Methods of Preventing
Cleaning newly installed pipelines to remove mill scale and drying them to remove hydrotest water will delay the formation of black powder. Some water, even at ppm level, exists in the sales gas composition. Therefore, any change in the atmospheric temperature can cause the water vapor to condense in the pipelines. Since water is an important factor in the support of environmental conditions necessary to form black powder, it is expected that the black powder problem in sales gas pipelines is not going to be a one-time occurrence, but it is likely to be cyclic. Accurate water monitoring devices can help to monitor the water dew point at strategic locations on the system to provide an alert when corrective action is required.
Water used to hydrotest pipelines will contribute in the formation of black powder in the long run. Oxygen scavengers are always added to this water; however, no corrosion inhibitors are added. Adding corrosion inhibitors will definitely reduce the chance of forming black powder; however, due to the unavailability of environmentally friendly corrosion inhibitors, the hydrotest water is not treated with corrosion inhibitors. Treating the hydrotest water with corrosion inhibitor will introduce a major environmental concern, especially with this large amount of water.
The most common and historical means of dealing with black powder is to filter it just before it enters a compressor, station, or processing plant. Filters need to be installed in clean pipelines; therefore, newly installed pipelines as well as existing ones need to be cleaned and dried completely prior to filter installation.
Although sandblasting pipe internals to remove mill scale is one way to remove mill scale, but it will expose the line surface to the atmosphere, and that will increase the corrosion rate during the initial hydrotest. Therefore, chemical or mechanical cleaning, after the initial hydrotesting, might be the best choice and time to remove mill scale and any corrosion products. However and as an alternative, a coating system such as Leighs Paints Pipegard P100 could be utilised after sandblasting. This and other such proprietary coatings not only prevent flash rusting and corrosion, but also promote or do not hinder flow efficiency through the gas line.
The following are recommendations to minimizing solids in newly constructed pipelines:
- Install end caps on the pipe after each day's construction.
- Enhance hydrotest drying operations and dew point monitoring.
- Chemically clean pipelines, using inhibited water, right after the initial hydrotesting.
- Run scrapers as proof of pipeline cleanliness prior to commissioning.
Read more about this topic: Black Powder In Gas Pipelines
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