What exactly do round metal expansion joints do? Explain its core function in one sentence
To be honest, many friends who have just entered the industry ask me, what the hell is a round metal expansion joint? I usually say this-it is the "airbag" in the ductwork, which absorbs the displacement caused by thermal expansion and contraction, and by the way, it also cleans up the vibration and noise. Without it, it would be a matter of time before the high-temperature pipe heated up, the weld cracked and the flange collapsed. To put it bluntly: the round metal expansion joint is to help you save money, repair and shutdown.
Before selecting, find out: pressure, temperature, compensation amount, which parameter is the most fatal?
When selecting a model, many people ask "which model is cheaper", which is the wrong way. Three core parameters-design pressure, operating temperature, compensation amount-you don't want to fool any of them. Pressure determines the wall thickness and number of layers of the bellows, and temperature determines the material selection (stainless steel 321 or 316L? Incoloy for high temperatures). Compensation amount? That directly determines how many waves are needed and whether to use a duplex structure.
A while ago, there was a customer of a power plant. The pipeline temperature was 450℃, the pressure was 0.6MPa, and the axial compensation amount was 80mm. He had to use a universal corrugated expansion joint (single wave). And the result? Two moonwaves deflated as soon as they were installed. Later, it was replaced with the high-temperature axial expansion joint we recommended, with a wave number added and a guide tube added, and it ran steadily for two years. You see, you can't save a single parameter.
Axial, transverse, pressure balanced…so many types, when to choose which?
Don't be deterred by this ranking, just remember an iron rule: the direction of displacement of the pipe determines the type. If the pipeline is straight and only has axial displacement of thermal expansion and contraction, then choose general corrugated expansion joint or external pressure single axial expansion joint is enough. If the pipe needs to be transversely misaligned (such as an L-turn), a double hinge transverse expansion joint or a large tie rod expansion joint is needed.
Then when to use the pressure balance type? Tsk, this is a pit. When the internal pressure of the pipeline is high, and the expansion joint can't produce blind plate force to remove the equipment (such as the inlet and outlet of steam turbine and pump), it is necessary to use the straight pipe pressure balance expansion joint or the curved pipe pressure balance expansion joint. This thing comes with its own balance structure, so it doesn't transmit thrust to the device.
And directly buried pipes? Then choose the directly buried (fully buried) expansion joint, the outer layer is anti-corrosion and waterproof, and it is directly buried in the soil. Air-cooled island? Special air cooled island vacuum pipe double hinge expansion joint, that's all custom made. In short, don't use general-purpose hard to fight special working conditions.
Will the direction of the guide tube and the pull rod be removed during installation? These details are wrong and scrapped directly
Two days ago, a worker took a photo and asked me, saying, could it be okay to install the deflector tube backwards? I said no, brother! The role of the guide tube is to guide the medium to flush while protecting the bellows from wear. The direction of the arrow must be consistent with the flow direction of the medium, otherwise the medium will punch the bellows directly, and the hole will be perforated in a few months. We also wrote about the specific function of the expansion joint guide tube in our FAQ, which is not a decoration.
Another, can the tie rod be removed? I've seen this problem at the scene no less than ten times. Note: Transport tie rods and angular tie rods are two different things. The transport tie rod (bolt) must be removed after installation, otherwise the expansion joint cannot be expanded and contracted freely. However, angular tie rods or large tie rods (used to withstand pressure thrust and limit displacement) must not be removed. How to adjust the tie rod nut? Generally, preload to the moment specified in the drawing. The function of the expansion joint tie rod is to bear the blind plate force and protect the bellows from being overpulled.
Do you still need to remove the screw of the expansion joint? Regardless of whether it is called a screw or a bolt, it must be loosened or removed after installation, unless it is a structural tie rod. You remember: Anything used for fixed transportation should be dismantled; Anything used to limit position or bear force should be kept.
Power stations, cement, chemical industry... What are the differences in the requirements of round metal expansion joints in different industries?
Different industries are really like a mountain apart. Power station industry, such as boiler smoke duct, has high temperature, large pressure fluctuation and much dust. Corrugated expansion joints are commonly used in power station industry, which require high temperature resistance, wear resistance and anti-wear layer in the guide tube. What about the cement industry? The air duct of clinker production line is full of dust, and the abrasion is serious. The metal corrugated expansion joint in cement industry must be thickened with wave wall and even lined with ceramics.
The chemical industry is complicated-corrosive media, toxic gases, high-pressure vacuums are all possible. At this time, either use PTFE-lined hoses, PTFE compensators, or stainless steel bellows with coating. Rubber compensators are also available, but have limited temperature resistance. Vacuum pipes? Special hose for upper vacuum.
Desulfurization system Then you have to use desulfurization flue gas baffle door with non-metallic expansion joint or rubber PTFE compensator. You see, every industry has its own "temper". General models can only cope with regular working conditions, and they must be customized when they encounter hard stubbles.
Supplier only sells generic models? Be careful to suffer big losses-these customization capabilities are the real skills
Something heartbreaking at the end. Many suppliers push the general-purpose type in all working conditions just for that product manual. You believe it, he ran faster than anyone else when something went wrong. Really powerful manufacturers can customize non-standard parts according to your pipeline direction, medium, temperature, pressure and corrosiveness. For example, we have made a super-large-diameter flue gas pipeline before, and there are no standard parts. We used a large-diameter thick-walled expansion joint, and redesigned the wave height, wave pitch and guide tube length.
There are also complex working conditions that need to compensate axial and transverse displacements at the same time. Is there a compound straight pipe bypass pressure balance expansion joint? No, then you can't take the job. As for the rotary compensator and sleeve-type pipe expansion joint, they are also sharp weapons in specific scenarios.
Therefore, when choosing round metal expansion joints, look at the price, and ask one more question: Can you make customization? Have you ever done a case in the same industry? Even if you spend a little more money, what you buy is reliable and safe. After all, when the pipeline collapses, the loss is more than a few expansion joints.