Magazine : World Pipelines (November issue)

As subsea and deepwater developments drive a growing requirement for ROVs and ROV-operated technologies, Vector International technical director John Stobbart looks at developments in diverless connection technology to meet this demand

As oil and gas prices soar, existing fields become depleted, and the industry moves into deeper and more hostile environments, subsea engineering capability is seeing growing attention and demand.  The global subsea oil and gas market is set to remain strong (following a market growth of nearly 90% in the last five years), and is forecast to total some $218 billion over the next five years.  Much of the focus is on deepwater exploration in Africa, Latin America, and North America, and, increasingly, Southeast Asia and Australia, but subsea techniques and technologies can also be valuable for extracting relatively small reserves in mature areas such as the North Sea, while in regions such as the Middle East and Russia much of the subsea market will be centred on export and trunk lines.  Additionally, some very real technology developments are being seen in the subsea processing arena. 

Among the multiple issues and challenges faced in subsea and deepwater installation, tie-ins and connections are a significant element.  From subsea pipeline and flowline tie-ins to christmas tree and manifold connections, flowline jumper installations, retrievable choke connections, and more, both horizontal and vertical, the growth of subsea engineering has focused increased attention on remotely installed connection technologies.  And even in areas where divers could be used, a growing preference for diverless operation is emerging on a risk basis.

While selection of the optimum connection method may not appear to be the highest priority or greatest challenge, there are some important factors to take into account that could make a valuable difference to efficiency, cost and long-term performance.  Given the high cost of installation vessels and ROV equipment, the often tight time window available in deep and harsh environments, and the close correlation between time and cost, ease of installation to minimise time demands is a primary consideration, for example.  Other critical factors include long term reliability and high integrity sealing performance, as well as flexibility to accommodate and facilitate adaptations to field architecture.  A further consideration may be size and weight, as a minimised space and mass envelope can be a valuable advantage in the case of compressed or congested subsea architecture.

Ease of installationWhile hub alignment is commonly a time-consuming element of connector installation (traditional pipe flange designs, for example, require the flange halves to be aligned accurately to facilitate bolting), diverless connectors should ideally be designed to minimise this requirement. 

For a number of pipeline connection techniques accurate subsea linear and angular measurements can become critical, as face-to-face contact with no angular misalignment between lines is required.  Any miscalculation of linear measurements may lead to angular errors, which could add to stresses at the connection point that could in turn impact on long term performance.  Successful connection of a jumper spool to two laterally spaced, upwardly facing pipelines, for example, would require the linear distance between the two pipelines and their angular orientation to be measured precisely – but this is a potentially costly and time-consuming process that can increase overall connection costs. 

A technology capable of accommodating misalignment is clearly advantageous.  The Optima diverless subsea connector from Vector International is one such example, which offers a self-alignment capability designed to make installation simpler and more efficient.

The connector consists of three articulated clamp segments which close around the mating hubs in a clamping action as the lead screw is turned by the ROV drive tool, pulling the hubs together (with the sealring held in place between them with a rotating and locking device) to provide a high performance metal-to-metal seal.  Uniquely, the connector can engage around a hub even with a misalignment of up to as much as 5° or an axial misalignment of two inches (whichever is the lesser), effectively addressing one of the primary challenges involved in subsea connector installation. 

This valuable angular and axial tolerance is a function of the hubs’ male-female configuration.  By increasing the target area (which is a significant advantage where sled pull-in systems are being used and precision is difficult to achieve), it results in a relaxation or enlarging of the final pull-in alignment and closure envelope, thereby minimising installation time and associated cost.

Optimised ROV compatibilityAmong other measures to maximise the speed and efficiency with which installation can be achieved, design features that make the connections as ROV-friendly as possible are fundamental.  The use of a single lead screw is one such feature of connector design that can contribute significantly to simple and quick connection and disconnection.  Equally, connectors that are compatible with the broadest possible range of ROVs and connection tools, and with a torque requirement that is within most ROVs’ capability, is a further consideration.  Other features to aid efficient installation include an easily ROV-installed sealring, an ROV-visible make-up indicator to confirm when full closure has been achieved, and a simple means of confirming seal integrity.

The sealring element of the connection is also an important consideration during installation.  Damage to a seal or sealing surface caused by bumping or scratching while the connector is being installed subsea is a potential cause of connection failure.  This is particularly so in designs where seal surfaces are used for alignment, which increases the susceptibility to damage. 

A compact but robust design to protect the vital components is therefore important.  The male to female mating system of the Optima connector’s hub profile, for example, provides added protection of the sealring, while the profile of the sealring itself minimises damage risk on installation by ensuring late contact of the seal faces.  Additionally, this profile eliminates potentially problematic secondary sealing systems (‘O’ rings) required for annulus testing, with seal integrity readily confirmed by an easily ROV-accessed annulus test port.  This removes the need to line test, and also provides a detection method for leakage throughout the connector’s lifetime.

Long term reliabilityOnce installed, reliability and long-term integrity are further factors of critical importance for remote connections in subsea and deepwater installations, again focusing attention on the sealing technology deployed. 

Double-action, metal-to-metal sealing is the optimum route to ensure joint integrity and reliability.  One such example is the innovative DuoSeal sealring, which features both a self-energised inner seal (the internal pressure in the line intensifies the sealing action and prevents leakage, ensuring internal pressure integrity), and a second energised seal which prevents ingress of water, with the ability to withstand high pressures at depths in excess of 3,000 metres. 

Equally valuable in the on-going challenge to ensure long-term reliability are measures to minimise corrosion – another key consideration in remote subsea and deepwater connections.  Materials and coatings used for the connector body and components for maximum strength and corrosion resistance come into play here.  Connectors that can also be fitted with sacrificial anodes for additional corrosion protection can provide a further benefit. 

FlexibilityGiven the wide range of applications, flexibility must be a central tenet of any diverless connector.  A connector that can be used with rigid or flexible pipe, for vertical or horizontal connections, and with a range of related special products to suit specific applications, will provide a high degree of flexibility.  Further, a modular design will provide greater scope for interfacing with other equipment, from goose neck connections to multi-bore connectors, ‘soft land’ systems, and ROV interface equipment and closings. 

In the case of the Optima subsea connector, for instance, the technology can also be adapted and incorporated into the operator’s own specifications to suit specific application requirements.  In one recent example, Vector worked closely with the contractor undertaking the front-end engineering design (FEED) for a project, to incorporate specific requirements into the connector design for connection of subsea flowlines to christmas trees, manifolds, and pipeline-end-manifolds (PLEMs).

Additionally, while on the one hand connections may well be required for a field lifetime, in other cases the field architecture may change with the development of new satellite fields or new injection wells.  A connector that meets this need by being as easily disconnected by ROV as it is connected will provide the necessary flexibility for changes and new connections to be made.  This was one of the drivers in the connector selection process for one project, where Optima connectors were to be used with a gooseneck or flexible pipe to connect a new well.

With deepwater development activity continuing apace, and some very real technology developments being seen in the subsea processing arena, a rise in global interest and demand for diverless connection is inevitable.  This is further reinforced by a growing preference for diverless operation, on a risk basis, even in shallower subsea applications where divers could be used.  Importantly, while a choice of diverless connections is available, consideration of certain key factors in selecting and specifying those to be used can contribute significantly to minimising installation time and costs, and to ensuring long term performance and reliability.

---end---