In the metallurgical high-temperature pipe system, the expansion joint is used to carry the displacement, not to make up the number. In the working conditions of power stations, cement and ironmaking, the medium temperature is always hundreds of degrees Celsius, and the stress of thermal expansion and contraction of pipelines is not absorbed, so the flange, bracket and equipment body will suffer. Compared with non-metals, metal expansion joints have advantages in pressure resistance, temperature resistance and service life. Therefore, bellows is the most used form in metallurgical industry-but specifically, whether it is a general-purpose corrugated expansion joint, a high-temperature axial expansion joint, or one with a guide tube depends on the design of the medium and pipe system.
Two days ago, I met a customer, who had to quote a high price with a general-purpose drawing, saying, "I used to buy it like this". Results the working conditions: the flue gas contains sulfur, the temperature is 650℃, and there is also transverse displacement. Where is this something that a general purpose type can do? The first step of type selection is to find out the displacement, pressure, temperature and media corrosiveness in the pipe system. High-temperature axial expansion joint with large axial displacement is the main force; It is necessary to absorb lateral or angular displacement, such structures as compound hinge transverse type and curved tube pressure balance type can be topped. In metallurgical conditions, sulfur-containing and chlorine-containing flue gas is often encountered. At this time, the material of corrugated pipe has to be changed-molybdenum and titanium are added to stainless steel, or corrosion-resistant alloy is simply applied. Don't take a general drawing everywhere. Different working conditions, the number of corrugated layers, wall thickness and fatigue life are completely different.
Detailed parts test suppliers more than main materials
In the supply link, is there a guide tube? Is it thick enough? Is the liner wear or corrosion resistant? The expansion joint tie rod nut is locked when it leaves the factory. Who has the final say whether to adjust it before installation? These details are easiest to be ignored in the inquiry stage, but they directly affect the performance after the upper pipe. The function of the guide tube is not as simple as "blocking the wind"-the high-temperature dusty airflow directly washes the bellows. Without the guide tube, the wall thickness of the bellows will be thinned sooner or later. Don't disassemble the tie rod nut indiscriminately. It is locked to protect the bellows during transportation and installation. Blind adjustment and blind disassembly can lead to mismatch of compensation and unstability of the bellows.
These have to be written into the purchasing requirements. In addition, although metal hoses and PTFE-lined hoses are not expansion joints, they are often used in metallurgical pipeline systems, such as pulverized coal transportation, circulating water and flue gas sampling pipelines. When purchasing, you can inquire together, and the supplier can package and supply the goods, so the on-site pipe fitting interface is more worry-free-don't underestimate this. The most annoying thing on the spot is that the pipe interfaces of different manufacturers don't match. You take a ruler to measure it for half a day, and people pull it over and install it directly.
Manufacturing and inspection capability to determine whether the expansion joint is reliable after fitting the pipe
After comparing technical parameters, we have to compare manufacturing and inspection capabilities. Many expansion joints used in metallurgical industry should be fatigue test, pressure test and airtightness test according to GB/T 12777 or related industry standards. These are not formalities-no matter how beautiful the fatigue life of the bellows is, if you don't pre-stretch/pre-compress before leaving the factory, the actual compensation amount after the pipe is put on will not match your calculation. What about that? See if the supplier has its own bellows forming equipment, whether the welds have been 100% non-destructive tested, and whether the factory inspection records dare to be shown to you. You only have to look at the weight and price, and you may end up buying a flat tube that can't be straightened. This kind of thing has happened more than once at the maintenance site, and the money saved is not enough to compensate for the loss of a day's shutdown.
Supply capacity is a hard target, and the maintenance window period does not wait for anyone
The maintenance window period of metallurgical projects is short, which is the industry consensus. It was agreed that the goods would arrive in two weeks, but the result was delayed for a month. Have you calculated how much the production line lost after stopping for one day? Reliable suppliers must have stock billets with common specifications on hand, such as general-purpose corrugated expansion joints, corrugated expansion joints for power station industry, and metal corrugated expansion joints for cement industry, which can be assembled and delivered quickly. Otherwise, you say that you are a big factory, and the delivery date is scheduled for three months. Can you afford to wait for the project?
The expansion joint is not a standard batch product, and the stress calculation, compensation amount and installation position of each pipeline are special. Therefore, when looking for a supplier, send the pipe drawing, media parameters, ambient temperature and life expectancy, and let the other party help you select and check. If you can't report a specific calculation book and only give you a general quotation, you will be substituted directly. The supply of metallurgical expansion joints is essentially selling technical schemes and production capacity, not selling iron knots. Low price is good, of course, but the premise is that the plan is right, the performance is capable, and the delivery date is reliable-one of the three is missing, and the little money saved will be returned from other places sooner or later.