The sinking of the tank sounds obscure, but if something goes wrong, it will be a big trouble. The foundation is not compacted, the backfill soil is soft, and the groundwater hollows out the soil-the tank sinks, ranging from a few millimeters to tens of millimeters. As soon as the can sinks, the connected pipeline bears the brunt: it is dragged to deform, crack, and the interface leaks. In serious cases, the whole pipeline has to be scrapped. At this time, installing a tank settling metal expansion joint is not the icing on the cake, but life-saving.
What the hell does it do? To put it bluntly, one end is connected to the tank wall and the other end is connected to the pipeline. When the tank sinks, it relies on the deformation of the bellows to eat the displacement, so the pipeline doesn't have to be carried hard. Just like when a person squats down, his knees are bent and cushioned, and his waist does not flash. Without this cushion, the welds, flanges, and brackets of the pipe all have to bear this extra displacement for the can, and something will happen over time.
How is tank settling different from ordinary thermal expansion?
The common pipeline expansion joint mainly absorbs the axial displacement of thermal expansion and contraction, the direction is clear, and the amount can be calculated accurately. That's not the case at all with tank settling. The direction of tank settlement is uncertain: it may be that the whole sinks evenly, or it may be that one side sinks more and the other sinks less; When there is a difference between soft and hard foundation, the tank wall will also tilt. Reflected on the pipeline, horizontal displacement, vertical displacement and angular displacement are all entangled together.
Therefore, that kind of general-purpose corrugated expansion joint can't be carried by one alone. In the case of tank settlement, double hinge transverse expansion joints or external pressure single axial expansion joints are often used in the field. The former relies on the combination of hinge and connecting rod to convert multi-directional displacement into angular displacement to absorb, which is suitable for the occasion where the pipeline turning space is limited; In the latter, the bellows is placed in the external pressure cylinder, and the axial displacement compensation is large, and the internal pressure thrust is restrained, which is more friendly to the fixed bracket. Which one to match depends on the expected settlement of the tank and the direction of the pipeline-whether it is horizontally led out or vertically connected, and whether there is a supporting bracket in the middle, all of which should be taken into account.
Type selection is not a pat on the head, the settlement amount should be asked for by civil engineering first
Many projects go wrong, that is, patting your head in the selection stage: estimate the approximate number, and just choose an expansion joint to install it. As a result, the tank settled beyond the design margin, and the bellows were crushed or cracked. When selecting tank settling metal expansion joint, the first step is to find the civil engineering professional to get data-the final settlement amount, uneven settlement value and settlement rate of the foundation. These parameters directly affect the compensation ability and fatigue life of the bellows.
After obtaining the settlement amount, determine the pipeline medium, temperature and pressure. Different media, bellows materials are completely two ways. For high-temperature flue gas pipelines, temperature-resistant alloys, such as Inconel 625 or 321 stainless steel, have to be used. The strength of ordinary 304 decays rapidly above 600℃; For corrosive media, you have to consider the PTFE-lined compensator or PTFE compensator. Don't be fooled by ordinary rubber compensators. Tank settlement is a long-term slow process. Rubber ages fast, and it will embrittle and crack in three or five years. At that time, you won't even have time to change it.
Installation is the hardest hit area, transport screw must be disassembled
To be honest, if the expansion joint is designed and selected correctly, it will be useless if the installation link goes wrong. Before the tank settling metal expansion joint is installed, the pre-stretching amount or pre-compression amount given by the manufacturer should be adjusted-this amount is calculated according to the positional relationship between the initial settlement and the final settlement of the tank, so as to keep the bellows in a reasonable deformation range during operation. Don't screw the tie rod nut to death, you have to leave room for movement, otherwise the expansion joint will be stuck, and it will be the same as not installed.
Two days ago, I met a customer. After the tank settling expansion joint was installed, I forgot to disassemble the transportation fixing screw. The screw is used to fix the bellows to prevent damage from transportation bumps when shipped, and it must be dismantled when installed in place. As a result, as soon as the tank sank, the bellows had no deformation space, and it was directly hard-pulled and cracked, and the medium leaked all over the ground. You say it was wrong or not? Just one screw, the whole equipment is scrapped.
In addition, pay attention to the direction when installing. Many expansion joints have guide tubes, and one end of the guide tube should be facing the direction of medium flow. If the guide tube is installed backwards, it will be washed away by the medium, and the bellows will be directly washed and worn. Also, pipe alignment should be accurate, and the installation error of the pipe system should not be pressed on the expansion joint.
Maintenance once a year, don't wait for tearing before crying
Tank settling is a slow process, which does not mean that it will be loaded once and for all. Check the bellows surface at least once a year for corrosion pits, cracks and scratches; Whether the guide tube is loose and falling off; Is there any abnormal displacement of the tie rod nut. If you find that the displacement is close to the design value, don't wait for it to fail, and quickly find the manufacturer to recalculate-whether to install the second-level compensation or adjust the pipe support, you have to plan in advance.
This thing is not like a valve, it can be turned off when it is broken. When the expansion joint is broken, it is directly torn, and the medium gushes out. High-temperature steam, toxic gas and corrosive liquid are no joke. Instead of repairing and shutting down production afterwards, it's better to take a look regularly, which won't cost a few dollars and won't take much time.
The tank settling metal expansion joint, to put it bluntly, is to add a flexible buffer between the storage tank and the pipeline. Don't think it has a simple structure, and it can't be carried at critical moments. It all depends on whether the three links of selection, installation and maintenance are in place. Foundation settlement won't say hello in advance, and pipes can't afford to wait, so you weigh it.