Forensic inspection of buried aviation fuel lines

A recent report by the BBC exposed a little-known secret that beneath the UK lay a vast network of fuel lines that were originally created to supply resources to the British Air Force. Created during war time under the utmost secrecy, the project was hailed as one of the greatest British engineering feats. Today, these fuel lines span hundreds of miles of countryside and remain largely hidden from view other than a few holes in the tarmac at UK airports, forming an essential infrastructure to enable fuel to be moved between key locations.

Corrosion can present a problem for those tasked with managing these pipelines, as it can occur from either outside or inside the pipe. Corrosion of any metal structure is rarely welcome, so where aviation fuel is a consideration, it is of great concern as a leak could result in disaster! An organisation that managed one of these assets required an inspection to determine the extent of the corrosion. In this instance, they had two options:

• Dig down to the pipe and assess the pipework from the outside of the pipe
• Or to inspect the pipe from the inside

The first option would likely cost approximately 20 times the second option. Part of the reason for such a high cost is the fact that the environment presents a risk of explosion due to the presence of aviation fuel and the fumes generated, potentially putting the workforce at risk.

OMS presented the organisation with an option to carry out inspection from within the pipe using camera and laser technology. The proposal was sufficiently appealing to win the project. Work commenced with the primary objective being to determine the type of flange joint located at the end termination of a long pipe which was used to transport fuel by rail for use at a major international airport. In order to carry out the inspection, OMS used an ATEX-rated camera with bespoke modifications. In order to be suitable to operate in an explosive environment, the camera had reduced capabilities and only provided limited lighting and image resolution, and other than a flexible push rod, had no means to transport itself towards features or areas of interest. This meant that OMS had to create a solution which enabled the end of the camera to be articulated into a variety of positions in order to gain the best possible views of the pipe flange area, maximising the limited light and resolution.

Internal inspection of the pipe

Initially, an ATEX zone 0-rated camera with articulation modifications was deployed to gain access through a small diameter ‘T’ section into the larger diameter pipe which was to be inspected. Then the camera head was navigated into the location where it was possible to see the end of the flange. This manoeuvre was by no means simple, and in the same way a surgeon carrying out keyhole surgery must position a camera into the right place to perform an operation, requires a great deal of skill and patience. A key discovery was made possible under magnification - a feature which initially appeared to be a weld, when viewed at close range was, in fact, a man-made set of grooves. 

Further investigation revealed that grooves of this type could only occur as a result of a flat, bolted-on plate joined to a flange.

Typical bolt on plate with grooves The ASME B16.5 code requires that the flange face (raised face and flat face) must have a specific roughness to ensure that this surface is compatible with the gasket and provide a high quality seal.

Using photogrammetric knowledge, it was relatively straightforward to estimate the dimensions of the grooves from the knowledge gained about the pipe diameter, then confirm that the grooves were of the right order of magnitude for a flange plate.

Finally, it was possible to review the heat affected weld zones in order to an area set back from flange face to confirm the type of welded flange that was used in the project some fifty years previously. While undertaking this work it was also possible to assess the level of cleanliness and corrosion within the pipework.

While it may appear a daunting task to use a very low resolution ATEX rated camera with no means of controlling its location or operation to perform a complex forensic investigation of a pipe, OMS rose to the challenge and fulfilled the task leading to a 20 fold cost saving.

OMS has been involved in a wide variety of projects where the company’s ‘forensic’ abilities have been required, such as:

• Whose blade shaves the closest: Gillette
• Who won the Indy 500: Team Green Racing
• Why pipes for Keystone were not in specification: TransCanada Corporation

Dr. Clarke, OMS’ Managing Director and a Fellow of the Remote Sensing and Photogrammetry Society, states: “my background in photogrammetry has been invaluable in my work, and in a case like this, it can mean the difference between a failed survey resulting in the client digging up the pipework or success in identifying the flange type being used”.

Reference: Dowling, S. (2016) The UK’s network of secret fuel lines that helped win WWII. BBC News website, http://www.bbc.com/future/story/20160513-the-uks-network-of-secret-fuel-pipes-that-helped-win-wwii.

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