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SCENARI - SCENARIOS
struzione sia durante la vita operativa.
Quando gli attraversamenti sono
complicati da condizioni ambientali
difficili, l’analisi di predizione del
comportamento nel tempo è estremamente
complessa e articolata.
La costruzione di una condotta è realizzata
saldando tra loro le barre di
tubo opportunamente preparate e
adagiandole lungo un percorso predefinito.
La progettazione e la tecnologia
di costruzione variano a seconda
che si tratti di condotte a terra o
sottomarine.
In genere le condotte sottomarine richiedono
un livello tecnologico elevato
sia per la costruzione, per via dei
mezzi impiegati, sia in seguito per la
gestione e la manutenzione delle linee.
Le condotte a terra sono interrate,
con pochissime eccezioni in casi di
attraversamenti o ambienti particolari
quali la zona Artica e sub-Artica; questo
sia per aumentarne la sicurezza
sia per ridurre l’impatto sull’ambiente.
Le condotte sottomarine sono solitamente
esposte, posate sul fondo del
mare, interrate e/o protette esclusivamente
in corrispondenza degli approdi
costieri o di sezioni potenzialmente
esposte ad azioni ambientali estreme
o attività di pesca, mercantili e dell’industria
degli idrocarburi.
Per la costruzione delle condotte sottomarine,
l’ambiente di posa spesso
richiede l’uso di mezzi specifici, di notevole
dimensione e costo, che sono
le navi posatubi. Tali mezzi navali possono
essere delle officine di lavoro
galleggianti, ove trovano alloggio fino
a centinaia di persone, che abitualmente
lavorano a ciclo continuo, con
turni tra il personale. Le attività seguono
lo schema funzionale delle condotte
a terra, ove però si svolgono sulla
terra ferma quante più attività preparatorie
possibili e ove la parte di varo
e di eventuale lavoro sul fondo assume
una importanza molto maggiore.
La necessità di evitare sollecitazioni
e deformazioni eccessive che possano
compromettere l’integrità presente
e futura della condotta ha portato
allo sviluppo di tecnologie e mezzi
di posa sempre più potenti e sofisticati nel controllo
delle sequenze operative.
Le condotte, sia terrestri sia sottomarine, operano in un
contesto che potrebbe comportarne il deterioramento
nel tempo, sia per ragioni identificabili in sede di progetto
che per ragioni inaspettate. Pertanto la realizzazione
di una condotta prevede sempre l’implementazione di
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POSA OFFSHORE. Per la posa di condotte
sottomarine è richiesto un livello tecnologico
molto elevato. Ogni nave posatubi è dotata
di stazioni di saldatura, controllo saldature
e rivestimento dei tubi. Il sistema
di tensionamento permette di calare in mare
la condotta mediante l’avanzamento
della nave. Gli interventi sui fondali
sono effettuati dall’uomo se le profondità
non sono elevate, ma laddove aumentano
è possibile intervenire solo con sofisticati
strumenti telecomandati denominati
Rov (Remotely Operated Vehicle).
OFFSHORE LAYDOWN. A very high technological
level is required to lay subsea pipelines.
Each lay-barge is equipped with stations
for welding, welding control and pipe coating.
The tensioning system enables to lay the pipeline
into the sea as the barge moves on.
Operations on the seabed are carried out
by people when the sea is not too deep.
But when it is very deep you can operate only
by means of sophisticated remote-controlled
instruments called Rov (Remotely Operated
Vehicle).
equipaggiamenti e programmi di gestione a garanzia della
funzionalità nel tempo previsto in sede di progetto per
l’esercizio.
Roberto Bruschi lavora in Snamprogetti come responsabile
Ricerca e Sviluppo nel settore sistemi di condotte. In questo
settore è anche direttore Progetti speciali.
Eni’s Way
decreased considerably,
settling at excellent
performance levels,
and this testifies to the
attention given by the
different sectors of the
industry to
technological innovation
to transport
hydrocarbons by
pipeline.
