Causa de fuga e incendio del empaque de la válvula de globo

Cuando se puso en marcha la nueva planta atmosférica y de descompresión de 6 000 kt/a de una determinada empresa, el embalaje de losválvula de globode la línea de materia prima del horno de calentamiento se filtró y se incendió, provocando el cierre de la planta. El análisis de desmontaje de la válvula de globo encontró que el espacio entre el eje del vástago de la válvula y el orificio del asiento de sellado no era el adecuado. Se llevó a cabo una modificación estructural para la válvula de globo similar del dispositivo y se logró el buen funcionamiento del dispositivo.

La fuerza de fricción de la superficie de sellado de la válvula de globo es menor que la de la válvula de compuerta en el proceso de apertura y cierre, que es resistente al desgaste, tiene un buen rendimiento de sellado, pequeña fuerza de fricción entre las superficies de sellado, larga vida útil, apertura pequeña altura, estructura simple, fabricación y mantenimiento convenientes, carrera pequeña, tiempo de apertura y cierre corto y fácil de trabajar. A menudo se usa en la válvula de línea auxiliar de la válvula de control.
 
El 6 de octubre de 2012, durante la operación de 6000 kt/a atmosférica y descompresión de cierta refinería de petróleo, el instrumento verificó la válvula de control FV-4008B de la línea de materia prima del horno atmosférico, se cambió el medio a la línea auxiliar , y las válvulas delantera y trasera de la válvula de control estaban cerradas. Abra la válvula de globo de la línea secundaria. Una vez que se completa la válvula de control de verificación del instrumento, el medio se cambia al proceso original; las válvulas delantera y trasera de la válvula de control se abren y la válvula de la línea auxiliar se cierra. En el proceso de cierre de la válvula de la línea auxiliar, el aceite de la materia prima se escapó del empaque y se incendió. El fuego se extingue con un esfuerzo. Cortar la alimentación; reemplace la válvula de accidente y desmonte y analice la válvula de globo.
 
1.válvulas con fugas
1.1. Los parámetros técnicos de la válvula se muestran en la Tabla 1
Tabla 1 Parámetros técnicos de la válvula

1.2. The structure of the valve is shown in Figure 1.
 

Figure 1 The structure of the valve
 
2. Cause of leakages
2.1. Inspection of disassembly of valves
After the fire, the valve was disassembled and inspected. After the valve was disassembled, it was found that most of the sealing seat on the valve had been unscrewed. The sealing seat is threaded; the packing lost the sealing pretightening force, and the packing was flushed by the medium. The valve stem lost its sealing protection; the medium leaked, and a fire occurred, forcing the device to shut down. After measurement, the matching gap between the sealing seat hole and the valve stem is 0.28 mm, and the standard gap should be 0.365 to 0.575 mm, as shown in Figure 2.


Figure 2 The structure of the valve after disassembly
 
2.2. Reasons for packing leakage
After inspecting the disassembled valve, it was considered that the gap between the valve stem and the upper sealing seat was too small, which is smaller than the standard gap. The standard gap is 0.365 to 0.575 mm, but the gap of the accident valve was only 0.28 mm. Under high temperature, the valve stem and the upper sealing seat are thermally expanded and stuck. Because the upper sealing seat has a positive thread, the thread rotates in an upward tightening direction in the valve opening process, and the thread becomes tighter and tighter; the sealing is strengthened, so the packing will not leak in the valve opening process. In the closing process of the valve, the screw thread rotates in the direction of loosening. Because the upper sealing seat and the valve bonnet are not welded, the upper sealing seat moves downward together with the valve stem, and the valve stem and the upper sealing surface separate from the valve seat; the gap becomes larger and larger. The pre-tightening force of the valve packing decreases, which cannot meet the requirements of the sealing medium, and the packing is flushed by the medium. The valve loses its sealing, and the medium leaks, causing a fire. The leaking part of the valve packing is shown in Figure 3.
 

Figure 3 Leakage locations of valve packing
 
3. Improvement measures
(1) After the accident, the valves of the same model were measured, and the gap between the valve stem and the upper sealing seat was 0.30 to 0.40 mm. The upper sealing seats of 8 stock valves were processed, and the diameter of the inner hole was enlarged; the gap was 0.65 to 0.70 mm, and the upper sealing seat and the valve bonnet were welded to prevent the upper sealing seat from being unscrewed when the valve is closed. It is installed on site and put into use. For the 7 replaced valves, the manufacturer replaced the upper sealing seat. After the replacement, the gap between the upper sealing seat and the valve stem was measured to be 0.58 to 0.70 mm, and the pressure test was qualified as a spare.
(2) When opening and closing the globe valve, use steady force without impact. When the valve is fully opened, turn the handwheel a little to prevent the threads from being loosened and damaged.
(3) Strengthen the post-maintenance of the packing. During the inspection, check whether there is any leakage in the stuffing box. The problems found in the inspection should be dealt with technically in time. The valve stem must be kept clean, and the packing needs to be filled with lubricating oil. The maintenance of the gland and bolts is also very critical, and some corrosive media will also damage them. For each overhaul of the control valve, the sealing packing must be replaced, and the gland and bolts depend on the situation.
(4) The filler cannot be used beyond the expiry date, and the use cycle should be controlled to be less than its working cycle, so that it can avoid unexpected situations.
 
4. Conclusion
The structural modification of 8 valves was done. The valves are in good condition after operating for 6 months, which proves that the valve modification is successful. The valve modification saved a lot of time for the smooth operation of the device. At the same time, it also improved the further understanding of the valve structure by the equipment technicians, and provided experience for the subsequent management of the equipment.