CORROSION CONTROL
It’s in the pipeline
Pipeline rehabilitation is well worth undertaking when cash is short. Sandra Rolfe-Dickinson, knowledge
leader at MWH Pipeline Engineering, looks at how to get more ‘bang’ from your budget
MWH believe that structural analyses are vital in correctly specifying the rehabilitation or renovation required for pipelines
I
n today’s climate, businesses need to ensure the properties of the pipes in their original state thickness measurements, or physical samples
that they are getting the maximum benefit to be known, so physical investigations done on being taken. In the latter case laboratory testing
from the money they spend on rehabilitating site can determine the amount of deterioration can yield the tensile strength of metallic
their pipelines. This means prioritising asset that has occurred over a given timeframe. pipework, or the crushing strength of more rigid
investigation, planning targeted rehabilitation and Working in Tauranga, New Zealand, MWH materials. This actual strength data can be fed
careful consideration of the methods to be used. helped a client with serious problems. Their back into the analyses to give a realistic
For critical or high consequence pipelines, catchment was being degraded by sulphuric acid, interpretation of the strength of the pipeline. An
condition assessment and remaining life a by-product from septic sewage but they did not example of this type of project is the work MWH
predictions are an essential component of know where best to spend their limited budget. undertook for a client last year. This involved
asset management. So MWH took samples from pipe walls and did taking wall thickness measurements and
Water, and wastewater, consulting and laboratory tests to assess the strength of the samples from three strategic water mains in an
construction services company MWH has a team sewer materials. Structural analysis of this data, area where major road reconstruction was to
of specialist structural pipeline engineers who are plus information on burial depths and traffic take place. MWH assessed the different loads
experienced in the behaviour of pipelines under loading enabled MWH to prioritise which sewers from the various road plant, and established the
various loading conditions, and are able to assess were at highest risk of failure. One of the sewers residual strength in the pipelines. MWH found
the condition and remaining life of assets in a predicted to fail did actually fail during the study. that structural rehabilitation would be essential
distressed condition. This knowledge has proved This approach was combined with a more before the road works were undertaken.
invaluable on a range of recent projects where traditional risk and consequence analysis. The MWH believes that structural analyses are vital
the clients knew they had a structural problem client was delighted with the work, as they could in correctly specifying the rehabilitation or
with their sewerage or water networks and had a now see which sewers to spend on immediately, renovation required. By understanding the
budget for rehabilitation. However, they did not and which could be left for longer periods. residual strength of the pipelines under
have the information that would enable them to consideration, it can be determined whether or
prioritise and target this expenditure effectively. Principles not structural, semi-structural or non-structural
In some cases it is well known which Key to the success of any work undertaken is the liners are needed. Physical site investigations
pipelines are in need of rehabilitation, but in ability to take principles broadly used for the combined with a knowledge database and
others such as areas where whole sewerage structural design of new pipelines, and adapt expertise enables MWH to give a ranking of
catchments are deteriorating due to hydrogen them to be relevant to pipelines that have been pipelines in terms of structural capacity. When
sulphide corrosion, it is much more difficult to in the ground for many years. This enables combined with further risk and consequence
prioritise expenditure. This is where MWH’s traditional load and load-bearing capacity analyses this results in a prioritised list of the key
knowledge management comes to the fore as equations to be manipulated to make them pipelines for rehabilitation or repair. The end
the company not only have an in-depth relevant to the given situation. result is an effective asset management plan that
knowledge of the history of pipe material Frequently an important part of the process is gives the client significant cost efficiencies and
developments but they also have an extensive to have some sort of physical site investigations ensures they are getting maximum benefit for
library of historical pipe standards. This enables undertaken. This might involve in situ wall the current ‘bucks’ available. ■■■
November 2009 Water & Wastewater Treatment 31
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