How much pressure can high-pressure metal expansion joints carry?
Steam pipe pressure 10MPa, can you use ordinary corrugated expansion joint? I said, aren't you looking for excitement? Many people think that the expansion joint is a soft connection, and you can use it just by choosing a model. When you encounter high-pressure conditions, accidents will happen in minutes. High-pressure metal expansion joints are not simply thickened by the wall thickness of the bellows-that thing is called "thick-walled straight pipe", not expansion joints.
Design Core: Flexibility vs Strength, How to Play Seesaw?
The core of high-pressure design lies in how to balance "flexibility" and "strength". With every extra layer of bellows, the stiffness goes up a step, but the compensation capacity will also be discounted. Just like a seesaw-to withstand pressure, you have to sacrifice part of the displacement. Then how to choose? For example:External pressure single axial expansion jointThere is a unique skill-let the medium pressure act on the outside of the bellows, avoid the stress concentration at the root of the bellows, and it is particularly stable under high pressure conditions. AndStraight pipe pressure balanced expansion jointAndCurved tube pressure balance expansion jointTwo bellows cancel out the pressure thrust of each other, which is suitable for high-pressure large-diameter pipelines, and the internal pressure thrust cannot be transmitted to the fixed bracket at all.
But don't think you'll be all right with these models. The number of layers, wave height, wave pitch, material thickness, each parameter directly affects the voltage level. For example, the expansion joint of the same DN500 has a design pressure of 1.6MPa and 6.4MPa, and the bellows structure is completely different. When selecting, the manufacturer will give a "pressure-displacement" curve, and you have to find that intersection point-not only to meet the working pressure, but also to leave enough displacement margin, so that you can't get stuck at the limit.
Don't just look at pressure when you choose: temperature, medium and space can't be less
Just staring at pressure parameters, that's a novice job. For example, the steam pipeline of a power station, with high temperature and pressure, is generally usedCorrugated expansion joint for power station industryOrHigh temperature axial expansion jointCooperate with the guide tube to reduce erosion. The role of the guide tube is clearly stated in the common questions and answers-to guide the high-speed airflow away and avoid the bellows from being directly washed. Hot air ducts in cement industry, with large dust content, have to chooseMetal Corrugated Expansion Joints in Cement Industry, lined with wear-resistant layer, the bellows has to be thickened. If you match it blindly, it will leak in half a year, and the maintenance cost will be ten times more expensive than the expansion joint itself.
Let's talk about installation space. Some pipeline shafts are extremely narrow, with large axial displacement but no space in the lateral direction, so you can only chooseCompound hinge transverse expansion jointOrCompound straight pipe bypass pressure balanced expansion joint。 If the pipe is more than 2 meters in diameter,Large diameter thick wall expansion jointIt is preferred, but the lifting and support capacity must be considered. These details are clearly marked on the drawings, so don't slap your head to save trouble.
Installation is a pit: arrows and pull rods, 90% of people get it wrong
What does the direction of the arrow on the expansion joint point to? That is the flow direction of the medium. It is useless to install the guide tube backwards, and the bellows is directly washed and scrapped by the airflow. This question is specifically explained in the FAQ-the arrow must coincide with the direction of the pipe media flow.
Does the tie rod nut adjust? Of course it has to be tuned. When leaving the factory, the tie rod is locked to protect the bellows from bruising during transportation. After installation, it must be loosened, otherwise the compensation amount will not come out. However, under high-pressure conditions, sometimes it is necessary to retain some preloading force-why? Because the internal pressure thrust will stretch the bellows, if the tie rod is completely loosened, the bellows may be overstretched and cause instability. Therefore, when installing, you must adjust the tie rod nut according to the design drawings, leaving an initial pre-compression amount or pre-stretching amount. This is a job that you can't do without experience. How to adjust it specifically, you can see the question and answer on our station "How to adjust the tie rod nut of the expansion joint".
Maintenance: Fatigue Cracks and Corrosion, Two Killers
Fatigue cracking and corrosion. High-pressure pipelines start and stop frequently, and a little fatigue damage is accumulated every time the bellows expands and contracts. Want to live longer? Select multi-layer bellows structure, each layer shares the stress, and the fatigue life can be improved several times. In terms of materials, ordinary 304 can't bear the high-temperature and high-pressure corrosive environment, and it has 316L or even Inconel. For example, the 304 bellows used in the steam pipeline of a power plant had intergranular corrosion cracks in two years. After replacing it with 316L, it was fine for five years.
Regularly check the surface of the expansion joint for bulging and discoloration. Bulging is often caused by local overload, which leads to plastic deformation of bellows, and discoloration may be due to overtemperature or chemical corrosion. If you find an abnormality, stop it quickly. Don't wait until it leaks before repairing it. In addition,Metal hoseAndRotary compensatorUnder high-pressure vibration conditions, it can be used with expansion joints to share part of fatigue load.
In the end, it's not a panacea
No matter how bullish the high-pressure metal expansion joint is, it can't withstand ultra-high pressure (such as above 20MPa) or violent vibration. In this kind of working condition, you have to matchMetal hose、Rotary compensatorOrSleeve type pipe expansion joint。 Sleeve type expansion joint is not afraid of high pressure, but its sealing performance is not as good as that of bellows, so it can be selected according to the medium. Selection consultation Don't pat your head, pull the manufacturer together to calculate-pressure, temperature, displacement, fatigue life, one by one. Saving trouble for a while, accident for a lifetime.
Expansion joints are not universal pieces, and each item has to be designed individually. The working parameters in your hand determine how much pressure it can bear.