National Grid’s Gas Transmission business has been exploring an innovative new survey technique to identify defects in buried pipelines. Senior Pipeline Engineer Peter Martin explains Stress Concentration Tomography.
To operate our Gas Transmission network safely and reliably, it’s essential we understand the condition of our assets, and particularly our buried gas pipes. We use a lot of inline inspection to do this, where we put devices including Pipeline Inspection Gauges (PIGs) into the pipe itself to look for any defects.
While these do a great job, some of our pipelines can’t be internally inspected in this way due to their age and risk of corrosion. For those pipes, we need to explore their condition externally, which means inspecting them from ground level.
We already use several technologies to achieve this, but as a business that thrives on innovation we’re always on the lookout for new techniques to complement existing ones.
Through a number of Network Innovation Allowance (NIA) funded innovation projects, we’ve been researching the potential of an inspection technology called Stress Concentration Tomography (SCT). It’s an easy-to-use piece of kit that is operated from the ground. A technician simply walks the length of the pipe holding the system. It collects magnetic data about the pipe below, identifying any stress points that could require attention or repair.
Through previous projects we’ve already shown that SCT works in practice. Earlier this year, we completed the latest leg of our investigation – and it delivered some interesting results.
This latest project set out to understand whether SCT could improve on our current survey standards, and we identified three areas where we felt this was possible: identifying welds (which can be prone to decay), estimating pipeline depth and capturing the lateral position of the pipe.
Our results showed us that:
- SCT is more effective at locating the position and depth of a pipeline than existing methods, including inline inspections (ILI). This is useful, because having more accurate data means we can identify problems quicker and plan future works more efficiently.
- SCT’s performance in measuring the depth of cover above a pipeline was broadly equivalent to the current best available technique, but in some cases it was noticeably better. Understanding depth of cover is important, because if ground cover is too shallow it can put our pipes at risk. Again, by having better information, we can manage any works more efficiently.
- While SCT didn’t perform quite as well as inline inspections (ILI) at detecting welds, it was able to effectively locate defects found using ILI in nearly all instances.
- Additional development of the SCT system is required for it to be used within the field by our engineers – and to fully realise the benefits of the technology.
We’re pleased with the outcome of the latest SCT project. It showed us that SCT has the potential to improve on some of our current techniques. But it remains an emerging complementary technique and is still relatively immature in its development.
What it has shown us is that the system has the potential to help us reduce the risk of failure on buried pipelines. We’ll now look at doing further work to improve the system’s capabilities and embed the technology into our business in the future.