Nickel plating, tin hanging and lead soldering repair process for turbine shell and pig iron valve shell

Abstract

The invention relates to the technical field of repair welding, and discloses a repair process for patching a turbine shell and a pig iron valve shell with nickel plating, tin hanging and lead soldering, which comprises the following steps of: patching and welding, removing shell materials at corresponding positions of the corroded valve shell or turbine shell to form a notch, manufacturing a repair welding plate consistent with the notch in shape by using a plate, and welding the repair welding plate with the shell notch, a hydrostatic test is carried out after welding to ensure no leakage; nickel plating is conducted on the welded and repaired valve shell or turbine shell according to the nickel plating process requirement; tinning is conducted on the inner surface of the valve shell or the turbine shell after nickel plating, pure tin powder is adopted for tinning, the inner surface of the valve shell or the turbine shell is preheated through a flame drying gun, the pure tin powder is placed on the preheated surface of the valve shell or the turbine shell after burning, molten tin powder is arranged on the inner surface of a heating area, and tinning is conducted on all the inner surfaces needing to be repaired in this way; and lead welding: after tin plating is completed, a layer of lead-antimony alloy is welded on the inner surface of the valve shell or the turbine shell subjected to tin plating. The corrosion resistance of the valve casing of the exhaust valve is greatly improved, so that the service life of the valve casing is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of welding repair technology, specifically a repair process for turbine housings and cast iron valve housings involving excavation, patching, nickel plating, tinning, and lead soldering. Background Technology

[0002] The high-temperature exhaust gas from two-stroke marine engines flows at high speed through the exhaust valve housing and turbine housing. The exhaust valve housing and turbine housing are usually made of cast iron. Their inner surfaces are in contact with the exhaust gas, and are often subject to sulfuric acid corrosion, high-speed high-temperature airflow corrosion, and electrochemical corrosion of the cooling water cavity, which can cause the housing wall to become thinner or even corrode and leak.

[0003] Repairing thinning of the valve housing and turbine housing of marine main engine exhaust valves and other components, as well as corrosion and leakage, has always been a challenging task.

[0004] Document CN 112705906 A discloses a welding repair method for the outer shell of a preheating boiler, including the following steps: determining the location of the defect, cleaning the area around the defect, determining the repair area based on the shape and size of the defect, and marking the repair area; heating the marked area, with the heated area extending 10-15mm outward from the center of the repair area; tapping the marked area while it is red-hot to make it recessed into the shell surface; embedding the corresponding repair plate into the recessed area according to its size, and welding the repair plate into the recessed area; grinding the weld smooth; and performing flaw detection on the weld area of ​​the boiler outer shell, followed by a hydrostatic test after confirming no defects are found. However, in corrosive environments, this beryllium copper welding repair method only provides a sealing function and cannot provide corrosion protection against the medium.

[0005] Therefore, a new technical solution is needed to solve the above-mentioned technical problems. Summary of the Invention

[0006] To address the aforementioned problems, this invention discloses a repair process for turbine housings and cast iron valve housings involving patching, nickel plating, tinning, and lead soldering. This process, which involves patching, welding, pre-plating with nickel, tinning, and lead soldering, is used to repair thinned valve housings and turbine housings that are corroded and leaking. The service life of the refurbished valve housings and turbine housings is greatly extended.

[0007] The technical solution of this invention is: a repair process for turbine housings and cast iron valve housings involving excavation, patching, nickel plating, tinning, and lead soldering, comprising the following steps: Step 1, patching and welding: Remove the corresponding part of the housing material in the corroded valve housing or turbine housing to form a gap. Make a patching plate with the same shape as the gap using sheet metal, and weld the patching plate to the gap in the housing. After welding, conduct a water pressure test to ensure there is no leakage. Step 2, nickel plating: Plate the welded and repaired valve housing or turbine housing with nickel according to the nickel plating process requirements, ensuring that all inner surfaces in contact with exhaust gas are nickel plated. Step 3, Tinning: Tin the inner surface of the valve housing or turbine housing after nickel plating in Step 2. Use pure tin powder for tinning. Preheat the inner surface of the valve housing or turbine housing with a flame torch. After burning, place the pure tin powder on the preheated surface of the valve housing or turbine housing. Quickly apply the tin powder with a knotted cloth to make the molten tin powder evenly distributed on the inner surface of the heated area of ​​the valve housing or turbine housing. Apply a layer of pure tin. Tin all the inner surfaces that need to be repaired in this way. Step 4, lead soldering: After tinning, solder a layer of lead-antimony alloy onto the inner surface of the tinned valve body or turbine housing. The composition of the lead-antimony alloy is Sb7Pb93.

[0008] Preferably, in step 1, if the minimum wall thickness at the corrosion location is less than 1 / 3 of its designed wall thickness or original wall thickness, or if the corrosion has already caused leakage, patching and welding should be used.

[0009] By adopting the above technical solutions, we can avoid the waste of time caused by excessive patching and repair, as well as the failure caused by insufficient repair, thereby improving the operability and standardization of the process.

