Cleaning a Pipeline for Internal Inspection

Most pipelines are regularly pigged to ensure optimum performance from an operational point of view, but the level of cleanliness is not always sufficient for in-line inspection with a smart pig or intelligent pig. Crude oil pipelines with a high wax content, all types of fluid pipelines containing scale, and dry gas pipelines containing very fine dust can all pose difficulties. Wax, scale and dust in pipelines, even in small quantities, can downgrade the data from an in-line inspection pig or smart inspection pig, even if the pipeline cleanliness is acceptable from an operational point of view. Therefore, prior to a pipeline inspection survey it is essential to clean the pipeline thoroughly to remove wax, scale or dust by using Pigtek heavy-duty cleaning pigs.

A clean pipeline will give higher quality inspection data than a pipeline containing debris. If this debris is loose and is low in quantity, then the inspection pig will probably push the debris ahead of it without any problem. However, if the quantity of debris is high, then there is the possibility that some debris will be over-ridden by the inspection pig, reducing or eliminating its ability to inspect the pipewall and the inspection pig may also become damaged. The longer the pipeline, then the worse the effect of debris will be to the inspection pig due to the ever increasing accumulation of debris ahead of the pig and around the pig as the distance travelled increases.

Pipeline scale or hard wax that is adhered to the pipewall will affect the inspection data from that part of the pipeline; a thin layer may not cause too many problems, but a thick layer of scale or hard wax in a pipeline could prevent any data being obtained in that location.

Preparing a Pipeline for Smart Pigging or Intelligent Pigging

If the operational cleanliness of a pipeline is equivalent to inspection cleanliness, then inspection can proceed. If it is not, or there are doubts as to the internal condition of the pipeline, then heavy-duty cleaning pigs may be required as part of a progressive pipeline cleaning programme.

If a progressive pipeline cleaning programme to include heavy-duty cleaning pigs is required, then pigging should start sooner rather than later. Adequate time, including contingencies, must be allocated to perform the pipeline cleaning effectively. If not then pipeline inspection could be delayed, or if the cleaning operation is cut short then the success of the inspection run may be compromised.