Pipelines can be
classified according to:
environment to be
crossed, for example
overland pipelines or
sub sea ones, with subcategories
that further
qualify their main
characteristics such as
elevation profile, the
nature of the terrain,
etc.; product
transported, whether
liquid, gas or
multiphase, with subcategories
that qualify
the fluidodynamics of
the transport such as
pressure, temperature,
speed, etc.;
construction materials,
either the typical carbon-manganese steel or special,
corrosion-resistant alloys, and the weldings they are
assembled with; and construction technologies, in particular
those related to the laying operation and the work needed for
burial, both for overland and sub sea pipelines.
In general, the facilities to transport hydrocarbons by
pipelines don’t interfere significantly with human activities,
since the pipelines are buried at such a depth so as to
minimize all sort of interference, or they are laid on the
seabed, yet they require very careful managing, considering
what they are worth and their foremost position in the energy
policy of a nation. The execution of a pipeline is affected by
the features of the territory to be crossed, by the need to
minimize the environmental impact, especially during
construction phase, and by legal restrictions imposed in
densely populated areas. Choosing the best route must
reconcile technical-economic requirements with the need to
protect the sites involved, keeping within the range of
variation of the parameters linked to the technical- economic
feasibility of a crossing.
With regard to sub sea pipelines, seabed crossing entails
significant technological effort. Deciding on the route cannot
be carried out using a direct view of the area, as is done with
aerial photographs and on-spot visual inspections for onshore
pipelines. The reconnaissance phase is totally instrumental,
entrusted to the use of highly sophisticated technologies and
bound to the interpretation of measurements. Environmental
difficulties and the need to use advanced technologies to get
project data make optimal route selection a very crucial
Eni’s Way
phase in a sub sea crossing project, which provides the basis
for the technical-economic assessment of the work’s
feasibility.
The designer’s first objective is to define the pipe diameter
needed to convey a given quantity (flow per time unit) of the
product (chiefly oil or natural gas, or a mix of the two) from one
place to another. During this phase, the entry pressure of the
product is defined, taking into account, among other things,
the fluid properties, expected changes along the route,
depending on the type of pipeline (sub sea or overland) and
the type of fluid being conveyed (liquid or gas), load loss, etc.
The choice of materials for pipes used to convey hydrocarbons
depends mostly on the fluid conveyed (gas or liquid, more or
less corrosive, etc), and passes though a decision-making
process that involves several types of analyses.
A pipeline conveying petroleum products such as oil and
natural gas needs be resistant enough to bear the stress
caused by the loads which will be imposed on it, both in its
construction phase and its operating life. When crossings are
hindered by difficult environmental conditions, the analysis of
behavior prediction over time is extremely complex.
To build a pipeline they weld together the lengths of pipe after
duly preparing them and laying them along the chosen route.
Planning and construction technology change depending on
whether an overland or a sub sea pipeline is involved.
Generally speaking, sub sea pipelines require an advanced
technological level, both to build them, owing to the means
employed, and afterwards to operate and maintain them.
Onshore pipelines are buried underground, except for very few
exceptions in the case of crossings and of distinctive
environments, such as the Arctic and sub-Arctic area. They
are buried both to improve security and reduce environmental
impact.
Sub sea pipelines are usually exposed, laid on the seabed,
and are buried and/or protected only when reaching the shore
or with stretches potentially exposed to extreme
environmental conditions, or to fishing, merchant and
hydrocarbons industry activities.
In building sub sea pipelines, the laying site often requires
using special, very large and costly units, namely, the pipelaying
ships. These vessels can be floating working stations,
which can accommodate up to hundreds of people, who
typically work in shifts around the clock. The work follows the
same functional sequence as overland pipelines; however, as
much preparatory work as possible is carried out onshore and
the launch phase and possible seabed work take on far
greater importance. The need to avoid stress and excessive
deformation that may compromise the present and future
integrity of the pipeline led to the development of increasingly
powerful and sophisticated technologies and laying barges to
control operational sequences.
Both overland and sub sea pipelines work in a context that
may bring about their deterioration over the course of time, for
reasons that may have been identified in the drawing board
stage, or for unexpected reasons. Hence pipeline building
always includes the implementation of equipment and
management programs to guarantee functionality over the
span of time foreseen in the planning stage.
Roberto Bruschi works with Snamprogetti as Pipeline Systems- R&D
Manager. In this sector he is also Special Projects Manager.
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