Excessive limit is not just "screwing too tight" as simple
Two days ago, a buddy from a thermal power plant complained to me that their power station industry leaked after installing corrugated expansion joints for only three months. When removed, the limit nut is pressed against the end plate, and the bellows is directly pulled into an "eight" shape. I am too familiar with this scene-many people's first reaction is that the quality of the expansion joint is not good, but in fact, the root is most likely at the limit.
The limiting devices (tie rods, nuts, ear plates) were originally designed to protect the bellows from excessive stretching or compression during transportation or installation. However, if you regard the limit as a dead block, or the amount of pre-compression/pre-stretching is not accurate during installation, the displacement direction changes as soon as the pipeline runs, and the limit changes from "bodyguard" to "shackle". And the result? The actual displacement of the bellows exceeds the design value, which ranges from corrugation instability and weld cracking to scrapping of the whole expansion joint or even pulling off the pipe. Don't ask me how I know-I have been in this business for more than ten years, and I have seen more than I have cultivated.
The root is mostly in the installation stage, so don't rush to throw the pot to the product
"The cold tightening amount is adjusted according to the design value", but how many on-site workers screw it directly to the end to save trouble? Or a general-purpose corrugated expansion joint was selected during the selection, and as a result, the actual thermal displacement of the pipeline was 30% larger than the design value, so the limit was naturally "stuck". There is also a common pit: the pipe support is loose or the foundation sinks, which leads to the deviation of the displacement direction, and the limiting device becomes the main stress point instead. And guess what? 90% of cases can be solved by adjusting the tie rod nut without replacing new parts at all.
So don't doubt the product when you come up. Ask yourself first: Did you find out the function of the expansion joint tie rod during installation? The tie rod is only for transportation and protection, and must be adjusted to the working position after installation. Does the screw of the expansion joint need to be removed? The answer is: the transport screw must be disassembled, and the limit nut should be cleared.
How to judge whether the limit is really "too big"? Don't rely on the feel
Take a caliper to measure the actual distance from the peak to the trough of the bellows, and compare the allowable compression/tensile limit given by the manufacturer. For example, in the product information of our site, the general-purpose corrugated expansion joint usually has the maximum compression amount and stretching amount marked. Under normal conditions, there should be a 3-5mm gap between the tie rod nut and the ear plate. Once it is dead, it means that the limit is too large. There is another local method: after shutting down, remove one nut and push and pull the expansion joint by hand. If you can move easily, it means that the original limit is fine. If you don't move at all... then you can basically confirm the diagnosis.
Remember, feel can deceive, but data won't. The function of the expansion joint guide tube also needs to be clarified-it is responsible for guiding the flow direction of the medium and protecting the bellows. If the limit is too large, the bellows will be deformed, and the guide tube will be easily damaged.
The solution is divided into three steps. Don't come up and move the knife
First step, loosen the nut. Turn the limit nut back, leaving the free clearance required by the design. For details, please refer to our article "How to Adjust the Tie Rod Nut of the Expansion Joint". Pay attention to re-check the pipe alignment after loosening to prevent deflection. In the second step, if the bellows has been permanently deformed (uneven wave pitch) after loosening the nut, then you have to consider replacing it. In the third step, for the excessive limit caused by insufficient pre-stretching, you can re-do cold tightening: use a jack to push the pipe to the designed displacement position, and then lock the nut.
If the conditions on the scene don't allow for cold tightness, don't force it. We also have double hinge transverse expansion joint or straight tube pressure balance expansion joint, which can absorb multi-directional displacement through its own structure and avoid single-point limit overload. The metal corrugated expansion joint in cement industry has been wear-resistant for the dust environment, and the high-temperature axial expansion joint comes with a guide tube and an insulation layer-choosing the right model can save half of the trouble.
Prevention is always less worried than remedy
In the selection stage, don't only look at the nominal diameter. Calculate the thermal expansion, installation temperature and ambient temperature of the pipeline clearly, and then select the corresponding model according to the expansion joint model and size comparison table. For example, steam pipeline, see what category steam pipeline belongs to, and then choose high-temperature axial type or straight pipe pressure balance type. Friends of cement factory remember to read the page of metal corrugated expansion joint in cement industry, wear-resistant design is not a gimmick. Also, it is recommended to read the article on the role of the expansion joint guide tube, which can help you avoid at least 30% of the selection pits.
By the way, the adjustment of the expansion joint tie rod during installation is a technical job. Our website has detailed steps for the correct installation method of large tie rod expansion joint, and the last step is to make sure to adjust the limit nut back to the working position. Don't be like that thermal power plant buddy who thinks that if you tighten it, everything will be fine.
When do you have to change? Don't hesitate
The bellows has visible cracks, bulges, serious uneven wave pitch, or the sound of media leakage-don't hesitate to change it directly. Note that the new one should match the displacement of the original pipeline, and don't buy a larger size to limit it back. Our double straight pipe bypass pressure balance expansion joint or curved pipe pressure balance expansion joint here can absorb greater displacement in a limited space, which is especially suitable for old pipeline transformation. If you are really too lazy to calculate the data, you can send us the on-site photos and pipeline parameters, and directly recommend the model for you-we do this every day, which is much more reliable than you groping for yourself.