A combination of pigging and chemical treatments is an effective way to keep corrosion in check.
Pigging is a complex science with many variables that come into play. Every line has unique characteristics, influenced by factors such as system design, pressure, production, chemical use, and temperature and flow rates. In terms of the pig selection, variations in size, design, material and special modifications are employed by us to cope with system conditions.
Modifications in pigging strategies and pig specifications may be required, and we’re always happy to provide this guidance.
Preparing a Pipeline for Inhibition
It is important to clean a pipeline to bare steel to enable the inhibitor to form a molecular bond with the steel. If the pipe has no pigging history or has been pigged with inefficient pigs like balls, a progressive approach is recommended to reduce the chance of plugging the pipeline with solids.
Progressive pigging controls the amount of solids removed at each stage so that manageable amounts of debris are removed. By-pass porting can be employed to assist in keeping loose debris like sand or wax moving. It can be difficult to determine cleanliness; however, the level of debris carried with and on the pig is a good indicator.
Removing Hard Scale or Deposits
Removing hard deposits and scale from the pipe wall and pits requires the use of a wire brush pig. Since brush pigs scrape sideways vs. spinning like a grinder, they must be run numerous times to ensure that the pipe wall is clean. Pipetech recommends that clients assume the pipe has tenacious scale, and make as many brush runs as possible.
Inhibitor Batch Application
A batch film of inhibitor is applied between pigs (pill format), so that the chemical batch is kept in a solid column. Pipetech advises careful selection of pigs, as they can influence the success of the treatment. Inhibitor batch trains are
designed solely to apply corrosion inhibitors. The Lead and Filming pigs are run as a matched set and are customized according to the ID or wall thickness of the pipeline. The Lead pig holds the batch or “pill” in place. The Filming pig
is designed to displace inhibitor behind the pig in an even film on the pipe wall.
Contact time between the inhibitor and the pipe is important for molecular bonding. Since it’s rarely practical to run a long enough batch to ensure adequate contact time, a controlled amount of inhibitor left behind will ensure minimum contact time with full pipe coverage.
Gauging of Pipetech Lead & Film Pig Batch Sets
It is important for Operations to know that there is a sizing relationship between the Lead and Film pigs. The filming pig has been proprietarily altered per wall thickness of the below ground line pipe. In order to gauge wear for a batch set of pigs, Operations will gauge the Lead pig only with an appropriate Pipetech Pig Sizing Ring. If the Lead pig is deemed worn beyond efficiency, the mated filming pig will be considered worn as well.
Best practice is to keep separate Maintenance pigs from Inhibitor Batch Lead and Film pigs. It is recommended that Operations do not use maintenance pigs for lead pigs in a batch film set.
To prevent damage to the inhibitor film a brush pig should not be used for maintenance pigging. An all-cup pig is sufficient for liquid removal in a gas system. In systems with solids, a properly gauged oversize cup/disc pig will be
more effective in moving debris and disturbing biofilms.
Prior to each inhibitor application, the brush pig is recommended to prepare the pipe internal to bare steel and potentially clean any pitting present. In essence the brush pig will prepare the pipe surface for bonding of the new inhibitor.