Technical analysis of precision stainless steel pipe

1. Heat transfer performance of precision stainless steel tube: for the condenser of generator set, when the cooling tube material is replaced by Navy brass stainless steel, the heat transfer changes are as follows: the heat release conditions of both sides of the heat transfer tube are the same, that is, the heat release form heat release coefficient of both sides are the same, but the heat resistance change of the tube wall caused by the material wall thickness of the heat transfer tube The change of wall thickness effect is relatively small.

The effect of wall thickness is only 2% of the total thermal resistance, the effect of material is relatively large. According to Hei standard, the material heat transfer coefficient of naval brass is 1.01 (tube diameter is 25x1), while that of stainless steel is 0.89 (tube diameter is 25x0). 6）。 Therefore, it can be seen that the stainless steel pipe of the same specification is about 11% lower than that of the copper pipe. However, due to the relationship between the total heat transfer coefficient the square root velocity, when the cooling water velocity of the stainless steel tube increases 2m / s to 2.3m/s, the total heat transfer coefficient can be increased by 7%, the surface gloss cleaning coefficient of the stainless steel tube can also be increased to 0.9, so that the total heat transfer coefficient of the two pipes is basically close.

The total heat transfer coefficient of stainless steel tube is worse than that of copper tube, the thermal conductivity of stainless steel tube is higher after being used for a period of time. The reason is that the pollution scaling of cooling pipe will have adverse effect on heat transfer. Heat insulation caused by corrosion scaling can reduce the heat transfer coefficient by up to 50%.

2. Vibration of precision stainless steel tube bundle: the strength elastic modulus of stainless steel are higher than those of copper. However, since the original seismic calculation of the tube bundle was based on the natural frequency of the tube to avoid resonance caused by a turbine speed of 3000 rpm, it can be concluded that the distance between the diaphragms is relatively large. In other words, the steam outlet of the steam turbine reaches the sound speed to determine the cooling span value of the condenser. In order to ensure that the condenser cooling pipe will be damaged, the calculation result is about 900mm. Therefore, according to the distance of the original condenser baffle plate, it is necessary to add a small baffle plate.

3. Improve the corrosion resistance of precision stainless steel pipe. The corrosion resistance corrosion resistance of stainless steel are much better than that of copper tube, but the corrosion resistance of austenitic stainless steel to chloride ion is poor. Different stainless steel pipes can be selected according to the content of chloride ions in cooling water. TP304 TP304L can be used when the chloride content in cooling water is small. TP316L TP321 can be used when the content of chloride ion in water is high.

4. The tube is connected to the tube sheet. If the tubesheet is made of stainless steel clad plate, the tube tubesheet can be expanded sealed to ensure that the condenser does leak has a service life of 30 to 40 years. If only the tube is replaced, the tube tubesheet will expand. To ensure that there is no leakage at the joint, grooves can also be made on the sealant tube sheet.

5. Manufacturing process of precision stainless steel pipe. The strength elastic modulus of stainless steel pipe are higher than other materials, especially copper pipe, have good plasticity high elongation.