When a pipe is heated to expand, the displacement is nothing more than deflection along the axis, perpendicular to the axis, or angular-these three basic directions are the underlying logic of the classification of metal expansion joints. Coupled with the headache of blind plate force in high-pressure pipelines, the pressure balance type specially dealing with thrust has been born. So to put it straightforwardly it's simple:There are four main types of metal expansion jointsEach corresponds to a core displacement scenario. Let's take it apart and talk about it one by one.
Category I: Axial Expansion Joint-Specialized in "Expansion and Contraction"
It is the most common type, none of them. Once the steam pipe heats up, the pipe can be extended by tens of millimeters. Axial expansion joints are designed for this linear displacement along the axis. Representative products haveUniversal corrugated expansion joint、High temperature axial expansion joint、External pressure single axial expansion joint。 It is basically standard on the steam pipeline of the power station-directly on the pipeline, you expand yours, and I compensate mine.
Deflector tube. The high-speed medium flushes the bellows directly, and it will wear out in less than a few cycles. Therefore, when selecting the type, we must check the medium flow rate. The guide tube can hold the airflow, so that the bellows is only responsible for deformation but not for anti-scour. A few days ago, a customer took the drawing and asked "the specific function of the expansion joint guide tube". In fact, this is what it does-protect the bellows and prolong its life.
Category 2: Transverse expansion joint-to deal with "left-to-right sway"
Instead of stretching and contracting straight, pipes sometimes swing from side to side. For example, earthquakes, foundation settlement and installation errors will cause lateral displacement. At this time, the transverse expansion joint needs to be shot.Compound hinge transverse expansion jointThe hinge structure allows the bellows to bend in the horizontal direction and absorb the lateral displacement. AndLarge diameter thick wall expansion jointSpecially used on large smoke ducts, with thick wall and high rigidity, which can withstand negative pressure and dust erosion.
"How to adjust the expansion joint tie rod nut?" Note that the tie rod is not for you to screw to death. Its role is to limit the maximum amount of displacement and prevent excessive stretching or compression of the bellows. If it is screwed too hard, it is equivalent to locking the compensation stroke, and there is no place to run when the pipe expands thermally, but the equipment is broken. The correct way is to loosen the nut to leave the design displacement margin during installation, so that the expansion energy saving can move freely.
Category 3: Angular Expansion Joints-Allow "Angle Turning"
Some pipe displacements have both axial and rotational components, such as the exhaust pipe from the boiler outlet to the steam turbine, where the direction of thermal expansion is straight and oblique. That's when angular expansion joints come in handy. It allows the pipe to be angularly deflected in a certain plane through a hinge or gimbal hinge. Typical products areCurved tube pressure balance expansion jointAndCompound straight pipe bypass pressure balanced expansion joint-They can not only absorb angular displacement, but also synchronously balance pressure and thrust, killing two birds with one stone.
The measured data show that a standard angular expansion energy saving absorbs a rotation angle of ±5° to ±10°. Think about it. For large-diameter pipes, this angle can easily be converted into tens of millimeters of end displacement. Without it, the pipeline is hot, the flange interface is directly misaligned, and the steam leakage is not negotiable.
Category 4: Pressure balance expansion joint-get the "blind plate force"
The most terrible thing about high-pressure pipelines is not displacement, but blind plate force. The medium pressure acts on the end face of the bellows, and the thrust generated can push the fixed bracket askew or even push down. What to do? With two symmetrical bellows, one absorbing displacement and the other counteracting thrust, the piping system is forced to self-balance.
Representative product isStraight pipe pressure balanced expansion jointAndDouble hinge expansion joint for air-cooled island vacuum pipeline。 The former is used for general high-pressure pipelines, while the latter is specially aimed at the vacuum working condition-when the air-cooled island pipeline is vacuumed, the negative pressure will also generate huge axial force, and the double hinge structure can both balance and compensate. When selecting, don't just focus on the unit price. Although the pressure balance type is more expensive, it can save a lot of civil construction costs of heavy fixed brackets. Calculating the general ledger is often more cost-effective.
Three-step selection, don't step on pits
After understanding these four types, there are actually three steps to select:
The first step is to calculate the displacement. The amount of thermal expansion of the piping system-how many millimeters in the axial direction, how many millimeters in the transverse direction, is there any angular deflection?
The second step is to look at the working conditions. What is the medium temperature? How much pressure? Is there any corrosion or scouring?
Step 3, match the model. For example, if there is a smoke baffle door next to the high-temperature flue, which requires both axial compensation and corrosion resistance, then choose the axial type lined with stainless steel, such as High temperature axial expansion joint。 Another example is the dust collection pipeline in the cement industry. The dust erosion is serious, so we have to go upLarge diameter thick wall expansion jointOr models with abrasion-resistant liners.
If you are still unsure, just flip through our product page-each model is marked with the applicable displacement and pressure range, and the model, size and stiffness configuration are clear at a glance.