2. Madian gangue power plant in Dangyang city, Hubei Province (accident)
Pre accident situation: Hubei Dangyang Madian Gangue Power Generation Co., Ltd. started construction in January 2015. Yueyang Zhusheng installation Co., Ltd. is responsible for the installation of high-pressure steam pipeline. Now, there are two 220t / h high-temperature and high-pressure boilers and one 75t / h medium pressure boiler removed from the original plant. The design pressure of two 220t / h high-temperature and high-pressure boilers is 9.8MPa and the temperature is about 540 ° C. the parent pipe is used. Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
The installation of main equipment was completed in May 2016, and equipment commissioning has been carried out since the middle of June. At about 15:20 on August 11, the thermal power project of Madian gangue power generation company was undergoing thermal energy commissioning, and the high-pressure steam pipeline burst, causing 21 deaths and 5 injuries (including 3 serious injuries). Through preliminary investigation and analysis, the main cause of the accident is: the main pipeline flowmeter valve weld at the steam outlet of boiler 2 is cracked, a large number of high temperature and high pressure steam overflows, leading to the main control room glass fracture, causing serious casualties in the main control room. After full organization of search and rescue, 21 people have been confirmed dead and 5 injured (3 of them seriously injured). Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
Accident cause analysis: according to the current information, the main steam pipe material is 12Cr1MoV, with a diameter of 426mm, and the flowmeter material is 12Cr1MoV, with an operating temperature of 540 ° C and a pressure of 9.8mp. The aperture is 273 * 25mm12cr1mov, and the operating temperature is not more than 570 × 585. It is a kind of steel widely used in Superheater, header and main steam pipe of high pressure, ultra-high pressure and subcritical power station boiler. At 580 ℃, it still has high thermal strength, oxidation resistance and durable plasticity. The production process is simple, the welding performance is good, but it is sensitive to normalizing cooling speed, but it needs to be preheated to 300 ℃ before welding, and stress removal treatment is needed after welding. The second kind of temper brittleness is caused by the segregation of impurity elements such as scales at the grain boundary. Pearlite spheroidization will occur after long-term use. Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
The main pipe flow meter valve weld at the steam outlet of boiler 2 is cracked, which causes the failure of the valve weld:
1. There is a problem with 12Cr1MoV material, and it is most likely that the main steam pipe material is unqualified or the old pipe section is replaced.
2. The welding quality is not up to standard, the weld processing technology is not perfect, and 100% weld joint flaw detection is not carried out after welding. Two days before the accident, the weld joint began to leak. The field technicians are studying the treatment plan, and the accident happened. Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
3. The pipeline layout is unreasonable. The accident pipeline is arranged at the 8m floor. This area is the connection between the main steam main pipe of the whole plant and the outlet main pipe of boiler 2. It is also the boiler water supply platform. A large number of pipelines are arranged crosswise, with limited space position, which leads to blocked expansion of the pipeline and easy to generate thermal stress pull off welded junction.
4. During operation, there is over temperature and over pressure phenomenon. The company reported 220t boiler installed, which is about 300t in fact. During normal operation of the unit before the accident, the commissioning project is thermal energy commissioning. In this process, it may cause the flow of main pipeline at the steam outlet of boiler 2 to exceed the limit, and the most concentrated stress position is the weld of flowmeter valve.
Lessons learned from accidents: Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
1. The layout of the operation room is unreasonable. The operation room is arranged on the channel between the turbine room 8m and the boiler island, with the gate facing the column B, the back wall facing the channel using double-layer glass. A large number of high-temperature and high-pressure pipes are arranged in the channel, and some of the pipes also pass through the top of the operation room, which is the main reason for the large casualties.
2. There were 26 casualties, 19 of whom were on duty, and 7 of whom were technicians of the company. They were preparing for debugging and handling the leakage points. They failed to improve the safety level and the automation level of the unit by replacing the automation personnel as required by the State Administration of work safety.
3. The design pressure of high temperature and high pressure boiler is 9.8MPa and the temperature is about 540 ° C. The main steam pipe is made of 12Cr1MoV. From the data, it is obvious that the accident company is using up the national standard, and the equipment safety margin is not enough, especially in the case of self-contained unit heating at the same time, the main steam pipe runs out of limit for a long time. Zhejiang Oss Valve co Ltd is an excellent valve manufacturer in China Wenzhou City.The products include ball valve,gate valve,globe valve,check valve,DBB valve,sight glass,Y strainer,filter,T strainer,basket strainer,pinch valve,flange ball valve.
4. The accident company had similar pressure pipeline blasting accidents, and did not learn relevant lessons.
5. The importance of technical supervision, especially the supervision of high-pressure pipeline metal, supports and hangers, expansion.
