV 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, couplingBaker 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.

AcknowledgmentThe 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.

Page 7: OGJ Nordstream

TECHNOLOGY

Marco Casirati Jarleiv MaribuNord Stream AGZug, Switzerland

John Grover Daniel FehnertBaker Hughes PPSDubai

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 pigsAll 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 pigsFlooding, 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).

Page 8: OGJ Nordstream

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 pigsDewatering 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 toolsSealing 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

Page 9: OGJ Nordstream

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 selectionGiven 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).

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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.

ResultsThe 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.

DewateringTemporary 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 0.048Section 2 378 394,670 226 53:16 5,772 4 0.035Section 3 548 572,167 201 40:68 7,596 6 0.102

Injection pressure

Back pressure

Pig speed

Air injection shut offonce pigs reach~60% (734 km)

35

30

25

20

15

10

5

00 200 400 600 800 1,000 1,200

1.2

1.0

0.8

0.6

0.4

0.2

0.0

Pre

ssur

e, b

arg

Length, km

Pig

spe

ed,

m/s

ec

DEWATERING PRESSURE, PIG VELOCITY FIG. 4

Page 11: OGJ Nordstream

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.

NitrogenAvoiding 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 treatmentThe 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).

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TECHNOLOGY

Eprinted and posted with permission to Baker Hughes Inc from Oil & Gas JournalMay 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.

EnvironmentalThe 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 authorsMarco Casirati ([email protected]) 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 ([email protected]) 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 ([email protected]) 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 ([email protected]) 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.