Seeking advice on warming up the pipes during turbine startup

Do you mean that the cut-off valve is a quick-close valve?

I have the same problem; I only know about warming the pipes in segments, but I don’t know why

Is there such a saying? Firstly, heating the pipes is intended to ensure that pipe fittings, flanges, and other components with varying wall thicknesses are heated evenly; secondly, it prevents water hammer from occurring within the pipes. Therefore, the steam should flow at a low rate; thus, the main steam gate valve is definitely closed, and the pipes are warmed through bypass valves.

Segmented pipe heating is a good approach; it’s also a matter of safety – firstly to prevent water hammer, and secondly to ensure even heating! We usually first heat up to the gate valve before the quick-shut valve, and then heat up to the area in front of the quick-shut valve!

To prevent steam from entering the turbine, it is possible to warm the pipes all at once if you can ensure that the final valve is completely airtight; however, for safety reasons, the pipes are warmed in stages

Taking fully condensed steam turbines as an example, there are mainly two reasons: 1. In most cases, the steam used for shaft sealing in these turbines is obtained by depressurizing the main steam. So generally, the area in front of the main steam valve is warmed up first (which takes time); once the steam temperature there reaches the required level, the shaft seal steam is activated to establish the vacuum system (the oil system and the condensate water system should have been established earlier). After the pipes in front of the quick-shut valve are warmed up to the required temperature (which can be done in a short time), the machine is started. If you heat the pipe directly up to the quick-close valve, once the pipe has been properly heated, start using the shaft seal steam to create a vacuum system (during this time, your main steam can only be vented in order to maintain its quality, which results in steam waste). If there is a problem with the vacuum system and it cannot be established properly in a short time, the main steam will continue to be vented. If this period is too long, the main steam will heat the quick-shut valve, and through heat conduction, the turbine casing will be affected; as a result, the upper and lower sections of the casing are prone to uneven heating. If your shaft seal steam is independent steam, you first start up the shaft seal steam to establish the vacuum system, and then heat the pipes up to the quick-close valve (which takes a long time); this means that even though the shaft seal steam is available for a long period, the machine cannot be started. On some high-demand turbines such as those from Siemens, there is a requirement regarding the duration for which shaft seal steam is supplied (if shaft seal steam is supplied for an extended period without starting the main engine, the shaft at the seal area may become locally heated and bent). Segmented warming up can avoid the above two problems. 2. Regarding the safety issues mentioned by those upstairs: if the quick-close valves and speed control valves are not tight, water can get into the cylinder