Titanium steel clad plate material is widely used in pressure vessels in the chemical industry, and has good corrosion resistance, rigidity and economy. Some key, core, and high-pressure projects in the chemical industry also use titanium-steel composite plate materials. The connecting pipe of the container body adopts the structure of forged tube, liner flanging and composite welding ring, which not only improves the design and production of the container. Requirements, but also improve the requirements of container inspection. Due to the large diameter of some container equipment, the pressure of the airtight test and the helium leak test is low, resulting in some small defects on the titanium clad fillet welds or hidden dangers in the quality of the titanium clad fillet welds. Can not be found, after a relatively high pressure hydrostatic test, it can be found that there is leakage in the titanium clad fillet weld. The following are several methods for finding leakage defects in titanium clad fillet welds.
1. Air tightness test
In the case that the liquid penetration method cannot detect the leakage point of the titanium liner of the nozzle, it should be ensured that the inner surface of the titanium liner, all titanium welds and the clad layer base material within the adjacent 100mm range, and the narrow space between the nozzle and the titanium liner should be dried Keep it clean. Fill in 0.3MPa nitrogen gas from the leak detection nozzle of the connected pipe, and after maintaining the pressure for 30 minutes, brush the inner surface of the titanium liner, the titanium weld and the multilayer base material within the adjacent 100mm range with soapy water, and observe whether there are soap bubbles. No soap bubbles means that no leakage points have been found, that is, this detection method cannot detect micro-leakage defects in the weld seam of the titanium liner that takes over in this state.
2. Ammonia leakage test
In the case that the reverse air tightness test cannot detect the leakage point of the titanium liner of the connecting pipe, the ammonia leakage test is carried out on the narrow cavity of the connecting pipe and the titanium liner. Vacuumize the narrow cavity between the connecting pipe and the titanium liner through the leak detection nozzle (vacuum degree to 93.7kPa), fill the ammonia gas for testing and raise the pressure to 0.3MPa, wet the ammonia leakage test paper with phenolphthalein solution on the titanium liner On the inner surface of the cylinder, all titanium welds and the multi-layer base metal within the adjacent 100mm range, keep the pressure for 3~4h in a wet state, and observe whether there is discoloration on the test paper. There is no discoloration on the test paper, indicating that the reverse ammonia leakage test cannot detect the micro-leakage defect of the weld seam of the titanium liner sleeve in this state.
3. Helium leak test
In the case that the ammonia leak test cannot detect the leakage point of the titanium liner of the connecting pipe, a helium leak detection test is performed on the narrow cavity of the connecting pipe and the titanium liner. Seal the inner surface of the titanium liner, the titanium welds in different areas, and the multi-layer base metal within the adjacent 100mm range into several airtight small spaces with adhesive tape, fill in 100% pure helium gas from the leak detection nozzle, and the pressure rises to 0.3MPa, Hold the pressure for 2 hours, and use the cumulative leak detection method of the helium mass spectrometer sniffing gun to detect several confined spaces of the titanium liner and the clad base material. After sniffing, it was found that there was a helium leakage rate of 3.1×10-7 Pa m3/s in the area between the flange of the titanium liner and the multi-layer fillet weld of the container. The helium leak detector alarmed, but the specific location of the micro-leakage point could not be determined. .
4. Penetration testing
The fluorescence penetration method should be used to find micro-leakage defects, and the fluorescence penetration method should be used for the alarm area of the helium leak detector, and the detection and evaluation should be carried out in accordance with the requirements of NB/T47013.5-2015 level I, so as to find out the micro-leakage defects; Fluorescence penetration method is also used for other fillet welds, and inspection and judgment are carried out according to the requirements of Class I. After finding out suspected points, they are dealt with together according to the repair plan.
5. Re-soldering
When liquid leak test, air tightness test, ammonia leak test, helium leak test and penetrant test cannot find out the location of micro-leakage defects, all multi-layer fillet welds in the tested area can only be removed and re-tested welding.
After operating the above five detection methods, it can be known that the above detection methods can be used successively according to different leakage situations, or several methods can be used at the same time.
The liquid seepage method is generally used for the situation where there is water in the narrow space behind the strip cover or the back of the pipe liner after water pressure, and it cannot be completely removed. Since the area to be tested is at the lowest point of the equipment, the back of the possible leak is filled with water, resulting in leak defects that cannot be detected by air tightness, ammonia inspection, helium inspection, and penetration inspection. However, the sensitivity of this method is relatively low, and the detection results are greatly affected by the operator.
Before the airtightness test and the ammonia leakage test, the residual water in the narrow space on the back of the strip cover or the connection liner must be cleaned, otherwise, the sensitivity of the airtightness and ammonia leakage test will be seriously affected. Due to the sensitivity, some small leaks cannot be found through the airtight test; due to the low test pressure, the ammonia leakage test holds pressure and observes for a long time, also due to its sensitivity, a few micro-leakage defects cannot be detected.
The helium leak detection test adopts the cumulative sniffer leak detection method mode, but it can only identify the leak area, not the leak point, and it needs to be combined with the penetration test to find the location of the micro-leakage defect. This detection method is cumbersome to operate, and it is difficult to remove the residual helium in the narrow space on the back of the cover plate or the connection liner after the leakage defect is repaired, which affects the detection of the overall helium leak detection test of the container equipment in the later stage.
The method of removing the weld and re-welding is generally not recommended, and this method is generally only applicable to welds in a small range of possible leakage areas.
After operating the above five test methods and comparing their advantages and disadvantages, it can be known that the above detection methods can be used successively or simultaneously according to different leakage situations. Years of inspection practice have proved that when there are different degrees of leakage in the fillet welds of the stripped cover plate of the titanium-steel composite plate container or the liner of the nozzle, the leakage defects of different degrees can be found through the detection of the above six test methods.
Baoji Taicheng Clad Metal Materials Co., Ltd is a titanium steel composite plate manufacturer located in China's Titanium Valley. Our factory has proven strength. Whether it is product quality or service, it is the primary condition for our continuous development and progress. Therefore, we provide you with High-quality products and services are what we must do. If you have any product-related questions or needs, welcome to consult and cooperate!
