The Core Function of a Metal Expansion Joint: What Problem Exactly Does It Solve?
To put it bluntly, metal expansion joints are the "expansion joints" of pipes. When the pipeline transports high-temperature medium or changes in ambient temperature, it will expand and contract thermally; Coupled with equipment vibration and foundation settlement, if these displacements are not treated, the stress at the pipeline interface will be concentrated, ranging from leakage to tearing. The metal expansion joint absorbs the displacement and stress through the elastic deformation of its own corrugated structure. In industries such as power stations, cement and chemical industries, pipelines are often hundreds of degrees, and they can't run without them. By the way, the "compensator" often said in the industry is the same thing as the expansion joint. Don't be confused by the name.
Common types of metal expansion joints on the market, how should you choose?
There are more than 20 kinds of products in our station alone, such as general-purpose corrugated expansion joint, high-temperature axial type, directly buried (fully buried) type, external pressure single type, compound hinge, straight pipe pressure balance type, curved pipe pressure balance type, metal hose, rectangular expansion joint and so on. It looks dazzling at first glance, but the selection logic is actually very simple: look at the working conditions. Axial displacement dominated? Choose general-purpose type or high-temperature axial type. Space constraints require lateral or angular compensation? Composite hinge or curved tube pressure balanced type is more suitable. Buried pipes? Special for direct burial type. For large-diameter, thick-wall, high-temperature and high-pressure applications, external pressure single-type or large-diameter, thick-wall expansion joints are obtained. Metal hoses are mostly used for equipment connection and vibration reduction. Don't use the general-purpose model to carry the large angular displacement, which is equivalent to making it "fold".
The 3 Parameters That Are Easiest To Be Overlooked When Selecting
The first is the amount of displacement. Many people only look at the theoretical value calculated by the length and temperature difference of the pipe, and ignore the installation error and cold tightening pre-deformation. The second is the stress rating. Metal hoses have pressure standards, and expansion joints also have design pressures. Overpressure is a potential safety hazard. The third one is the deflector. The deflector is not optional – it protects the bellows from high-speed fluids, reduces flow resistance, and also prevents media deposition. One of our previous customers didn't install a deflector, and the bellows was worn out in half a year. In addition, the data of expansion joint weight table, model size, it is best to compare with the manufacturer's manual when selecting the model, and do not rely on experience to estimate.
The easiest mistakes to make at the installation site
Two days ago, I met a customer. After the expansion joint was installed, the tie rod nut was screwed to death directly. As a result, as soon as the system heated up, the bellows bulged. The function of the tie rod is to limit the displacement during transportation and installation. After installation in place, the nut must be adjusted to the working position. The specific clearance is according to the manufacturer's instructions. There is also the direction of the arrow, which refers to the flow direction of the medium. If the guide tube is installed backwards, it will take a ride, increase resistance and even cause vibration. Should the screw be disassembled? Look at the type. The screw of the expansion joint of the large tie rod is removed after installation, otherwise it can't compensate; While some tie rods are permanent structures and have to be retained. Get it in the wrong direction, and the equipment has to be reworked.
How long do metal expansion joints last? How to extend it?
There is no uniform life span, depending on the working conditions. High-temperature axial type on steam pipeline, use good materials and stainless steel, pay attention to heat preservation, can be used for more than 10 years; The desulfurization flue gas environment is corrosive and its life will be short, so it is necessary to choose corrosion-resistant PTFE-lined or non-metallic expansion joints. Key points of daily inspection: whether there are cracks, corrosion pits and deformations in the bellows; Whether the guide tube is loose; Whether the tie rod nut is abnormally loose. Don't wait for a leak before replacing it. Regular inspection can save a lot of maintenance costs. Also, enough cold tightness is reserved during installation, which can also effectively prolong the fatigue life.