By-Pass Pigging - A 'Simple' Technology with Significant Business Impact

Abstract Bypass pigs are similar to normal pigs but have bypass ports to allow for a certain amount of fluid flow through. The bypass flow can "smooth out" the liquid surge. As for non-bypass pigging, all materials present in the pipeline before pig launch will be "pigged" out during the pig passage and nothing will "leak" backward through the bypass ports. Compared to non-bypass pigging, the use of bypass pigging can significantly reduce the production deferment as a result of pigging, capacity requirements for the slug catcher or separator, and the cost of wax inhibitors and risk of wax maintanence pigging. Bypass pigging has been around for many years but simply not been used enough, particularly its potential in handling the pigging slug and reducing production defermerment. This paper presents a case history of a recent successful application in Malaysia. Application of bypass pigging in the trunkline system of Malaysia LNG (MLNG) resulted in very significant production benefits, at virtually zero cost. Background Over the years, regular pigging (non-bypass) has been widely used in the industry to clean up pipelines (removal of debris and liquid holdup/slug), and sometimes to apply corrosion inhibitors. However, the liquid and debris volumes generated from the regular pigging operations, under normal production rates, will arrive at the receiving facilities within a short time period and may overwhelm the liquid/solid handling capabilities of the receiving facilities (slug catcher, separator, …), and bring gas starvation risks and even tripping risks in downstream facilities. To mitigate these risks, production levels are reduced during pigging operation. Applying bypass ports will slow down the pig travel speed and allow debris or liquid surge to travel faster than the pig. Just as with non-bypass pigging, all material present in the line before pig launch will be "pigged" out and nothing will "leak" backwards through the bypass ports because pressure behind the pig is always higher than pressure in front of the pig. The bypass flow can "smooth out" the liquid surge (Figure 1) and transport the solid debris as slurry, and wet the top of the line with the liquid (corrosion inhibitor). By applying bypass pigging, production deferment is reduced or avoided.