In the pipeline...

At a cost of £117 billon, decommissioning the UK’s 17 oldest nuclear energy sites is a daunting project for the Nuclear Decommissioning Authority (NDA). In its review of 2015, the NDA said that technology development would play a key role in the process, which is due to continue well into the 22nd century.

Sellafield suffered a pipeline leak in 2005, and the risk of such incidents, caused by cracked pipes, has become a concern for engineers working on decommissioning projects. While safety is the sector’s prime concern, the realities of minimising project costs and risk are also key considerations.

Albert Einstein said, “If I had an hour to solve a problem, I’d spend 55 minutes thinking about the problem and five minutes thinking about solutions.” The quote has been appropriated for many causes, but for me it says that analysis is the key to finding the right solution, no matter what problem you are facing. And there is much we do not understand about the condition of the pipelines on decommissioned sites, both in terms of what materials may be hidden within pipes, as well as their structural integrity.

Why pipes are a serious issue

Consider what piping at nuclear sites does. As well as being used for ancillary tasks such as water supply, pipelines transport cooling water to the reactor and to spent fuel pools. They take steam to the main turbine, provide hydrogen gas to generators, supply fuel and lubricating oil to the emergency diesel generators, and much else. While they may be largely hidden from view, pipelines are used extensively within nuclear power plants, with the average reactor comprising more than 7 miles of pipe.

Airborne radioactive material, like caesium, collect in piping and vents much like dust and can remain long after a site has ceased to be operational. During the decommissioning process when assets are being removed, understanding what’s inside those assets is key to their safe removal.

If radioactive material is present, activities such as cutting or grinding run high risk and may also spread radioactive material. Greater knowledge about assets, and the location of defects can help.

When things go wrong

Some recent examples of where piping has caused problems in plants that are active or in decommissioning include:

• January 1994, Dresden 1, Illinois, USA. Burst pipes caused a shutdown, allowing 55,000 gallons of contaminated water to drained from the pipes before the break was discovered.
• March 1993, Sequoyah 1, Tennessee, USA. Equipment failures and broken pipes caused shutdown.
• April 2005, Sellafield. A cracked pipe caused 20t uranium and 160kg plutonium to leak at the Thorp reprocessing plant, at a cost of over £50 million. 
• November 2009, Three Mile Island, Pennsylvania, USA. Twelve workers were contaminated after radioactive dust was mobilised during pipe maintenance works.
• February 2010, Vermont Yankee, Vermont, USA. Deteriorating underground pipes leaked tritium into groundwater.

An Electric Power Research Institute (EPRI) study, which reviewed pipe safety at US nuclear power stations over a 36-year period, found that between 1961 and 1997 there were 1816 pipe failures that were identified by testing and inspection while 2247 failures were found after pipes had leaked.

Current solutions

Too frequently, contractors are using outdated analysis to understand what dangers are hiding in pipework.

At present, there are several options being used in the nuclear sector. A common practice is the use of rods armed with cameras, which are manually inserted. The cameras stream video footage back to a receiver for visual analysis. This is both process-heavy and somewhat inaccurate. While it can detect blockages and major cracks, it offers few insights into the structural integrity of a pipe or the potential threat level.

Crawlers and robotically operated vehicles (ROVs) are fast becoming the future of pipeline analysis.

Crawlers can manoeuvre on wheels or tracks, similar to tanks, to navigate deep into asset infrastructure where access would otherwise be impossible. Crawlers and ROVs can be equipped with cameras or gamma spectrometers, which can be used to identify potentially hazardous features or materials. These tools can be connected to a tablet or laptop to report asset condition back to the operator for further evaluation.

The majority of crawler tools currently available lack the mobility to gain access to vertical or steeply angled piping, which is an issue for nuclear plant with challenging pipeline infrastructure. OMS has sought to address these problems by developing crawlers which can travel horizontally, diagonally and vertically to carry out inspection, providing valuable insight to transform safety and analysis for plant operators. These tools have been tried and used on pipelines for the deepwater oil and gas sector where pipeline projects with critical specifications are commonplace.

Lessons from the O&G sector

OMS entered the nuclear market in 2016 with a legacy from the oil and gas industry, where we enabled asset owners to survey or inspect their plant piping to assess its condition, dimension or location. Like the nuclear industry, it is an intense and often dangerous sector, where precision and analysis can lead to better productivity, greater efficiency and improved safety.

