What causes the corrosion of deepwater pipes?

Deepwater pipelines are extremely important as they transport oil and natural gases from the distant gas and oil reservoirs to the awaiting consumers. In the US, it is estimated that there have been major natural gas and oil pipelines built since 1998.

Pipelines are properly planned and designed to ensure that there is a small probability for damage and repairs. However, several factors remain to be a threat to the integrity of these pipes. Among these is the inevitable corrosion of pipelines.

There are different causes of corrosion. The decay of pipes is commonly caused by the following:

Stress-corrosion cracking

Image Source: corrosion.ksc.nasa.gov

Stress-corrosion cracking is the cracking of the pipe due to the combined action of corrosion and tensile stress. Tensile stress is caused by the cyclic fluctuations that occur in the operation of the pipelines. These fluctuations reduce the threshold stress of the pipes.

Microbiological-influenced corrosion

Image Source: bti-labs.com

 
Microbiological-influenced corrosion is caused by the presence of microorganisms. While the existence of microorganisms on the metal surface does not necessarily conclude to metal decay, their by-products promote corrosion and accelerate it.

Galvanic couple formation

Image Source: sciencedirect.com

Galvanic corrosion is caused when two dissimilar metal types are in contact with each other through the presence of an electrolyte. In this type of corrosion, one of the metals which has more active corrosion potential forms the anode and corrodes, while the metal which has less corrosion potential forms the cathode and is protected. The circuit of this type of corrosion is completed by the environment in which the cathode promotes the oxidation of the other metal, hence weakening the integrity of the pipe.

Countering corrosion underwater and at great depths is risky and challenging, not to mention costly. A detailed and careful plan and installation of the pipelines is a must. Apart from the financial repercussions it can cause, leaking of pipelines has adverse effects on the environment and in the long run, in the health of the people.

Dr. Ali Ghalambor is known in the industry circuit for his remarkable contributions in the oil and gas sector. For more information on offshore pipelines and pipeline corrosion, visit this blog.