The welding furnace using 1mm stainless steel tubes and 6mm stainless steel plates is leaking – how to fix it?
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This post was last edited by zzhaichuan on 2019-3-4 at 11:49. It’s a stove powered by natural gas for home use; the smoke flows inside a φ12×1 stainless steel tube, with water on the outside of the tube. The tube ends are fitted with 6mm stainless steel plates (with holes that are somewhat large, measuring φ14). The welder said that TIG welding can be used without any problems with this gap. After welding, as shown in Figures 1 and 2, a gas tightness test at 5 bar was conducted with no leaks. Here’s the key issue: once water is filled and heated, the entire lower part starts to leak. I took it back and tested it under 5 bar pressure – no leaks – but as soon as water was added and it was heated, it started leaking everywhere (heartbreaking). . Leakage is most severe when the lower tube sheet is heated to around 500 degrees and the water inside is at around 30 degrees. I don’t know how to prevent it from leaking now; or will it definitely leak due to uneven stress from such heating? Experts in this field, please take a look and tell me where the problem lies and how to solve it This is the picture before heating; this is the picture of leakage after heating (it breaks my heart every time I see it)
It seems that in the areas where self-fusion occurs and the covering layer is thin, there are leaks
Are you burning this tube sheet directly with fire? It is recommended not to burn it directly; try leaving a 500 mm gap in the middle and adding a fire-resistant stainless steel plate.
I haven’t figured it out. I initially thought that the welding height was insufficient, and the heat stress caused cracks in the weld. But you conducted another airtightness test, and there was no leakage. That’s strange then. Does it only leak water and not air?:o
In systems with fixed tube sheets, thermal stress can cause cracks at the welds. If the strength of the tube sheet and heat exchange tubes is insufficient, the welds are prone to cracking under the effect of thermal stress. The temperature should not be too high; the temperature of the water-based heat transfer medium generally should not exceed 120–150°C. Water quality also needs to be taken into consideration, as chloride ions can cause stress corrosion in stainless steel, leading to leaks over time (since this system has not been in use yet, this is probably not the cause)
The temperature difference stress is too high; it is necessary to increase the thickness of the tube sheet and the tube walls
At first, the cause couldn’t be identified; it wasn’t a leak. When natural gas burns, 1.6 kg of water is produced per cubic meter, and that water is formed as a result of condensation
Thank you all for your answers. At first, I couldn’t figure out the cause; it wasn’t a leak. When natural gas burns, 1.6 kg of water is produced per cubic meter, and that water is formed as a result of condensation. When the temperature of the shell-side water is below 50 degrees, there is a lot of condensate; when it is above 80 degrees, almost no condensate appears. Moreover, the water level in the tube side does not decrease during combustion (it actually rises due to expansion), and it remains unchanged even after cooling to room temperature, which proves that there is no leakage.
How do you test for gas? Use soapy water? Still hold the pressure. Since the operating temperature of yours is quite high, you can increase the pressure a bit and give it a try