How to Choose Boiler Flue Expansion Joint? Follow these 5 steps and make no mistake
Two days ago, I met a customer. It took less than half a year for the boiler flue to crack the expansion joint, and the whole production line stopped for two days. When I asked, I found out that when I selected the model, I just patted my head-I bought it when I looked at it. You say it was wrong or not? In fact, choosing the expansion joint of the boiler flue is really not as mysterious as you think. As long as you understand these 5 steps thoroughly, you will basically not roll over. Let's go straight to it.
Step 1: Find out the temper of your flue-temperature, pressure and medium are the lifeblood of model selection
Don't ask "which model is cheaper" as soon as you come up. Find out three numbers first:Maximum operating temperature, working pressure, media composition。 For example, is there sulfide in the smoke? What is the water content? These things directly determine the material and structure of the expansion joint. Let's talk about the temperature: ordinary carbon steel bellows can be carried to about 400℃ at most, and if it is higher, stainless steel or superalloy must be used. From our stationHigh temperature axial expansion jointThat's what they do. In terms of pressure, non-metal is enough for low-pressure flue (such as after desulfurization), but in the positive pressure area of the waste heat boiler outlet, metal rectangular expansion joints or structures with reinforcing ribs must be installed. By the way, the medium contains a lot of dust, so remember to add a guide tube, otherwise the bellows will wear out as fast as cutting tofu with a knife-this will be described later.
Step 2: Metallic or Non-Metallic? Look at the flue shape and temperature before deciding
Do you choose metal expansion joints or non-metal expansion joints? Actually, it's very simple —Look at the shape first, then the temperature。 Circular flue Metal corrugated expansion joints or general-purpose corrugated expansion joints can be used. Rectangular flue Then you have to get onRectangular non-metallic expansion jointOrMetal rectangular expansion joint。 The temperature is lower than 200℃, the pressure is not large, and the non-metal (fabric fiber expansion joint) is cheap and corrosion resistant, especially suitable for desulfurization systems. High temperature and high pressure, such as the flue outlet of a power station boiler, then honestly use metal, like oursCorrugated expansion joint for power station industry、Metal Corrugated Expansion Joints in Cement IndustryAll tried and tested. Think about it, the non-metallic skin can last to death at 300℃ at most. Beyond this number, it is like a burnt plastic bag, and it is only a matter of time before it collapses. So, don't be cheap, temperature is the key criterion.
Step 3: Calculate the compensation amount, fix the guide tube, and pair the flange-don't let the details fool you
This step is the easiest to overlook, but it is also the hardest hit by rollovers. Calculate the amount of compensation first: How long is the flue? What is the temperature difference? Check the thermal expansion coefficient, and one multiplication is the theoretical compensation value. In actual selection, the margin must be left, which is generally enlarged by 15% ~20%. thenguide tube— — In our background, people often ask "the specific function of the guide tube". Simply put, it is to protect the bellows from being washed by high-speed smoke. You decide whether to add it and for how long depending on the flue gas flow rate and particle content. From our stationexpansion joint guide tubeIt's matching, don't weld yourself blindly. Finally, for the flange: the flange bolt aperture and gasket material must match with the system. For example, the flue gas contains acid, so the flange gasket has to be polytetrafluoroethylene, and the ordinary asbestos gasket will rot in a few days. Tsk tsk, it's true that the details make or break.
Step 4: Don't step on several lightning during installation-the direction, pre-stretch and tie rod can't be saved
The installation stage is most afraid of "I thought". You think the arrows on the expansion joints are decorations? Wrong! The direction of that arrow is the direction of medium flow. If you install it backwards, the force direction of the bellows is completely wrong, so wait for air leakage. One more,Pre-stretchingOrPre-compression— — Many expansion joints are at free length when they leave the factory. If you don't adjust them according to the designed displacement value after installation, they will either be overstretched or compressed and stuck. We have a special articleCorrect installation method of expansion joint of large tie rodIt is very clear in it. And one more common question:How to adjust the tie rod nut of the expansion joint?To put it simply and roughly, after installation, the locking nut in the middle has to be loosened for a certain distance to allow the bellows to expand and contract freely. Some workers try to save trouble and screw the tie rod to death directly. Isn't that equivalent to turning the expansion joint into a rigid tube? Why do you want it? Therefore, the directional arrow alignment, the tie rod nut leaves a gap, and the pre-stretching if necessary are indispensable.
Step 5: How to check daily? How often to change? Teach you three tricks to prevent problems before they happen
After installation, everything is not fine. The flue vibrates in high temperature every day, and the expansion joint will be tired sooner or later. You do a visual inspection at least once a month: to see if the skin is bulging, the metal ripples are cracked, and the flange joints are leaked. The second trick: touch or listen to the sound with your hand-hold a screwdriver against the bellows and stick it to your ear during running. If you hear a "hissing" sound, there is a high probability that it will be a slight leak. The third trick: during the overhaul, the endoscope must be disassembled to see the wear of the guide tube. As for the replacement cycle, there is no fixed standard, but we have done statistics. The average life of metal expansion joints in flue of power station boilers is 5~8 years, and that of non-metals is 2~4 years. Depending on the working conditions, if you find that the wall thickness of the bellows has been thinned by more than 30%, or the skin has penetrating damage, don't hesitate to change it. One of our customers was delayed for half a year, and as a result, the pipe burst caused the furnace to shut down, resulting in heavy losses. Remember: Preventative replacement is always more cost-effective than accidental downtime.
Okay, you follow these 5 steps, and the expansion joint of the boiler flue will basically not fall out. If you are still unsure, go directly to the product page on our site, for exampleMetal rectangular expansion joint、Non-metallic expansion joint (fabric fiber expansion joint)、High temperature axial expansion jointThe parameters are all complete.