As part of ongoing maintenance activities, colleagues from GT Operations carry out regular inspections along our pipeline routes, including ‘line-walking’ patrols, to identify potential threats to the pipelines.
These patrols began to highlight several instances where our pipelines were buried at shallower depths. Shallow pipes in agricultural fields are at greater risk of accidental strikes from farming activities such as ploughing.
Across GT, reinforced concrete slabs were used to protect pipelines with low depth of cover. Unfortunately, complications such as corrosion can occur as a result, particularly if the slab sinks.
To overcome this, an earlier innovation project (NIA-NGGT0007: Impact Protection Slabs) was carried out to develop flat polyethylene (PE) slabs as an alternative. These slabs were cheaper, and their installation was quicker and safer. Alongside this, they give an early visual warning about low depth of cover over a pipeline due to their bright yellow design.
These PE slabs are intended to protect pipelines from vertical impacts but don’t protect them horizontally, so in 2016, the team began a follow-up project looking at developing new PE slabs that further protect the pipelines. Working with Rosen, the project was carried out in three phases:
- Phase One evaluated agricultural practices and soil types in the UK to establish a risk profile of which equipment would be likely to impact our buried pipeline
- Phase Two focused on the development of the protective design, taking into consideration the risks identified in Phase One. An initial field trial was also carried out at this stage to determine the minimum thickness of the slabs – 30mm. Two design concepts were selected at this stage for prototype manufacture and carried forward to Phase Three.
- Phase Three focused on undertaking full-scale testing of the two prototype systems. This testing aimed to demonstrate the suitability of each solution, both in terms of ease of installation and ability to protect our pipelines.
The two designs selected for testing included a flat sheet design and an articulating modular design. The flat sheet is based on those developed in the previous project but is thicker. When installed, two of the sheets are added at an angle and secured in the centre to form a ‘roof’ over the pipeline. The modular design includes joint features that can be connected to form a protective ‘blanket’ that sits over the pipework.
During the testing, despite the modular design being easier to install, the joint sections often separated when put under pressure, reducing the protection to the pipeline. This outcome led to a recommendation of using the thicker flat sheet design and since then, flat PE slabs have been moved into general use across many of our pipelines.