Flowline connection flies in the face of fast-track field development. Alignment often has to be attempted 20 times or more before a perfect fit is achieved, due largely to the multiplicity of bolt holes on a typical flange. The upshot is an extended vessel hire period - not ideal for operators of deepwater pro jects, where cost pressures are already intense.
One solution to the process is a connector developed by Vector International, based in Port Talbot, UK. The connector, known as Optima, can slot onto a hub, either with an angular misalignment of 5°, or with an axial misalignment of 2-in. Either way, the acceptable closure envelope is extended, leading to consistent, first-time connections, according to Vector. Also, the level of security provided by the external seal allows the connector to function in water depths up to 3,000 meters or beyond.
Vector is better known for its high pressure Techlok clamp connectors with lightweight flanges for topside applications. The new system was tested in collaboration with Halliburton Subsea Services, which has conducted ROV-deployed installation trials at its deepwater tank simulator in Aberdeen.
Optima took two years to engineer, based on consultations with all the main flowline installation contractors, which included numerous leading exploration and production companies. According to Vector's Sales and Marketing Director Ian Robinson, "their priority was consistently reliable connection first time. They also wanted a system that would be:
- Adaptable for fast-track deepwater projects - the misalignment capability suits late design changes
- Integratable with all trees, manifolds, flowlines and risers
- Smaller, compact and simpler to install, in turn allowing smaller and lighter manifolds to be deployed
- Predictable - there are so many variables involved when attempting to tie pipes together at the right time
- Subsea engineers wanted the ability to cope with design changes imposed during the field's life (they wanted the system to be simple to disconnect and re-connect)."
For deepwater applications, there were added concerns such as the sealing retention system. Clients were anxious about connectors dropping to the ocean floor and having to be retrieved. "They also had problems with corrosive environments and external pressures at greater depths," claimed Robinson.
Vector addressed the corrosion problem by employing Capcis in Aberdeen for the materials evaluation. The solution was a high grade, forged nickel alloy which appears to offer a design life for the connector of 25 years. For added corrosion protection, sacrificial anodes can be fitted. As for pressure, Optima connectors have withstood 11,000 psi in trials witnessed by Bureau Veritas.
Among Optima's other features are a minimum radial misalignment of 10 mm. "This gives you more scope when pulling the pipe across the ocean floor post-connection," Robinson claims. The system also features dual action metal-to-metal sealing - a self-energized inner seal prevents egress of the pipeline's contents, while a self-energized outer seal blocks ingress of seawater.
Once mating has been accomplished, seal integrity can be confirmed instantly through an ROV-accessed annulus test port (with visible status indicator). The ROV then moves forward to complete the next connection. Normally, annulus testing is protracted by secondary sealing systems such as O-rings, which have to be taken out re-placed following each test. These are not required with Optima.
Another feature is the hub profile, which provides a male-to-female mating system. "The seal ring is located positively in the male hub prior to assembly," says Robinson. "The hub protects the seal ring so the latter cannot be damaged." However, should failure or seal damage occur, an auxiliary seal could be fitted deeper into the hub following modifications, he claims.
Vector settled on a single lead screw for the connector, rather than two, requiring a maximum of 6,000 Nm of torque for the installation, which is within most work ROVs' capability. "With a single screw, you can introduce larger sizes, bringing the clamp into operation quicker." There is also an emergency removal system for the clamp and allowance is built into the calculation formula for external bending moment. Optima connectors will be available initially in nine standard sizes from 2-6 in. (10,000 psi-rated) and 8-14-in. (5,000 psi).
