Issues regarding the minimum thickness of heat exchanger shells in GB151
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GB151 specifies minimum wall thickness requirements for the shells of heat exchange equipment. I’m wondering what determines these minimum thickness requirements – is it related to the material of the shell? Is it mandatory to comply with them? Also, if the corrosion margin is increased in the design, does the wall thickness need to be adjusted accordingly? It would be great if you could provide a more detailed answer. Thank you!
1. The determination of the minimum thickness of the heat exchanger shell is primarily aimed at ensuring sufficient rigidity of the shell, thereby reducing deformation and facilitating the installation of the tube sheet and tube bundle. Especially for the shells of floating-head and U-tube heat exchangers, since there is no tube sheet to provide support and these units need to be disassembled, it is even more necessary to ensure a certain thickness. 2. In the case of horizontal heat exchangers used in a stacked configuration, their saddles and connections exert significant local stresses on the shell-side cylinder. To this end, it may be appropriate to increase the minimum thickness of the shell by 3; increasing the minimum thickness of the shell-side cylinder is also helpful for conducting leakage tests on the pipe joints in the shell side of heat exchangers that have high design pressures on the tube side. If there is a larger margin for corrosion, then the thickness must be increased accordingly. The reason is given above; point 151 only states that CS, LAS, and SS must comply. Decide for yourself factors such as the costs associated with non-ferrous metals, as stiffness is something that cannot be quantified
It seems similar issues were discussed before as well, but I can’t find them at all. Let me share my views: 1. The standard for minimum thickness only specifies the value, without explaining the origin of this minimum thickness. In my opinion, this minimum thickness might be derived from empirical formulas or based on practical experience in engineering. The person who commented on the second floor explained the reasons behind setting this minimum thickness quite comprehensively. 2. The minimum wall thickness is related to the material of the shell; the stiffness of different materials varies, which is why GB151 specifies different minimum thicknesses for carbon steel, low-alloy steel, and high-alloy steel. Another reason might be considerations related to the cost efficiency of the materials. 3. If designed in accordance with GB151, the requirements regarding minimum thickness must be followed; if the corrosion margin specified in the design is increased, it should be adjusted accordingly. GB151 specifies a corrosion margin of 1 mm for low-alloy steels, and if the corrosion margin is 2 mm, an additional 1 mm should be added to the minimum thickness. Corrosion allowance is not taken into account in the low-alloy steel standards; if a corrosion allowance is required, it should be added to the minimum thickness. Those with different opinions, please speak below.
One more thing to add regarding the 2nd floor: in order to meet welding requirements, the steel plates must have a minimum thickness.
The answers for the 2nd floor and 3rd floor are basically complete
So, what are the smallest thicknesses that people have actually seen in practice for carbon steel and stainless steel respectively?
Minimum thickness for carbon steel and low-alloy steel: Floating head type, U-tube type: Nominal diameter (mm) 400–700, 700–1000, 1000–1500, 1500–2000, 2000–2600; Minimum thickness (mm): 8, 10, 12, 14, 16. Fixed tube sheet type: 6, 8, 10, 12, 14. Minimum thickness for high-alloy steel: Floating head type, fixed tube sheet type, U-tube type: Nominal diameter (mm) 400–500, 500–700, 700–1000, 1000–1500, 1500–2000, 2000–2600; Minimum thickness (mm): 3.5, 4.5, 6, 8, 10, 12