Common faults of tower equipment and repair methods

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Common faults and repair methods of tower equipment. Tower equipment is a type of stationary equipment specific to chemical production. It is responsible for tasks such as distillation, absorption, drying, cooling, and gas humidification of certain media in chemical production. Tower equipment typically features a tall tower body with a circular cross-section, and its base is firmly connected to the concrete foundation via anchor bolts. In chemical production, tower equipment is subject to pressures, temperatures, and electrochemical corrosion from the internal media. The defects and failures resulting therefrom cause damage to the tower equipment, affect its proper operation, and reduce its service life. Therefore, a clear understanding of the defects and failures in tower equipment is necessary, and sufficient attention should be paid to them. Different defects and failures caused by various factors should be correctly identified in order to apply appropriate methods for eliminating them. Common defects and failures of tower equipment are as follows: ① Fouling on the working surface area of the inner wall of the tower. The occurrence of such a fault will result in a reduction of the effective volume inside the tower and the flow area of the channels, a decrease in heat transfer efficiency, an increase in the flow resistance of the fluid, and a reduction in flow rate. ②The flange seal of the tower equipment has lost its sealing capability. This type of failure usually occurs at the flange connections of multi-section towers and at the flanges of the inlet and outlet pipelines of the equipment. When the sealing performance is compromised, it leads to leakage from the equipment itself, reducing its production capacity and contaminating the surrounding environment. In the event of a leak of highly toxic substances or flammable and explosive materials, severe accidents can also occur. ③The wall thickness of the equipment housing has been reduced. When the wall thickness of the shell of a tower device is reduced, the strength of the tower decreases, and its ability to withstand pressure is weakened. When the wall thickness is significantly reduced, the equipment loses its usability and must be scrapped. ④Local deformation of the equipment housing. Local deformation of the shell of a tower equipment refers to a change in the original cross-sectional area of a particular part of the shell, resulting in local indentations or protrusions. The occurrence of these defects will significantly reduce the reliability of the equipment’s operation. ⑤Cracks in the equipment housing. This type of failure mainly occurs on both sides of the weld or near the rivet holes. Shell cracks can be divided into non-penetrating cracks and penetrating cracks. Non-penetrating cracks pose a risk to tower equipment, while penetrating cracks lead to leaks and damage to the shell. When defects and failures occur in tower equipment, it is necessary to shut down the equipment for repairs promptly to prevent damage accidents. The causes of various defects and failures are different, and the repair methods employed also vary. The repair methods for defects and failures in tower equipment are introduced as follows. I. Methods for repairing fouling on the working surface 1. Mechanical de-scaling method: Manual mechanical de-scaling. The method of using manual tools such as brushes and shovels to remove scale from the working surface of equipment housings is known as manual mechanical descaling. This method is mainly suitable for removing some chemically insoluble deposits. Due to the use of manual tools for descaling, the workload for workers is high and efficiency is low. Hydraulic mechanical descaling method. Water is ejected from the nozzle of the spray gun at high pressure and speed, exerting force on the scale to remove it. The scaling is removed using hydraulic mechanical descaling methods, which reduces the workload on workers, increases production efficiency, and allows the removed scaling to be discharged along with water. Mechanical or electric cleaning method for removing scale. Compressed air or electricity is used as power to drive the mechanism for removing scale. This method is suitable for removing scale from inside pipes. Sandblasting descaling method. Compressed air is used to carry sand particles, which are then ejected at high speed from a nozzle to remove deposits from the inner wall of the tower. This descaling method is less efficient and more costly, so it is rarely used. 2. Chemical descaling method: This involves using chemical solutions to react with the scale buildup, and then removing the resulting substances in order to eliminate the scale on the tower walls. Chemical descaling is commonly used in situations where mechanical descaling is not feasible, such as the removal of scale between tubes in shell-and-tube heat exchangers. After removing the scale with chemical solutions, it should be washed again with steam and water; this allows the removed scale to be discharged along with the water, while also preventing the chemical solutions from corroding the metal casing. II. Repair methods for loss of sealing