This type of installation requires an S-Lay vessel, which is basically a floating welding factory, where pieces of 12 m long pipes are continuously joint and lowered to the seabed. The pipeline from the vessel to the seabed takes an S-shape that is why we call the method S-Lay. The layout of an S-lay vessel is shown below.

 

The main parts are: 1. Pipe transfer crane 2. Pipe storage area 3. the double joint factory 4. the main fire line 5.the tensioners, 6.the stinger

S-Lay is currently used for pipelines with diameter from 10 to 30'' in waterdepth up to 2500 m (1000t tension force). With the completion of the vessel Pioneering Spirit (2000t tension force) from Allseas, S-lay will be possible for pipelines with OD of 68'' 

Vessel Name Max Tesion Diameters Record
Depth [m]
DP
Seven Borealis 600 t 5" - 46" OD   YES
Lorelay 265 t 2" - 28" OD 1650 m YES
Global 1200 500 t 4" - 60" OD   YES
Castorone 750 t 4" - 60" OD   YES
Solitaire 1000 t 2" - 60" OD 2750 m YES
Pioneering Spirit 2000 t 2" - 68" OD    YES
Tog Mor 100 mt 60" OD 100 m NO
Stingray 140 mt 6" - 60" OD 100 m  

Advantages:

High pipelaying rate: 2-7 km/day

Wide range of pipeline diameters: 4" - 60" OD

Long vessels with large pipe storage capacities

Several production stations (welding, NDT, field joint coating): 6-10 stations

Many experiece contractors and economical aspects

Disadvantages:

Installation depth resticted on vessel tension capacity;

 

Pipelaying in detail

Pipe transfer onboard

Pipe temporal storage

Bevelling pipe Ends

Line-up

Preheating pipe ends

Welding the bead pass

Welding the hot pass

Welding the filler passes

Welding the cap

Ultrasonic testing

Entering the tensioner area

Grid blasting

Preheating for applying the field joint coating

Field joint Coating (FJC)