TECHNICAL CONDITIONS OF CONSTRUCTION AND OPERATION OF THE GAS PIPELINE ON THE BOTTOM OF THE BALTIC SEA INVESTMENT DESIGN ASSUMPTIONS Prof. Bolesław Mazurkiewicz.

TECHNICAL CONDITIONS OF CONSTRUCTION AND OPERATION OF THE

GAS PIPELINE ON THE BOTTOM OF THE BALTIC SEA

INVESTMENT DESIGN ASSUMPTIONS

Prof. Bolesław Mazurkiewicz – Technical University in Gdańsk

ISSUES

1. Undersea pipeline design process

2. Laying of the undersea pipelines

3. Protection of the undersea pipelines

4. Intersection of the undersea pipelines and their connection to the offshore platforms

UNDERSEA PIPELINE DESIGN PROCESS

I Stages:

• an initial stage

• measurement and investigation stage and data collection• stage of design works• laying stage

II An initial or preliminary stage:

• type of transported medium

• outer diameter• design pressure• maximal and minimal design temperatures• Scheduled pipeline route• anticipated operation period• type and quality of the pipeline structure, ballasting and protecting materials• anticorrosive protection systems • pipeline wall thickness, ballasting jacket thickness, weight in immersed condition and depth under sea bottom

III Measurement and test stage and data collection

geophysical investigations bathymetrical investigations geotechnical investigations oceanographical investigations

IV Design work stage• an initial design for justification of advisibility of selected route or necessity to change it

• technical design being basis for the pipeline implementation on selected route. Pipeline division into design sections differing definitely in bathymetry, design wave, geotechnical conditions and environment risks.

• Decision on necessity to immerse pipeline below the sea bottom.

• Determination of design safety coefficient within pipeline stability and strength.

V Laying stage

Actions on undersea pipelineType of interaction Cause

Weights Gravity forces

Lift Hydrostatic forces

Liquefaction

Resistance forces Velocity of fixed currents

Oscillatory velocities in wave motion; tearing off of whirls

Lift and tear off forces (crosswise) Velocity of steady currents

Oscillatory velocities in wave motion; tearing off of vortexes

Forces of inertia Oscillatory of molecule acceleration in wave motion

Tensile forces Pipe laying vessel tension; trension cable; pipe laying vessel motions; internal medium pressure; thermal shrinkage

Compressive forces Gravity forces

Pushing out during pipe laying; pipe laying-vessel motions; thermal expansion

Twisting Pipe laying –vessel motions

Connection of hanging loops

Outer pressure Hydrostatic forces

Ground

Internal pressure Medium pressing;

Stroke of pressed medium

Dangers threating the sea pipelines

Danger Prevailing type of ground, region

Geometrical and physical characteristics

Lanslides of the bottoms;runoffs of the bottoms

Soft clays of the delta regions (water depthe less than 60 m)

Width, length, strength and thickness; shear strength and other geotechnical data; expected translocations of considered region or zone

Turbidity currents Soft clays Phenomenon range, equivalent fluid velocities and densities, ground strength and other geotechnical data

Clotted bottoms Mouth deposits Changes of width and level in zone; shear strength and other geotechnical data of caking and surrounding deposits

Intrusions of crystallized salt Mouth deposits Width and expected uplift (elevation), ground shear strength and other geotechnical data

Slopes Regions with seismic danger Width and expected slope translocation, strength and other ground properties

-Liquefaction-Interaction of wave and sea bottom

-loads resulting from the earthquake

Sands , clays

Sands, clays

Width and thickness of the liquefied zone , strength and other ground properties

Local erosion Soft clays and sands Depth and width of the local erosion zone

Lack of pipeline support Sands receptive to erosion; hollow properties

Scope between supporting places, ground strength

Sand waves Debris currents; strong bottom currents

Wave height and range of threaten region

Laying of the undersea pipelines

legend:• Pływaki = floats• Układanie rurociągów za pomocą.... =

Pipeline laying by means of:a. barge up to 25.0 m depth;b. semi-submersible pipeline laying platform

up to 300 m;c. pipeline laying vessel up to 3 000 m

(depending on type of stinger’s type).

INTERACTION DURING LAYING

LEGEND:•siły pionowe = vertical forces•barka = barge•siła ciągnienia = tension force•wysięgnik = stinger•siły poziome = horizontal forces•dno morza = sea bottom•profil prądów …. = crosswise current profile•węzłów = knots

Preventive activity in case of dangers threatening undersea pipelines

Environmental danger

Preventive actions

Pipeline burying

Pipeline uplift Ballasting jacket

Pipeline anchorage

Heavier pipeline

Hydrodynamical forces

Tearing off of wortexes

Local erosion and lack of support

Sand waves

Creeps and runoffs of the bottom deposits

Turbidity currents

Pipeline floating

Deposit caking

crystallization of salt

Slopes, earthquakes

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Ground liquefaction The pipeline should be designed in such way, so that its unit weight would be as much as possible approximate to the unit weight of the liquefied ground and the pipeline is to be burried below the liquefaction level or to anchor it.

