Two days ago, a customer called and asked, "Which is the radial direction of the expansion joint?" I asked him back, did you use the arrow as a radial reference when you installed it? He froze for a moment. In fact, this problem is particularly typical. Many field engineers and technicians will confuse radial and axial directions. The consequence of confusion is very direct-the selection is wrong, the pipeline will still be broken after installation, and the compensator will be installed for nothing. Today, let's make this direction clear at once.
Let's make it clear: What is radial?
The radial direction of the expansion joint refers to the direction perpendicular to the centerline of the pipe, that is, the direction radiating outward from the center of the circle. For example, if you take a round tube, the direction along the length of the tube is axial, the direction around the tube is called circumferential, and the radial direction is along the radius, pointing from the inner wall to the outer wall. Used on expansion joints, radial displacement is the compression or stretching of the bellows in a direction perpendicular to the axis. For example, when the pipeline shifts up and down or left and right, the compensator bears radial displacement. Isn't it intuitive? But why do 90% of people do the opposite? Because everyone stares at the "axial direction", the main direction of thermal expansion and contraction, ignoring the lateral offset.
What does the direction of the arrow on the expansion joint mean?
Many products, such as general-purpose corrugated expansion joints and high-temperature axial expansion joints, will be marked with an arrow on the shell. This arrow points to the direction of the medium flow, and it also reminds you that the expansion joint mainly compensates for axial displacement-that is, thermal expansion and contraction in the direction of the arrow. Arrows are not radial markers. There are no arrows in the radial direction, because the radial displacement is absorbed by the lateral stiffness of the bellows, and the amount of radial compensation allowed by expansion joints of different structures varies greatly. And guess what? Some customers took the arrow as a radial reference, and forced the expansion joint to be crooked. As a result, the bellows was twisted into a twist before it was pressurized. Alas, sorry for the tube.
What kind of expansion energy saving carries radial displacement?
Look at the type. For example, the compound hinge transverse expansion joint is specially used to absorb transverse (radial) displacement. Its structure has two sets of bellows plus hinges, so that the tube can swing in the vertical direction. There are also expansion joints of large tie rod structure (such as straight pipe pressure balance expansion joints). The function of tie rod is to limit axial displacement and guide compensation force to radial direction. Conversely, like external pressure single axial expansion joint, its design mainly eats axial displacement, radial capacity is very weak. When selecting, if the direction is reversed, the bellows will be twisted, and the flange will be cracked. This is not to scare people. There have been enough accidents at the scene to write a case book.
How to judge in actual operation?
Here are three stupid ways for you to remember and not step on pits:
- First, look at the product nameplate or drawings.It will be marked with "lateral compensation amount" or "radial displacement", generally in millimeters. If not, look for the technical parameter table, which is written separately in the axial and radial directions.
- Second, find the guide tube of the expansion joint.The guide tube is usually along the axis direction. If there is a significant gap between the guide tube and the inner wall of the pipe, this expansion joint allows certain radial deflection. On the contrary, with minimal or even no clearance, it is a pure axial type.
- Third, look directly at the structure.There is a high probability that those with tie rods and hinges can eat radial, while those without such constraints are mostly pure axial. For example, in our products, compound hinge transverse expansion joint and straight pipe pressure balance expansion joint are good at radial compensation, while general-purpose corrugated expansion joint and external pressure single axial expansion joint should not be expected to carry radial direction.
Whichever of these three methods you use is better than blind guessing. One more detail: How to adjust the expansion joint tie rod nut? If you buy the model with a tie rod, be sure to loosen the tie rod nut to the designed position before installation, otherwise the tie rod locks the radial displacement and becomes a rigid connection. For specific adjustment methods, please refer to the FAQ of this site.
One last word of reminder
Don't use the radial direction as the axial direction, and don't expect a general-purpose expansion energy saver to hold a few millimeters of pipe misalignment. When installing, if you find that there is a deviation from the pipeline and forcibly tighten the expansion joint with bolts to make do, you are sentencing the bellows to death. The correct approach is to use double hinge transverse expansion joints or large tie rod expansion joints to specifically absorb this radial deviation. I really can't figure it out. Looking through the product information of this site, the displacement parameters of each model are clearly written-how much in the axial direction and how much in the radial direction, at a glance. For example, for straight pipe pressure balance expansion joints, the radial compensation amount is clearly marked in the selection table, so just follow the selection.
Alas, the direction is right, and expansion and energy saving will help you carry it for ten years; If the direction is reversed, it will leak in three months.