Black powder has become a significant problem in natural gas pipelines. It mainly consists of iron compounds such as magnetite (mill scale) and iron sulphide together with sand and clay, salt, weld slag and even iron. These deposits are normally black in color and can be in a dry, dust form or wet when combined with hydrocarbon liquids, compressor oils, etc.
Black powder is generated during gas production and in wet gas pipelines when hydrogen sulphide, carbon dioxide or oxygen are present in the gas or by bacterial corrosion of the steel. The powder is then distributed through the pipeline with the gas flow, but is deposited when the velocity is not high enough to keep it moving (Dr John Smart – “Movement of Black Powder in Pipelines”). As sediment is deposited, the flow in the pipeline is disrupted and reduced, thereby allowing more sediment to accumulate. System through puts are affected and energy costs increased to maintain design flow rates. Blockage can occur especially during cleaning and damage caused to plant such as compressors.
Pigging plays an important role in the management and prevention of the formation of black powder and we have designed pigs specifically for some of these tasks. Our Foam Disc pig or BD6 both have superior wiping action, when considering liquids removal, especially after hydrostatic testing and Pit Cleaning Pig™for removing debris from corrosion pitting.
If there are a large amount of deposits, removing too much at once could plug the line and methods such as progressive pigging or bypass pigs will minimize the risk. To ensure Black Powder doesn’t become a problem, pigging should be carried out on a regular basis, maintenance programs should avoid the potential for blocking the line or having to deal with large volumes of debris after cleaning.
It is essential to remove Black Powder and clean the pipeline thoroughly prior to running ILI tools. Substantial down time and failures caused by the powder can be avoided by following a thorough cleaning procedure.