Time to dust off the derbies

Excerpt

4142020

The cleaning of a gas pipeline and the removal of dust in preparation for a successful ILI campaign is a project in itself and should not be underestimated in scope and effort. A careful definition of the cleaning approach and commitment by both pipeline operator and service provider resulted in a successful cleaning campaign and ultimately high-quality inspection reports as input to the pipeline’s integrity management.

A 204 km, 16 in. gas transportation pipeline suffered from a black dust problem ever since its commissioning in 2005. Although the system had undergone a regular cleaning and maintenance programmed starting in 2014, in 2017 it was time for a reliable metal loss inline inspection and an additional cleaning campaign was needed to ensure its success. Of course, it had to be ascertained that the inspection data would meet the required quality standard, but just as important was that the MFL tool would pass the pipeline unhindered and without affecting operations.


Lead up to pre-inspection cleaning

Right from the start of operations in 2005, this particular pipeline system suffered continued arrival of dust at delivery to the power station and industrial consumers. In the following years, filter systems were upgraded to protect the users and the power station turbines.
In 2007, a pigging study on removing the black powder was performed by expert consultants. The objective of the study was to provide advice to the pipeline operator on the best option for pipeline cleaning methods.
The report concluded that a progressive mechanical cleaning campaign using various types of pigs was the preferred option. Although both gel cleaning and chemical cleaning could have been an option to achieve similar goals, the high logistical effort, cost and inevitable interruption of the gas supply disqualified these as valid solutions.

In correlation with the extensive study, the dust was qualified as ‘black dust’ with a high magnetite content, likely resulting from the mill scale present at the pipe wall of the internally uncoated pipeline. At the time, the expert engineers speculated the quantity of dust to be removed could be between tens of tons to hundreds of tons.
However, not only was the shear amount of debris a concern to pigging experts, the known wear on cleaning tools in black dust pipelines also raised concerns about the associated risk of pigs becoming lodged in the pipeline – possibly affecting uninterrupted delivery . Seven years later, a regular pigging campaign for the removal of dust and regular maintenance finally commenced in 2014.

Over a three year period, up to autumn 2017, the operator performed 88 pig runs. 16 pig runs were performed in a three week period in an attempt to prepare the pipeline for the upcoming scheduled ILI programmed. Throughout the campaign, the cleaning runs continued to bring 40 - 80 kg of sludgy dust into the receiver trap , which was not acceptable criteria for a successful ILI run . A high degree of pipeline cleanliness is an essential pre-condition for successful ILI runs . It is not just about the inspection tools passing the pipeline reliably , without risk of damage , loss of seal or even blockage ; presence of debris would also compromise the quality of the data collected by the tool sensors and , ultimately , compromise the complete and accurate inspection report data that are an essential input to any integrity management system ...