Pipeline defects – how to avoid them
Pipeline failures are a major cause of concern for all stakeholders with an interest in pipeline installation. Although pipeline safety and integrity has improved dramatically in recent years the consequences of a failure are significant, causing enormous damage to the environment and the pipeline operators – both financial and reputational.
When a new pipeline is being installed operators are focused on ensuring the pipe is safe, reliable and productive. They must adhere to strict standards set by several organisations and want to install pipes with first-class integrity and no defects.
In this article we look at the major causes of pipe defects and consider what can be done to avoid them.
Corrosion
Corrosion, the process where materials made from metal deteriorate through oxidation (rusting), is probably the biggest cause of pipe defects. Reports suggest it was responsible for 18% of all pipeline incidents between 1998 and 2017.
Corrosion can occur both internally and externally. Internal corrosion is caused by transporting corrosive substances such as oil and gas, often under high pressure. External corrosion is caused by outer conditions like heat, water or a harsh environment such as acidic soil. Physical defects in the pipe such as uneven shape or form, or issues resulting from poor handling or installation can also cause corrosion.
Corrosion risks
The corrosion process causes metal loss, reduction in pipe wall thickness and loss of strength which can lead to pinholes, cracks and splits. Corrosion is a time-critical issue – and failing to tackle it quickly can cause leakage and even rupture of the pipe – resulting in lower production, environmental damage and reduced income.
Stress corrosion cracking
Stress corrosion cracking (SCC) is caused by the combination of a corrosive environment and high pressure so is a particular risk for buried or subsea pipelines. Clusters of small cracks appear on the pipe’s surface and if left untreated the clusters can start to link together. This forms longer and deeper cracks which can eventually result in pipeline failure. SCC also creates weak points along a pipe that make it more vulnerable to incidents such as third-party damage or overpressure.
Weld defects
During welding defects can occur for several reasons, such as poor welding technique, substandard materials and physical attributes such as dents caused by the manufacturing process or poorly matched pipes. Weld defects can cause pinholes, cracks, incomplete welds, porosity and other problems that lead to weak spots or corrosion sites within the pipe. These kinds of defects are often not spotted until a late stage, when the weld has passed through several processes, possibly even aboard a pipelay vessel at sea, causing delay and significant cost.
Reducing the risks
Pipe manufacturers and pipeline operators can limit the risks of pipeline defects. Oxidation can be reduced by selecting the most appropriate materials for the project, adding corrosion inhibitors in the pipe treatment process, using anti-corrosive pipe coatings and in-line cleaning systems to remove contaminants. SCC risks can be mitigated by applying coatings such as fusion-bonded epoxy and/or using a system such as cathodic protection. The risks from weld defects can be reduced by using good quality materials and employing the correct welding tools and technique.
Pipe and pipeline inspection
Inspection helps oil and gas operators identify and prevent pipe defects, keep their projects running efficiently and meet their regulatory requirements. Corrosion and other defects can be spotted and fixed during the manufacturing process, leading to better quality pipes. Inspection during the installation phase allows corrections to be carried out on the spot, enabling a project to continue without disruption. Once a pipeline is operational regular inspections can help prevent further issues from occurring.
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Posted 20.11.19
[5 minute read]