One trend that has been emerging in the recent years in the design of umbilical systems is the progressive increase of the size and weight of end terminations. Driven by the need to integrate functions normally found on manifolds, this emerging trend poses extremely severe challenges to installers and appears to be compounded by the differing requirements of parties in the supply chain (FEED contractors, termination design companies, operators, and manufacturers). Invariably the installation contractor has had no involvement with termination design until presented with the actual equipment to be installed. The following analysis details the way in which excessive termination dimensions impact the offshore oil and gas industry.
Oversized terminations often require a bespoke solution leading to an industry wide spread syndrome of “re-inventing the wheel”. These bespoke solutions increase the overall cost of the operations and restrict the choice of vessels capable of carrying out the installation. Carousels may have to be deployed instead of reels to be able to handle large volumes and masses. All these factors lead to an increase in direct costs not only for umbilical installations but also for the decommissioning phase, an aspect that is often neglected when designing umbilical. Systems equipment specifically built for installation may no longer be available at the time of decommissioning when the oversized terminations have to be recovered from the seabed.
The increased size and weight of terminations has a direct effect on the lead time which is increased by the inevitable need to identify bespoke rather than standardised solutions. Bigger and more complex terminations demand longer fabrication and assembly lead-times, and in some instances have to be disconnected and reconnected to facilitate load-out of umbilical systems all adding to an increase in time and risk. When operating at the limits, if not beyond, of current installation vessel capabilities, the overall vessel time is increased. In recent years the pace at which terminations have been growing far exceeds the pace at which new, higher spec vessels, can be brought to the market. Extreme installation requirements have, therefore, to accommodate availability issues associated with a limited number of vessels capable of installing them. This situation can have an impact on the duration of the umbilical installation campaign.
As well as terminations, bend stiffeners and bend limiters have also grown in size and weight. One of the factors that led to this situation is the lack of a clear definition of the acceptable level of risk which leads to over-engineering issues. Excessive safety factors adopted in the various design stages may lead to issues such as a very high minimum bend radius which can significantly complicate the umbilical system installation process.
More stringent and complex installation requirements may also restrict the installation window with consequent economic and operational risks.
Terminations are not always appropriately designed for lifting; when lifting points are present these are usually of limited functionality being designed for vertical lifting rather than for over-boarding. Larger deployment towers are therefore needed on the installation vessel and multiple cranes may also have to be used. Although the industry has acquired good experience with these types of operations, they inherently carry a higher level of risk that could be avoided with more appropriate termination designs. Larger and heavier terminations invariably lead to higher risk of damaging the umbilical during installation. Bend restrictors/limiters can break simply because of the weight of the terminations coupled with incorrect handling. The integration of functions into one single large and/or heavy unit carries higher risk of increased vessel downtime and loss of vessel schedule with consequent significant economic impact on a project.
With the increased risk associated with the installation of such large and heavy terminations, and not always being aware of the impact on the attached umbilical, the long term reliability of the umbilical system is put into question, long after the installation vessel has been demobilised.
Following an Umbilical Manufacturers’ Federation initiative, several major umbilical installation contractors (Subsea 7, Saipem and Technip) and OTM Networks collaborated towards the launch of a joint industry project for the development of a best practice document. This document will address the need to standardise the shape of umbilical terminations and identify guidelines for their size and weight.