1. Where is the gasket hidden in the non-metallic compensator structure?
The non-metallic compensator not only has gaskets, but also the position and selection of gaskets directly determine whether the equipment can be used normally。 Many people get non-metallic compensators (that is, what we often call non-metallic expansion joints and fabric fiber expansion joints), and when they unpack them, they are blinded-why are there no gaskets? Did the manufacturer miss it?
Don't hurry. Instead of lying alone in the case waiting for you to discover, the spacers are hidden on the flanged connection surface. The body of the non-metallic compensator consists of a skin (usually multi-layered composite fiber fabric), thermal insulation cotton, and an internal support frame (such as wire mesh or steel plate). A layer of gasket is usually pre-installed on the flange surface, or a special groove is opened to place the gasket. The function of this layer of gasket is to fill the tiny gap between the flange and the pipe and prevent media leakage. That soft, black or gray strip you see that sticks to the flange is the spacer.
For the convenience of transportation, some manufacturers will make the gasket into a split structure, bag it separately when leaving the factory, and stick it on the spot. At this time, if the workers are sloppy, or the list is not clearly written, there will be the embarrassment of "no gasket". So customers who ask "Do non-metallic compensators have gaskets?", in all likelihood, have encountered this situation.
Second, why do some people say that non-metallic compensators don't need gaskets? It's a pit
I met a customer two days ago, who made hot air ducts, and purchased a batch of rectangular non-metallic expansion joints. Their installation master insisted: "The non-metallic compensator itself is soft, and the flange is tight when pressed, so there is no need for extra gaskets." The result? As soon as the machine is turned on, the air leaks, the hot air whistles out, and the flange surface is still smoking. Later, after checking, there was no rubber pad attached to the flange surface, all by the elasticity of the skin itself.
Alas, this statement is pure pit. The elasticity of the non-metallic skin does provide some sealing compensation, but that is for the thermal expansion and contraction displacement of the pipe, not for the microscopic irregularity of the flange surface. Stainless steel flange will be deformed after welding, only by skin compression, over time, bolt pre-tightening force attenuation, air leakage is inevitable. What's more, some non-metallic expansion joints (such as those used in desulfurization flue gas pipelines) have negative pressure inside, and the flange sealing surface is directly deflated without installing gaskets, and the consequences are more serious.
So don't believe the "no spacers" nonsense. Regular manufacturers, such as the non-metallic expansion joints (fabric fiber expansion joints) provided by us, clearly mark the gasket installation area on the flange surface when they leave the factory, and some even vulcanize the gaskets on the flange.
3. How to choose the gasket material? High temperature, corrosion and low pressure are different
The wrong choice of gasket is more scary than not installing it. Different working conditions, gasket materials are completely two worlds.
- High temperature conditions (> 400℃): For example, flue gas pipelines in power stations and cement industries. Ordinary rubber gasket burns when it goes up, so you have to use ceramic fiber paper gasket or graphite composite gasket. The temperature resistance of ceramic fiber can reach 1200℃, but the texture is brittle, so the tightening force of bolts should be well controlled and cannot be crushed. Graphite gasket has better flexibility, but it is easy to be oxidized, so it is not suitable for strong oxidizing media.
- Corrosive media (acid, alkali, salt spray): For example, the non-metallic compensator behind the desulfurization flue gas baffle door. Gaskets must be resistant to chemical corrosion, commonly used are polytetrafluoroethylene (PTFE) coated gaskets, or PTFE composite gaskets. Note: The PTFE compensator itself has a flange surface seal, but most non-metallic expansion joint flanges still need additional gaskets, so don't get confused.
- Low pressure and normal temperature (: For example, ventilation and dust removal system, ordinary nitrile rubber gasket or asbestos-free compression fiber gasket is enough. Cheap and easy to install, replace if it breaks.
Gasket thickness. Too thick bolts can't be pressed tightly, too thin to fill the depression. Generally, if the flange surface has good flatness, use 1.5-2mm; If the weld is raised, it is recommended to use more than 3mm. Do not use a 1mm standard gasket for one-cut cutting.
4. If the gasket is not placed correctly during installation, the compensator is equivalent to white installation
If the gasket is installed in the wrong position, the displacement function of the compensator will be scrapped directly. For example: Once the field worker attached the gasket to the inner ring side of the non-metallic compensator, that is, the inner side of the skin. As a result, the pressure of the operating medium blew the gasket displaced, blocking the expansion gap of the compensator. The rectangular non-metallic expansion joint was originally designed to compensate ±50mm in the axial direction, but it stuck at 15mm, and the tie rod was bent.
There are three correct ways to do it:
First, the gasket must be attached to the inside of the bolt hole on the flange face, but not into the inner diameter of the pipe. That is to say, the outer diameter of the gasket should be smaller than the distribution circle of the bolt hole, and the inner diameter should be larger than the inner diameter of the pipe. Otherwise, the media will scour the edges of the gasket, resulting in early failure.
Second, for round or rectangular non-metallic expansion joints, if there is a stop groove (groove) on the flange surface, the gasket should be embedded in the groove to prevent lateral slippage. If there is no stop slot, it is recommended to apply a layer of sealant to assist in positioning.
Third, the order of bolt tightening should be particular. Screw diagonally first, afterburn it three times, and the final torque reaches 80% of the design value. Don't screw it to death. The flange frame of the non-metallic compensator is relatively thin, and excessive bolt force will cause the flange to deform, and the gasket will not be compacted.
Since it's so troublesome, why not seal with a monolithic molded flange? Because the non-metallic compensator has to bear multi-directional displacement when working, the connection between the flange and the pipe must be soft and adjustable, but the integral seal ring will limit the displacement. So spacers are the necessary price.
V. Summary: There are gaskets, but it depends on how the manufacturer matches them
Do non-metallic compensators have gaskets?Yes, but there are three situations：
- Most regular manufacturers install gaskets on the flange surface when they leave the factory (or distribute them with accessories);
- In order to save costs, a few low-priced products may not be equipped with gaskets, so customers need to buy them themselves;
- Very few unprofessional installation teams cancel the gaskets on their own, resulting in leaks.
Are flange gaskets standard or optional? What is the material? What is the thickness? Check this article during on-site installation, and don't let a few cents of gaskets pit tens of thousands of yuan of equipment.
By the way, we have both non-metallic expansion joints (fabric fiber expansion joints) and rectangular non-metallic expansion joints in our station, as well as matching rubber compensators, PTFE compensators and other products. If you are unsure about the selection of gaskets, send the working condition parameters directly to technical support, and we will help you set the specifications. After all, do non-metallic compensators have gaskets? The answer is yes, but it is called yes when used correctly.