I. What is truly high quality? Don't just look at bellows thickness
When many people buy expansion joints, their first reaction is to weigh the thickness of the bellows. Thick = strong, thin = cut corners-this idea holds true for most mechanical parts, but not necessarily for metal expansion joints. Two days ago, I met a customer and purchased a batch of corrugated pipes called "thickening". As a result, they cracked in less than three months after installation. Why? Because the core of high-quality metal expansion joints lies in design life and material matching, not pure stack thickness.
The rigidity, fatigue life and corrosion resistance of the bellows are the key. You can check out our websiteHigh temperature axial expansion jointIts bellows is made of heat-resistant alloy steel, and the wall thickness may only be 1.5mm, but after special molding and heat treatment process, it can withstand the high temperature above 600℃. However, the "thickened" products of some manufacturers are made of ordinary 304, which is thick, but intergranular corrosion occurs quickly at high temperature, and the thickness becomes a burden-the stress is greater and the cracking is faster. So, don't be fooled by "thickness", it depends on the material grade, wave number design, and whether you have done fatigue test.
2. Record of selection and pit stepping: what do power stations, cement and desulfurization conditions want
Different working conditions, the expansion joint is like wearing different shoes. The steam pipeline of the power station has high pressure and temperature, and is accompanied by water hammer impact. If you take the universal ripple compensator up, it is equivalent to wearing slippers to run a marathon. Special ones recommended for power station industryCorrugated expansion joint for power station industryThis product usually comes with a multi-layer bellows, plus a guide tube and anti-torsion tie rod, which can absorb axial and lateral displacement.
What about the cement industry? The dust is large, the temperature fluctuates wildly, and there are often solid particles in the pipes. At this time, the corrugated groove of the ordinary expansion joint is the natural "ash collecting groove", which will hinder the expansion and contraction after the accumulation of particles, and directly jam in severe cases. The right thing to do is to chooseMetal Corrugated Expansion Joints in Cement IndustryIts guide tube is designed to be made of wear-resistant material, and a dust jacket is installed on the outer wall of the bellows to reduce the risk of dust accumulation.
The desulfurization system is even more troublesome-wet flue gas, containing sulfides, with a pH value as low as 2~3. In this environment, 304 stainless steel is just like paper paste, and pitting and stress corrosion cracking quickly occur. Must use duplex stainless steel or high nickel alloys, such as oursDesulfurization flue gas baffle doorThe matching expansion joints are made of 2507 super duplex stainless steel. You spend that extra money on good materials, which is much more cost-effective than changing the bellows every three years.
Third, the installation is wrong, no matter how good the expansion joint is, it is in vain-the doorway of the tie rod, guide tube and arrow
The installation link is the hardest hit area for rollover. Let's talk about the pull rod first. Many people think that the tie rod is for fixing, and after installing it, screw the nut to death-guess what? That is equivalent to welding the expansion joint to death. How does it compensate for the displacement? The correct method is: loosen the locking nut on the tie rod during installation, let the expansion joint be in a free state, and then adjust the length of the tie rod after the pipeline pressure test is completed to limit the maximum displacement. Specific how to adjust, you can refer to our siteHow to adjust the tie rod nut of expansion jointThe answer is illustrated by a graphic.
Let's talk about the deflector. The role of the guide tube is to allow the medium to flow smoothly through the bellows, avoiding high-speed fluid from directly washing the corrugations, and at the same time protecting the bellows from contacting hard particles. Some on-site installers try to save trouble and install the diversion tube in the opposite direction-the direction of the arrow is the flow direction of the medium. Installing it in the opposite direction will not only fail the diversion function, but also increase the resistance. Please see the analysis of pictures and texts in the stationSpecific Function of Expansion Joint Guide TubeBoth the arrow pointing and the welding direction are indicated. Don't underestimate this arrow. Last month, a cement plant was installed backwards, and the bellows were worn out by fly ash. It took three days to shut down and replace it.
IV. Life and maintenance: How long does it take for metal expansion to save energy? The key lies in fatigue and corrosion
I've asked many engineers, and their biggest concern is: How many years will this thing last? There's actually no fixed answer. The design life of high-quality metal expansion joints is usually 1000~3000 full displacement cycles, which is about 5~10 years according to normal working conditions. But the actual lifespan looks at two killers: fatigue and corrosion.
Fatigue is easy to understand. The pipeline expands and contracts repeatedly, and the bellows are like curved iron wires, which will break more times. If your system starts and stops once a day, the design life is 3,000 times, which corresponds to almost 8 years. However, in order to save costs, some power plants choose a smaller expansion joint when selecting the model, which leads to each displacement exceeding the design value. The actual number of cycles that can be carried may only be a few hundred times, and it will be wasted in one year.
Corrosion is more covert. Many users only pay attention to the rust of the outer wall and ignore the chemical corrosion of the inner wall. For example, the condensed water in the steam pipe, if the pH is low, will form pit erosion at the bottom of the bellows. During regular inspection, you can use an endoscope to look inside the bellows or measure the wall thickness. If more than 15% thinning is found, it is recommended to replace it in advance. Also, don't wait until it leaks before replacing it-once it penetrates, the media spewing out can be more than just a problem of losing an expansion joint.
V. Summary: Three core dimensions of purchasing high-quality metal expansion joints
To say a thousand words, choose high-quality metal expansion joints, you only need to keep an eye on three items:
- Material matching condition: Heat-resistant steel for power stations, wear-resistant belt for cement and dust-proof, duplex stainless steel for desulfurization. Don't use 304 to take it all cheaply, and it will be yourself who will suffer in the end.
- Designed to withstand fatigue: Require the supplier to provide the fatigue life curve to confirm that the maximum displacement is within the design range. If you don't know how to calculate yourself, let the manufacturer select the model according to the standard, such as oursUniversal corrugated expansion jointAll have a clear table of displacement parameters.
- Install in place: The tie rod nut must be loosened, the guide tube arrow must be right, and the limit must be readjusted after pressure test. These three steps are done, and 80% of early failure can be basically avoided.
Expansion joints are "small parts, big responsibilities" in pipeline systems. It's not expensive to replace a new one if it's broken, but the damage caused by downtime can be dozens of times. Only after the three links of selection, installation and maintenance are cut to death can your pipeline system run steadily for more than ten years.