Discussion on the Replacement of Pressure Pump with Oxygen Cylinder for Hydraulic Pressure Test

Discussion on the Replacement of Pressure Pump with Oxygen Cylinder for Hydraulic Pressure Test

1 Introduction

Hydrostatic test is a necessary process after the installation of the heat pipe. The traditional hydraulic test is to use a pressure test pump to fill the water after the pipeline pressure, pressure to a certain value after the test. However, the complexity of the pressurized pump to extend the hydrostatic test time, can find a more convenient than the use of pressurized pump equipment it? This paper replaces the use of oxygen cylinders pressure test pump low pressure heat pipe hydrostatic test feasible Sexuality was discussed, and tried to reform the pipe in Xinyu Zhongwu Road.

2 theoretical discussion

The pressure test pump provided the desired pressure for the hydrostatic test by continuing to inject water into the filled pipe. The newly filled oxygen bottle pressure index of about 15MPa, while the external supply of low-pressure steam pipe pressure required for the test pressure is generally not more than 1.5MPa. In addition, the safety rules for the rubber band used as an oxygen zone made it clear that the pressure must be tested? 1.9? MPa. Obviously, the oxygen zone can be used as the connecting link between the oxygen cylinder and the test pipeline, and its connection method is simpler than the pressure test pump. Oxygen cylinders are an essential piece of equipment for pipe installation and are easier to find than pressure test pumps. The pressure reducing valves and pressure gauges on the oxygen bottles make the operation simple and easy to control.

The crux of the problem is whether the oxygen dissolved in water causes a drop in pressure that affects the accuracy of the hydrostatic test. The data show that 1 liter of water at 20 ℃ 1 atmosphere dissolved oxygen 0.031 liters at 20 ℃ 10 atmospheric pressure dissolved oxygen 0.297 liters. Obviously, as the pressure increases, the oxygen solubility in water increases significantly. It is conceivable that due to the small contact surface between oxygen and water (only the cross-sectional area of ​​the pipe to be measured or the water injection pipe is large), the dissolution will not be completed instantaneously. That is, when oxygen is injected into the water at the test pressure as shown in FIG. 1 Dissolution does not necessarily reach saturation. In this way, in the pressure test stage, it is possible that oxygen will continue to dissolve in the water, resulting in pressure drop, causing the pressure gauge pointer down, is not conducive to determine the strength of the pipeline. Oxygen in the water dissolution process, the molecular dynamics involved in the dissolution rate is very complicated, obviously, in this regard to find a simple law has been impossible. In this way, we only discuss whether it can make the oxygen dissolved in water does not affect the pressure of the pipeline under test. We think of the connection method and water injection method in Figure 2. When water injection, the water level must be raised to the upper side of the valve (the specific water level depends on the diameter and length of the test pipeline), at least 20cm above the valve. In this way, after the oxygen is pressurized to the test pressure through the water injection tube, only the valve is closed and the oxygen in the test tube becomes quantitative, neither increasing nor decreasing, so it will not cause water pressure in the test tube Variety. The above analysis proves that it is completely feasible that oxygen can be replaced by a pressure test pump.

3 steps

The first step, the pipeline water. Install the pressure gauge, water valve and other accessories, open the exhaust valve to be tested pipeline, close the drain valve, through the nozzle into the clean water until the water is filled pipe and over a certain value of the water valve, close the exhaust valve , Stop filling.

The second step, oxygen belt connection. The oxygen bottle (bottle pressure greater than the test pressure) on the rubber band connected to the water pipe.

The third step, slowly boost. Slowly open the valve on the oxygen bottle, pay attention to observe the pressure gauge on the oxygen bottle, pressurized to a certain value, you should stop to check the pipeline, no problem, then continue to pressure, generally 2-3 points rose to test pressure.

The fourth step, pressure check. For low-pressure heat pipe, pressure holding time to 5-10 minutes is appropriate in the test pressure to maintain the time, such as the pressure gauge pointer does not drop more than 0.02MPa, and no distortion of the visual pipe, that strength test pass.

Finally, rigorous testing. The pressure down to the working pressure, a comprehensive inspection of the pipeline can be used 1.5g below the head hammer in the seam 1.5-20mm Department gently tapping, such as pressure gauge pointer does not drop, the pipe weld and flange connection Department did not find leakage, that can be considered tight test.

4 application examples

The method is applied in Zhongli Road Heating Pipeline Reconstruction Project in Xinyi. The width of Zhongwu Road is 42cm, and the heat pipe (219) crosses Zhongwu Road at a height of 3.5m above the elevation of the road. rising. After the installation of the pipeline, using the method of hydraulic pressure test, the test pressure of 0.9MPa, after the pressure reaches the test pressure 40 minutes, pressure gauge pointer no change.

5 Conclusion

Replacement of pressure test pump with oxygen cylinder for hydrostatic testing is theoretically feasible and has been tested by practice. This method is easy access, easy to operate, easy to find oxygen cylinder compared to the pressure test pump. Due to the pressure limitation of the oxygen zone, this method is only suitable for steam pipes with steam pressure not exceeding 1.0MPa. When the pipeline is longer, it should be carried out sub-pressure test.