Maintaining the functioning and safety of transmission pipelines across a range of industries, including oil and gas, food and chemicals, depends heavily on pipe inspection gauges, or ‘pigs’.
These can range from simple devices for cleaning oil pipes, preventing blockages and increasing production to ‘smart pigs’ that are replete with onboard sensors – magnetic, electromagnetic and inertial technology that can detect leaks and give precise location data for potential problems.
While pigs have been used in process industries for years, companies are now using modern manufacturing techniques and developing technology to create specialised pig devices.
One such technology is a commercial ice pigging machine from Suez Advanced Solutions. Ice pigging, developed by Professor Joe Quarini from the University of Bristol, is a process for clearing pipes that uses slush ice instead of water.
Quarini and his team began by experimenting with commercial ice makers that freeze water into a slurry, which is then stirred to form small ice crystals. To prevent the crystals fusing and forming one ice block, the team uses a freezing-point depressant. Commonly this is salt, but it can be altered depending on the end product. For example, sorbitol is used as the freezing-point depressant for cleaning a toothpaste plant.
Because slush ice can be pumped like a liquid but can move product in the pipe like a solid pig, it can pass through variations in pipework without becoming stuck. The ice pig enters a pipe and is propelled along the line, forming an interface with the product and cleaning the wall as it travels. At the outlet, pure product is recovered until the ice is detected, when it is diverted to waste. The line is then clean for the next product.
Suez recently launched the first factory-ready, hygienic ice pigging machine, the AQL500, suitable for the food and fast-moving consumer goods sectors.
The food sector has much to gain from such applications, says Matt Stevenson, head of ice pigging at Suez. “A UK food producer recently revealed that in its modern factory, 11-19% of ingredients don’t make it to the final product. Clearly, there is a need to be more resource-efficient.”
Five years of development went into the AQL500. The machine, with a 500-litre tank, is de-signed for permanent installation into a production facility, connected to the process line and the factory control system. The device is fully automated, controlling ice manufacture, ice storage and conditioning and – most importantly – the ice pigging process itself. “The ice is always ready for use,” says Suez ice pigging process engineer Tim Deans. “The process offers improvement to line cleaning and can recover up to 90% of the product. Ice pigging can reduce water and chemical requirements and overall effluent discharge, resulting in reduced down-time and increased productivity.”
The company doesn’t see ice pigging replacing the standard clean-in place (CIP) process – rather, it is more of a pre-cleaning process that makes CIP “vastly more efficient”, says Steven-son. “The cost benefit for the end-user is based on improved product recovery, reduced cost on effluent treatment and faster changeover.” The first units look set to be installed in the UK or US in the next few months, he says.
Meanwhile, scientists at Sellafield are using 3D printing to update the nuclear facility’s pig transport capsules. The devices have been used since the 1980s in a pneumatic tube system to carry nuclear samples for analysis around the vast site in Cumbria. The team hopes that, if successful, the project could save millions of pounds in manufacturing costs.
Decades of wear and tear have left many of the polymer pig capsules in need of replacement. The manufacturer that originally delivered the pigs is no longer in business, so it was a question of making a new range that would fit and operate within the existing network of pipes from scratch – which would be time-consuming and expensive – or opt for trying 3D printing instead, says Dr Penny Rathbone, lead engineer on the project.
Choosing the second option, Sellafield has begun making prototypes by scanning one of the last working pig capsules and producing a 3D-printed replica at a fraction of the former timescale and cost.
Depending on the kind of sample being transported, the pigs may have two or three layers of containment, including a shielding layer, followed by a sealed outer canister that transports the samples – it is the outer layer that is to be 3D-printed, but further down the line the shielding layers could be printed, too.
“Use of materials in 3D printing is still limited, and we can’t make it out of the existing polythene,” says Rathbone. “Because of the issue of impact resistance, we are looking at ABS, which has good impact properties and high toughness. We are also looking at nylon, which has equally good impact properties.”
The printed replicas are micro-structurally different from moulded and machined capsules, and engineers at Sellafield are testing them to examine whether they can operate safely within its pneumatic tube systems. In particular, they will be looking at how the printed materials with-stand landing heavily when they come out of the airlock. This test will involve running instrumented pigs through the tube to measure the loads on the capsule, and performing multiple one-metre drops. This stage will be followed by microscopic analysis to visualise any surface damage, along with other tensile and compressive tests during the next couple of months.
While 3D printing itself uses a lot less material compared to traditional machining methods, she says she was surprised to find that they were a lot heavier than the original pigs. “Part of it is because of the material chosen, but part is that the process just puts down a lot of material,” she says.
The team hopes that instrumentation on the pigs when they are in the tubes will reveal whether the additional weight makes them faster or slower, and the effect that it could have on impact.
While there are still months of testing to go before it is decided whether to push ahead with 3D printing for the final pigs, Rathbone is impressed with the process. “What would have taken months to redesign and rebuild, we can now do in hours,” she says.
Did you know? 3D printing at Sellafield
Using 3D printing for pig capsules is just the start for Sellafield, says project lead engineer Dr Penny Rathbone. The nuclear site will soon house an innovation centre for manufacturing, which will include 3D printers so that staff from around the facility can learn the latest techniques and make new components. The team has already used the technology to create other prototypes, including a pond swimmer – a self-contained device that can be placed into a pond to measure radioactivity or water temperature.