Professional Engineering

As the Deepwater Horizon disaster showed over the summer, extracting and transporting oil from beneath the seabed faces numerous hazards and untold consequences when things go wrong. The explosion and subsequent fire in the Gulf of Mexico in April was responsible for the deaths of 11 workers, the pollution of thousands of square miles, and the devastation of wildlife, fish stocks and livelihoods. 

More than four million gallons of oil leaked into the sea and the cost – still being worked out six months later – has been put at $10 billion.

America’s worst environmental disaster brings home the importance of maintaining sound infrastructure in the oil industry and it is a daily battle. Pipes can crack and fracture; oil can leak out. The hostile environment, a build-up of impurities in the oil, even the operating temperatures can cause damage.

Many oil pipeline leaks are caused by corrosion, which can build up and penetrate the pipe skin. A build-up of corrosion can bore a hole through the wall of the pipe or cause thinning, which undermines its strength and integrity leaving weak spots prone to fracture.

Pipes in topside structures can corrode because of an accumulation of salt deposits left by sea spray. Sand carried by the oil through the pipe can build up inside the pipe walls, causing corrosion and leading to cracks. 

But keeping an eye on corrosion and preventing a leak is easier said than done. It is not as if an operating team can just go down deep into the sea and inspect the pipework each day to make sure everything is okay and in full working order. 

This is where the National Physical Laboratory (NPL) comes in. The laboratory, which is the UK’s National Measurement Institute, is helping the oil industry overcome such challenges. It works with companies such as BP and Shell to measure and understand the effects of corrosion and cracking on materials used in pipelines and other structures.  

Alan Crossland, team leader for corrosion and erosion management at BP, says: “It’s all about keeping hydrocarbon in the pipe and out of the environment. We operate in very aggressive environments, very deep waters, and we want to keep the hydrocarbon in the pipe. Everything is about assuring ourselves that the material is fit for purpose and the design is right and that we are not going to have any issues.”

Alan Turnbull, lead scientist of the electrochemistry and corrosion group at NPL, says: “We can do the science and we can then think about how we solve the industry’s problem by developing a new test method. It could be a predictive tool, it could be a new measuring technique. Our job is to come up with solutions and their job is to highlight for us what their measurement problems are.” 

One of the NPL processes tests and measures the operating temperature above which stainless steel pipes in marine environments need to be coated.

The process involves using information from an oil and gas operator to simulate a section of a pipeline and conduct experiments on how it is affected by seawater. The pipeline is contained so that the temperature of its surrounding environment can be controlled. Seawater is dripped on to the surface of the pipe and the environmental temperature increased so that the water evaporates and salt is left as a residue. The NPL team can then determine the threshold temperature for cracking and establish industry standards for coating requirements. 

The NPL team also conducts tests on the interior surface condition of a pipe to measure the buildup of salt and sand which are transported in the oil. 

Such buildups can lead to corrosion and cracking, says Turnbull. The task at hand is to identify that process and to investigate its effects, he says. 

He says that the equipment used in these types of tests is not new and is relatively straightforward. It is the technique that is unique. “The real issue is to explore and understand how the damage develops,” he says. “So often when you do a stress corrosion test, there are only so many you can do. The form of these doesn’t change much. What we are focusing on is using new techniques to understand what is controlling the cracking process.” 

Another testing and measurement process monitors the performance of inhibitors, which are chemicals designed to prevent corrosion. However, once the inhibitor is set in place inside a pipeline deep beneath the sea, it can be difficult for the oil operator to know how well it performs and how effective it is in preventing corrosion. The performance of inhibitors under solid deposits and in the presence of prior corrosion is a particular challenge.