Container weld leakage
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There is a on-site issue for everyone to discuss: the weld between the outlet at the bottom of the filter and the head started to leak after 3 months of use. Process: Storage tank -- Centrifugal pump -- Filter -- To other units. Medium: Beverages (such as tea beverages, Orange Juice Plus, etc.). Operating conditions: The centrifugal pump operates intermittently, running for 9 seconds and stopping for 30 seconds. Phenomenon: The pressure is 0.6 MPa momentarily when the centrifugal pump starts, and 0.3 MPa under normal conditions. Upon shutdown, the outlet pressure instantly returns to zero, and then rises by 0.03 MPa after 1 second. Then it tends to 0. Product format: Bag filter. The fluid enters the filter through the inlet, passes through the filter bags, and exits from the bottom; the pipe at the bottom outlet runs horizontally in a tangential direction relative to the bottom of the end cap. Test: The filter undergoes a hydraulic pressure test at 1.0 MPa for 30 minutes upon leaving the factory, with no leakage or deformation occurring. Material issue: No similar problems have occurred with products from the same batch, so the material should be fine. Discussion topic: What causes leakage at the bottom weld?
Is it a welding quality issue, or fatigue damage caused by pipe vibration?
There are issues with the weld quality of the filter cylinder itself; vibrations also cause leaks at the head welds, as well as at the welds of the connecting pipes. It’s necessary to consider the design and manufacturing aspects of the pressure vessel cylinder
Thank you all. I’m sorry; I may not have explained it clearly enough: Material of the equipment: SUS 304. Thickness of the material: Calculated according to GB150 standards, with a design pressure of 1.0 MPa and a design temperature of 100 degrees; the actual operating temperature is below 30 degrees. Weld quality: The weld quality is fine. The filter started to leak after being in use for some time; the leaking area was repaired using TIG welding, but leakage occurred again after a while. Location of the leak: the weld between the head and the bottom nozzle. Vibration issue: The filter is fixed to the frame, and there is a certain distance between the centrifugal pump at the front end and the filter.
Based on the material you mentioned, it should be stainless steel; check the welding records to see if welding was carried out in accordance with the requirements for stainless steel. Another possible reason is the intermittent operation of the centrifugal pump, which causes stress due to pressure fluctuations; the welding stress at the bottom connections and fittings can lead to fractures over time.
It is possible that the vibration generated during the operation of the centrifugal pump causes fatigue in the welds, leading to cracks. Consider adding a section of hose or an expansion joint between the centrifugal pump and the filter to reduce this vibration; this might help.
It could be a centrifugal pump; the vibration that occurs during operation is the cause
It is certain that it is a welding issue; the small gap in the fillet welds leads to incomplete welding, and cracks occur when pressure changes frequently. The repairs carried out are only superficial, and the cracks are not completely eliminated, resulting in further leaks； Otherwise, why are the other filters fine?
It may be due to incomplete penetration of the joint weld, combined with equipment vibration
Designed based on stress analysis; GB150 is not required, and fatigue analysis is applied to the leakage areas
1. Is the welding material correct? 2. Is the sheet material correct? 3. Are there any defects in the weld?
Based on our factory’s experience in manufacturing containers, most cases of this kind are caused by issues with the quality of the welds – insufficient penetration inside the welds and the presence of internal stresses. Otherwise, it would be impossible for problems to arise after just a few months. Additionally, when using TIG welding for repairs, it is likely that no bevel was created, and only a layer was welded on the surface.
Are the welding materials and sheet metal suitable? The most likely cause is delayed cracking due to welding stress. It is recommended to recheck the process qualification and conduct a stress analysis.
1. Vibration 2. Welding quality issues (including whether the welding surface is clean) 3. Check again to see if there are any problems with the electrodes and materials used. Last edited by Chaochao on 2009-4-1 09:46.]
Thank you all for the lively discussions. Here are some clarifications regarding the questions raised: 1. Material thickness: 3 mm. 2. Double-sided welding is used, and there is no risk of under-welding with a plate thickness of 3 mm. 3. Material: 304; Welding material: TGS-308 (Tiantai Welding Materials) ； The selection of welding materials meets the requirements. 4. There is a distance of about 6 meters from the centrifugal pump outlet to the filter inlet, with elbows, sanitary butterfly valves, etc. in between. Centrifugal pumps experience relatively low levels of vibration. 5. Stress concentration may occur at the welds at the bottom; these welds are the joints between the pipe and the head, and they all have a slight curvature. However, I’m not sure how to confirm whether stress exists. This post was last edited by chenjf81 on 2009-4-3 08:46]
If none of the situations mentioned above apply, then it comes down to whether chloride ions in the medium cause stress corrosion
Medium: Beverages (such as tea-based drinks, Orange Juice, etc.), similar to the Kung Fu Master beverages we usually drink