Mistaken selection is the number one killer of short lifespan-material and construction determine how many years you will last
Two days ago, I met a customer who complained that the expansion joint in their factory leaked after two years. When I removed it, the bellows were rotten. Ask about the working conditions-high-temperature steam pipeline, with a pressure of 1.6MPa and a temperature of 350℃. As a result, the general-purpose corrugated expansion joint was chosen at the beginning, and the material was 304 stainless steel. Isn't this seeking death?
The matter of model selection, to put it bluntly, is "what horse matches what saddle". High-temperature working condition honestly high-temperature axial expansion joint, the material must be Inconel 625 or at least 321 stainless steel; For corrosive media, such as desulfurization flue gas, you have to consider lining PTFE hoses or non-metallic expansion joints (fabric fiber expansion joints), and even rubber compensators can carry them for a while. In cases where particle erosion is serious, such as air ducts in cement industry, metal corrugated expansion joints in cement industry must have wear-resistant guide tubes, otherwise they will be worn out in less than half a year.
Structurally, don't be sloppy. For pipelines with large axial displacement, straight pipe pressure balance expansion joint or compound straight pipe bypass pressure balance expansion joint is the positive solution; If you need to absorb lateral displacement, compound hinge transverse expansion joint or curved tube pressure balance expansion joint is right. Choosing the wrong type is like letting a sprinter lift weights, and scrapping is a matter of time.
The "invisible killer" of the installation link: the draw rod is not adjusted in place, the guide tube is installed backwards, and no matter how good the expansion joint is, it is useless
You can sit back and relax when you choose the right equipment? That's naive. The pits in the installation link, each deeper than the last. The most common one is that the tie rod nut is not adjusted properly. The function of the expansion joint tie rod is to limit the over-stretching or over-compression of the bellows, but many installation teams directly lock the tie rod, or simply don't dismantle the transportation fixtures. And guess what? As soon as the pipeline heats up, the expansion joint has no space to compensate, and the bellows is directly bulged and scrapped. The correct way is to remove the transport screw after installation, and then adjust the tie rod nut according to the compensation amount. For details, refer to the article "How to adjust the tie rod nut of expansion joint" in our station.
There is a more hidden problem-the deflector is installed backwards. The specific function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows from scouring. However, when the direction of the arrow is reversed, the medium directly impacts the root of the bellows, and the rate of corrosion and wear doubles. Remember: The direction of the arrow must coincide with the direction of the media flow. Don't laugh, at least 30% of the installers on the site will make this mistake.
Wear and corrosion in operation: medium temperature, particle erosion, chemical attack, how many of these pits have you stepped on?
During normal operation, the expansion joint can't be laid flat just by installing it. If the medium temperature exceeds the design value of 10℃, the fatigue life of the bellows may be directly discounted by 50%. Particle scour? That's even more like cutting meat with a soft knife. Some cement plants use ordinary metal rectangular expansion joints, and there is no guide tube inside. After half a year, the wall thickness of the bellows is ground from 3mm to 0.5mm. Do you think it can be perforated?
Chemical attack is more headache. The acid condensate in the desulfurization system is a fatal blow to the metal bellows. At this time, either choose a PTFE hose or PTFE compensator, or use a non-metal expansion joint (rubber PTFE compensator is also OK), but we must pay attention to the rubber aging problem. By the way: Is there pitting corrosion and intergranular corrosion on the surface of the expansion joint in your factory? If so, it means that there is a problem with material selection, so change it as soon as possible.
Regular inspection is not a formality: corrugated pipe cracks, rubber aging, non-metal layer peeling, early detection and early treatment
Many factory inspections are to walk around with a flashlight and see nothing. In fact, there is a precursor to the failure of the expansion joint. Fine cracks or "orange peel"-like deformation appear on the surface of metal bellows, which indicates that it is close to the fatigue limit. Rubber compensator or non-metallic expansion joint, pay attention to whether the surface has hardened, cracked, or delaminated peeling. Especially rubber, affected by ozone and ultraviolet rays, has a life span of three to five years. When the time comes, it should be changed. Don't wait for it to leak before stopping.
Also, check for any changes in the pre-tightening forces of the tie rods and bolts. After the expansion joint has been running for some time, the tie rod may loosen, causing the bellows to offset. If the bellows is found to have eccentric wear marks, it means that the pipe support may sink or the compensation direction is wrong. Early detection and early adjustment, it's still too late.
Environmental factors alone? Heat preservation, support and drainage are done correctly, and the life will be doubled directly
Environmental factors are often overlooked, but are often the last straw that crushes the camel. For example, the expansion joint installed outdoors does not do heat insulation, and the metal brittleness increases at low temperatures in winter, so the bellows is easier to crack. Another example is the expansion joint on the steam pipeline. If there is no reasonable drainage design, the condensed water will accumulate at the trough, forming a "water hammer", which will impact and damage the bellows. How to solve it? Set a drain valve at a low position, or choose a sleeve-type pipe expansion joint with drain structure.
Support is also critical. The expansion joint itself does not bear the weight of the pipe, and guide brackets and fixed brackets must be set nearby. Many sites use the expansion joint as a pipe support, but as a result, the bellows is flattened and scrapped in three months. Think about it, is it worth an expansion joint worth tens of thousands of dollars to be scrapped in advance because several brackets worth several thousands of dollars were not done properly?
When to change hard bracing: Precursor judgment of failure and targeted prevention strategies
Expansion joints are not maintenance-free for life. If the following signals appear, change them quickly and don't take chances: First, the bellows has obvious cracks or perforations; Second, the fabric layer of the non-metallic expansion joint peels off in a large area, and the internal thermal insulation cotton or steel wire mesh can already be seen; Third, the surface of the rubber compensator is hardened to the point that it can't be pressed, or there are bubbles bulging; Fourth, the whole expansion joint is obviously distorted, which indicates that the displacement of the pipeline has exceeded the design range.
According to the medium characteristics and working conditions, select the right type in advance (such as special products such as corrugated expansion joints for power station industry, double hinge expansion joints for air-cooled island vacuum pipelines, etc.), strictly implement the specifications during installation, and regularly check and adjust in time during operation. If conditions permit, install displacement monitoring sensors at key positions, and watch the expansion and contraction of the bellows in real time, and you will have a bottom in your heart.
To put it bluntly, there are three words to prolong the life of expansion joints-select, install and raise. Choose the right thing, install it well, and maintain it diligently. To achieve these three points, it is not a dream to serve for more than ten years.