【Q&A Question 106】April 16, 2018
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【Q&A Question 106】April 16, 2018: Briefly explain why it is necessary to warm the pipes before starting a steam turbine ①Before startup, since the main steam pipes as well as various valves and flanges are at a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress ； ②During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories; the pressure increase rate during this process should not be too fast, as otherwise the flange bolts, pipes, and valves may experience high temperature stresses due to the rapid temperature rise, leading to cracks or damage. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) The validity period for this question is 48 hours; within those 48 hours, 10 wealth points are awarded for correct answers and 2 wealth points for incorrect answers ； If the response is given after 48 hours, the score is halved, regardless of whether it is correct or not ； Mass posting of posts – rated based on the lowest score ； Replies that are unrelated to the answer are considered spam and will be deleted immediately. For management purposes, if you need to view content from a few days ago, please go to https://bbs.hcbbs.com/home.php?mod=space&uid=3862647&do=thread&view=me&from=space through the summary post below. The APP short-video skill competition has started! https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1951670
Answer: ① Before startup, since the main steam pipes as well as various valves and flanges are in a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress； ②During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories; the pressure increase rate during this process should not be too fast, as otherwise the flange bolts, pipes, and valves may experience high temperature stresses due to the rapid temperature rise, leading to cracks or damage.
Prevent water hammer from occurring inside the turbine and damaging the impeller.
⑴Before startup, since the main steam pipes, various valves, flanges, etc. are at a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress. ⑵During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories. The pressure increase rate during pipe warming should not be too fast, as this can cause significant thermal stress on the flange bolts, pipes, and valves due to the rapid temperature rise, leading to cracks or damage.
Gradually and evenly heat the pipeline to prevent stress-induced deformation due to uneven heating
Before startup, mainly because the main steam pipes, valves, and flanges are in a cold state, the high-temperature steam used for pipe warming releases heat through condensation when it comes into contact with the cold metal pipe walls, and this heat is transferred to the metal pipe walls. The condensed hydrophobic substance must be removed promptly at this time. During the pipe warming process, it is essential to strictly control the rate of temperature increase in the metal pipe walls and to increase the steam pressure gradually, in order to ensure uniform expansion of the pipes. If the temperature rises too quickly and the steam pressure increases too rapidly, it will lead to an increased temperature difference between the steam and the metal pipe walls as well as a higher heat release rate, which may result in cracks and deformation. The time required for pipe warming depends on factors such as the length of the pipes, the thickness of their walls, their diameter, the material used for the pipes, and the parameters of the steam. Generally, it takes 20–30 minutes to warm up medium-parameter turbines, while high-parameter turbines require 40–60 minutes.
⑴Before startup, since the main steam pipes, various valves, flanges, etc. are at a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress. ⑵During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories. The pressure increase rate during pipe warming should not be too fast, as this can cause significant thermal stress on the flange bolts, pipes, and valves due to the rapid temperature rise, leading to cracks or damage.
Before startup, since the main steam pipes, various valves, flanges, etc. are at a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress. During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories. The pressure increase rate during pipe warming should not be too fast, as this can cause significant thermal stress on the flange bolts, pipes, and valves due to the rapid temperature rise, leading to cracks or damage.
Before starting up, since the main steam pipes as well as various valves and flanges are at low temperature, if high-temperature, high-pressure steam is introduced immediately, the various pipe fittings in the pipeline will be heated unevenly, resulting in large temperature differences and thus significant thermal stresses that can damage the pipe fittings; therefore, it is necessary to warm up the pipes first. When warming the pipe, use the hand valve to regulate the flow rate, and do so slowly.
The purpose of warming the pipes during the startup of a turbine is to heat the low-temperature pipes evenly, raising their temperature to a level close to that of the steam at the time of startup, thereby avoiding the generation of excessive thermal stress.
①Before startup, since the main steam pipes as well as various valves and flanges are at a cold state, a small amount of steam is introduced into the inlet pipelines to allow the pipes to heat up gradually and expand evenly, thereby reducing thermal stress； ②During pipe warming, it is necessary to properly control the rate of temperature increase in the main steam pipes and their accessories; the pressure increase rate during this process should not be too fast, as otherwise the flange bolts, pipes, and valves may experience high temperature stresses due to the rapid temperature rise, leading to cracks or damage.