Management of Ageing Pipelines

A case study from the Netherlands

As the climate change concerns are getting more serious with each passing day, the need to reduce carbon emissions is increasingly being felt. A large part of the low-carbon future energy basket includes more of natural gas. The gas business is thus emerging as a core for dynamic practices that are moving in tandem with technology advancements. In this regard, new asset management practices are being adopted by gas companies all over the world, in an attempt to ensure sustainable energy security in the coming years.

One such player is the Dutch Gasunie Transport Services (GTS), which is a marquee player in the country, successfully meeting the challenge of monitoring its network that is about five decades old. The company has 40 bar regional gas transportation network of pipelines. It comprises pipelines, pressure regulating and metering stations, valve stations and gas receiving stations. The company has developed the Gasunie Network Improvement Program (GNIP), in which replacement of assets is carried out and prioritised based on their anticipated real-time condition.

GNIP

For cost-effective upkeep of its 50 year-old network, GTS carried out some risk assessments of major parts of its existing infrastructure. Therein, concerns related to safety and integrity, in addition to other risks, were identified. The issues identified with the ageing assets have had a bearing on the safe and reliable transmission and distribution (T&D) of gas.

Findings from these risk assessments formed the basis of the GNIP for the “regional 40 bar network”. GNIP can be considered a large-scale platform, which is based on bundling or classification of practices pertaining to preventative maintenance. In crude terms, assets are ranked based on their risks, which dictate their prioritisation on the GNIP platform. This, in turn, determines the order in which they are replaced. This way, planning and execution can be continuously held and monitored. Besides, the process can also be adapted by an increase or decrease of the replacement rate or a change of the ranking/prioritising of assets. Towards this, the programme includes a GNIP Verification Project (GVP), which entails a series of procedures for “Plan-Do-Check-Act” cycle.

The project involves annual rounds of verifications conducted by designated companies. The process involves verification at different stages. The final stage involves collection of all the verification data, which is combined and analysed in relation to the existing database of the company. The results from this stage aid in taking a call on the the assets’ integrity status.

Thereafter, these findings are punched into the risk assessment models, before being fed into the main GNIP to revise or update the status pertaining to the asset’s condition. For the purpose of a study of the GVP project, 146 valve stations were analysed, comprising over 900 valves and about 920 drain and sealant (D&S) pipes.

These segments of the network have been picked up, as the D&S piping component is crucial for the safety of operations. Being in operation for many decades, the actual/accurate condition of these components is often not known. Risks with regard to corrosion are the most relevant. Corrosive parts, after becoming fragile, have the potential to develop pinholes. In such events, gaps are created, which may result in natural gas leakages. Based on the duration of leakage and the pressure with which gas is being compressed into the pipeline, various degrees of damages are possible. In a worst case scenario, this may also lead to explosion.

The GVP comprises four stages. The process generates data for analysing the condition of valve stations in general and D&S piping in particular. The four stages are:

  • Visual inspection with regard to the original condition of the asset. This is held when the valve station is operational, that is prior to possible replacement of the asset.
  • Another round of visual inspection is held. This involves the excavation of valves for enabling visual inspection.
  • The excavated components are analysed, cleaned and the removed parts (corroded segment of the D&S piping) are identified for further investigation.
  • Examination of the cleaned/removed component is held. At this stage, measurements of the wall thickness and the depth of corrosion defects are recorded and measured against the required levels.

Results

Empirical statistical distributions are generated by GVP, for the design wall thickness of externally mounted sealant pipes, including the minimum required design wall thickness. As per the study conducted by GTS, there was a difference between the pipelines that were laid before 1990 and those that were laid after that year. A graphical analysis exhibits design wall thickness that exceeds the minimum requirement, pointing towards the fact that these pipelines are in a fair condition and do not call for immediate replacements. However, some observations recorded were lower than the minimum required design wall thickness. Most of these observations pertain to the valves, which formed a part of the pipelines that were laid prior to 1990. Thereafter, valve stations installed before 1990 were prioritised for replacement.

Meanwhile, a risk model is developed, which is used to determine the probability of failure in a D&S pipe. Herein, the rate of annual replacement of valve stations can be attuned from time to time, depending on the reduction of the probability of D&S piping failure. All this data is fed into the GTS’s asset register.

Conclusions

On the basis of the study undertaken, the following conclusions can be drawn –

  • The results of the GVP study confirmed the necessity of timely replacements of valve stations that were a part of the pipelines laid before 1990.
  • The data generated as a part of the GVP study is used as input for decisions to make changes to the GNIP.
  • The information generated in the study is also utilised for identifying assets that have the highest probability of a breakdown, mitigating the underlying risks thereof.

To sum up

GTS’s way of clustering its ageing pipeline assets and then carrying out a priority-based replacement and predictive maintenance can be utilised by many gas companies all over the world, especially the ones that have aged infrastructure. This practice will not only reduce resources and costs of running the business, it also holds significant potential for ensuring safety in gas T&D.

GTS still continues this practice, with timely adjustments carried out for modifying GNIP. The practice has yielded well for the company, particularly for valve replacements, which have been reduced by one-third from over 2020 per annum to 100 per annum. This has also resulted in significant cost savings of about EURO20 million per annum. As a part of its future plans, the company intends to renovate only those stations for which agreements have already been made with customers, conforming to the trend of “corrective maintenance”, instead of a large-scale renovation practice.

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