Boiler operation accident cases----5
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Incident description of a boiler overpressure and tube rupture accident in a power plant: On June 5, 1999, in accordance with the schedule for the boiler overhaul, a power plant was preparing the weight for the safety valve. At 11:30, the shift supervisor ordered the boiler to be started ； At 12:00, oil nozzles No. 1 to 3 were sequentially activated, and the boiler began to increase its pressure ； At 13:00, the reheater safety valve began to be weighted ； It ended at 13:30, after which the boiler continued to increase its temperature and pressure ； When the pressure rose to 15.8 MPa, the deputy director of the boiler plant and others went to the pulse safety valve platform on the side B of the boiler (at an elevation of 46.5 m and with an area of 11.69 m²) in order to perform a weight setting for the safety valves in the steam system. At 14:02, when the main steam pressure of the boiler rose to 16.2 MPa, the shift supervisor ordered an emergency drain test and a venting test to the atmosphere, while continuing to increase the temperature and pressure. At 15:06, when the main steam pressure reached 17.2 MPa, a loud noise was heard suddenly, and a large amount of steam and water gushed out. Hot steam quickly filled the boiler room. Upon inspection, it was found that the straight section of pipe running from the outlet manifold of the high-temperature economizer to the connection pipe leading to the steam drum had burst. The rupture occurred along the axial direction, with the crack being approximately 470 mm long ； Under the reaction force of the soda, a “∨”-shaped bend is formed in the middle part of the crack ； The blast opening was directly facing the safety valve of the secondary steam system, and the insulation layer of some of the connecting pipes on the secondary side was damaged. Eight people, including the deputy director of the boiler plant, were severely scalded, and five of them died despite medical efforts.
Analysis of the accident cause: The pressure of the safety door’s weight mechanism was 16.66 MPa, while the pressure at the time of tube rupture was 17.2 MPa. The temperature of the medium was around 290°C; the overpressure led to the tube rupture. During the setting of the boiler safety valve weight, when the main steam pressure reached 17.2 MPa, the actual working stress on the effective wall thickness of the steel tube exceeded the material’s tensile strength, resulting in instantaneous overload fracture and longitudinal cracking of the connecting pipe.
This post was last edited by The wise on 2016-12-17 at 22:10. Accident summary: 1. Special safety measures should be established for the boiler’s overpressure hydrostatic testing and hot-state safety valve calibration, in order to prevent overpressure from occurring due to too rapid pressure increase or loss of pressure control. 2. For boilers whose safety valves have not been calibrated, measures to prevent overpressure must be in place during the commissioning startup and the calibration of the safety valves, and these operations should be carried out under the supervision of a qualified person. 3. Prepare for potential accidents such as overpressure and overheating in the boiler, and implement preventive measures. 4. During the superhydrostatic test of the boiler and the adjustment of the thermal safety valve, it is strictly prohibited for persons other than those involved in the test to enter the site.
The risk of setting a fixed pressure on-site is too high; it’s better not to do it in the future.
The risk of setting a fixed pressure on-site is too high; it’s better not to do it in the future.
Inadequate risk assessment, emergency response measures, and safety technical plans, coupled with arbitrary on-site operations, have led to irreversible injury accidents
It could be an issue with the pipe material or with the installation; sometimes, the sliding pipe supports cannot move properly, which can also lead to serious problems