Ensuring Optimum Efficiency In Subsea Pipeline Design

April 2013, Vol. 240 No. 4

Matthew Guite, Director of Subsea, Pipelines and Risers, Theon Limited

As the distance of large-scale offshore tie-backs continue to extend, this presents fresh challenges in terms of pipeline design. As pipelines and flowlines are custom-designed, this provides opportunities for re-thinking during the concept, front-end and pre-feed stages of a project. This early investment in overall system design will help avoid nominal design ratings and “standard” designs – which can result in over design – a problem which is all too common.

Pipelines fulfil a vital role in transportation and there are several ways in which smarter thinking and well-thought-out, simple but clever designs could benefit a firm’s global operations and output.

Getting it right in the early stages pays dividends in the long run. First, productivity would benefit from a more holistic approach to and understanding of flow assurance results. Flow assurance is a vital step in the design process, but needs at all times to be grounded in reality and the information used to further the design, not be the design itself.

Equally, as much as cutting corners and over design can cause its issues – over-conservatism in pipeline design can restrict and limit the level of production. By exploring design liberally during the concept phase, the maximum potential of pipelines can be achieved, thus resulting in reduced expenditure associated with post-build alterations.

A key industry challenge is the greatly reduced number of engineers with 10 to 25 years of experience due to drastic cut backs in recruitment of graduates during the 1990s. This is impacting design work where a lack of experience is being felt and historical procedures are still in use which maintains a certain spread of experience within a design team no longer there.

By fully exploring options and challenging the design data a project manager can have confidence in the design process, using the results to demonstrate the design has been sufficiently reviewed and contested. This ensures the pipeline and overall system design is optimal. People and knowledge are vital parts in the pipeline design process; despite the fact that no two projects are the same, an identification of a robust pipeline design is of primary importance.

Strategic Optimization
Life of field design is a major consideration in the subsea pipeline design process. Subsea engineering and surface facilities should work together due to the specific and custom nature of each project. There is no ‘off the shelf’ blueprint for such projects and as such it is imperative there is a strategic approach to current and future needs of a pipeline. Any ill-conceived planning will have a massive cost implication down the road as making changes during the early design phase is significantly more cost-effective than when subsea equipment and pipelines are fully designed and installed.

There are also a range of additional pipeline factors that will influence the pipeline design such as: high pressure, high temperature and fluid characteristics. With variances in flow highly likely over the life of a field, this has a significant subsequent bearing on the design of subsea pipelines.

Market trends mean that as oil and gas discoveries are made in more remote areas pipelines must adapt to these surroundings while maintaining a constant and reliable level. Consequently, there is a fundamental requirement for firms to conceive a methodical and well-considered design plan that takes temperature range and changes across the life of the field into account. A lack of understanding and experience can lead to a severe lack of asset integrity, reduced flow assurance, corrosion, over-stressing and buckling – all costly maintenance jobs to have to correct or retrofit further down the line.

Installation Cost Benefits
Despite the fact that much subsea pipeline design is carried out during the front-end and pre-feed stages of the project, the major cost element of the project is during the installation phase. Much of this cost comes from vessel and material expenditure – with installation alone commonly absorbing as much as half of the project cost – making saving time vital.

Greater consideration of materials and utilizing experience during the design phase needs to be viewed as time well spent rather than delaying the proposed project start date. There is a knock-on effect on any irregularities as suitable design has the ability to maximize vessel capacity, the reel-ability of pipelines and aid in selection of the most appropriate materials for the project.

With each offshore pipeline installation typically costing firms millions of dollars, a 10-20% saving has a substantial impact on capital expenditure. Such measures will ensure that firms continue to operate as cost-effectively as feasible on global projects, anywhere from oil wells in the North Sea to as far afield as gas fields off the coast of Western Australia. By ensuring and re-considering all possible design options in the first instance, an optimum level of pipeline efficiency and integrity can be achieved.

Future Of Pipeline Design
The future of pipeline design will continue to evolve in terms of process, materials and planning. As composites and plastics come into more common use, the need to appraise the subsea pipeline design basis will become increasingly crucial.
It has also been suggested the topical issue of non-metallic pipelines and connection systems other than welding will aid in the advancement of pre-emptive subsea pipeline design process.

However, firms must evaluate the exceptional safety record of dependable materials against the reduced capital expenditure associated with these upcoming composites and plastics. With company reputation management being prime in today’s 24/7 media culture – the potential repercussions of a leak could be catastrophic to brand, people, and the environment. As carbon fiber, plastic/steel composites, fibreglass, and other reinforced systems become verified and more widely accepted this material advancement remains at an embryonic stage.

Another key issue will be that of a proactive design review within a project lifecycle. A shrewder approach in the early design phases will continue to allow for nominal design features to be filtered out before projects are set in stone.
Design will continue to have a vital role in the rethinking of projects and the heart of efficient project management lies with a robust design basis. As the distance of pipelines continues to extend and the demand for flow increases, there will be a continued requirement for design to encompass whole fields and the strategic requirements of these fields.

Experienced Engineers
The well-documented skills shortage within the oil and gas industry will have repercussions for the way in which firms can efficiently design subsea pipelines. Engineers with over 25 years of experience and consultancies are seeing a significant rise in the number of specialist pipeline design projects they are being requested to assist in developing.

The involvement of more experienced engineers can help ensure thorough design review processes and more phased stage gate planning. In many cases this is worthwhile due to the outcome of a robust design, increased cost savings, greater quality control, and more streamlined plans.
A constructive take on the skills gap is that it offers the global oil and gas industry an opportunity to engage in knowledge-transfer. This exchanging of key knowledge helps to ensure that core expertise, such as pipeline design, are retained by the sector. However, this is not a short-term goal and the knowledge of consultancies will continue to be vital to the advancement of subsea pipeline engineering and design in future years.

There is a considerable opportunity for oil and gas production to prosper as a result of taking the correct steps at an early stage, to ensure efficient and robust subsea pipeline design. Subsea pipeline design can aid production in achieving an optimal level (and cost-effectiveness) by considering the following factors:
• High pressure, high temperature, fluid characteristics, and highly variable flow over field life and the subsequent impact on design;
• Better understanding of what flow assurance results mean to the design;
• Requirements to challenge the design data provided and its robustness;
• Over-conservatism in design and not achieving maximum pipeline efficiency
• Consideration of life of field design and the link between surface facilities and subsea engineering;
• Pipeline and subsea structures installation – the large cost needs to be considered early in the design process;
• Project costs and impact of design from the start – on installation, capacity of vessels, reel-able pipelines and material choice;
• The future of pipeline design, in terms new materials – composites and plastics.
By challenging these core issues and taking an impartial analysis by means of utilizing an external consultancy, firms can expect to trim a significant sum from project expenditure. Firms will have to remain open-minded to not only the imminent needs of the pipeline, but also the long-term potential design requirements of the project.
Over-engineering is costing the global pipelines industry millions of dollars per project with extended costs from long-distance subsea tiebacks. Being prudent toward maximization of flow efficiency will see continued success into future generations.

Matthew Guite
can be reached at www.theonltd.com.

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