Ground-breaking welding operations on cracked gas pipeline 27 metres below the java sea while pipeline remained live.

DCN 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. Our engineers 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. A 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 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 DCN Director 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.”

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 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.

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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