Current requirements concerning large diameter pipeline burying (> 750 mm)

Pipeline laying zone Existing dangers / risks

Current requirements

Future probable immersion practice Remarks

Coastal zone water depth <10 m

Waves, currents, bottom erosion, mud landslides, dredging outlets

3 m

Burying as deeply as possible

Ports and anchorage Waves, currents, drawing works, anchoring

~ 3 m

Burying as deeply as possible

Burying may turn out to be insufficient. It should be considered change of the route or other protecting methods.

Coastal zone and small water depth zone. Distance from the coast 50 km or water depth 30 m

Waves, currents, fishery, anchoring ? dredging works ? variable

Burying required usually only due to stability respects.. Immersion level determined for each specific case.

It should be examined navigation and emergency anchorage statistics.

Pipeline laying zone

Existing dangers / risks

Current requirements

Future probable burying practice Remarks

Open sea, average water depth. 30 m < water depth 100 m. Distance to the coast 50 km

Waves, currents, fishery, ~ 1m

Sinking can be necessary due to stability respects

Protection against fishery can be made by means of suitable concrete jacket

Deep waters, water depth

> 100 m

Waves, fishery

~ 1 m

Sinking is not required

Protection against fishery with suitable concrete jacket

Areas close to platform. Distance to platform < 5 km

Currents, fishery, anchorage of the ocean – technical vessels

~ 3 m

Sink as deep as possible; backfilling

Burying may turn out to be insufficient. Other protecting methods should be considered.

Pipeline protection methods

1. Not protected pipeline rests on the bottom

2. Ballasted pipelines

3. Pipelines on stakes

4. Pipelines on supports (saddles)

5. Anchoraged pipeline

6. Rinsed out pipeline

7. Immersed pipeline – natural backfilling

8. Immersed pipeline – backfilling ( cover) of rock blocks

9. Immersed pipeline - concrete cover

Methods of undersea pipeline burying below sea bottom

1. Stream method (hydraulic loosening)

2. Sandy soil liquefaction method

3. Mechanical cutting method (deepening)

4. Plowing method (plowing)

Evaluation of trench deepening

Liquefacting units Conventional Hydraulical

cultivation

(towed cradles)

Undersea equipment and vehicles

Plowing after layin

g

Plowing before laying

Sandy bottom + - - - - + effective- not effective

Clayey bottom - + + + + +effective-not effective

Method interrelation on equipment on the sea

surface

- - + + + +dependent -independent

Impacts of the sea current - - - - + + small impact-big impact

Method development; conducting, lowering;

lifting

- - - - + Not difficult+difficult

Costs - - - - + +less expensive- expensive

Water depth - - + + - +deep-shallow

Previous experience + + - - + +there are experien

ces-no experiences

Required development and tests

- + - - + +lack of develop

ment- development

exists

Power consumption - - - + + +minor demand- big demand

Productivity - + + + + + large- small

Forces acting on the pipeline - - + - +small-large

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Damage risk of the undersea pipelines

Anchorage resulting from

machine failure

Anchorage resulting from collision of two

vessels

Running of the vessels at the

bottom of the sea

Total number of events

Annual frequency* and period of repeated damage (including pipeline getting torn)

3.9 ·10-3

256 years

> 4.5 · 10-5

< 22220 years

2.74 · 10-4

3650 years

4.22 ·10-3

237 years

* Frequency is defined as the number of events for year and pipeline kilometer ( km)

Note: In case of laying of the pipeline laying with concrete cover , risk of the pipeline damage caused by fishing tool drawing is not taken into consideration.

Intersection of the undersea pipelines

Types of the pipeline intersection solutions:1. existing pipeline,2. new pipeline3. concrete supports,4. Bags with injection mortar laid in piles,5. begs with sand and cement laid in piles6. hard rubber saddles7. separator8. injection9. pipes for mortar injection 10. pipeline clamped with clamping ring fixed to support11. support made with framework consisting of pipes12. conection of support of bottom by means of ground

anchors

Connection of the undersea pipelines to the offshore platforms

Connection of the pipelines with conventional type riser:1. hinge connection using rotational connectors;2. connection with use of dog’s leg type pipe section;3. connection by means of hyperbaric welding;4. connection with use of a straight section;5. deck;6. platform base.