Find out first: Why does the compensator need a guide bracket? It's not that you can pretend if you want
Many people think that the compensator will be bought and welded to the pipe. Tsk, if it is so simple, how can there be so many accidents of bellows bursting and welds pulling off at the scene? Two days ago, I met a customer. The universal corrugated expansion joint on the steam pipe leaked in less than three months. The manufacturer sent someone to take a look-the guide bracket was not installed at all, and the pipe swung directly laterally to twist the corrugated pipe into a twist. Fix? It can't be repaired, it can only be replaced.
The core function of the compensator (expansion joint) is to absorb the thermal displacement of the pipe, but it is itself "soft"-the bellows wall thickness is usually only a few tenths of a millimeter to a few millimeters. Without a guide bracket to limit the lateral displacement and bending of the pipe, the compensator is forced to bear loads outside the design, ranging from instability bulging to fatigue fracture. To put it bluntly, the guide bracket is to "draw the runway" for the pipeline, so that the displacement only goes in the direction of the compensator design.
Arrangement principles of guide brackets: spacing, position and fixing points, one by one for you to break clear
When arranging the guide bracket, the core is three things: distance, position and fixing point setting. Let's dismantle them one by one.
How to set the spacing?
For axial compensators (e.g. universal corrugated expansion joints, external pressure single axial expansion joints), the distance between the first guide bracket and the end of the compensator should not exceed 4 times the nominal diameter (4DN), and the distance between the second guide bracket and the first should not exceed 14 times the nominal diameter (14DN). Further afterwards, the spacing may be appropriately increased, but not more than 20 meters (for small calibers) or as determined by pipeline flexibility analysis.
A DN300 steam pipe, the distance between the guide brackets is directly dried 8 meters, and the first bracket is 5 meters away from the end of the compensator. As a result, as soon as the temperature rises, the pipe is bent into an S-shape at the inlet of the compensator, and the weld joint is torn on the spot. Therefore, don't pat your head, look up the table when you need it, and forget it when you need it.
How to put the position?
The guide brackets must be placed on both sides of the compensator and ensure that the bracket centerline coincides with the pipe centerline. If the bracket is offset, it is equivalent to adding an initial bend to the pipe, and the compensator is already stressed before it works. In addition, the guide bracket cannot be mounted directly above the corrugated section of the compensator-you have to leave room for the corrugated pipe to expand and contract freely. For products such as double hinge transverse expansion joints, the position of the guide bracket should also consider the rotation center of the hinge, which usually needs to be used with the limit bracket.
How to set the fixing point (main fixing bracket)?
The fixed bracket is used to withstand the thrust of the blind plate of the pipe and the elastic reaction force of the compensator. It must be set at either end of the compensator or where the direction of the pipe changes. If the fixing bracket is not firm, the whole plumbing system will twist like a snake. For example: a DN500 steam pipeline, with a pressure of 1.6MPa and a temperature of 300℃, has a blind plate thrust of nearly 40 tons. If the fixed bracket does not use reinforced concrete foundation, but is casually welded to the steel beam, the consequences will be weighed by yourself.
Different types of compensators have great differences in the arrangement of guide brackets- -Take general corrugated expansion joints, external pressure single axial expansion joints and double hinge transverse expansion joints as examples
You must never expect one stent solution to take all compensators. The working mechanism of each expansion joint is different, and the logic of bracket arrangement is very different.
Universal corrugated expansion joint
This expansion joint mainly absorbs axial displacement and can also withstand a small amount of angular and lateral displacement, but multi-directional mixing is not recommended in design. Therefore, the guide bracket must strictly limit the lateral swing and bending of the pipe. The first guide bracket is ≤4DN from the end face of the expansion joint, the second is ≤14DN, and then every ≤20 meters. Moreover, both ends of the expansion joint must be provided with a fixed bracket to prevent the axial peristalsis of the pipeline from pulling off the expansion joint.
