1. Heavy weight does not mean solid materials-the doorway behind the weight of imported expansion joints
Many people think that the heavier the weight of imported metal expansion joints, the more reliable it is. In fact, it is not necessarily. The weight mainly depends on the number of bellows layers, wall thickness, material (e.g. 304, 316L or high nickel alloy), and structural form. For example, for the same general-purpose corrugated expansion joint with a diameter of 500mm, a domestic manufacturer may use a single layer of 0.8mm stainless steel, while imported brands may use three layers of 0.5mm superposition in order to meet the higher cycle life and pressure resistance grade, which is lighter. Two days ago, I met a customer who was doing pipeline design, and insisted on bidding according to the weight. As a result, it leaked six months after installation-because the light bellows had insufficient rigidity, it didn't reach the design fatigue number at all. So, don't just look at the scale, look at the design parameters. The weight of imported metal expansion joints must be combined with fatigue life and stiffness, otherwise it is to dig a hole for yourself.
Second, structure determines weight: from general-purpose hinge to double hinge, what is the difference?
In the product line of this station, the general corrugated expansion joint (single axial type) is the most common, with a diameter of DN100~ DN2000 and a large weight fluctuation range. However, if you change to external pressure single axial expansion joint, because of the extra external pressure sleeve and protective structure, the same diameter may be 15% ~30% heavier. Another example is the double hinge transverse expansion joint. Because there are two sections of bellows, intermediate connectors and hinge pins, the weight is almost doubled. There are also air-cooled island vacuum pipe double hinge expansion joints, which are specially used for air-cooled islands of power stations. The hinge and limiting structure are more complicated, and the weight is more than 40% higher than that of ordinary expansion joints of the same caliber. Therefore, when choosing an imported brand, you have to find out which structure you want first-don't compare the double hinge with the weight of the general type, which is purely asking for trouble. The weight of imported metal expansion joints varies widely due to different structures. Be sure to specify the model before selecting the model.
3. The "invisible influence" of the weight of imported expansion joints on pipeline supports and hangers
After the expansion joint is installed on the pipe, the weight is really pressed on the support and hanger. For example, the metal corrugated expansion joint of cement industry used in a cement plant has a diameter of DN300 and a design temperature of 400℃. Because the imported brand uses thicker superalloy and reinforcing ring, the weight of a single set reaches 85kg, while the domestic similar specification is only 55kg. Results the original support and hanger calculated according to domestic weight in the design institute was found to be insufficiently rigid during installation, so two spring hangers were temporarily added to get it done. The cost of this modification is more expensive than the expansion joint itself. Therefore, in the selection stage, it is much more cost-effective to get the accurate weight data and check the support and hanger in advance than to go back and rework. When you buy imported expansion joints, do you only stare at the price? Once the weight of the imported metal expansion joint is not calculated correctly, the subsequent installation and operation and maintenance are all pits.
IV. What do you think of the weight table of imported metal expansion joints? Don't be fooled by "reference values"
Many official websites of imported brands will provide PDF versions of metal expansion joint weight tables, but note that they are usually estimated based on standard length, standard wall thickness and 304 material. If you need to line PTFE hoses or high temperature axial expansion joints (with guide tubes and insulation), the actual weight may deviate by more than 20% from the table value. The correct way is to ask the supplier to provide a detailed calculation sheet for the corresponding working conditions, and the weight must be written in the contract attachment according to the actual design results. There was a petrochemical project before, and the owner took the weight table on the imported brand sample to calculate the transportation fee. As a result, after the arrival, he found that each unit weighed nearly 200 kilograms, and paid an extra 6,000 yuan of over-limit transportation fee-purely without confirmation with the manufacturer. Imported metal expansion joint weight table can only be used as a reference, don't take it as a truth.
V. Comparison of examples: How to choose between power station industry and cement industry?
Corrugated expansion joints used in power stations usually require high cycle life and anti-vibration. For example, they are installed on the main steam pipeline. Imported brands often adopt multi-layer bellows + integral molding process, and the weight of a single unit is controlled to be lighter than that of the same specification in China, because the material strength is high and the bellows design is finer. On the contrary, the metal corrugated expansion joints in the cement industry have to deal with high-temperature dust and alkaline corrosion. Imported brands tend to increase the wall thickness and outsource stainless steel mesh sleeves, but the weight goes up. Therefore, don't be superstitious about "imports must be light" or "imports must be heavy", it depends on the specific application scenarios. When selecting, put forward a clear weight limit range (for example, "the net weight of a single unit does not exceed 120kg"), so that suppliers can make lightweight design on the premise of meeting the performance-this is the practice of professional procurement. The weight of imported metal expansion joints varies greatly in different industries, so don't fit all.
6. Write at the end: Weight is only the starting point, not the end
The weight of the imported metal expansion joint is an important information point in the selection, but it must be looked at together with the indexes of stiffness, fatigue life, temperature and pressure resistance. It is recommended that you directly ask the manufacturer for three pieces of data when you make your next inquiry: design calculation book, three-dimensional model weight and measurement report (weighing one by one before leaving the factory). Don't be too troublesome, I have seen too many cases of problems due to weight in projects-light bellows are torn, and heavy ones cause the bracket to deform. Remember, imported goods do not mean perfection, but the right parameters are really reliable. The weight of the imported metal expansion joint can save money and worry if you choose the right parameter, but if you choose the wrong one, it will be serial thunder.