The significance of steam purging before starting up a new unit

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Before starting up the new unit, the main steam pipeline needs to be purged with steam. The purpose of this is to thoroughly remove any weld slag, impurities, or residual materials remaining in the main steam pipeline. 2 sets of main steam pipelines were subjected to thermal stress tests to examine their thermal deformation. Principle for purging steam pipelines: raise temperature first, then pressure. Temperature rise refers to the process in which, after the boiler starts generating pressure, the process workshop verifies that all drain valves on the main steam pipeline are open, as well as the end valves, with the aim of preventing pressure buildup and of warming up the main steam pipeline first. The outlet valve of the boiler outlet drum controls the flow rate of steam into the main steam line; this flow rate must not be too high to prevent water hammer from occurring in the main pipes. At this time, pay attention to the pressure changes in the boiler; it is necessary to prevent the boiler from being overstrained, which could cause the water inside the boiler’s drum to enter the pipelines. After steam is introduced, the process operators should inspect the steam bus to confirm the presence of backflow water, and inform the process operators at the next station to get ready. After some time, steam will appear at the end of the main pipe; then, the pipe needs to be warmed up for a certain period of time to raise the temperature of the steam main pipe, with the exact duration to be determined as appropriate. In short, the steam valve should be opened slowly to prevent water hammer and ensure the safety of the pipelines. Post-pressurization refers to the purging of the steam user pipelines after warming up the bus lines. The valve at the inlet of the steam user pipeline is closed to build up pressure, after which the valve is quickly opened for purging. It is important to note at this point that one should not try to clean everything at once; instead, it is necessary to clean each area sequentially. Blow purge 4-5 times. After the purging is complete, instruct the boiler to shut down and maintain pressure; allow the steam main to cool down, then raise the temperature, and repeat the previous steps. The purpose of heating and cooling is to remove rust from within the pipeline through thermal expansion and contraction. It should be noted that: if it is a new unit, remove the inlet valve before the steam user to prevent thermal expansion of the steam pipeline from damaging the equipment. The steam pipeline needs expansion joints to relieve thermal stress; the expansion joints used in our facility are quite small and failed to perform their function, resulting in the entire steam pipeline shifting by 80 mm. Fortunately, the steam users are all separated from the bus. Otherwise, the consequences are unimaginable. I’ve written down some thoughts in haste; I hope those who are more experienced can offer some guidance.