External pressure single axial expansion joint
External pressure type bellows works under external pressure and has better stability, but its requirements for pipe guidance are more demanding instead-because the end of external pressure bellows is welded to the pipe, and once the pipe deflects, the bellows root will be subjected to huge bending stress. The spacing of the guide brackets is closer than that of the general type. Usually, the first bracket is ≤3DN away from the end face of the expansion joint, and the second is ≤10DN away. During on-site construction, I suggest adding an auxiliary guide bracket on both sides of the external pressure expansion joint, so as not to save those few channel steels.
Compound hinge transverse expansion joint
This expansion joint absorbs lateral displacement by the rotation of the hinge, and does not absorb axial displacement itself. Therefore, the role of the guide bracket is not to limit the transverse direction, but to ensure that the pipe swings freely in the hinge plane, while limiting the displacement in other directions. When installing, it is necessary to set a limit bracket on both sides of the hinge to prevent pipeline from twisting and deforming. Moreover, the fixing bracket must be arranged in the direction in which the centerline of the hinge rotation extends, otherwise the hinge will get stuck.
Four most common mistakes made on site: Guide brackets in wrong position, excessive spacing, lack of limit, neglect of end thrust
I have been in this business for more than ten years, and I will list the four most common pits I have stepped on and seen on the spot. You can see if you have hit them.
- Wrong position: The guide bracket is welded directly to the compensator bellows? Don't laugh. Someone really does that. The bellows is stuck by the bracket and cannot expand or contract freely, and it cracks at the first thermal cycle.
- Excessive spacing: As mentioned earlier, 4DN and 14DN are red lines. Beyond this number, the probability of pipeline instability increases exponentially. Especially for steam pipes, the elastic modulus of steel decreases at high temperature, and it is easier to bend.
- Limit bracket missing: For angular or transverse expansion joints (such as double hinge transverse expansion joints), not installing a limit bracket is equivalent to letting it "sway", and the hinge pin will quickly wear out and the bellows will twist.
- Ignore end thrust: The design strength of the fixed bracket must be able to withstand the blind plate thrust and the compensator stiffness reaction force. Many people only count the blind plate thrust and forget the elastic reaction force of the compensator itself. As a result, the fixed bracket was pushed askew, and the pipeline displacement was all squeezed onto the compensator, which was scrapped.
Practical case: A steam pipeline guide bracket layout rollover site-how to adjust it to comply with regulations
I handled a steam line in a chemical plant last year. The length of the pipeline is 80 meters, the material is 20#steel, the operating temperature is 280℃, the pressure is 1.0MPa, and four external pressure single axial expansion joints are used. One month after it was put into operation, cracks appeared at the root of the bellows of the third expansion joint. When I went to the site, the problem lies in the guide bracket: the first guide bracket is 5.5DN (exceeded) from the end face of the expansion joint, and the second is 18DN (exceeded), and the fixing bracket is only fixed to the cement floor with expansion bolts, and the bolts have loosened.
- Remove the original guide bracket, reinstall the first bracket according to 3DN (about 900mm), install the second bracket according to 10DN (about 3m), and then set one every 12m.
- The concrete foundation is re-poured with the fixed support, the anchor bolts are embedded, and the thrust of the blind plate (about 25 tons) plus the reaction force of the external pressure expansion joint (about 3 tons) is checked. The design load is 35 tons.
- An auxiliary guide bracket is added at each end of the expansion joint to further restrict the pipe swing.
After the modification, after half a year's operation, the bellows is in good condition and the weld has no cracks. The on-site manager of Party A said, "If I knew that the guide bracket was so critical, I should have let you do it in the first place." Right? Sometimes the money saved for the bracket is all turned into maintenance expenses to make up for it.
Summary: The guide bracket is not a supporting angle, it is the vital gate of compensator life
The arrangement of the compensator guide bracket is complicated and complicated-it has to consider the pipe diameter, temperature, pressure, compensator type and site space; It's easy to say it is simple – remember the three numbers (4DN, 14DN, fixed bracket thrust) and then perform according to the installation instructions on the expansion joint sample. But the most afraid thing is "Mr. Almost". I just put it on and regret it when I have an accident.
If you are unsure when arranging the compensator guide bracket, don't think about it for yourself. Flip through the installation manual provided by the manufacturer, or ask us directly. After all, if you get the wrong guide bracket, no matter how many compensators you change, it will be useless.