DCN International Diving and Marine
Contractors recently developed and employed a unique method that made it
possible to repair a crack in a 32-inch gas
pipeline three times more cheaply than by installing a bypass.
Engineers from the Dutch company came up with a completely new application for
an existing concept. Thanks to a number of innovative alterations, DCN was
able to introduce the method in the Java
Sea, where an extremely critical repair could be carried out on a live
operational gas pipeline. For the client, the new method meant a saving of
millions.
DCN director Wim Vriens talked about this
remarkable example of underwater innovation:
At the end of last year, DCN was awarded the
largest EPIC contract in the company's history. The Indonesian state-owned
company PGN (Perushaan Gas Negara), specialists in the transport and
distribution of gas, awarded DCN the order to seal a tear in a seven
year-old gas
pipeline located on the bed of the Java Sea. The crack had been
discovered in 2013, and temporarily sealed using a Plidco clamp. The gas that
flows through the pipeline is delivered to the Indonesian capital city of
Jakarta. Switching to another pipeline was not possible, so one of the
requirements imposed by PGN was that throughout the repair, the gas supply had
to be continued without interruption. In other words, the gas
pipeline had to remain fully pressurised, or the 29 million residents
of Greater Jakarta would have experienced considerable, long-term problems.
Hyperbaric
centre
To be able to meet this requirement, DCN
proposed carrying out the welding work underwater, in dry conditions, through
the use of what is known as a habitat. A habitat is a sealed working space that
offers divers a safe and protected working environment, while on the sea bed.
Others viewed the proposed alternatives with considerable scepticism, and
instead opted for a far more costly and complex alternative that involved
installing a bypass. "DCN was the only company that met the requirements
imposed by PGN, with its repair proposal," explained Wim Vriens. Because
gas supplied to Jakarta is entirely dependent on this one pipeline, PGN
demanded precise preparation of all work, including facilitation of simulated
test conditions. As Vriens continued: "The fact that we are the only
diving company in the world that have our own complete hyperbaric centre was
therefore a decisive factor in the awarding of the order. During the summer,
here in Bergen op Zoom, we carried out a series of dry runs and tests. We
endlessly simulated all the elementary welding tasks necessary to ensure the
long-term success of the repair at our own location. The tests were in fact
carried out by the same divers who would eventually be required to carry out
the work at a depth of 27 metres in the Java Sea, under considerable pressure.
After the extensive testing programme, all the risks had been identified,
minimised and managed."
Logistics
The implementation of the project itself also
called for a carefully planned logistic organisation. The first containers of
equipment were shipped to Singapore at the start of July, including the
complete saturation diving system and the habitat with suction anchors (piles).
The final batch of welding equipment and the pre-heat induction cables
developed and produced specially for the project were finally sent out by airfreight
at the end of July. Applying power to these cables after wrapping them around
the gas pipeline,
generates the necessary heat to preheat the pipeline to 70 degrees, before a
start can be made on the actual welding work. The hyperbaric centre at DCN
clearly played a central role in developing these unique cables.
Four sets
In Singapore, all the equipment was then placed
on the afterdeck of the vessel Normand Baltic, chartered for the work by DCN.
The Norwegian DP2 vessel subsequently sailed to the island of Batam at the
start of September, to collect the sleeves that were also specially produced
for this project. The sleeves are the definitive outer coating that had to be
welded tightly around the pipeline, as a sort of second skin. In line with the
specifications, four sets of sleeves were produced; one set for test welding,
one for simulating handling in the habitat, one for welding onto the cracked
torn pipeline and one spare set. The same requirements applied to the gas
containment clamps that first had to be placed over the existing Plidco clamp
on the pipeline.
Installation
In preparation for the offshore work 30 kilometres
off the coast, a multi beam survey of the entire environment was first carried
out. After studying the recordings, a start was made on installing the 5
six-metre long piles in the seabed made up of silt and clay. The first pile was
used as a trial, in order to determine the required suction force, and to
calculate the theoretical load-bearing capacity. The habitat subsequently had
to be placed on the remaining four piles. To ensure installation of the piles
within a tolerance of just 20 cm, a complete location-finding system was placed
on the pipeline, using acoustic, underwater beacons. These made it possible to
produce a three-dimensional chart of the underwater situation. Safety was the
first priority; we had to avoid coming into contact with the pipeline so as not
the cause the crack to spread further. The placement of the habitat with its
diving bell, which would serve as a safe haven throughout the project for the
nine saturation divers, went without a hitch. "This was certainly one of the
most critical moments of the project, and we were greatly relieved when the
habitat was put in place right first time," admitted Wim Vriens.
Following the hermetic sealing and purging of
the habitat to lower the water level, the first gas containment barrier – a
sort of safety clamp – was mounted on the pipeline, followed by the lower and
upper sleeve. The divers were then able to start on the demanding welding
process while the gas continued to be pumped through the pipeline. Over a
period of ten days, welding was carried out uninterrupted, while the welded
layers underwent continuous ultrasonic testing. Finally, the repaired section
of the pipeline was fitted with an anti-corrosion wrapping.
The entire repair project was successfully
concluded by mid-October, well within the agreed timeframe, on budget, without
any additional work being required and without a single personal injury. A
remarkable performance that was closely monitored by the entire subsea world.
Wim Vriens concluded,
"What DCN has demonstrated with this project is the company's innovative
attitude that enables us to tackle complex projects with simple solutions. In
coming up with those solutions, we are clearly willing to think out of the box.
Thanks to this creative approach, we are able to break out of existing
patterns, and deal with problems and dilemmas in an entirely new way. We come
up with solutions that others set aside as unworkable. This project is
incontrovertible proof of that ability."
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