Joint integrity is a constant concern on offshore installations, both above and below the water line. For decades, standard ANSI or API flanges were the only solution, but in recent years, new types of sealing systems have emerged for topsides piping and subsea flowlines. These have been designed with an emphasis on simplified installation, leak-free perfor-mance, and longer seal life.
Two competitors in this field, Vector and Steel Products Offshore (SPO), merged last year to form a new company, Vector International, based in Port Talbot, UK, and Drammen, Norway. The combined operation now offers three main products to the offshore sector: the SPO compact flange, and the Optima subsea and Techlok clamp connectors. Quick Release V Band Clamp
According to Marketing and Sales Vice President Ian Robinson, the merger was mutually beneficial. "Vector wanted SPO's product, a lightweight bolted pipe connector which was complementary to our Techlok system. Our sealing technologies are practically the same. They on the other hand coveted our global marketing and distribution capability."
Currently, the newly merged company has a turnover of £18-20 million, with 150 employees worldwide and aims to double sales to the offshore sector over the next three to five years. The market for conventional flanges alone is worth $1.5 billion.
"Our own largest market is the UK North Sea, which provides 30% of our offshore sales, followed by mainland Europe, including Norway and Denmark, with 25%, and North America with 20%," Robinson said. "Our fastest-emerging area, however, is the Far East, which we're serving from our recently opened offices in the Petronas Towers in Kuala Lumpur."
The company has other operational centers in The Netherlands, Houston, Calgary, and Dubai, and is also considering opening branches in the longer term in Latin America and West Africa.
SPO introduced its compact flange to the offshore sector in 1989, following initial design studies in collaboration with Statoil and Norsk Hydro. The first application was for connecting risers to Saga Petroleum's Snorre TLP. According to Robinson, Saga opted for the new system as being 70-80% lighter than most conventional ASME/ANSI flanges, and also leak-free. The weight difference still applies today, he adds. Additionally, the system employs smaller bolts than comparable ASME/ANSI flanges and provides a beneficial alternative to a pipe girth weld where leakage is unacceptable. The compact flange uses radial compression and a wedging action to effect a rigid, full contact between the seal faces that is unaffected by load fluctuations. The design also ensures that seal performance will not be impaired by static or dynamic loading and that the flange's fatigue life will exceed that of the adjoining welded pipe.
The SPO compact flange's main distinguishing feature is its face geometry. This includes a convex bevel, with the highest point (heel) adjacent to the pipe bore and a small wedge around the flange face's outer diameter. During the connection process, the bevel is closed and flange face-face contact ensues. The bolt's pre-load is then transferred as a compressive force between the flange faces at the heel, while a more minor compressive force is conveyed through the outer wedge. At the same time, the flange face is parallel to its back face, to prevent bending of the assembled bolt.
"With our system, we bring the bolting in closer to the bore of the pipe, and can thereby reduce the size of the flange pieces," Robinson says. "Sealing the bore closer to the pipe also means there is no need for subsequent re-tightening of the bolts or maintenance of the connection."
Vector says that none of the 50,000 compact flanges currently in service have ever leaked, largely due to the system's three seals. The first seal is right by the bore; the second is the inner seal ring, which is completely contained to safeguard against corrosion. The third seal is on the outer lip, at the point where the two flange faces come together. The latter provides back-up should one of the other seals fail. The system is approved by Norwegian standards body Norsok.
"It is also Statoil's chosen flange product of the future," Robinson says. "They intend to replace all existing flanges on their Norwegian platforms with our system."
Recently, Norsk Hydro specified the SPO compact flange for process piping modifications on the Troll C platform topsides, in readiness for tie-ins associated with the Fram Vest subsea development. On a live production installation, this type of work would normally entail extensive preparatory work to create a safe, gas-free environment suitable for welding.
"The combination of heat and potential combustion can be very dangerous," Robinson points out. In Troll C's case, the in-situ welding requirement was reduced through pre-fabrication onshore of 30 pipe spools with SPO compact flange ends, which were then bolted together offshore on the platform. Flange diameters ranged from 4 to 16 in., pressure-rated from 750-6,200 psi.
Schematic illustrates the SPO compact flange's weight-saving properties compared to a conventional flange.
