Learnings

Outcomes

Work Package 1: Review implications of using various mediums for ILI including:
Work Package 2: Design / construction / operational review
Work Package 3: Document future operational requirements
Work Package 4: Specify ILI requirements
Work Package 6: Vendor ILI assessment
Work Package 7: Cost benefit analysis
Work Package 8: Technical reporting of above tasks
The feasibility study to explore the options for how the Grangemouth to Granton pipeline could be internally inspected considered the different methods and mediums for undertaking the inspection against the required criteria of cost, viability, and quality of data. The mediums considered were compressed air, nitrogen and water in addition to combinations to maximise the benefits while reducing the drawbacks of a given medium alone. The feasibility study has demonstrated that technically and economically viable options for undertaking the inspection exist which will be explored further as part of the LTS Futures project.
Work Package 5: Pipeline route safety evaluation
All potential infringements have been identified and a preliminary risk assessed based on natural gas risk assessments undertaken. The QRA models for hydrogen will be updated to include the rupture tests being undertaken by FutureGrid at Spadeadam. These will be feed into the LTS Futures NZASP project QRA’s for both GB LTS and Grangemouth to Granton.
Work Package 9: Feasibility study for pipeline ammonia transportation options/technical issues
There are three possible ways to transport ammonia from Grangemouth to Granton, as a refrigerated liquid, a pressurised liquid or as a gas.
Transporting refrigerated liquid ammonia is not feasible in this underground pipeline because it is not insulated and so will cause refrigerating effects on surrounding ground and the heat leak (transfer) into the liquid will generate large amounts of flash gas.
Pressurised liquid at ambient temperatures is a possible option which would allow very high transfer rates (625 tes/hour = 15,000 tes per day). However, the hazard implications of a large inventory in the 457mm (18 inch) diameter pipeline (2,776 tonnes) is likely to lead to large land use planning zones (possibly of the order of 1500m each side of the pipeline). Most long distance underground pressurised liquid pipelines, e.g. in the USA, are not more than 219mm (8 inch) diameter.
Transporting ammonia as a gas is a possible, if an unusual option, because the relatively large diameter results in a low gas pressure drop. It is essential that the pressure is kept below the saturation pressure (3.6 barg at 2oC) to avoid liquid formation. It should be possible to transfer 30 tes/hour (= 720 tes per day) with inlet pressure 6.3 barg and exit at 4 barg. However, this would only allow production of 88 tes per day of hydrogen at Granton. Accidental release of ammonia gas would result in a buoyant plume with relatively small toxic hazard distances.
PD 8010 Part 1 specifies the substance factor for ammonia as 2.5 which results in the Minimum Distance to Occupied Buildings and therefore inner zone for land use planning, as 100m for 17.5 barg Maximum Allowable Operating Pressure and 85m for 7 barg MAOP.
Quantified Risk Assessment (QRA) would help to define pressurised liquid land use planning zones and establish the effects of possible mitigation methods. However further data on the condition of the pipeline is required before credible failure rates can be set for the QRA.
There appear to be three sections of the pipeline with residential housing within 500m of the pipeline. Societal risk analysis is required to assess which mitigation measures would be required once the QRA methodology is available for this pipeline.
Uprating LTS pipeline assessment
The uprating assessment has demonstrated that there is potential for capacity increases in all networks for design factors of both 0.3 and 0.5. The maximum capacity increase, estimated by the uprating assessment, is the upper bound of what could be achieved and could only be realised if the local network configuration can accommodate the necessary supply / demand to utilize the increased capacity. In addition, it draws attention to the need to assess all pipeline sections on a point-to-point supply route and identify the sections which provide the lowest increase in capacity and hence will limit the potential for uprating that pressure system.
Above ground surveys
The river crossing surveys, detailed line walk including depth of cover surveys, Close Interval Potential Survey (CIPS) and Direct Current Voltage Gradient (DCVG) have all been completed. Results of the surveys have not identified any problems and will be utilized by the LTS Futures project.

Lessons Learnt

This project is a pre-feed for the LTS Futures NZASP project. The outputs of which will provide a feasibility study into internal inspection of the Grangemouth to Granton pipeline and key surveys required to undertake an integrity assessment. Additionally, the Feasibility Study to assess the potential uprating of LTS pipelines to improve linepack capacity with a transition from natural gas to hydrogen will be utilized when developing the blueprint for repurposing and uprating within the LTS Future project.