Guide to selection and installation of flue flange expansion joint: 5 steps to do it, stop stepping on pits

Guide to selection and installation of flue flange expansion joint: 5 steps to do it, stop stepping on pits

I met a customer two days ago, and the expansion joint I bought leaked less than a month after it was installed. I was so angry that I slapped my thigh. After asking, he found out that he didn't even know the temperature of his flue, so he randomly bought a general-purpose model. Do you think this can be done without any accident?

The flue flange expansion joint, to put it bluntly, is the "joint" of the pipe, and the thermal expansion and contraction depend on it. Wrong choice, bad installation, the back is full of trouble. Today, I will break this set of things apart and crumble it to tell you. After five steps, you can become half an expert.

Step 1: Find out the temper of your flue-temperature, pressure, medium and displacement are all necessary

Don't be in a hurry to place an order. Take a notebook and write down these four numbers first:

• Temperature: What is the highest degree? What is the lowest degree? Don't just quote an average. For example, whether the flue gas temperature is 300℃ or 600℃, the material selection is very different. Excellent in high temperature situationsHigh temperature axial expansion jointOrdinary metal simply can't handle it.
• pressure: Positive or negative pressure? What's the value? There tends to be a slight negative pressure behind the flue gas baffle door, but the desulfurization tower outlet may be positive pressure. The pressure is wrong,Non-metallic expansion jointCould be deflated.
• Medium: Does the flue gas contain sulfur? Are there any corrosive particles? If so, we have to considerPTFE-lined hoseOrPTFE compensator。 Otherwise, it will be pierced in half a year.
• displacement amount: Which direction will the pipe move? Axial? Horizontal? Angular displacement How big is the quantity? This directly determines your choiceUniversal corrugated expansion jointStillCompound hinge transverse expansion joint。

Take a photo of the working parameters and send it to the manufacturer, which is ten times more reliable than your own guess. The manufacturer has experience and knows what to use at a glance.

Step 2: Model selection is not a guessing puzzle-metal rectangular expansion joint or non-metal expansion joint? Circular or rectangular?

Many novices come up and ask, "Which is better?" — There is no best, only the most suitable.

Fang smoke useMetal rectangular expansion jointOrRectangular non-metallic expansion joint； For round flueRound Flap Door (Double Seal)The idea of choosing expansion joints is similar. Look at the way out again: the flue gas temperature exceeds 400℃, and the metal is stable; Low temperature, heavy corrosion, but non-metallic ones are more durable (such asNon-metallic expansion joint (fabric fiber expansion joint)）。

Hey, there is an easy pit here: many people think that non-metallic expansion joints are bargains. In fact, in the low-temperature and high-corrosion environment of desulfurization and dust removal,rubber compensatorOrRubber PTFE compensatorLonger lifespan than metal. Don't just look at the price, look at the combined cost.

Is the amount of displacement large? Large displacements are preferably non-metallic or metal expansion joints with tie rods (e.g.Large tie rod expansion joint), for small displacementUniversal corrugated expansion jointThat's enough.

Step 3: Check these three things before installation-flatness of flange surface, direction of guide tube, and state of tie rod nut

Don't rush up when the goods arrive. Unpack first and check three things:

• flange surface flatness: Take the ruler against it, the unevenness exceeds 1mm, and it leaks 100% when installed. Hurry up to contact the manufacturer for exchange or on-site grinding.
• Direction of guide tube：Specific Function of Expansion Joint Guide TubeIs to protect the bellows from being washed by the medium. The direction of the arrow must be consistent with the flow direction of the medium! Just wait for it to wear out. How to judge? Look at the arrow on the guide tube, or search onlineThe direction of the arrow of the expansion joint refers to, illustrated by figures.
• State of tie rod nut: The tie rod nut may be loose during transportation and is generally locked at the installation length when leaving the factory. When you get it, check whether all nuts are tightened first, but note: after installation, remove some tie rod nuts (according to the displacement requirements), and don't lock them all foolishly. How exactly to adjust? refer toHow to adjust the tie rod nut of expansion joint, there are detailed steps online.

Function of expansion joint tie rodIt is to limit excessive displacement, not for fastening. Some people use the tie rod as a bolt and screw it to death. As a result, the expansion joint can't move at all, and when the pipe is hot, the bellows is directly torn.

Step 4: Installation and disassembly hand-in-hand-from hoisting to bolt tightening, every step is specified

Okay, let's go. In this order:

1. hoist: Use soft sling, don't use wire rope to directly strangle the bellows part. Bellows have thin walls, and a little scratch becomes a weak spot. The lifting point is selected on the flange or bracket.
2. Centering: Place the expansion joint in the middle of the pipe flange, and align it left and right, up and down. The deviation does not exceed 2mm. The consequence of crooked clothing is unilateral pressure, and the life span is halved.
3. threading bolts: The bolt is threaded from the inside of the flange to the outside, and the gasket is not leaked. It is recommended to use double nuts to prevent loosening.
4. Fastening sequence: Diagonal cross tightening, screw to specified torque in three times. Don't screw it all at once, or the flange will deform. For example: like screwing a tire, you have to do it symmetrically.
5. Removing transports: After installation, remove the transport screw or limit plate used to fix the expansion joint when leaving the factory. If it is not dismantled, the expansion joint is tied to death and cannot work properly. Many people forget this step, and as a result, it is scrapped as soon as it is turned on.
6. adjusting tie rod nut: According to the design displacement, loosen the tie rod nut to the designated position. For example, if the axial compensation is required to be 30mm, screw the nut to 30mm from the limit washer.Do you need to remove the screw of the expansion joint？ No need for full disassembly, just loosen to working position.

After the bolts are tightened, light the flange gap with a flashlight to see if there is any light leakage. Light leakage is not sticking flat, heavy tightness.

Step 5: Don't be lazy about routine maintenance – how often do you check? Where to focus on? How to deal with common failures?

It's not all right after installing it, so you have to check it out regularly. Frequency, once a quarter for general working conditions, and once a month for high temperature and high pressure wear.

• Bellows surface: Are there any cracks, corrosion pits, scratches? EspeciallyMetal rectangular expansion jointThe corner, stress concentration is easy to crack.
• guide tube: Is it worn down? Especially on the side near the elbow, the medium washes the most. If you find the perforation, change it quickly, otherwise the flue gas will be sprayed directly on the bellows.
• tie rod nut: Is it loose? Is the displacement stuck?How to adjust the tie rod nut of expansion joint-If the amount of displacement is not enough, loosen it a little; If the displacement is too large and it runs out, tighten it.
• Flange sealing surface: Is there an air leak? Test with soapy water or smoke.

How to deal with common failures?
-Air leakage: first tighten the bolts, and if it still leaks, change the gasket.
-Cracked bellows: Don't think about repair welding, just replace it with a new one. Repair welding creates stress concentration and cracks faster.
-Non-metallic expansion joint bulge: Generally, the internal pressure is abnormal or the temperature exceeds the standard. Check the process parameters.
-Metal hose (if used at the connection) abnormal noise: may be resonant, add pipe clamp or change direction.

One last word,Service life of expansion jointIt is directly related to model selection and installation. You save trouble in the first few steps, but it costs money to repair later. In turn, after understanding these steps thoroughly, it is not a problem to use an expansion joint for ten or eight years.

Okay, these five steps are all. If you follow, the flue flange expansion joint will basically not stomp on any more pits. If you have any questions, please leave a message.