Posted: 2 June 2017

Failures drop to zero after seal success

National Grid, PIG traps, PIG trap door seals, PIG trap closures, innovation, Gas Transmission, innovation value report

Newly installed PIG traps at our Training Academy at Eakring provide employees with practical, hands-on experience.


Gas Transmission’s Innovation Value Mid-Term Report looks at how new ideas transform into real value for customers. One example features PIG traps and how a new project is reducing failures across the network. Project Lead Steve Johnstone tells us more.

The seals around points on our pipelines where pipeline inspection gauges (or PIGs) are loaded and unloaded have historically been prone to damage. Our project has pinned down the root causes – and slashed the number of failures to zero.

PIG traps are the points where PIGs are loaded and unloaded in a pipeline. The PIGs themselves are an essential part of inline inspection, helping us monitor the integrity of our pipelines to ensure they’re safe, fit for purpose and secure.

The National Transmission System (NTS) contains 208 of these PIG traps, all holding a volume of gas at line pressure, typically 70barg. Whereby, a failure in the seal of a PIG trap door would result in gas being released into the atmosphere.

Understanding an upward trend

Between 2008 and 2013, we saw nine failures in door seals, an upward trend that warranted investigating.

We identified the cause and impact of every failure.

To understand its cause, we carried out a project to explore ways of improving the performance of PIG trap doors. This laid the foundations for a follow-up innovation project that was completed earlier this year.

In it, we investigated whether the seal used on PIG trap doors was fit for purpose. Through this work, we also identified the cause and impact of every failure, which included misjudged maintenance and human error. For each failure, we wrote a detailed explanation of the incident, which greatly improved our understanding of how best to manage and maintain these seals.

Avoiding future failures

Based on what we learned, we made several recommendations for avoiding future failures. These included improving the level of training we provided to our operations staff and updating our inspection and maintenance procedures.

On training, we developed a new PIG trap maintenance training package that all our pipeline and compressor mechanical technicians now complete. It’s also been embedded into several existing courses including ‘Pigging Operations and Maintenance’, and our ‘Engineer Training Programme’. What’s more, newly installed PIG traps at our Training Academy at Eakring also provide employees with practical, hands-on experience.

Providing this practical training better equips our employees to maintain and monitor pig trap door seals, thus reducing the likelihood of future failures and improving safety conditions.

Sharing what we’ve learned

We’ve made these modules available to other gas networks for use.

We’ve also made significant changes to how we maintain PIG trap door seals and report their condition. Work procedures have been updated to improve inspections and ensure we capture more detailed information about the condition of every door seal. This improved inspection, maintenance and reporting means defects are spotted sooner and, where necessary, are repaired at an earlier stage.

Following the completion of the project, no further door seal failures have been reported. And assuming three incidents are avoided a year, this adds up to cost savings of £10,000 a year.

It’s a really strong result for us – and a positive reflection on the improvements we’ve made in training, reporting, inspection and maintenance activities within National Grid and beyond.

Fast facts:

£10k – savings made each year

0 – trap door seal failures since new training has been rolled out

8.5 tonnes – of CO2e typically saved each time a failure is avoided

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To find out more about Gas Transmission’s innovation portfolio – and how it’s benefiting our customers – read our Mid-term Innovation Value Report.

Gas innovation in full flow
“It’s a strong result that positively reflects on the improvements we’ve made in training, inspecting, reporting and maintaining PIG trap doors”

Steve Johnstone, Project Lead, National Grid.