I have been in this business for 18 years, and I have seen many users ask me: Isn't it done when the expansion joint is installed? There's not so much attention to. Every time I hear such words, I know that the expansion joints of this pipeline are probably installed for nothing again.
The core of metal expansion joint installation technology is one sentence: what you install is not a part, but a living joint that can absorb the displacement of the pipe. Put it right, and it works quietly; Wrong install, it's a time bomb.
Find out one thing first: Which direction of displacement does the expansion joint want to absorb?
Before installing, you have to figure out whether it is absorbing axial elongation, lateral deflection, or angular displacement. The direction is reversed, and the rest is all for nothing. For example, in a straight pipe section of a steam pipe, the thermal expansion and contraction mainly follow the direction of the pipe axis.Universal corrugated expansion jointOr external pressure type will do; If the pipe has an elbow and a lateral deflection, it must be usedCompound hinge transverse expansion jointOr the universal hinge type, hard take the general type to absorb the lateral displacement, and the bellows is directly twisted into a twist for you to see.
And the orientation of that guide tube. Don't look at it as inconspicuous. If the medium is installed backwards, it will directly wash the inner wall of the bellows. Whether it is high-temperature steam or smoke with particles, it won't take long to give you a leak. The direction mark is usually welded on the nozzle. Before installation, be sure to check whether it is consistent with the flow direction of the medium. This action takes less than 30 seconds, which can save tens of thousands of trouble later.
Pre-stretching and pre-compression: nine out of ten people are lazy
When manufacturers leave the factory, they generally preset the initial displacement of the bellows. If you weld it directly at the site, as soon as the pipe expands and contracts, the bellows may be dried directly against the tie rod, so it will be wasted.
Tell me the truth. The year before last, the high-temperature axial expansion joint installed on the steam pipeline of a chemical project had an ambient temperature of 15℃ and a pipeline operating temperature of 230℃ during installation, and the cold tightness was not adjusted in place. As a result, the bellows cracked after one cycle of operation. When dismantled, it shows the typical characteristics of crack penetration and fatigue fracture at the trough position.
How to tune it? It is simple: compress or stretch the bellows to the design cold tightness value before installation. There are specific numerical drawings, which are calculated according to the difference between ambient temperature and operating temperature. This step is lazy, followed by the accident of equipment parking.
Hoisting and welding are real skills
When hoisting, the wire rope must not be strangled directly on the bellows. The wall thickness of the bellows is just that, the thinnest part is less than 1mm, and it is a pit when knocked, which is the starting point of fatigue crack in the later stage. You have to hold the end tube, or pad it with a guard plate. If you find a pit on the surface of the bellows during hoisting, don't hesitate to scrap it and replace it with a new one-this thing can't be repaired.
You should pay more attention when welding. The grounding wire is clamped at both ends of the expansion joint, either bypass the bellows with a bypass wire, or carefully check the bellows immediately after welding for any electrical injury. There are several incidents of electric arc piercing the bellows every year. Think about it, with such a thin pipe wall, an electric spark is a hole, and it may not be found by pressure test, and it will leak as soon as it is put into production.
Be sure to remove the transport fixtures after installation
Tie rods, nuts and positioning blocks are locked for you in order not to bump when sent by the manufacturer. Many people forget to loosen the nut after installation. As soon as the pipe expands, the force is all transmitted to the bracket and flange. The expansion joint doesn't play a role at all, and the flange surface may leak.
The displacement indicator points to zero position and the tie rod nut is loosened to the design value. The installation is completed only after these two steps are completed. There was a customer before who forgot to loosen the tie rod after installation. After a heating season, the fixed brackets were all deformed. He came to us for after-sales service. After checking the reason, it was found that the transportation fixtures were not disassembled.
The pressure test stage is also particular
During the hydraulic test, the limit device should be installed to prevent the bellows from excessively elongating. Once the limit is exceeded, the bellows is plastically deformed and directly scrapped. Not to mention the air pressure test. When the bellows bears pressure, it will produce blind plate force. If the bracket doesn't calculate this force well, the pressure test site will fly directly for you. This is no joke.
There is another detail. Don't forget to drain the water after the pressure test. Cases of water accumulation, freezing and cracking corrugated pipes in winter occur every winter. You don't believe it? Check how many bellows are so bad after the first cold snap in the Northeast every year.
Finally, talk about some practical installation taboos
The expansion joint cannot replace the pipe support and hanger, and the middle cannot bear the weight of the pipe. Some people use it as a support, and the bellows will leak for you over time. When installing, don't hard break the bellows to the flange hole. If the wrong mouth exceeds the tolerance, you have to adjust the pipe. Use the expansion joint as a jack. Sooner or later, it will give you a leakage point.
If you keep an eye on all these places, you basically don't have to worry about the expansion joint. If you install it, it can run safely for ten or eight years. One day, when you hear an abnormal noise in the pipe, or find abnormal spots of condensation and frost on the surface of the bellows, check it quickly-it is probably that something has happened to the bellows.