Marine pipeline construction

Andrew Palmer

KIVI 17 april 2003

S-lay J-lay

pipe made up at sea pipe made up on shore

reel pull and tow

surface tow

mid-depth tow

bottom tow

bottom pull

* Overall safety record was very good for the activity setinvolved(one high potential lifting incident during Solitaire mobilisation, onemedical treatment case on the survey vessel)* 105 km of 22" concrete coated pipe laid in under 18 daysincludingpull in and lay down. * Average lay rate of ~6.9 km/day (or over 4 meters/minute)* Peak lay rate ~7.8 km over a 24 hour period * No weather downtime & very minimal mechanical downtime* Program completed 11 days ahead of the 30 day plan (lump sumcontract)* 28 kilometres were laid between the live Magnus gas lines (100meters apart)

King Installation Planning Decisions Allseas S-lay Installation w/ Solitaire

advantages of S-lay

whole length of barge can be used for operations at multiple stations (line-up, welding, radiography, field joint infill, tension)

disadvantages of S-lay

in deep water, tension has to be highand/or stinger has to be long

laybarge J-lay

laybarge J-lay

laybarge J-lay

weld x

advantages of J-lay

tension can be much lower, particularly in deep watertouchdown point is closer to barge, and spans are shorterno stingerpipe less exposed to wave actionbarge can lower pipe and then weather-vane around

disadvantages of J-lay

welding all carried out at one or two stationsinflexible if breakdown occursnot suitable for very shallow water unless ramp can be rotated into horizontal position

KIVI 17 april 2003

mechanics of pipelayingV

U

in deep water (>100 m) the pipe is (almost) a catenary, and its shape is determined by the interaction between the submerged weight w per unit length and the horizontal tension U

only in small boundary layers near the seabed touchdown and the stinger lift-off is the flexural rigidity F significant

the maximum curvature is ≈ w/U

surface tow

bottom tow

mid-depth tow

tow

for all tow methods, the pipe has to have a uniform low weight during the tow

for bottom tow, the route has to be surveyed carefully, and the pipe must have an abrasion-resistant coating that can stand up to being dragged across the seabed

reeling

PLUTO (Pipe Line Under The Ocean) England to France, 1944

100 km+, two kinds of 3-inch pipe, one steel ERW, no coating, the other a hollow submarine cable

vertical axis reel (e.g.Global Chickasaw, Hercules)

two types of reelships

horizontal axis (e.g. Apache, Deep Blue, Skandi Navica, Seven Oceans)

strain

stress

compressive tensile

strain

stress

compressive tensile

Bauschingereffect

curvature

moment

0

curvature

moment

abc

0

curvature

moment

0

ramp0

01

2 3

32

1

curvature

moment

0

ram

p

3

32

1

4

4

5

straig

hten

er

6

6

0

5

how much wall thickness is needed to prevent buckling during reeling ?

sometimes said: D/t < 20 or 22 not so!

larger diameters require a smaller D/t

quantify

pipe diameter D, wall thickness t

reel diameter b

+=

=−

=

−=

=

b

fDtD

b

fD

D

t

f

D

t

bD

01.0

1/

01.0

safety offactor geometric if so

0.85) < ileyield/tens and 1, asfactor girth weld taking(

01.0strain buckling DnV

/strain bending maximum

ramp

buckle!

curvature

moment

ramp

buckle

weak

strong

reel

pipe with concrete weight coating cannot be reeled

links choice of construction method to design of pipeline

if stability is a governing factor, requires the steel thickness to be increased to give the pipeline enough weight

expensive (particularly for CRA pipe)

leads to other difficulties (such as upheaval buckling)

means that anti-corrosion coating has to resist potential mechanical damage

alternative flexible concrete weight coating

polymer-modified rubber-like concrete

more expensive than conventional concrete, but much cheaper than steel (per kg of submerged weight)

can be applied

gives mechanical protection to anti-corrosion coating

piggy-back

carrier

internal

insulation

pipe-in-pipe

open bundle

closed bundle

carrier

annulus

internals

closed bundle

carrier

annulus

reeled bundles

simple pipe-in-pipe systems can be reeled (e.g. Seahorse and Tarwhine projects)

studies have shown that more complex bundles can also be reeled

possibility of helical bundles (Husham patent 1895)

carrier diameter and wall thickness limited by reeling capacity

reeled bundles compared with towed bundles

reeled

carrier diameter limited submerged weight can be largeroute can be curved

towed

carrier diameter not limitedsubmerged weight during tow needs to be smallfinal route must be straight