It is frequently necessary to displace the contents of a pipeline or umbilical tube (fluid B) with another fluid (fluid A). If we don’t use a pig to separate the liquids, there will be mixing at the interface (axial mixing). The mixing zone requires us to overflush the line to effectively remove fluid B from the line.

The Initial Startup is the moment of truth where everything from subsurface to topsides becomes a single entity and has to work together. Design disconnects will become apparent.