[0010] Preferably, the wall thickness around the notch in step 1 is controlled to be at least 5mm-6mm, the board material is 5-6mm Q235 board material, and the water pressure test is 6-8Bar.

[0011] By adopting the above technical solution, sufficient "thermal buffer space" is provided for welding to avoid burn-through caused by excessively thin wall thickness, and stress concentration is reduced by regular notch shape, thus reducing the risk of corrosion at the notch by 50%.

[0012] Preferably, the tinning in step 3 is carried out within 4 hours after the nickel plating in step 2, the tin content of the pure tin powder is above 99.9%, and the inner surface of the valve housing or turbine housing is preheated to 280-340°C.

[0013] By adopting the above technical solution, the tinning process should be carried out within 4 hours after nickel plating in step 2. Otherwise, oxidation of the nickel plating surface will lead to tinning failure or a sharp decline in the tinning effect.

[0014] Preferably, the formula for calculating the preheating temperature in step 3 is: Wherein, Tp is the preheating temperature, Ceq is the carbon content, t is the plate thickness in mm, and during welding, the interpass temperature should be kept not lower than the preheating temperature.

[0015] By adopting the above technical solution, preheating ensures that the pure tin powder is fully melted, avoiding the bonding gaps caused by unmelted particles, and does not damage the upper nickel plating layer. Exceeding 380°C will cause the nickel plating layer to oxidize.

[0016] Preferably, in step 4, the thickness of the lead-antimony alloy on the inner surface of the valve housing or turbine housing is 4–6 mm.

[0017] Preferably, in step 4, the interlayer temperature of the weld is maintained between 170-200℃. After each section is welded, while the arc is extinguished and the weld is still red-hot, the weld is quickly hammered with a pointed hammer until the weld wave disappears.

[0018] By adopting the above technical solution, when tensile stress is generated during weld crystallization, external force is used to help it plastically extend, thereby reducing thermal stress and improving its density. Rapid hammering while hot is the key to reducing stress. Cleaning away residue can eliminate stress and refine the weld structure to prevent cracking.

[0019] The advantages of this invention are as follows: 1. This invention uses a repair process of patching and welding, pre-plating with nickel, tinning, and lead welding to repair the thinning of the valve shell and turbine housing of the ship's main engine exhaust valve and the resulting corrosion and leakage. This greatly extends the service life of the valve shell and turbine housing after refurbishment and repair.

[0020] 2. The present invention uses tinning within 4 hours and 99.9% pure tin powder to avoid oxidation of the nickel plating layer. The 99.9% high-purity tin powder reduces the "bonding gap" caused by impurities, thereby increasing the peel force between the tinned layer and the nickel plating layer from 2MPa in the existing process to more than 5MPa.

[0021] 3. This invention greatly improves the corrosion resistance of the exhaust valve body, thereby effectively increasing the service life of the valve body. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0024] like Figure 1 As shown, the repair process for turbine housings and cast iron valve housings, including patching, nickel plating, tinning, and lead soldering, includes the following steps: Step 1, patching and welding: Remove the corresponding part of the housing material in the corroded valve housing or turbine housing to form a gap. Make a patching plate with the same shape as the gap using sheet metal, and weld the patching plate to the gap in the housing. After welding, conduct a water pressure test to ensure there is no leakage. Step 2, nickel plating: Plate the welded and repaired valve housing or turbine housing with nickel according to the nickel plating process requirements, ensuring that all inner surfaces in contact with exhaust gas are nickel plated. Step 3, Tinning: Tin the inner surface of the valve housing or turbine housing after nickel plating in Step 2. Use pure tin powder for tinning. Preheat the inner surface of the valve housing or turbine housing with a flame torch. After burning, place the pure tin powder on the preheated surface of the valve housing or turbine housing. Quickly apply the tin powder with a knotted cloth to make the molten tin powder evenly distributed on the inner surface of the heated area of ​​the valve housing or turbine housing. Apply a layer of pure tin. Tin all the inner surfaces that need to be repaired in this way. Step 4, lead soldering: After tinning, solder a layer of lead-antimony alloy onto the inner surface of the tinned valve body or turbine housing. The composition of the lead-antimony alloy is Sb7Pb93.

[0025] In step 1, if the minimum wall thickness at the corrosion location is less than 1 / 3 of the designed wall thickness or the original wall thickness, or if the corrosion has already rotted through and leaked water, patching and welding should be used to avoid wasting time due to excessive patching and to avoid failure due to insufficient repair, thereby improving the operability and standardization of the process.

[0026] In step 1, the wall thickness around the notch is controlled to a minimum of 5mm-6mm, the plate material is 5-6mm Q235 plate, and the water pressure test is 6-8Bar. This provides sufficient "thermal buffer space" for welding, avoiding burn-through due to excessively thin wall thickness, and also reduces stress concentration through the regular notch shape, thus reducing the risk of corrosion at the notch by 50%.

