1. What is the use of flanged structure? — Not just for good connection
Old masters who have done pipeline installation know that what are non-metallic compensators (that is, we often call non-metallic expansion joints) most afraid of? I am most afraid of air leakage and liquid leakage at the connection. The flange structure is not a decorative piece thought up by patting your head. It solves two flaws:Seal failure and stress concentration。
Think about it, if the medium in the pipeline is high-temperature flue gas or corrosive gas, and the flange compression force is slightly uneven, the ordinary flat compensator will easily tear away from the edge. Flanging is equivalent to adding an extra "reinforcing rib" outside the fabric fiber layer, which expands the area under pressure by a circle. According to JB/T 12235-2015 standard, the qualified flange height is at least 1.5 times of the flange thickness. After pressing, the flange material will be completely wrapped by the flange surface, forming a labyrinth seal-this is not metaphysics. The measured data show that the leakage rate of non-metallic expansion joints with flanges is more than 70% lower than that of non-flanged joints.
Two days ago, I met a customer who insisted on using the old model without flanges, saying to save money. As a result, after three months of operation, water began to seep at the flanging place (actually, the place without flanging), and it was enough to buy ten sets of flanging pieces once it was stopped. Alas, some money really can't be saved.
2. Checklist before installation: flange, pipe centering, pre-tension or pre-compression
Many installation accidents are not problems when installing, but they are not checked before installing. You got oneNon-metallic expansion joint (fabric fiber expansion joint)Don't rush to the nozzle, go through the list first:
- Is the flange surface flat?Lean against it with a ruler. If the flatness exceeds 2mm, find the manufacturer to adjust it. Forcing the bolts will cause flanging bias.
- What is the pipe alignment deviation?The standard is that the radial deviation does not exceed 1/3 of the allowable displacement of the compensator. For example, for a product with a design compensation amount of 30mm, if the pipeline is misaligned by more than 10mm, don't hard install it, otherwise the flange may be torn directly when the machine is turned on.
- Pre-stretched or pre-compressed?This depends on the operating temperature of the system. After the steam pipe heats up, the pipe will extend, and the compensator will compress for a certain distance in advance; The cold medium pipe is pre-stretched in reverse direction. The specific values are available on the factory certificate, so the installer should not adjust them according to his feeling.
By the way, the direction of the guide tube has to be right-the arrow of the medium flow direction points to the exhaust port or downstream. Installing the guide tube backwards will block the fluid, increase the pressure loss, and it is easy to accumulate dust and corrode. You can flip through the question and answer of "Specific Function of Expansion Joint Guide Tube" on this site, which is very clear in the picture.
3. Disassembly of installation steps: From hoisting to bolt tightening, which step is easy to overturn?
Hoist in place, bolt through, tighten. But rollovers are often in the details.
When hoistingThe most delicate thing about non-metallic compensators is the fabric layer. Never use wire rope to strangle directly, you have to wrap it with a sling or soft rope. I have seen someone try to save trouble. As soon as the chain is hung, the flange is pressed out of a dent. When the flange is installed and clamped, the dent becomes a leak point.
Bolt tighteningIt's the hardest hit area. What is the standard torque? Many people don't know that the flange bolt torque of a non-metallic compensator is generally half less than that of a metallic expansion joint-because the fabric layer cannot withstand excessive compressive stress. Generally, it is enough to screw the M20 bolt to 80-100N·m. If it is screwed too hard, it will press the flange into a piece of paper and lose its elasticity. The order must also be particular: twist alternately diagonally, and complete it in 2-3 passes. And guess what? Some workers twisted the wind cannon to the end in one breath, and found that the flange surface was warped the next day.
Do you want to disassemble the transport screw?For this question, refer to the question and answer of this site "Does the screw of the expansion joint need to be dismantled"-the answer is that it must be dismantled! The transportation screw is temporarily fixed. If it is not removed, the compensator cannot be freely expanded and contracted, and the thermal expansion and contraction of the pipeline are all suppressed on the screw, ranging from the bending of the screw to the deformation of the pipeline support.
4. Pits that leaked after installation in those years: uncompact flange compression, medium corrosion, direction of guide tube
After loading the pressure test, it bubbles as soon as it pumps air. Where's the problem? Uncompacted flanging is most common. There are only three reasons: the flange bolts are not screwed in place, the flange thickness is not up to standard (the standard requirements are not less than 1.2 times the thickness of the fabric layer), or the flange itself has burrs that cut the flange.
Media corrosion is a hidden killer. If the pipeline is wet flue gas after desulfurization, which contains sulfate ions, the ordinary silicone rubber coating can't last for half a year. In this case, fluororubber or polytetrafluoroethylene coating should be usedNon-metallic expansion jointThat is, the "PTFE Compensator" series of this site. Don't ask me why I know – I've seen a power plant where the compensator behind the flue gas baffle door used plain rubber and was powdered in three months.
You don't have to repeat the direction of the deflector, right? Let's talk about another unpopular pit: when the pipeline vibrates heavily (such as the blower outlet), the welded spot of the guide tube is prone to fatigue cracking, and debris falls into the pipeline. In this case, it is recommended to use integral molding of the guide tube or add internal reinforcing ribs.
5. Debugging and acceptance: How to judge that the installation is in place?
- Step 1: Appearance inspection.See if the flanges are all pressed down by the flange, and whether there are any exposed, folded hems and wrinkles. Measure the flange clearance with a gauge, and the error of four corners is not more than 0.5mm.
- Step 2: Stress test.Do hydraulic pressure test at 1.5 times the design pressure (Note: Non-metallic compensator cannot do air pressure test, there is risk of bursting!). It is qualified if the voltage is stabilized for 10 minutes and there is no leakage.
- Step 3: Displacement test.Push and pull the pipe manually to observe whether the compensator can be flexibly expanded and contracted. Or simulate thermal displacement with the help of a hydraulic jack and confirm that the limit pin (if any) is in the correct position.
- Step 4: Insulation restoration.Many installers adhere the insulation layer to the outer surface of the non-metallic compensator. As a result, the heat dissipation of the fabric layer is blocked at high temperatures, which accelerates aging. The correct way is to keep a gap of more than 50mm between the insulation layer and the compensator, or use a detachable insulation sleeve.
Installation date, operator, actual pre-stretch amount, bolt torque value. These data can save big problems when maintaining and checking faults in the future.
After so many words, the core is actually one sentence:Flanged non-metallic compensator installationIt is a "anti-dumb job", and every step has standards to follow. Don't be lazy, don't take it for granted. By the rules, a compensator will last seven or eight years.