Determination of storage tank wall thickness (Phase II recommendation)

The design pressure is as you said, but an additional thickness allowance must be added. Moreover, the standards specify detailed requirements for the minimum wall thickness; when determining the wall thickness, it must be the maximum of the calculated thickness, the thickness required for hydrostatic testing, and the minimum wall thickness.

At normal pressure, the main issue with containers is stiffness rather than strength. Furthermore, the wall thickness should also be determined based on the calculated thickness rather than the design pressure.

The wall thickness calculated using the tank wall thickness formula is only 1.2 millimeters – why is it so small? Suppose the size of the storage tank is a diameter of 4.5 meters and a height of 9 meters. The medium is water; what should be the thickness of the tank walls and the bottom of the tank? What materials to use, and explain the reasons.

The calculated wall thickness must also include a corrosion allowance before being rounded off; in such cases, the stiffness of the tank must be taken into account.

The height-to-diameter ratio of this storage tank you mentioned is greater than 1; in fact, it’s already 2. In this case, you need to consider increasing the wall thickness, and also determine whether anchor bolts should be used to resist wind pressure. Other measures include installing reinforcement rings or wind-resistant rings on the tank walls, as well as choosing materials in the most economical way and determining wall thicknesses that are optimal.

A simple method is provided: (1) For containers made of carbon steel and low-alloy steel, when the inner diameter D ≤ 3800 mm, the wall thickness S ≥ 2D/1000 mm, with a minimum value of 3 mm; an additional corrosion margin shall be applied. When the inner diameter D > 3800 mm, S is determined based on transportation and on-site manufacturing and installation conditions. (2) For stainless steel containers, take S to be no less than 2 mm. 　

If there is negative pressure, the wall thickness must meet the requirements for both positive and negative pressures.

The pressure-free condition mentioned by the poster refers to a storage tank at atmospheric pressure; in such cases, the wall thickness of the tank must be calculated in accordance with the specifications for vessels under atmospheric pressure or by referring to the design standards for cylindrical metal oil storage tanks. First, it is necessary to determine the location of the point of maximum stress, which, as the poster said, is 300 mm above the floor. Secondly, it is necessary to determine the calculated thickness here; this value is determined based on hydraulic calculations, and it is linearly related to the density of the liquid, the height of the liquid, as well as the allowable stress of the material. If the calculated thickness determined by the poster is very small (it’s impossible to verify this as no design parameters were provided), and the material used is ordinary, then there might be an error in the data input or in the unit conversions. The final nominal thickness is the specified thickness, which is obtained by rounding up the calculated thickness plus the corrosion allowance plus the thickness variation; if this specified thickness is very small, the stiffness of the tank as well as the feasibility of manufacturing must also be taken into account.

The minimum thickness requirement must be met

You have used the wrong value for the hydrostatic pressure of the liquid column.

The design calculations for atmospheric pressure vessels should be carried out in accordance with JB/T4735 for welded steel atmospheric pressure vessels. In addition to considering strength, attention should also be paid to the stiffness of the vessel body; although the wall thickness is usually thin, reinforcement rings should be provided.

I would also like to know this: what exactly should be the static pressure of the liquid column? For this device, with a diameter of 4.5 meters and a height of 9 meters, what is the static pressure when it is filled with water? Please advise. Last edited by bobo315 on 2008-12-5 08:18]

Yes, section 12.2 of JB/T4735 covers the design of tank wall panels. In addition to the thickness calculated using formulas, there is also a requirement for a minimum thickness; of course, factors such as wind load must also be taken into consideration, and all these aspects need to be verified.

Static pressure is calculated using the formula ρgh.

In this case, the main considerations are stiffness and manufacturing feasibility; even welding very thin sheets poses a problem.

That is, 1000×9.8×9=88200, and the unit is PA?

One can first use the strength calculation formula for computation (the design pressure can be taken as the hydrostatic pressure of a liquid column), and then compare it with the minimum thickness required by JB/T4735-1997 (which, in my opinion, should be the thickness sufficient to ensure stiffness); the larger of the two values should be chosen.

Design of storage tanks: If it is a horizontal tank, it should be designed in accordance with the requirements for horizontal storage tanks； If it is a vertical storage tank, it must be designed accordingly. The design of such tanks must meet strength requirements; the wall thickness is calculated based on the most hazardous operating conditions. If the wall thickness is too small, the minimum thickness required for pressure vessels must also be taken into account. Additionally, stiffness requirements must be considered as well, and the thickest wall thickness applicable under various operating conditions should be used as the standard. In your case, when there is 300 mm left, the wall thickness is 1.2 mm – so why don’t you consider the situation when the tank is filled to capacity? It has a tendency to generalize. One must think things through carefully and not be one-sided. I still need to study hard*.