Under what circumstances do oil transfer stations carry out \"reverse transfer\" operations?

One case is when the flow rate is too high and reverse transfer is required; the other case is when transporting viscous fluids, and when there is a shortage of fluid at the first station, reverse transfer is needed to prevent the fluid from solidifying during the shutdown process.

Only pipelines carrying thick crude oil are reversed in flow; this reversal occurs in two situations: when the oil supplied by a station does not meet the pipeline’s minimum flow requirement, so that oil must be transported at that minimum level, with a portion of it being reversed in flow intermittently to prevent the pipes from clogging； Before putting the pipeline for easy-to-solidify crude oil into operation, hot water is pumped back and forth to establish a stable ground temperature field; oil can be transported through the pipeline only when certain conditions are met

The oil supply at the previous station is insufficient, so it’s not possible to suspend supply for an extended period; reverse transfer can be carried out: lol

I agree with what was said on the 3rd floor; there is relevant content in the specialized courses for oil and gas storage and transportation. The textbook mentions a concept known as the \"minimum allowable flow rate for hot oil pipelines\" (the minimum flow rate permitted under thermal conditions), which can be determined using the Sukhov or Liebengünth formula. When the actual flow rate in hot oil pipelines may approach or even fall below the minimum flow rate permitted for safe operation, measures must be taken to ensure the safe functioning of the pipelines. One such measure is the use of forward and reverse pumping methods, alternating between them in order to keep the actual flow rate above the allowed minimum level. It is worth noting that there is another \"minimum allowable flow rate\"; in order to prevent hot oil pipelines from entering unstable operating zones, the flow rate must be greater than a \"critical flow rate\" – the minimum flow rate permitted by the pipeline’s characteristics. Therefore, the allowable minimum flow rate for a certain hot oil pipeline is the larger of the two values. On the other hand, reverse transfer is used when starting up hot oil pipelines; one method for starting such pipelines is \"preheating before operation\". Hot water is one of the available media. If the pipes are long and a large amount of water is used, in order to save water and heat and avoid contaminating the environment with large quantities of preheated water, hot water is often circulated back and forth to preheat the pipes.

Addition: I have recently read professional books carefully and realized that I didn’t study them thoroughly enough before. Thank you to alumnus Haichuan for his active participation in the discussion

The purpose of installing reverse flow systems in oil transfer stations depends on whether it is crude oil or refined oil that is being transferred. In general, such systems are used in crude oil transfer stations to prevent the formation of wax deposits within the pipelines, to avoid issues that can arise from prolonged shutdowns, and to ensure safe operation. For refined oil products, the reverse transfer process can also be used in certain sections of the pipeline to meet market demands.