Efficiency is in the pipeline

Despite the economic climate, new hurdles such as regulation, carbon accounting are driving innovation, especially in pipelines, says Sandra Rolfe-Dickinson, MWH technical director of pipeline engineering (Europe & Africa)

It is a tall order, but the water industry needs suppliers to design cost effective, sustainable short and long-term solutions, which also deliver pipeline efficiencies and reduce carbon emissions. Additionally, as water companies may be financially penalised by Ofwat for poor Service Incentive Mechanism (SIM) scores, we have to ensure that the customer experience is not compromised.

Similarly, although successive Asset Management Plan (AMP) periods have made the industry ever more efficient, it feels like clients in the current AMP5 are saying, “You were clever and innovative before, now you must be even more so.’’ Clients want us to challenge long-held industry standards, specifications and ways of doing things to create both new approaches and efficiencies.

Key to increased efficiencies in most water companies is better use of existing assets. This is particularly critical with pipelines, as reasons for poor performance can include failure history, inadequate capacity, and internal corrosion causing dirty water. Carbon reduction is another big concern for UK water companies and many now require their contractors and suppliers to report their emissions and demonstrate how they are taking action for carbon reduction.

No-dig options
The industry’s need for greater carbon accountability is giving new impetus to no-dig techniques like sliplining, spray lining, pipe bursting and directional drilling. The most significant carbon emissions savings come from reduction in the amount of plant required for no-dig rehabilitation solutions. Trenchless technologies mean fewer diggers, little or no muck away, and no need to process and transport pipeline bedding materials. The graph shows a 90% reduction in carbon emissions for the no-dig solution versus the conventional open-cut solution. The majority of this saving comes from the reduced need for plant.

As pipe diameters and installation depths increase, so do carbon savings from plant emissions and also from the embodied carbon due to plant manufacture. Trenchless technologies usually use plastic pipe to rehabilitate existing pipelines which contain significantly less embodied carbon than metallic pipe materials.

Increasingly, no-dig pipeline installations are selected in place of open cut construction to save costs, minimise disruption and practicality. For example in the joint venture Optimise, MWH is delivering a multi-million pound mains replacement programme.

This includes major pipeline rehabilitation projects within the client’s capital programme. To avoid the disruption, huge expenditure and significant carbon emissions these might cause, Optimise required alternative and low carbon solutions. To achieve this MWH designed and implemented innovative pipeline rehabilitation solutions. These methods could bring savings of many thousands of pounds not just to this joint venture, but to other clients. Four typical no-dig processes being used by MWH and Optimise include:

  • Directional drilling – installation of a new pipeline on a new route
  • Pipe bursting – displacement of an existing host pipe and simultaneous installation of a structural replacement pipe of the same or greater diameter
  • Loose fit sliplining – similar to pipe bursting, except a pipeline smaller than the existing main is installed
  • Close fit sliplining – reducing the diameter of the polyethylene liner pipe before reverting once in place
  • Spray lining – typically carried out on cast, spun or ductile iron water mains in response to a water quality issue

To gain maximum benefit from these and other no-dig techniques, water companies need to conduct a comprehensive desk-top study of options. This will identify constraints such as adjacent services, numbers of previous repairs and connections onto the pipeline to be rehabilitated, any changes in size, alignment and direction. Many such constraints would require digging down onto the pipeline, and if too many, a rehabilitation option might quickly become uneconomic. Additionally, to gain efficiencies it is vital to programme work effectively.

For example, if rehabilitation is to be on short lengths of disparate pipelines, real savings will not be achieved. To reduce rehabilitation costs and minimise impact on the local community, programmes must target areas where volumes of work can be executed on an ongoing basis.

Two of the techniques mentioned, directional drilling and pipe bursting, give the client a completely new asset, with a lifetime in excess of 50 years. Sliplining with a loose liner also gives a new asset, which does not rely structurally upon the host pipeline, but does require a reduction in hydraulic capacity to be acceptable to the client.

Techniques such as spray lining, which rely upon the structural integrity of the existing pipeline, need a reliable condition assessment to understand the assets being improved. This clearly involves more effort in investigation and design stages. Condition assessment of existing pipelines is crucial to the longevity of a solution relying upon the integrity of the host pipeline. Pipeline structural condition can vary along its length for many reasons, including changing soil conditions, different loadings, stray currents, material deterioration et cetera.

Condition assessment is based on discrete locations where the pipeline has been exposed and evaluated and assumes the condition of the pipeline at the testing site is representative of the pipeline as a whole.

How many test locations are required per kilometre of pipeline for this to be supportable is difficult to answer and depends on the specific conditions of that pipeline. Similarly, basing the decision on previous failure history can be unreliable unless it can be clearly established why and how the pipeline failed. Pipelines subject to failures caused by third party damage or localised corrosion may well be sound for the majority of their length, and identifying this may lead to more cost effective solutions.

To conclude, driving efficiency and new design into the pipeline renovation area of the water industry includes a full understanding of the client’s requirements, effective condition assessment of pipelines, correct selection of rehabilitation technique based on optioneering, and proper programming of rehabilitation site works.

This is not rocket science, but done well it can deliver improved efficiencies, reduced carbon emissions and significant cost savings.

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