A growing number of pipeline operators are now turning their attention to the relatively new phenomenon of black powder in gas lines, because of the substantial effects it has on their pipeline systems. Consisting mainly of iron and sulfur as well as iron oxide in different chemical combinations, black powder can be found in both dry and wet gas lines and in conjunction with any other contaminants such as water, liquid hydrocarbons, and sand etc.
Black powder not only influences the flow performance of the pipeline, but it can also impair the function of installations such as valves and pipeline measurement systems. Since the performance and efficiency of pipeline inspections can be significantly reduced due to the particular characteristics of the powder, the development of specific cleaning methods for black powder posed an urgent challenge.
Even in relatively short pipelines containing dry black powder, conventional cleaning tools show both low efficiency and heavy wear on the polyurethane of the cleaning equipment used. The combination of heavy wear and low cleaning efficiency means that a large number of cleaning runs are required, thereby causing both heavy operating efforts and high spare part costs.
Due to the urgency of the problem, a range of methods have been developed. For example, the use of magnetic inspection tools provides better cleaning efficiency, but it is marked by heavy wear on the tool components. Similarly, other cleaning procedures such as batch washing and gel pigging are more effective than standard cleaning. However, since up to eight single cleaning tools are usually required to separate the different fluids, solvents and chemicals, this method is both laborious and expensive. The problem is further exacerbated by the fact that all the fluids and chemicals inserted as part of such methods must subsequently be removed from the pipeline by means of a complex procedure.
Combining the advantages of regular cleaning tools with those of magnetic inspection tools, ROSEN’s new technological approach also incorporates a specifically developed bypass system. All these different components make a specific contribution to the cleaning process as a whole. Carried by support wheels to prevent wear of wall-touching components, the tool is sealed with polyurethane guiding and sealing discs. At the same time, spring-supported magnetic brushes improve cleaning capability. Since all these mechanical components can be adapted to any pipeline properties, optimal cleaning efficiency is achieved under a wide range of different conditions.
The central feature of the new concept is a calculated bypass flow running through the middle of the tool. The negative pressure created as a result of the acceleration of the medium permits flow into the bypass from where it is transported to the downstream area of the tool by means of purpose-built channels.
The specific dynamic of the tool’s flow means that an optimized value of powder particles can be removed from the pipeline wall. Moreover, the bypass flow through the middle of the tool transports additional powder particles.
The overall characteristics and performance of such complex interlinked processes must be calculated with extended methods of ‘Computational Fluid Dynamics’. Thus the brush/magnet system not only ensures surface cleaning but also the required differential pressure. Furthermore, the actual pressure and flow in the line is taken into account to optimize cleaning performance and to prevent run problems due to excessive bypass. To monitor overall performance and function, each tool is equipped with a data acquisition system which measures temperature, absolute and differential pressure, and acceleration in three orthogonal directions with one data triple per second (minimum, maximum, average).
The efficiency of the new cleaning technology was proven during extensive in-house tests conducted for the two tool sizes of 48″ and a 56″. Thus the 48″ tool collected 39 barrels of black powder in its receiver during a run in more than 170km of dry black powder. The condition of the tool after the run was such that it could be launched again without the need to replace any parts. The tests thus indicate low operating costs and high cleaning efficiency even in heavily contaminated pipelines.