[0027] The tinning in step 3 should be done within 4 hours after nickel plating in step 2. The tin content of the pure tin powder should be above 99.9%. The inner surface of the valve housing or turbine housing should be preheated to 280-340°C. Tinning should be done within 4 hours after nickel plating in step 2. Otherwise, oxidation of the nickel plating layer will lead to tinning failure or a sharp decline in the tinning effect.

[0028] The formula for calculating the preheating temperature in step 3 is: Among them, Tp is the preheating temperature, Ceq is the carbon content, and t is the plate thickness in mm. During welding, the interlayer temperature should be kept no lower than the preheating temperature. Preheating ensures that the pure tin powder is fully melted, avoiding gaps caused by unmelted particles, and does not damage the upper nickel plating layer. Exceeding 380℃ will cause the nickel plating layer to oxidize.

[0029] In step 4, the thickness of the lead-antimony alloy on the inner surface of the valve body or turbine housing is 4-6 mm. In step 4, the interpass temperature of the weld is maintained between 170-200℃. After each section is welded, immediately after the arc is extinguished, while the weld is still red-hot, the weld is quickly hammered with a pointed hammer until the weld wave disappears. When the weld crystallizes and generates tensile stress, external force is used to help it plastically extend to reduce thermal stress and improve its density. Hammering while it is hot is the key to reducing stress. Cleaning the residue can eliminate stress and refine the weld structure to prevent cracks.

[0030] Those skilled in the art should understand that the embodiments of the present invention described above and shown in the accompanying drawings are merely examples and do not limit the present invention; the objectives of the present invention have been fully and effectively achieved. The functions and structural principles of the present invention have been demonstrated and explained in the embodiments, and any modifications or variations of the embodiments of the present invention may be made without departing from the stated principles.

Claims

1. A repair process for turbine housings and cast iron valve housings involving patching, nickel plating, tinning, and lead soldering, characterized in that... Includes the following steps: Step 1, patching and welding: Remove the corresponding part of the housing material in the corroded valve housing or turbine housing to form a gap. Make a patching plate with the same shape as the gap using sheet metal, and weld the patching plate to the gap in the housing. After welding, conduct a water pressure test to ensure there is no leakage. Step 2, nickel plating: Plate the welded and repaired valve housing or turbine housing with nickel according to the nickel plating process requirements, ensuring that all inner surfaces in contact with exhaust gas are nickel plated. Step 3, Tinning: Tin the inner surface of the valve housing or turbine housing after nickel plating in Step 2. Use pure tin powder for tinning. Preheat the inner surface of the valve housing or turbine housing with a flame torch. After burning, place the pure tin powder on the preheated surface of the valve housing or turbine housing. Quickly apply the tin powder with a knotted cloth to make the molten tin powder evenly distributed on the inner surface of the heated area of ​​the valve housing or turbine housing. Apply a layer of pure tin. Tin all the inner surfaces that need to be repaired in this way. Step 4, lead soldering: After tinning, solder a layer of lead-antimony alloy onto the inner surface of the tinned valve body or turbine housing. The composition of the lead-antimony alloy is Sb7Pb93.

2. The repair process for turbine housing and cast iron valve housing by patching, plating, tinning, and lead soldering according to claim 1, characterized in that: In step 1, if the minimum wall thickness at the corrosion location is less than 1 / 3 of its designed wall thickness or original wall thickness, or if the corrosion has already caused water leakage, patching and welding should be used.

3. The repair process for turbine housings and cast iron valve housings by patching, plating, tinning, and lead soldering according to claim 1, characterized in that: In step 1, the wall thickness around the notch is controlled to be at least 5mm-6mm, the plate material is 5-6mm Q235 plate, and the water pressure test is 6-8Bar.

4. The repair process for turbine housing and cast iron valve housing by patching, plating, tinning, and lead soldering according to claim 1, characterized in that: The tin plating in step 3 is carried out within 4 hours after the nickel plating in step 2. The tin content of the pure tin powder is above 99.9%, and the inner surface of the valve housing or turbine housing is preheated to 280-340°C.

5. The repair process for turbine housings and cast iron valve housings by patching, plating, tinning, and lead soldering according to claim 1, characterized in that: The formula for calculating the preheating temperature in step 3 is: Wherein, Tp is the preheating temperature, Ceq is the carbon content, t is the plate thickness in mm, and during welding, the interpass temperature should be kept not lower than the preheating temperature.

6. The repair process for turbine housings and cast iron valve housings by patching, plating, tinning, and soldering lead according to claim 1, characterized in that: In step 4, the thickness of the lead-antimony alloy on the inner surface of the valve housing or turbine housing is 4-6 mm.

7. The repair process for turbine housings and cast iron valve housings by patching, plating, tinning, and lead soldering according to claim 1, characterized in that: In step 4, the interlayer temperature of the weld is maintained between 170-200℃. After each section is welded, while the weld is still red-hot and the arc is extinguished, the weld is quickly hammered with a pointed hammer until the weld wave disappears.

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