Proper maintenance of pipelines reduces the occurrences of failures due to internal corrosion to a remarkable degree. Primarily, the two methods employed in maintaining a pipeline are mechanical cleaning (pigging) and chemical treatment, (corrosion inhibitors & biocides) often used in combination. The technique known as batch filming uses a "pill" of concentrated chemical contained between two pipeline pigs; a lead pig and a filming pig (referred to as a pig "train"). In theory, the filming pig allows a small volume of chemical to continuously bypass the rear of the filming pig as the train moves down the pipe. This method is intended to coat the inner surface of the pipeline in a uniform layer of protective corrosion inhibitor. In practice it is very difficult for operators to determine the consistency of the coverage, and the thickness of the film deposited by a batch filming procedure. It is also very challenging to determine how long the chemical film can remain effective after it has been applied, especially if subsequent cleaning pigs are used as part of the maintenance schedule. To replicate the batch filming process at a pilot scale, a flow loop was modified with the capabilities of launching multiple 4" (10 cm) diameter pipeline pigs. The discussed methodology enabled researchers to batch film a pipe and analyze the thickness/coverage of the coating while varying specific parameters (contact time, pig design, chemical type and dilution ratio). The method also allowed for the observation of the effect of various cleaning pigs on the integrity of the applied film. The test scheme may provide valuable information to pipeline operators and chemical vendors about the use of batch filming and its reliability, as well as providing design insight to pig manufacturers.
In previous studies, InnoTech Alberta has explored the effectiveness of various cleaning pig designs through a devised test method involving the use of a flow loop.5 Following successful development and application of the test method, more challenges involving pigging practices were explored. As stated in previous works,5 maintenance pigging and inhibitor application are the two main methods to prevent internal corrosion of pipelines. Inhibitor application typically comes in one of two forms: continuous injection, and batch filming.6 With continuous injection, the chemical is dosed at a controlled rate into the pipeline and travels downstream with the fluid. This method is sometimes used when bottom of the pipe corrosion is the main issue. In this case the chemical should be denser than the carrier fluid, allowing it to flow along the bottom of the pipe, reaching the problematic areas.