Find out what kind of expansion joint you are installing first-a few common types on flues
Two days ago, a brother from the construction site called and said that the flue expansion joint was installed backwards, and he was extremely anxious. I asked him what model he installed, but he hesitated and couldn't say it. Tsk, you don't even know what you're holding, how can you judge the pros and cons?
The expansion joints used on the flue, to put it bluntly, are in three categories: metal, non-metal, and sleeve type. There are several kinds of metal ones, such asUniversal corrugated expansion joint、High temperature axial type expansion joints, and specially used on square fluesMetal rectangular expansion joint。 Non-metallic are mainlyNon-metallic expansion joints (fabric fiber expansion joints)Andrubber compensator, especially in power stations and cement plants. And there's alsoSleeve type pipe expansion jointBy the sliding compensation of the inner and outer tubes, the structure is simple but easy to get stuck.
Before you act backwards, look at which category this one in your hand belongs to. Why do you want to figure it out? Because the "signal lights" for judging positive and negative are different. Most of the metal corrugated sections have arrows and guide tubes; The non-metal section looks at the frame direction and sealing surface; For sleeve type, look at the opening direction of the sleeve. Stop messing around, messing around is messing around.
How do you judge if you are acting backwards? Look at arrows, deflectors or tie rods?
Okay, now that you have confirmed the type, the next three steps of self-examination method, don't jump a step.
Step 1: Look for the arrow.Most metal expansion joints, such asUniversal corrugated expansion jointOrHigh temperature axial expansion joint, an arrow is printed on the bellows when it leaves the factory, indicating the direction of the medium flow (usually the direction of flue gas or hot air flow).The direction of the arrow must be consistent with the actual flow direction of the medium。 If the arrow is in the opposite direction, it is installed backwards. But note: Some older expansion joints don't have arrows, or the arrows are covered by paint, then you have to look at step two.
Step 2: Look at the deflector.We have previously sent a question and answer "The Specific Function of Expansion Joint Guide Tube", the core of which is that the guide tube should face the direction of medium flow to prevent high-speed airflow from directly washing the bellows. How to judge? You take a flashlight and shine it in from one end of the pipe, or use an endoscope (if you don't have one, stick in and take a photo with your mobile phone camera) to see whether the bell mouth of the deflector is facing the direction of incoming air or its back. The bell mouth is right in the direction of incoming air, otherwise it is installed backwards. Metal rectangular expansion joints and non-metallic expansion joints often have guide tubes inside, and the operation method is the same.
Step 3: Check the pull rod/nut position.If it is an expansion joint with a tie rod (such asLarge tie rod expansion jointOrCompound hinge transverse expansion joint), tie rods and nuts are usually used to limit displacement or pre-stretch. Are there any special requirements for the installation direction of the tie rod? Generally speaking, the tie rod itself is not distinguished between positive and negative, but its fixed end and movable end may correspond to the fixed bracket of the pipe. See the manufacturer's drawings for details. In addition, if the adjustment nut on the tie rod is installed on the wrong side, it will cause the expansion joint to fail to compress or stretch properly, which is also regarded as a "reverse installation".
These three signal lights are on correctly, and it is basically fine. If one doesn't match, hurry down to read the remedy.
What will go wrong if you install it backwards? Don't wait for a leak to regret it
What can be done if the arrow is reversed? The worst thing is to rush the airflow. Alas, naive. Let me tell you a few real consequences:
- The guide tube is installed reversely → the bellows is worn through by the airflow.There are dust particles in the flue gas, and the back of the guide tube is washed at a high speed (the bellows that should have been protected is exposed instead). In a few months, holes will be worn out, and air and ash will leak. Maybe the whole maintenance period will have to be stopped.
- Install the tie rod nut backwards → insufficient compensation.When the pipeline expands thermally, the expansion joint is stuck by the tie rod, which produces huge thrust, which can break the pipeline support at the light and rip the bellows at the worst. Especially for power stations and cement industriesStraight pipe pressure balanced expansion joint、Curved tube pressure balance expansion jointOnce the tie rod system is installed backwards, the accident probability doubles.
- Non-metallic expansion joint skin direction reversed → seal failure.The skin of non-metallic expansion joints (fabric fiber expansion joints) usually has front and back sides. The front side is temperature-resistant and corrosion-resistant, and the reverse side is ordinary cloth. If installed backwards, the high-temperature smoke directly contacts the opposite side, and it can be burned through in a few minutes. We had a customer install it backwards before, and it smoked after half a day of turning it on.
Therefore, don't wait for the air leak to regret it. If you find that it is installed backwards, you will have to deal with it on the same day. Even if it is delayed for two days, it will be better than the later explosion.
Remedial Steps: To Dismantle or Not to Dismantle? How to tune the scene?
That really acts backwards, what should I do? There are two situations:
Situation 1: Haven't suppressed the test run yet, or just finished installing and found
This is the easiest-disassemble and reload. But note:Fix the pipe before dismantling itEspecially likeHigh temperature axial expansion jointThis kind of stiffness itself is relatively large, and the pipeline may sag or displace after removal. Hold it with a temporary bracket, then loosen the flange bolts at both ends of the expansion joint, and rotate it 180° as a whole (if the direction of the guide tube and the arrow is reversed, rotation of 180° can usually be corrected). When rotating, ensure that the bell mouth of the guide tube faces the direction of airflow. For non-metallic expansion joints, you may just turn them over as a whole, but pay attention to the marking lines on the skin.
Case 2: Has been welded or the pipeline is in working condition
This is a little troublesome, but it doesn't mean hopeless. For example: If you are loadingSleeve type pipe expansion jointIf the sleeve is reversed (the end that should have been extended is retracted), you can try pushing the sleeve from the outside with a jack, pushing it into the correct position, and then re-welding the limit plate. However, this operation is risky, so it is best to ask the manufacturer for guidance.
ForMetal rectangular expansion jointOrNon-metallic expansion jointIf both sides have been welded, you may considerReplace only the internal guide tube。 Open the access port on the side of the expansion joint (many rectangular non-metallic joints have access ports reserved), take out the old guide tube, turn the direction and put it back. You don't have to dismantle the whole pipeline, which saves big problems.
If the tie rod nut is installed backwards, it is simpler: loosen the nut, change the orientation of the positioning plate on the tie rod, or directly change the position of the two nuts. For specific adjustment methods, please refer to our Q&A "How to adjust the expansion joint tie rod nut", which has detailed steps.
Tips:When adjusting on site, remember to draw alignment marks on flanges and pipes with markers to avoid turning too much or too little. After adjustment, do an air pressure or hydraulic pressure test to ensure no leakage.
Do this step more before installation, and never say goodbye to installing backwards
After all, the best remedy is prevention. Just do one more step before you install- -Take a photo for confirmation。 Take a picture of the arrow on the expansion joint, the direction of the guide tube and the nameplate information, together with the direction of the pipeline, and send it to the manufacturer's technician for confirmation. Now it is more convenient to send a picture on WeChat, which saves two hours of construction period than after installation and then dismantling. In addition, read the product manuals on our site, such asMetal rectangular expansion joint、Non-metallic expansion joints (fabric fiber expansion joints)、High temperature axial expansion jointThese product pages are marked with the installation direction requirements. It takes 10 minutes to watch it, which is a hundred times better than you pondering it on the spot.
The expansion joint is installed backwards, most of which are caused by "feeling almost the same". Don't be the same. This step may be an unplanned downtime. If you find it useful, remember to collect this article and turn it out before installing it next time.