In industrial production, some continuously operating equipment leaks due to various reasons. Such as pipes, valves, containers, etc. The generation of these leaks affects the stability of normal production and the quality of products, and pollutes the production environment, causing unnecessary waste. What’s more, after leakage of some media such as toxic gas and grease, it will also cause great harm to safe production and the surrounding environment.
For example, the Qingdao Huangdao oil pipeline explosion on November 22, 2013 and the Tianjin Binhai New Area dangerous goods warehouse explosion on August 2, 2015 caused huge loss of life and property to the country and the people. The causes of these accidents are all caused by medium leakage.
Therefore, the leakage of some industrial products cannot be ignored and must be dealt with in time. However, it is also a technical problem how to remedy the leakage of equipment that is under pressure and contains flammable and explosive substances or toxic chemical media.
The plugging of equipment with pressure, oil or toxic substances is a special welding under abnormal working conditions. It is different from normal welding specifications and emphasizes safety during operation. Safety construction measures to prevent accidents must be formulated before welding to ensure the personal safety of the workplace, welders and other workers. Welders must be experienced and skilled. At the same time, there must be welding engineers with rich technical experience to provide technical guidance on various safe operations.
For example, for a certain type of fuel tank, it is necessary to know the capacity, ignition point, pressure, etc. of the oil inside, and to ensure that no personal injury or even greater safety accidents will be caused during the welding process before construction and operation.
Therefore, before and during welding construction, the following points must be done:
First, safe pressure relief. Before welding to plug the leak, it must be determined whether the pressure of the equipment to be welded will constitute personal injury. Or under the influence of the welding heat source, the equipment has a safe pressure relief channel (such as a safety valve installed), etc.
Second, temperature control. Before welding, all cooling measures for fire prevention and explosion protection must be done. During welding, welders must strictly follow the minimum and minimum heat input specified in the process documents, and safety cooling measures must be implemented while welding to prevent fire or explosion.
Third, anti-poisoning. When sealing and welding containers or pipes containing toxic substances, timely ventilation of leaked toxic gases and timely supply of fresh air must be done. At the same time, it is necessary to do a good job in the pollution isolation of the outflow of toxic substances.
The following are several welding plugging methods commonly used in engineering practice for everyone to learn and improve.
1 Hammer twist welding method
This method is applicable to the welding method of cracks or blisters and pores of low-pressure vessels and pipelines. Use small-diameter electrodes for welding as much as possible, and the welding current must strictly follow the process requirements. The operation adopts the rapid welding method, and the heat of the arc is used to heat the periphery of the leak. Weld edge hammering the weld.
2. Riveting welding method
When some cracks are wide or the diameter of trachoma or air hole is large, it is difficult to use hammer twisting. You can first use a suitable iron wire or welding rod to rivet the crack or hole to reduce the pressure and flow of leakage, and then use a small current to quickly Welding is done. The main point of this method is that only one section can be blocked at a time, and then fast welding, one section is blocked and the other section is welded. As shown in Figure 1
3. Top flow welding method
Some leaks are caused by corrosion and wear and thinning. At this time, do not directly weld the leak, otherwise it is easy to cause more welding and bigger leaks. Spot welding should be done at a suitable position next to or below the leak. If there is no leak in these places, a molten pool should be established first, and then, like a swallow holding mud and building a nest, it should be welded to the leak bit by bit, gradually reducing the size of the leak. area, and finally use a small-diameter electrode with a suitable welding current to seal the leak, as shown in Figure 2.
4. Diversion welding method
It is suitable for welding when the leakage area is large, the flow rate is large or the pressure is high, as shown in Figure 3. According to the shape of the leak, make a supplementary plate with a shut-off device. When the leakage is serious, a section of diversion pipe is used for the shut-off device, and a valve is installed on it; when the leakage is small, a nut is pre-welded on the repair plate. The area of the patch plate should be larger than the leak. The position of the intercepting device on the patch must be facing the leak. A circle of sealant is applied on the side of the patch that is in contact with the leak to allow the leaked medium to flow out from the guide tube. To reduce leakage around the patch. After the repair plate is welded, close the valve or tighten the bolts.
5. Sleeve welding method
When the pipe leaks in a large area due to corrosion or wear, use a piece of pipe with the same diameter or just enough to hug the diameter of the leak as a sleeve, and the length depends on the area of the leak. Cut the sleeve tube symmetrically into two halves, and weld a diversion tube. The specific welding method is the same as the diversion welding method. In the welding sequence, the ring seam of the pipe and the sleeve should be welded first, and the weld of the sleeve should be welded last, as shown in Figure 4.
6. Welding of oil leakage container
Continuous welding cannot be used. To ensure that the temperature of the weld cannot rise too high, spot welding is used and the temperature is lowered at the same time. For example, after spot welding a few points, immediately cool the solder joints with water-soaked cotton gauze.
Sometimes, it is necessary to make comprehensive use of the above various plugging methods, and the welding plugging needs to be flexible in order to ensure the success of the welding plugging.
However, not all metal materials are suitable for the method of welding plugging. Only ordinary low carbon steel and low alloy steel can use the above various plugging methods.
Austenitic stainless steel must be repaired by welding when it is determined that the base metal near the leak can produce large plastic deformation, otherwise it cannot be repaired by welding.
The medium in the heat-resistant steel pipe is usually high-temperature and high-pressure steam. Leaks that occur after long-term service cannot be repaired under pressure. Low-temperature steel is not allowed to be repaired by hot-press welding.
The above various welding plugging methods are all temporary measures, and do not have the mechanical properties of metals that can be achieved by welding in the strict sense. When the equipment is under the condition of no pressure and no medium, the temporary plugging and welding state must be completely removed, and re-welded or repaired in other ways to meet the use requirements of the product.
summary
Welding plugging technology is an emergency technology needed in the continuous production process with the development of modern production. It takes a certain amount of time to deal with leakage accidents, and the leak should be completely replaced afterwards. The application of leak plugging technology should be flexible. To deal with a leak, multiple methods can also be used for joint welding. The purpose is to prevent leakage after welding.
Post time: Mar-22-2023
