What are the horizontal vessel support requirements?

Horizontal vessels are divided into internal and external horizontal vessels according to pressure. Horizontal vessels are supported by supports. When the container size is small, the support for the support and additional to the container load is relatively small, can be ignored; but when the container diameter is large, due to the self-weight of the equipment as well as wind load, seismic load caused by the external load and container operating pressure compared to can not be ignored, the load must be taken into account.

Horizontal container design is therefore based on the operating pressure (internal or external pressure), in accordance with general pressure vessel design requirements to determine the wall thickness (generally controlled by the circumferential stress strength, circumferential stability control stiffness), and then take into account the additional load and check the wall in the additional load of circumferential, axial strength and stability, so that the container in a variety of operating conditions, not only to ensure that the circumferential strength and stiffness, but also to ensure that axial strength and stiffness. Strength and stiffness in circumferential direction and axial direction under various operating conditions.

The current applicable design code for horizontal vessels is NP/T 47042-2014 ‘Horizontal Vessels’. The standard applies to the design pressure is not more than 35 MPa, in the uniform load, by two position symmetrical saddle support horizontal container support.

Horizontal vessel design also includes horizontal support design. There are three types of horizontal vessel supports: saddle-type support [Figure 5-1(a)], ring-type support [Figure 5-1(b)] and leg-type support (or support-type support) [Figure 5-1(c)]. At present, the applicable design specification for supports is NB/T 47065-2018 ‘Vessel supports’.

Various types of horizontal vessels, including storage tanks, heat exchangers, etc., usually use saddle-type support. The structure and size of the saddle, except for special circumstances require additional design, generally according to the nominal diameter of the equipment can be selected standard form of support. Because for the horizontal container, in addition to consider the film stress caused by the operating pressure, but also consider the weight of the container in the shell caused by the bending stress, so even after the selection of standard saddle, but also on the container strength and stability of the calibration.

 Horizontal container placed on the double saddle and its force situation and double pivot point of the beam is similar to the beam of multiple pivot points in the beam of the bending stress is smaller, but the requirements of the pivot points are strictly maintained in the same level, which is difficult to achieve for all types of large horizontal container. Due to the uneven settlement of the foundation, multi-support container in the support at the support reaction force can not be evenly distributed, so the general horizontal container is best to use double support.

When double support is used, the position of support should be considered on the one hand to take advantage of the strengthening effect of the head, and on the other hand, it should be considered not to make the bending stress in the shell caused by the load too large, so the position of support is determined according to the following principles.

① It can be seen from the mechanics of materials, for the double support on the uniformly loaded simply supported beam, if the full length of the beam is L, when the length of the outstretched end A = 0.207L, the maximum bending moment in the middle of the span of the double support and the absolute value of the bending moment at the support section are equal, so that the cross-section in the middle of the span of the double support and the cross-section at the support to maintain the same strength as far as possible, taking into account the support cross-section there is still except for the bending moment of the other load, so for the Horizontal container usually take A≤0.2L (A is the distance from tangent line of head to centre line of support, L is the distance between tangent lines of two heads), otherwise the stress at the section of support will be too large due to the action of outreach of container.

 ② Since the bending rigidity of the head is greater than that of the cylinder, the head has local strengthening effect on the bending of the cylinder. If the support is adjacent to the head, it can make full use of the reinforcing effect of the head on the cross-section of the cylinder at the support. Therefore, A≤0.5Ri (Ri is the inner radius of the cylinder) should be made as much as possible under A≤0.2L.

The size of the saddle wrap angle has a direct effect on the stress on the cylinder at the saddle, and is generally 120°, 135°, 150°.

In order to prevent thermal expansion and bending of the cylinder due to the weight of the cylinder and material to cause additional stress on the horizontal container, only one of the double support is allowed to be fixed, the other one is movable. The base bolt hole of the movable support should be opened into a long round hole, and the long axis is along the axis direction of the cylinder; in order to make the movable support move flexibly, sometimes the rolling support can be used.

For the double saddle on the horizontal container stress for accurate theoretical analysis is very complex, at present domestic and foreign container design specification is mostly used Zick in 1951 in the experimental research on the basis of the proposed approximate analysis and calculation methods.

The ring type support is generally applicable to large diameter thin-walled vessels and vacuum operation of thin-walled vessels. At least one ring seat should be a sliding support structure, except for vessels operating at room temperature and pressure.

The main advantage of the legs is the simple structure, but its support reaction force to the shell caused by a large local stress, and therefore only used for lighter small equipment.