capability at equipment connections. Depending on the various reasons for the loss of sealing capability at the flange connections of equipment, the following repair methods are available: ① For bolts that have become loose, simply tighten them. If the bolt is damaged, it should be replaced with a new one. ②When the gasket is damaged or deteriorated, it should be replaced with a new one. ③ For flange sealing surfaces with radial grooves, these grooves should be rewelded; after rewelding, they should be filed flat to restore their proper geometric shape. ④If warping occurs on the flange sealing surface, it should be leveled or the flange replaced. III. Repair methods for reducing the wall thickness of equipment housings 1. Inspection of the wall thickness of the housing When conducting a preliminary inspection of the wall thickness, the commonly used method is drilling for measurement. When the workload of checking the shell wall thickness is large, instruments can be used for measurement, such as ultrasonic non-destructive thickness gauges. Know the actual wall thickness of the shell. Then determine whether to continue using the device, repair it, or replace it. 2. Repair methods for reduced wall thickness of the equipment casing: The reduction in the wall thickness of the equipment casing can occur either locally or throughout the entire casing. For the repair of locally thinned shell walls, the patching method can be used. The thinned part of the housing will be cut off and repaired using welding patches. If the device housing is generally thinned, it should be replaced entirely. IV. Methods for repairing local deformation of equipment housings: For minor, localized deformations on the equipment housing that have not yet resulted in cracks, a drawing die can be used to pull the protruding parts back to their original position, thereby restoring their original geometric shape. A reinforcing layer should be welded on the surface of the corrected housing to prevent further local deformation there. If the local deformation on the shell is severe, the aforementioned method of local thinning and patching of the shell should be used for repair. V. Methods for repairing cracks in equipment housings Before carrying out repairs, it is necessary to inspect the cracks on the housing in order to select the appropriate repair method. 1. Inspection of cracks in the equipment housing: Cracks that appear on the housing are referred to as visible cracks if they are obvious. In addition, some extremely small cracks, namely those that cannot be detected by visual inspection, are called invisible cracks. Invisible cracks can generally be further divided into penetrating cracks and non-penetrating cracks. For invisible cracks, appropriate methods should be used during inspection; common inspection methods include kerosene penetration testing and magnetic particle testing. 2. Repair of shell cracks: Repair that does not penetrate the crack. During repair, a groove at an angle of 50° to 60° should first be chiseled along the crack, with the depth of the groove being slightly greater than that of the crack. Then, the segmented backward method is used for surfacing welding in order to reduce thermal stress and thermal deformation during welding. The width of the surfacing should exceed the width of the crack groove, and its height should be slightly above the outer wall of the shell. Repair of cracks that have penetrated through. Penetrating cracks are divided into narrow cracks (cracks with a width of 15 mm or less) and wide cracks (cracks with a width of more than 15 mm), and their repair methods are as follows. Repair of narrow cracks that have penetrated. During repair, first chisel a groove along the crack. When the steel plate thickness is less than 15 mm, a “V”-shaped groove can be chiseled out ； When the steel plate thickness is greater than 15 mm, an “X”-shaped groove should be used (that is, “V”-shaped grooves are cut on both sides of the steel plate) to facilitate welding on both sides of the shell. During welding, if the crack length is less than 100 mm, it can be welded in one go; if the crack is longer, the segmented backward welding method should be used. Repair of wide cracks that have penetrated. During repair, first use an oxy-acetylene flame to cut away a piece of steel plate that includes the entire crack. The length of the cut steel plate should be 50 mm to 100 mm longer than the crack, and its width should be at least 250 mm, so as to prevent the welding heat effects from occurring due to the welds being too close together. Then, a groove is machined along the edge of the shell cut, and a patch plate is made according to the shape and size of the cut; a welding groove is also machined on the outer edge of this patch plate. Finally, align the patch plate with the cutout on the housing and weld them together using arc welding. During welding, a symmetric segmented welding method from the center to the ends should be employed. Special note: The above three methods for repairing cracks are only applicable to low-pressure equipment with a working pressure below 0.7×105 Pa. In the case of cracks in high-voltage equipment, repair is generally not carried out; instead, replacement is used as a solution.