Using X-rays and other forms of radiation has been a standard tool for testing pipelines for decades, but until now it's been largely confined to factories and land-based pipelines instead of the deep seabed. That’s changing as GE adapts its medical X-ray systems to work in the crushing pressures of the deep oceans, as part of a remote-controlled submersible rig for examining pipelines in place.
Pipelines are a vital part of the modern economy. Carrying oil, natural gas, and even water, there are a surprisingly large number of them running for thousands of miles under the oceans of the world. The problem is, they need periodic inspection to make sure there aren’t any structural flaws, that corrosion hasn’t taken hold, and that valves are still working properly.
With land-based pipelines, this is a pretty straightforward, albeit time-consuming task. In the bathypelagic zone of the deep oceans, however, it's another matter. At a depth of 10,000 ft (3,048 m), the pressure is 300 atmospheres or 4,400 lb/sq in (309 kg/sq cm), and the temperature drops to 4ºC (40ºF). That’s not only hard on the pipelines, but also on any testing gear sent down to inspect them, and especially on electronics. The result is a logistical nightmare with costs many times that of inspecting land pipelines.
One way of testing the pipelines is to use radioactive isotopes to beam gamma rays through the pipe sections. This is relatively simple and the radiation source is self-generating, but the shielded casings or “bombs” holding the isotopes are heavy, bulky, and difficult to handle. X-ray machines are more compact, lighter, and give better resolution, but they need power and the electronics have to be guarded against pressure and seawater, yet kept cool enough to operate properly.
For engineers from GE Healthcare, GE Oil & Gas, BP, and marine engineering firm Oceaneering, their task was essentially one of taking GE’s medical X-ray detector, disassembling it, and re-engineering it so it could work inside a marinized pressure housing. Of particular importance was protecting the Digital Detector Array (DDA), which produces the radiographic image. This is a glass screen about the size of a computer monitor, and it's very fragile, hence the need for a casing to protect it from pressure and contact with seawater.
According to Oceaneering, the medical X-ray detector provides marine engineers with better image contrast, the ability to estimate pipeline wall thickness, real-time data transmission, wider X-ray exposures, and the ability to handle most pipe sizes, which means the pipes don’t need to be stripped of their protective coatings for testing.
The device is designed to fit inside a handling machine, which is attached to a deep-sea submersible rig. This rig latches around the pipeline and slides along it as it takes incremental X-ray images. It looks for signs of erosion or corrosion, foreign objects, blockages, or valve problems.
“This is not what we normally do,” says mechanical engineer Karen Southwick at GE Healthcare. “X-rays are giving us an insight. You don’t know something’s wrong and then you see it. Whether it’s a small spill or a catastrophic one, this is hopefully preventing that. Ideally, we will be able to have data for every pipeline that’s in the water.”
The video below explains the project.
Sources: GE, Oceaneering
