^ After welding the joints the pipeline is pushed down the ramp, or stinger as its known. The pipeline could be suspended for a kilometre behind the lay barge before touching down on the seabed, depending on water depth. It therefore has to be kept under huge tension or the weight of the suspended catenary would cause an immediate buckle. Tensioners on the lay barge prevent the pipeline from running down the stinger, although there wouldn't be much length to run down as the new joints are constantly being welded on.
Here is the Acergy Piper on another project in Brazil. You can clearly see the welds (field joints) where the 12 metre sections of pipe have been welded together.
Each section is welded on, then each weld is subjected to a multitude of testing, including Xrays, for integrity. A tin wrap is put around the weld and then the void used to be injected with bitumen, but now more environmentally friendly compounds are used. That is called a field joint.
The ramp doesn't reach the seabed - that would be impossible in deep water, but just extends maybe 100 metres or so to spread the load of the pipeline. It may be longer than that - everything on these barges is at huge scale.
In bad weather a temporary laydown head will be attached and the pipeline laid down on the seabed. The end needs to be sealed as you don't want corrosive salt water to flood the line. Once the weather is OK, the pipeline is recovered and normal operations resumed. When things went well this barge could lay 4 to 5km a day - earning the crew good bonuses.
At the end of a job a laydown head is welded on, as shown here... the end of that Brazil project.
You can see all the guys lining the railings (all in full PPE!) to watch the laydown head go down the stinger. This is the end of the job and they'll be looking forward to going home and spending their hard earned dollars. This was a special case as I think it was the last pipeline the Piper laid - it was laid up in Sicily after this. Special case for me too. At the time there were rumours we were going to follow the Piper around the world supporting pipelay projects, which would have been fantastic. That was in late 2008 - the financial crash in 2009 ended those hopes overnight.
And once a the pipe was laid down, the Piper raised the stinger and departed the work site...
The end of a pipeline is usually connected to a prefabricated spool and riser at a platform by hyperbaric welds carried out by divers. If the water's too deep for divers then ROV-friendly systems have to be designed to connect spools using the underwater vehicles.