Is it possible to pig multi-diameter pipelines?
For economic reasons, a number of dual diameter pipelines have been designed and built in recent years. An existing riser or J-tube at a platform may require that there is a difference between the pipeline and the riser diameters. Tying a line into an existing pipeline may result in a change in diameter from one to the next. Dual and Multi-diameter pigs have had to be designed and tested to allow such systems to be pigged. These include pre-commissioning pigs for dewatering the lines; operational pigs to allow liquid hold-up to be removed from gas lines and inspection pigs to provide information on the line. Typical examples of dual diameter lines include a 10″ x 8″ line, a 20″ x 16″ and a multi-diameter line 11″ x 12″ x 14″. The biggest line is the Åsgard gas export line, which is 28″ x 42″ in the Norwegian sector of the North Sea. This can be both pigged and inspected. Q. How often should a pipeline be pigged? Pigging frequency depends largely on the contents of the pipeline. Some sa
