What exactly does the expansion joint arrow mean? — Many old masters have misunderstood
When installing expansion joints on site, the most common mistake is to stare at that arrow and ponder. Do you think the arrow indicates the flow direction of the medium? Not necessarily.The position of the guide is the key。
Take the product of this site for example, any expansion joint with a guide tube-such asUniversal corrugated expansion joint、High temperature axial expansion joint— — The arrow actually marks the corresponding relationship between the medium flow direction and the installation direction of the guide tube. When installed backwards, the upflow surface of the guide tube becomes the backflow surface, which is equivalent to letting the bellows directly impact the high-speed fluid. It would be strange to have a long life.
By the way, some manufacturers, in order to save money,Non-metallic expansion jointOrrubber compensatorThere is no guide tube on it at all, and the arrow is just a decoration. However, the metal expansion joints used in chemical pipelines are most likely equipped with guide tubes, so you can't just look at the surface of this arrow.
What will happen if you act backwards? — Real cases tell you
Two days ago, a buddy in the chemical industry circle sent a photo, one in their factoryUniversal corrugated expansion jointAfter less than three months of use, the bellows tore directly at the root. When I remove it, the direction of the arrow is 180 degrees opposite to the flow direction of the pipe. The reverse installation of the guide tube causes the high-speed medium to directly scour the bellows, and the superposition of thermal stress makes it hell if it is not bad.
The medium temperature and pressure in industrial pipelines are high. This kind of mistake ranges from leakage to stop, to bellows explosion and damage to equipment. If you think about it, if chemical media are corrosive, such as sulfuric acid and caustic soda, it is no joke to leak out.
Later, the buddy counted it. Because of this parking shutdown for maintenance, the production line stopped for two whole days, and the loss was at least hundreds of thousands. So,Chemical Metal Expansion Joint Added BackwardsThis matter is really not as simple as "install it backwards and reinstall it".
How can you tell at a glance if you are pretending to be reversed? -Don't just look at the arrow, look at the guide tube
The arrow thing may have been altered when it was installed, or the mark was not clear when it left the factory. The most reliable method:Look at the guide tube。
Looking in from one end of the expansion joint, the guide tube should extend in the direction of media flow. If it isSingle axial typeOrExternal pressure single type axial typeOne end of the guide tube is welded on the inner side of the connection tube, and the other end is freely suspended, and the suspended end must face downstream.
In addition, there are expansion joints of tie rod construction-such asCompound hinge transverse type、Straight pipe pressure balance type— — The nut position at the end of the tie rod can also assist in the judgment. Usually the tie rod is locked in the shipping state and should be loosened after installation. If you find that the tie rod is holding its strength in the direction of thermal expansion of the pipe, it is mostly installed wrong.
To insert here,How to adjust the tie rod nut of expansion joint？ There is a special article about this before this site. When adjusting, make sure that the amount of pre-stretch or pre-compression is restored to the design value, otherwise it will be useless if it is installed in the right direction.
What should I do if I find it installed backwards? — — Case by case handling
Don't worry, look at the situation first.
- No media yet:Removing and reinstalling is the most hassle-free. Just screw off the flange bolts, turn around and put them back in. Note:Large diameter thick wall expansion jointHeavy weight, use soft sling when hoisting, don't use wire rope to strangle bellows.
- Has been put into operation:There is pressure and temperature in the pipeline, so you have to stop the machine to relieve pressure. After pressure relief, remove and check the bellows for damage. Minor scratches can be sanded, but if they have been deformed or cracked-just replace them with new ones. Don't hesitate, this stuff can't be made do.
In addition, the adjustment of the tie rod nut is critical. Refer to what we have compiled earlierExpansion joint tie rod nut adjustment methodEnsure that the amount of pre-stretch or pre-compression is restored to the design value. If you are not sure, you can contact the technical support of this site, don't screw it yourself.
By the way, if you useCurved tube pressure balance expansion jointOrStraight pipe pressure balanced expansion jointThis type of structure itself has strict restrictions on the direction of the flow channel, and the probability of backwards installation will be much lower-but once backwards installation, disassembly is more troublesome because there are also balanced bellows and end structures.
How to avoid pretending backwards in the future? — — Three moves done
To be honest, most of the anti-installation cases are because the installation team does not work according to the drawings. There are three preventive measures:
- When purchasing, the manufacturer is required to mark the flow direction arrow with eye-catching red paint on the outer wall of the expansion joint, and provide an installation instruction manual. Don't be too troubled, the direction of the guide tube will be clearly written in the instructions.
- Before installation, let the field technician and the construction squad leader jointly check the pipeline PID diagram and the expansion joint identification. Sign and confirm before working, and it is convenient to hold accountable if something goes wrong.
- For high temperature and large pipe diameter situations such as power station industry and cement industry, it is recommended to chooseDouble-sealed round flapper doorOr an expansion joint with a positioning pin structure that physically limits reverse mounting. Such asDouble-sealed single-axis circular baffle door, itself has directionality, and when installed backwards, it can't match the flange hole at all.
Finally, selection is also important. For media pipelines with clear flow direction, preference is given toStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion jointBecause this kind of structure needs to balance the pressure and thrust, once the flow direction is wrong, the force on the bellows will directly double.
If you're working on chemical projects, don't just save hundreds of dollars. Regular manufacturers-such as this site-will stamp and mark their products, and there are also directional marks for guide tube welding.
Chemical Metal Expansion Joint Added BackwardsIt's not a matter of luck, it's a matter of management. Stuck the installation process and this won't happen.