Issues regarding the compensation for lateral thermal displacement of pipelines
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As the title suggests, I’ve spent a whole day thinking about this problem yet still can’t understand it; I just don’t get this horizontal displacement compensation. First, the book states that displacement includes axial displacement, lateral displacement, and angular displacement. I don’t understand – is this lateral displacement the same as radial displacement? If so, I’m not sure how the compensator carries out compensation, and whether lateral displacement needs to be compensated as well The axial aspect is easy to understand: as pipes expand when heated and contract when cooled, their length changes, and elastic components such as bellows are needed to absorb the increase in length or compensate for the decrease. However, the lateral displacement is not easy to understand; if a pipe gets thicker or thinner, compensation is required – what will happen if no compensation is provided? How does a bellows compensate for the expansion and contraction of a pipe, after all it is inserted axially into the pipe? Experts, it would be great if there were diagrams or animations, so I can understand it better.
Sir, I just checked – the company has this book, \"Petroleum and Chemical Process Design\". I was wondering, which volume is it in exactly?
Sir, I’ve found it, but I haven’t seen yet how the horizontal displacement is compensated for
There are two pipes connected vertically, and the thermal expansion and contraction of one of these pipes causes lateral displacement in the other pipe. If this displacement is excessive: (1) it will cause the supports and hangers on the pipes to lose their stability； (2) If connected to a device, the forces and torques at the device’s interface will be particularly large ； (3) If there are fixed points on the pipe, it will generate particularly high shear stress on the pipe ；
Regarding axial displacement, the thermal expansion and contraction of the pipeline itself, as long as it occurs within the temperature and pressure ranges specified for the material, has no adverse effect on the pipeline. However, since the pipelines are connected to each other, without compensation, their thermal expansion and contraction will be restricted, which leads to stress. The use of compensators allows the pipelines to expand and contract as needed
Axial displacement is caused by the thermal expansion and contraction of the metal pipe itself. It is one-dimensional. Lateral displacement can also be understood as radial displacement; a small portion of it is due to the Poisson’s ratio conversion of axial strain. Most of it is caused by the axial displacement of other pipe fittings. It is two-dimensional. Angular displacement can be understood as one end being fixed while the other end moves. Similar to rotation around a fixed point, the vertical component of axial displacement is quite important, as it relates to pipe support. If a pipe on a fixed bracket shifts upward by a few millimeters, then the pipe becomes suspended in mid-air, and the support serves no purpose anymore. It is precisely because of the importance of axial displacement that stress analysis after piping is conducted. Stress analysis divides displacement into vertical displacement and horizontal displacement (including the horizontal component of lateral displacement and axial displacement); of course, other coordinate systems can also be used for decomposition depending on the actual situation. Axial displacement is generally balanced using spring supports.
In other words, this lateral displacement is caused by the thermal expansion of another pipe, which causes this pipe to deviate from its original position, rather than the pipe becoming thicker or thinner?
I understand that radial displacement is caused by the thickening or thinning of the pipe, so I thought the same was true for lateral displacement. From what you’ve said, it seems that lateral displacement is caused by the thermal expansion and contraction of other pipes, which causes this pipe to deviate from its original position and thus result in lateral displacement?
For a tube, the lateral displacement is entirely caused by the Poisson’s ratio. But for a piping system, it represents the superposition of various displacements of the pipes; in such cases, the displacements caused by the influence of other pipes are more common and greater in magnitude. Because according to the former, it will never exceed εx = -νεy. The direction can only shorten radially, which is obviously not in line with reality. So, it depends on what your reference point is: a single pipe or a piping system.
In fact, in actual operating conditions, it is all calculated by stress analysis software. We only need to know the lateral displacement, which can be eliminated using spring supports or other types of pipes.
When a straight pipe bends and equipment is connected to it, lateral displacement occurs; the openings of large-sized equipment cannot be moved, so it is necessary to use tie rods or flexible hoses to absorb this lateral displacement!