Optima is an ROV-operable subsea connector, for operations in water depths to 3,000 m and beyond. Unlike conventional ANSI flanges, Robinson says, it is also designed for ROV intervention. All Optima connectors are equipped with a metal-to-metal double action sealing system called DuoSeal. The self-energized inner seal prevents seepage, while the (external) self-energized seal guards against water ingress. "This is a major concern in very deep water," he points out.
Typical subsea applications include christmas tree and manifold connections, flowline jumper installations, retrievable choke connections, and pipeline repairs/tie-ins. Uniquely, Vector says, Optima connectors are capable of engaging around a hub with an angular misalignment of 5° or an axial misalignment of 2-in.
"Operators ask for this feature," Robinson says, "because the action of pulling a pipeline across the sea floor incurs a huge drag." The system is engineered to provide (in theory) consistent first-time closure through relaxation on final pull-in.
Last year, Vector was contracted by ABB Offshore Systems to supply Optima connectors in diameters ranging from 14 to 28 in. – the largest sizes produced to date – for Statoil's Snohvit subsea project in 350 m of water in the Barents Sea. Four of the largest connectors will be used in the 160-km multiphase pipeline taking Snohvit's gas to a new LNG plant on the island of Melkoye. Others will be deployed on templates associated with the subsea production system, which will be controlled directly from this plant. Corrosion resistance, and the ability to work in a wide range of temperatures were strong factors in the Optima's selection for this project.
"These connectors have a design life of 50 years," says Robinson, "and are made from F65 and duplex stainless materials. In the past, we've also supplied compact flanges in titanium."
Vector has had to modify the system, due to environmental sensitivities (this is the first field development in the Barents Sea, although exploration drilling activity is currently suspended), and the need to interface with ABB's ROV manipulators. During the fall, the system underwent six weeks of trials both in Port Talbot and at the independent Vaseco test center in northwest England, all witnessed by Statoil. Following an initial hydro test, a 28-in. nominal bore connector was subjected to:
Throughout the test program, the Optima proved to be leak-free.
Once the systems have been proven in operation on Snohvit, Vector expects more orders for other subsea projects and is preparing to invest in further R&D and manufacturing capability. Studies have also been mounted with FMC Konsberg and ABB for potential application in BP's Plutonio development offshore Angola, and in numerous other deepwater projects.
Vector's longer-established, four-bolt Tech- lok clamp connectors can withstand higher tensile loads than conventional ANSI flanges, where the flange face has a tendency to break up under strain. With the Techlok system, this situation is avoided through use of a pressure-energized bore seal, which ensures the connector remains leak-proof, even under severe pressure and bending conditions. Even if the pipe moment is increased to the verge of pipe failure, the connector and joint integrity remain sound.
As with the SPO compact flange, the Techlok's metal-metal seal rings are confined within the connection, and cannot be damaged by bending loads or bolt over-tightening. Techlok clamps are produced in sizes from 0.5 to 24 in., all held in place by four bolts, compared with up to 24 bolts for a conventional flange, according to Robinson.
Among the current offshore applications, Technip-Coflexip has ordered 350 clamp connectors from Vector for flowlines linked to the TPG 500 jack-up platform for BP's Shah Deniz project off Azerbaijan. The connectors are being manufactured in duplex and super duplex steels, in sizes from 1 to 16-in., for pressures up to 10,000 psi. In the North Sea, 315 Techloks made from carbon steel and 316 stainless steel are being provided to main contractor Amec for modifications to topsides process piping on BP's Miller platform. Other consignments are being prepared for the Thunder Horse semisubmersible, the Kizomba B TLP and for Husky's White Rose FPSO.
Two years ago, Vector also worked with Wood Group as part of a "leak reduction initiative" on BP's Magnus enhanced oil recovery project, east of Shetland. Leaking joints are hazardous, impair production efficiency, and are costly to repair. The program involved thorough inspection of all joint components – connectors and associated interfacing equipment – at each stage of production and testing, prior to shipment to the installation.
The cost of repairing or replacing such components, once operations have started, can be 10-15 times greater, Robinson says. Additionally, Vector supplied its reverse integrity testing (RIT) rings to test flowline and compressor discharge pipework. The rings apply a constant gas or hydraulic pressure for around 15 min, after which any failure in the seal ring can be detected as a significant loss of hydraulic pressure.
Flange Clamps Screwfix Overall, the various measures undertaken limited the number of leaking joints to less than 1 %, brought cost savings of over £100,000 through avoiding re-work alone, and were instrumental in ensuring that the project started up on time, Vector says.