Tony Joynston, Eclipse Magnetics, UK, discusses some common downstream problems often arising from the pigging process.
Pipeline operators and energy producers face daily challenges maintaining infrastructures and dealing with contamination enemies, such as the formation of black powder, which can jeopardise the wellbeing of pipelines.
Black powder is an unavoidable contaminant which occurs in virtually all oil and gas pipelines. It forms when the carbon steel pipeline wall reacts with water, oxygen, hydrogen sulphide and/or carbon dioxide.
It can vary in chemical composition, particle size and consistency. Depending on pipeline conditions, it mostly consists of iron oxides, iron sulphides, chloride, sodium and also natural process residues such as silica, sand, and clay. Very often it forms as a sludge but can form as a liquid suspension or dry powder. It tends to stick to the pipe wall, in doing so exposing it to corrosion formation.
Excessive accumulation can be detrimental to upstream and downstream equipment and the integrity of the finished product. It also reduces the pipe diameter, thereby restricting flow. In addition, continued exposure increases the risk of pipe fracture and leakages of finished product or toxic gases, and even fires or pollution.
Black powder costs the pipeline industry millions every year in downtime, product loss and maintenance costs, not to mention environmental issues. It is estimated that pipeline corrosion costs the US gas industry US$1.4 billion annually.
What is pigging?
Black powder formation is unavoidable, but measures can be employed to minimise the adverse consequences and disruption it causes. Stage 1 protection is to remove the black powder as it starts to accumulate in the pipeline.
The tried and trusted method of cleaning the internal pipe surfaces is a process widely known as ‘pigging’. A typical ‘pig’ is a bullet shaped fixture which fits tightly to the profile of the internal pipe wall. Typically, this involves placing the ‘pig’ into a ‘pig launcher’: pressure is then built up behind the pig in order to push it along the pipeline until it reaches a ‘pig catcher’ or ‘receiving station’ …
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