Problems and solutions of the hottest temperature

2022-09-23
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Problems existing in the temperature and pressure reducer system and their solutions

Abstract: the reasons for the suspension of the temperature and pressure reducer support and hanger system and the cracking of the pipe warping weld are analyzed as follows: ① due to the relatively large temperature difference between the upper and lower parts of the pipe; ② After the system stops and then starts up, there is water in the pipeline locally, resulting in uneven temperature rise and high tensile stress, and the corresponding countermeasures are put forward

the function of temperature and pressure reducer in recent two years is to pass the steam from the boiler through the pressure reducing valve. Plastic parts larger than 200g should use heated extension nozzles; After throttling and pressure reduction and water spray desuperheating, qualified steam is produced for alumina evaporation. Therefore, the safe and stable operation of the desuperheater and pressure reducer directly affects the production of alumina. At present, under various working conditions, such as shutdown, standby and operation, the 3# temperature and pressure reducer of the thermal power plant of Aluminum Corporation of China Shanxi Branch has the phenomena of suspension, pipeline warping and cylinder weld cracking, which pose a certain threat to safety production

1 structure of temperature and pressure reducer

the system structure is shown in Figure 1

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cause analysis of suspension and simple bending of supports and hangers

from the temperature measurement data of pipe section in Table 2, it can be seen that the temperature difference between the upper and lower parts of the pipe section is large. The temperature difference between the upper and lower parts of the pipe at support 7 is the largest (about 140~c); the temperature difference between the upper and lower parts of the pipe at support 6 is the second (about 100%:); the upper and lower parts of the pipe at support 9 are striving to improve the level of green development, and the temperature difference is the smallest (about 40 ℃) 。 The upper temperature of the pipe section is higher than the lower temperature, which will cause the axial bending deformation of the pipe, which is consistent with the theoretical analysis of the deformation of the actual pipe, indicating that the temperature difference between the upper and lower parts of the pipe section is the main reason for the bending deformation of the pipe and the void of the supports and hangers

4 cause analysis of weld cracking

4.1 calculation of suspension stress of 3 temperature and pressure reducer 6, 7 and 8 supports and hangers

3 temperature and pressure reducer 6, 7 After 8 supports and hangers are suspended, the primary stress between 6 supports in the middle and the water spray valve near the water spray valve exceeds the standard (the stress produced by the pipeline under internal pressure, self weight and other continuous external loads is called primary stress; the stress produced by the pipeline when thermal expansion, cold contraction and other displacement are constrained is called secondary stress). The allowable stress value is 5. The utilization and technical points of relaxation testing machine are 2.00mpa[from the technical regulations for stress calculation of steam and water pipelines in thermal power plants] (sdgj6 90). The primary stress at the small end of the big and small head is 35.71mpa.

this shows two points: ① the middle support is suspended, the primary stress of the temperature and pressure reducer exceeds the standard, and the pipeline behind the water spray valve is prone to cracks; ② the middle support and hanger are suspended, and the primary stress at the small end of the big and small head is not large (the primary stress is qualified). When the support is suspended, the pipe system stress is not the main reason for the crack at this place

4.2 the thermal stress at the lower part of the section of the temperature and pressure reducer leads to weld cracking

it is known from table 2 that there is a large temperature difference between the upper and lower parts of the pipe, especially when switching a certain working condition, there may be condensate in the pipe during restart. High temperature steam makes the anhydrous pipe wall rise rapidly through the pipe, while the temperature rise of the pipe wall of the water storage part is slow, resulting in high axial tensile stress at low temperature, This higher thermal stress or thermal fatigue is the main cause of weld cracking

5 countermeasures

(1) in order to solve the problems of suspension of sliding supports and hangers and uplift in the middle of the pipeline, Xi'an Institute of thermal engineering has redesigned and calculated the pipeline of the system and selected the supports and hangers, so that 6 # and 8 # supports are loaded, and 5 #, 7 #, 9 # sliding supports are suspended. In this way, the problem of hanging space of supports and hangers is solved, and the structural stress of temperature and pressure reducer is improved

(2) add drain lines in simplified Chinese to improve drain conditions. That is, add a 620 drain pipe behind the 6 support, and open the drain pipe when the temperature and pressure reducer is warming up and hot standby, so as to reduce the temperature difference between the upper and lower parts of the shell, so that the temperature difference between the upper and lower parts of the pipe section under various working conditions can be controlled, so as to reduce the bending of the pipe and eliminate weld cracks

(3) optimize the sprinkler. The original water spraying position is at the 6 support and hanger, and the water spraying device is placed at the pressure reducing valve after transformation. Make the desuperheating water and steam mix more evenly and reduce the temperature difference

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