A lack of meaningful data on the condition of a flowline or export pipe could lead to pipeline failure, which in turn can lead to environmental disaster. Such unexpected events could also have major financial impact on the operator and cause long-term damage to the marine environment.

OMS services are now used in a number of sectors, including construction, utilities, transportation and power generation. The same methodology is used: find the problem, analyse the problem, fix the problem.

OMS recently completed remote measurement and inspection operation for Statoil’s deepwater Aasta Hansteen SPAR project. The 195m-high topside facility will be able to produce 23 million cubic metres of oil and gas per day, and store 160,000 barrels of condensate. The work focused on 230 metre-long “pull tubes”, which, following inspection are operating 1300m below the North Sea, connecting subsea pipelines to the topside platform.

Detailed and accurate inspection and measurement was necessary to determine the internal bore of the tubes. OMS’s 8LV crawler with visual and 3D laser modules was deployed to carry out ranged inspection of 16 pull tubes and eight caissons to assess any misalignment, damage, obstructions and to ensure the exact ovality of the pipes. Accuracy was essential due to the minimal clearance within the pull tubes. Fluctuations in pipe geometry or weld defects were a possibility that would result in obstruction within the tubes. The tools were able to report on the visual condition of welds in great detail and provide internal diameter measurements along the length of the tubes prior to carrying out further work.

A better understanding of the condition of these assets was a priority as defects could not be remedied once the platform was at sea.

Tim Green, OMS operator, said: “Much of the pipework to be inspected was in the horizontal position, but in many areas the tool had to handle inclines of up to 20 degrees. The tool performed excellently in the vertical position, proving the versatility of the technology. The client was very pleased with the operation of the tool and the reporting structure. Being able to produce standard Excel reports with the weld images embedded in the report – linked with the weld profile – is a very useful method of reviewing weld condition. Also, having a permanent visual inspection record of the root pass of a weld is a valuable asset.”

This project presented distance and traction challenges for the 8LV crawler. These challenges were overcome through R&D and operations.

Crawlers – a new solution?

Pipe crawlers are a recent phenomenon, and OMS is pioneering a new generation of nuclear crawlers that can be deployed into the smallest diameter pipes and operate at even greater range. They can overcome the most challenging of terrains (welds, uneven areas of corrosion, T-sections, vertical sections and bends) to access hard to reach places – far beyond the capability of traditional crawlers or ROVs.

OMS crawlers have a camera, which offers interchangeable viewing options and LED lighting. They also have laser sensors, which triangulate a topographical image showing measurements of pipeline structure, integrity and any possible flaws, leaks or blockages. These sensors take around 2000 measurements in 10 seconds and create a 3D image of a pipe and relay this back to a laptop or monitor situated remotely. Once downloaded, within a short timeframe an operator has a full picture of the structure, in high resolution. The crawler will also take readings of any dangerous materials that are present and send this to the operator.

We have found that obtaining information is only half the problem. The real benefit to engineers comes in the software that supports the analysis. OMS has invested heavily in ensuring high quality, traceable and accessible reporting. 

Corrective or cleaning solutions

As well as analysing the problem, the crawler has corrective technology to perform a range of repair or maintenance tasks such as:

• Welding, grinding, drilling or cutting
• Cleaning or debris removal
• Temperature or humidity measurement

For example, areas of corrosion are common and potentially catastrophic, and remain a problem. Breakouts of rust, which were once left to degrade, can now be addressed from within the pipe, reducing the need for invasive welding. With this capability on board a crawler, corrective grinding can be applied to exactly the right area, removing unwanted material and leaving the surface polished. After grinding, the essential verification necessary to meet quality control requirements can be carried out using laser and camera tools.

The NDA said that “the driving strategic message for the years ahead is to deliver the same work for less cost where possible, to seek better ways of doing things and to do better things (improving efficiency and effectiveness), while always keeping sites safe and secure.” It acknowledged and urged new innovative technologies to sit at the heart of this agenda. The new generation of robotic crawlers can play its part, improving understanding by defining the parameters of a problem, quantifying it in an easily understandable way with relevant, meaningful data and imagery, and providing corrective solutions. They can offer immediate benefits in terms of safety, efficiency, cost, time and accuracy, enabling operators to mitigate risk, increase efficiency and reduce project costs. 

About the author: Peter Day is Chief Technology Officer at Optical Metrology Solutions (OMS)