A spiral plate heat exchanger consists of two enclosed and independent spiral channels. If there is a leakage in the channels, it can be difficult to determine the exact point of leakage. To accurately locate the leakage point, a drilling method is used. When drilling, the drilling position should be on the same spiral channel at one end of the heat exchanger, arranged in a cross-shaped pattern. During drilling, care should be taken to prevent iron chips from falling into the heat exchanger, so as to keep the channels unobstructed.
       Water filling and pressure testing for leakage detection
　From one channel that has not been drilled, use a pressure pump to fill the heat exchanger with water and create a certain pressure. At this point, water will leak out from the location of the heat exchanger leakage, flow into the other channel (the drilled channel), and drip down from the layer closest to the leakage point. (At this time, the end of the heat exchanger with the drilled hole should be placed downward.) By observing the location of the dripping water, one can determine the layer where there is internal leakage. At this point, cut a section of the heat exchanger's un-drilled side on the same layer as an observation hole. From this observation hole, the specific leakage point can be accurately located.
　Repair of internal leakage
　1. Hole digging: After determining the location of the internal leakage point, start cutting a hole from the outermost layer of the heat exchanger corresponding to the leakage point, starting from the outside and moving inward until reaching the layer with the internal leakage point. The cut hole should be oval in shape, with the size of the outer layer being larger and gradually decreasing inward. Generally, the size of the holes on each layer of plates differs by 40mm. If the leakage point is located deeper, the hole cut on the outer layer should be larger.
　2. Debris removal: After cutting the hole, carefully remove the oxide debris left on each layer of plates. This is crucial for ensuring that the repair plate can be tightly welded to each layer of spiral plates during the welding process. Use a chisel and a small hand grinder for mold repair to remove the oxide debris. Be careful to remove as much debris as possible to prevent it from falling into the heat exchanger.
3. Replacement and patching of plates: To ensure the quality of repairs, plates cut from each layer of the heat exchanger are not reused. Instead, replacement and patching plates are used, which should be made of the same material and thickness as the spiral plates of the heat exchanger. The perimeter of the replacement and patching plates should be 15mm to 20mm larger than the holes cut from each layer of the heat exchanger, and they should also be oval-shaped, with a curvature consistent with that of the spiral plates in each layer of the heat exchanger.
4. Welding of internal leakage points and patching plates:
1) When welding internal leakage points, it is necessary to carefully inspect whether the leakage points are cracks or sand holes. If necessary, a handheld grinding wheel can be used to clean the leakage area and grind out grooves to ensure welding quality.
2) When welding repairs, J422 welding electrodes with a diameter of 3.2mm are used, and the current is controlled between 100-120A [1]. The leakage points are welded first, followed by the patching plates of each layer, with welding progressing from the inside out layer by layer.
3) The oval-shaped patching plates are welded closely to the inner arc surface of the heat exchanger for ease of operation and to ensure welding quality.
4) To facilitate the smooth installation of the oval-shaped patching plates into the heat exchanger, a section of round steel can be welded onto the patching plates. After spot welding the oval-shaped patching plates, the round steel can be removed.
5) Short round steel supports are also welded between each layer of patching plates (mainly to increase the rigidity of the oval-shaped patching plates relative to each other). The number of short round steel supports welded onto each layer of patching plates depends on the size of the patching plates, generally with 2-3 supports welded onto the slightly larger outer layers of patching plates and 1-2 supports welded onto the inner layers of patching plates.
6) The outermost steel plate has a thickness of δ12mm, so the originally cut steel plate can be directly installed in its original position for alignment and welding.
7) During welding, after each layer of oval-shaped patching plates is welded, the welding position should be carefully inspected. If there are sand holes, repair welding should be carried out to ensure the welding quality of each layer.
Pressure testing and drilling hole sealing
After welding the internal leakage points and patching plates, a pressure pump is used to fill water into the channels that have not been drilled, forming a pressure of 0.5? Maintain a pressure of 1.0 MPa for a certain period of time, ensuring no pressure relief occurs. Seal the drilled holes: Use short round steel sections with the same diameter as the drilled holes to seal and weld the drilled hole locations and observation holes. Then, conduct a hydraulic pressure test on the channel, applying a pressure of 0.5 to 1.0 MPa, ensuring no leakage occurs. Precautions during the pressure test: 1) Before cutting holes in the heat exchanger, use steam to blow out any chemical residues inside the heat exchanger to prevent combustion during gas cutting and potential safety accidents. 2) Before repairing the heat exchanger, confirm whether it is severely corroded to determine if repair is still necessary.