Key design considerations for pressure vessels containing explosive media

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In terms of structure: (1) Structure of the inlet pipe for flammable and explosive liquid media: When the liquid medium enters the container horizontally, wall flow can occur easily; when the temperature of the container shell is high, scaling or other accidents may arise. Therefore, the flammable and explosive inlet pipe structure should be designed such that its end is positioned away from the inner wall of the shell, extending into the equipment, with the pipe end cut at a 45° downward angle. It is preferable for the length of the pipe extending inward to be below the liquid level in the actual installation, this to avoid static electricity generated by the impact of liquid surface due to high-level differences. (2) Install safety devices such as return pipes on the container: The material is fed into the container via a pump; if the workers operate improperly and the exhaust valve is not opened, more and more medium will accumulate inside the equipment, increasing the pressure in the container. This can lead to damage to the sealing surfaces of the flanges, resulting in high-speed overflow and the generation of static electricity, which may cause an explosion. We install a return port above the actual liquid level in the equipment, allowing excess fluid to flow back into the original device; this prevents waste of fluid and eliminates safety hazards. (3) Install an electrostatic grounding system: To prevent explosion accidents involving flammable and explosive materials caused by static electricity, pressure vessels should be equipped with electrostatic grounding measures. To achieve electrostatic grounding, an electrostatic ground plate structure should be used; the ground plate is made of stainless steel and features two holes, one for joint welding and the other for fixing wires. (4) Selection of accessories such as pipe flanges and level gauges: Plate-type butt weld flanges are widely used due to their simple structure and ease of fabrication; however, their sealing reliability is poor, making them unsuitable for use in containers containing flammable and explosive substances. Therefore, for pipe flanges, it is preferable to use necked butt weld flanges with higher strength levels and better sealing performance. As for the type of sealing surface, concave-convex surface sealing or keyway surface sealing, which offer better sealing performance, is recommended. The selected level gauge should be equipped with a protection device to prevent leaks. Furthermore, the pressure rating of all attachments must meet the requirements of the vessel. It should be noted that for pressure vessels handling explosive media, the nominal pressure of the pipe flanges must not be lower than 1 MPa. Testing requirements: (1) For pressure vessels containing flammable or explosive materials, 100% non-destructive testing must be carried out on all Type A and Type B welds on the equipment. The testing methods can be radiographic testing or ultrasonic testing (including Time-of-Flight Diffraction ultrasonic testing TOFD, recorded pulse-emitting ultrasonic testing, and unrecorded pulse-reflecting ultrasonic testing) ； When non-recordable pulse-reflectance ultrasonic testing is used, radiographic testing or diffraction time-of-flight ultrasonic testing should be employed as supplementary local testing. (2) The pressure test is an important basis for the acceptance of pressure vessels, and it is also a mandatory test for such vessels. It puts stress on the overall strength of the equipment, the density of welding joints, and the sealing performance of sealing structures; it also helps to reduce residual stresses in the equipment and close any cracks in its structure through short-term overpressure. Pressure testing is divided into hydraulic testing and pneumatic testing. For pressure vessels containing flammable and explosive media, if a hydraulic test is used, after passing the pressure resistance test, an airtightness test should be conducted on the equipment as well. Taking advantage of the greater permeability of gases compared to liquids, this allows for a more stringent assessment of the sealing performance of the sealing structures and the integrity of the weld joints ； If a pneumatic test is used, a leak test can generally be omitted.