By-pass pigs are similar to normal pigs but have by-pass ports to allow for a certain amount of fluid flow throughput. The by-pass flow reduces the pig speed and can "smooth out" the liquid surge. This is because the longer pig residence time allows that more liquids are naturally produced out of the pipeline, leaving a smaller liquid volume in the pig-generated slug. Like for non-by-pass pigging, all liquids and solids present in the pipeline before pig launch will be "pigged" out during the pig passage and nothing will "leak" backward through the by-pass ports. Compared to conventional pigging (i.e. without by-pass), the use of by-pass pigging can significantly reduce (ⅰ) the production deferment as a result of pigging, (ⅱ) the capacity requirements for the slug catcher or separator, and (ⅲ) the cost of wax inhibitors and risk of wax maintenance pigging. The by-pass pigging technology has been available for quite some years now but it has simply not been used enough. The technology has large potential in handling the pigging slug and reducing production deferment. This paper presents recent field experience with by-pass pigging for two field cases. Application of by-pass pigging in the gas supply pipeline system of a LNG plant in South East Asia as started in 2012 resulted in very significant production benefits, at virtually negligible cost. Also the by-pass pigging for a pipeline in China in 2012 was successful.
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