Batching is how a single pipeline can ship gasoline, diesel, and jet fuel one after another without dedicating a separate line to each. This guide explains how batches move back to back, what happens at the interface where two products meet, how batches are tracked, and why batching is central to refined-products pipelines.
Batching in one line: Batching is the practice of shipping distinct product batches - such as different grades of gasoline, diesel, and jet fuel - sequentially through the same pipeline, one directly behind the next with no physical barrier between them. The products touch only at a short mixing zone called the interface or transmix. Operators schedule the sequence to minimize contamination, track each batch's position, and cut it into the correct tank at the destination, giving refined-products pipelines the flexibility to serve many products on one line.
In a batched (fungible or segregated) products pipeline, one product is pumped in behind another in a planned sequence. There is usually no mechanical separator between them; the liquids stay largely apart because turbulent pipe flow mixes them only in a limited zone at the boundary. That mixing zone, the interface, grows slowly with distance as diffusion and the pipe's velocity profile blend the two products.
The scheduling of the sequence matters. Shippers order the batches so that adjacent products are compatible - for example placing a lower-grade gasoline next to a higher grade rather than diesel next to jet fuel - which limits the value lost at the interface. Some operators inject a small separating batch or use a batching pig between highly incompatible products.
The commingled material at the boundary is called interface or transmix. Because it is a blend of two products, it fails the specification of both, so it is cut out at the delivery point and either downgraded into a compatible batch, reprocessed, or sent to a transmix processing plant that redistills it. Managing interface volume - keeping it small and cutting it accurately - directly affects the economics of a products line.
Operators track each batch's location using the known pumped volumes, flow measurement, line fill, and density or other quality sensors that detect the interface passing a point. As a batch nears its destination, operators divert (cut) it into the correct tank at the right moment. In oil and gas, batching is standard on refined-products and NGL pipelines, and increasingly relevant where crude of different qualities shares a line. The interface-detection instruments and batch positions are monitored through the pipeline control system.
They do not fully separate - turbulent flow mixes them only within a limited interface zone at the boundary, while the bulk of each batch stays intact. Careful scheduling of compatible adjacent products and accurate cutting at the destination keep contamination and value loss small.
Transmix is the commingled mixture that forms at the interface between two batches. It meets neither product's specification, so it is cut out and either downgraded into a compatible product, reblended, or sent to a transmix plant that redistills it into usable fuels.
They track batches using pumped volumes, flow measurements, line fill, and quality sensors - such as density meters - that detect the interface passing a point. That lets them cut each batch into the correct destination tank at the right moment.
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