Heat treatment
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Dear everyone, I would like to ask for your advice. Our company has a atmospheric pressure storage tank with a capacity of around 10,000 cubic meters. The bottom plate of this tank is leaking, so we are currently replacing it. The medium stored in the tank is alkali type 32, and the tank has a diameter of 24 meters and a height of 20 meters； The weld is a lap weld; the thickness of the bottom plate is 18 mm, while that of the edge plates is 10 mm. May I ask whether heat treatment is required after repair, and what testing methods are generally used for the bottom plates of storage tanks after welding? Chemical process machinery
Whether heat treatment is required depends on the material and thickness. Generally, for lap joints, kerosene penetration testing and surface coloring should be sufficient. Since you haven’t worked with this type of alkali tank before, you can also check the testing methods specified in the original documents; as long as they are consistent, that’s fine
It is necessary to check whether the manufacturing requirements of the relevant standards are met; the material used is also unclear. Moreover, does such a large device have a large furnace for heat treatment, or is only local heat welding used?
Is 32 the concentration? The temperature will not exceed 150°C, and carbon steel as the material is sufficient, so heat treatment is not required. The welds must undergo non-destructive testing plus vacuum testing (); kerosene leakage testing is not applicable (())
For large storage tanks, heat treatment is generally required for the wall panels that have cleaning holes; welds on the bottom plate and edge plates do not need post-weld heat treatment.
In section 7.8 of HG/T20581-2011, Table 7.8.1 specifies the maximum operating temperature in sodium hydroxide solutions; this temperature requirement is dependent on the concentration. The maximum allowable temperature can be calculated. The main concern is stress corrosion. Generally, alkali tanks are equipped with heating, and the bottom plate does not usually reach such high temperatures, so heat treatment is not necessary.
Alkali equipment – the medium needs to be clean, right? – is it lined equipment or stainless steel equipment? If it’s stainless steel, make sure to conduct a intergranular corrosion test.