Find out first, what kind of equipment is the metal expansion joint?
Metal expansion joints, also called corrugated compensators, are flexible connectors mounted on pipes. It mainly relies on the deformation of the bellows to absorb the displacement and vibration caused by thermal expansion and contraction of the pipeline, so as to avoid the pipeline being cracked or broken. To put it bluntly, it just puts an elastic joint on the pipe.
Are metal expansion joints and corrugated compensators the same thing? Yes, and no. Say "yes" because the core of the vast majority of metal expansion joints is the bellows; Say "no" because there are members of the metal expansion joint family of non-corrugated structures such as sleeve types and rotary compensators. So you can think of corrugated compensators as the mainstream branch of metal expansion joints, but don't draw an equal sign.
Classified by displacement: axial, transverse, angular, you should know these faces
What types of metal expansion joints are included? The most commonly used division method is by absorbing displacement.
Axial typeExpansion and contraction of the absorbent pipe along the axis. Representative products are:
- Universal corrugated expansion joint: The most basic and widely used model, suitable for pipelines with ordinary temperature and pressure.
- High-temperature axial expansion joint: with heat insulation layer and high-temperature resistant material, it can serve hot air ducts above 500℃.
- External pressure single axial type expansion joint: Bellows bear external pressure, good stability, suitable for high pressure steam pipeline.
- Straight Pipe Pressure Balanced Expansion Joint: By balancing the bellows to offset the blind plate force, it is suitable for equipment with fixed ends and unable to bear pressure thrust.
Transverse typeAbsorbs displacement perpendicular to the axis of the pipe. The double hinge transverse expansion joint is typical-two hinge groups are used to restrain the bellows so that it only bends to the side and cannot twist around itself.
Angular typeAbsorbs the angular displacement at the bend of the pipe. Curved pipe pressure balance type expansion joint is a representative of this kind, which is mostly used in the corner of L-shaped or Z-shaped pipe.
Special needs according to working conditions: These "non-mainstream" models specialize in solving difficult problems
Some pipes are unusual, so they have to use special expansion joints.
Direct buried (fully buried) type expansion joint— — The heating pipeline directly buried underground cannot be equipped with an inspection well. The shell of this expansion joint should be made into a structure that can withstand soil pressure, and the interface must be waterproof. It is the only option when directly buried heating pipes are laid.
Sleeve type pipe expansion joint— — Rely on the relative sliding of the inner and outer sleeves to compensate the displacement, which is suitable for low-pressure large-diameter pipelines. The price is much cheaper than that of corrugated pipelines, but the sealing performance is a soft rib and needs regular maintenance.
Rotary compensator— — The displacement is absorbed by the rotation of a pair of rotating arms, and the compensation amount is large. It is especially suitable for long-distance direct burial laying of steam pipelines, which saves brackets compared with traditional expansion.
Large diameter thick wall expansion joint— — The diameter exceeds 1 meter and the wall thickness is increased, which is specially used in large-flow and low-pressure pipelines such as flue gas desulfurization and induced draft fan outlet of power station. Ordinary bellows are easily unstable under this working condition, so it is necessary to use reinforced design.
Does a metal hose count as a metal expansion joint? Close relatives, but don't mix them
This is the easiest pit to step on when selecting a model. Metal hoses and metal expansion joints look similar and have similar names, but their functional emphases are different: expansion joints mainly absorb thermal displacement, and metal hoses are mainly used to connect equipment with relative motion, such as vibration damping joints at pump inlet and outlet, and compensate for installation deviations.
You use the metal hose as an expansion joint, it has few corrugations, short fatigue life, and will crack soon; Conversely, use the expansion joint as a hose, which is not soft enough, and the vibration of the equipment will still be transmitted. When purchasing, read the working condition description clearly: if there is thermal displacement, choose expansion joint; if there is vibration or frequent disassembly, choose metal hose.
Inferred from industry application: Which type should I choose for power station, cement and desulfurization?
Another dimension-the industry pushes back. The working conditions of different industries vary greatly, and products have long been "specialized".
Corrugated expansion joint for power plant industryThe main steam and the reheating steam pipeline have high pressure and high temperature, and the external pressure single axial type or the high temperature axial type are preferably selected; Air-cooled island vacuum pipeline is a large-diameter low-pressure vacuum condition, and the double-hinge expansion joint of air-cooled island vacuum pipeline is needed, which has low stiffness and good seal.
Metal Corrugated Expansion Joints in Cement Industry: The flue gas at the head and tail of the kiln has a large dust content and a drastic temperature fluctuation. When selecting the general-purpose type or the high-temperature axial type, the guide tube should be thickened to prevent the dust from washing and wearing the bellows.
Desulfurization system: The flue gas of wet desulfurization contains acidic corrosive medium, which cannot be carried by ordinary stainless steel, so it is necessary to use PTFE-lined hose or PTFE compensator as an anticorrosive layer; At the same time, the desulfurization flue gas baffle door should be matched with the double seal design. At this time, the expansion joint must be matched with the baffle door.
So, what are metal expansion joints included? The answers are different by displacement, special needs and industry. However, there is one principle that remains unchanged: first find out the pipeline medium, temperature, pressure and displacement, and then compare it with the specific models in the product information of this site. Don't ask "which is cheaper". The wrong choice of expansion joint can lead to air leakage or pipeline overturning. Which one is lighter and which one is heavier, don't I need to say?