How "abnormal" is the flue working condition-high temperature, corrosion and displacement are many
Anyone who has worked in an oil refinery knows that the flue is a "hellish examination room" for expansion joints. The temperature is always five to six hundred degrees, and in case of catalytic cracking or sulfur recovery, there are also corrosive gases such as sulfur dioxide and hydrogen sulfide in the flue gas. Maybe with some more condensate acid, the metal wall can gnaw holes for you.
And don't think that the flue is just a straight pipe. The displacement of the pipe can run tens of millimeters when it expands and contracts by heat. Coupled with the vibration of the fan and the settlement of the equipment foundation, the displacement in three directions-axial, lateral and angular-all came at once. To put it bluntly, it is the norm to throw in ordinary expansion joints and leak in two or three years.
Therefore, when picking the flue expansion joint of an oil refinery, the first thing you have to understand is that you are not buying standard parts, but customizing a scheme for "abnormal" working conditions. It is best to leave a 20% margin for the temperature, pressure and displacement written on the drawing. Don't stick with the boundary value, otherwise there will be endless troubles.
Should I choose metal or non-metal? Rectangular or circular? Combined with our products to understand
Flue temperatures exceeding 400°C, preference being given to metallic ones. We have one on our stationHigh temperature axial expansion joint、Corrugated expansion joint for power station industryThese are made of stainless steel or high nickel alloy, which have high temperature resistance and good pressure bearing capacity. However, if the temperature is not high (below 300℃) and there is acidic condensate in the flue gas, the non-metallic one will be more robust.
OurNon-metallic expansion joint (fabric fiber expansion joint), andRectangular non-metallic expansion jointThe skin is made of fluororubber and polytetrafluoroethylene, which is very resistant to acid and alkali corrosion. Moreover, the non-metallic structure has a large amount of compensation displacement and is light to install. The disadvantage is that it can't bear pressure, and the air duct system is fine.
Let's talk about shape. Many refinery flues are square-the inlet and outlet of desulfurization tower, the flues before and after the electrostatic precipitator, which has to use rectangular expansion joints. OurMetal rectangular expansion jointSpecially do this work, the four corner welds are strengthened, and there will be no stress concentration cracking. Circular flue is simple, universal corrugated expansion joint or directly onUniversal corrugated expansion jointJust do it. Bottom line: Look at the cross-sectional shape of the pipe. Don't connect the square pipe to the round one in order to save money, which takes time to install and is easy to leak.
The parameters that are easiest to ignore in the selection are guide tube, tie rod and pressure balance
Two days ago, an old customer called and said that the expansion joint of their catalytic flue had worn out in less than a year. I asked him if he had installed the deflector? He froze. You see, this is a typical pit-high-temperature flue gas is sandwiched with catalyst dust, and the particle scour speed can reach 20 or 30 meters per second. There is no guide tube, and the bellows is directly exposed, so it is strange that it is not worn out.
One is to guide the flow direction of the medium and reduce the vortex; The second is to block the scouring of the bellows by particles. Therefore, when selecting the model, it is necessary to confirm whether the guide tube is configured, especially in the dust-containing flue gas working condition.
Another pit is the pull rod. Many people think that the tie rod is fixed during transportation, and it will be dismantled at the scene. Wrong! Some expansion joints require that the tie rod be retained after installation, which is used to restrain excessive displacement or withstand internal pressure thrust. Like ourCompound hinge transverse expansion jointThe tie rod is a structural part and cannot be disassembled. Removing it is equivalent to letting the bellows carry the thrust hard, and it will crack sooner or later.
When it comes to thrust, we have to mention the pressure balanced expansion joint. Some flue systems in refineries have high pressure (such as the waste heat boiler inlet), and ordinary axial compensators generate huge blind plate forces that push the pipes around and around. At this time, we have to use the pressure balance type, such as oursStraight pipe pressure balanced expansion jointOrCurved tube pressure balance expansion jointIt uses two sets of bellows to cancel out the internal pressure thrust of each other, so that the pipe and equipment will not be injured.
Installation: How to fit baffle doors, expansion joints and hoses to avoid trouble
If you choose the right expansion joint, if you fool around with the installation, it will still be useless. Flap doors and expansion joints are often placed next to each other in refinery flue systems. For example, for switching flueRound Flap Door (Double Seal)OrDouble-sealed single-axis circular baffle doorWhen they turn on and off, a torque is transmitted to the flue. If the expansion joint is installed too close, the operating force of the baffle door may twist the bellows.
Install an expansion joint on both sides of the baffle door and leave a short joint in the middle, so that the force when the baffle door is opened and closed is separated from the thermal displacement of the pipe. In addition, it is best to use a length of metal hose between the expansion joint and the baffle door-like oursMetal hoseOrPTFE-lined hose, can not only compensate for small displacements, but also absorb vibrations, killing two birds with one stone.
The direction of the arrow on the expansion joint refers to the flow direction of the medium. Never install it backwards. Install the guide tube backwards to become a baffle, and the erosion will be increased after the airflow is blocked, and the life of the bellows will be directly discounted. Before each installation, it is best to turn out the article "What is the direction of the arrow of the expansion joint" on our station and read it again. Anyway, it is no trouble.
Leaked after a few years of use? Sharing common fault causes and troubleshooting ideas
We in this business are most afraid of hearing "the expansion joint is leaking again". In fact, there are only a few reasons for leakage, so just follow the investigation.
First, look at the crack location.If the crack is at the peak or trough, there is a high probability that it is fatigue-or the displacement compensation amount is small during type selection, and the bellows is over-stretched every day; Either there is additional vibration in the system. Solution: Switch to multi-wave structure or add limit tie rod. OurExternal pressure single axial expansion jointThe fatigue life is one cut longer than ordinary ones.
Second, look at corrosion marks.Once acidic condensate appears in the flue, stainless steel will also undergo pitting or stress corrosion cracking. At this time, you have to consider lining the tetrafluorine scheme, or directly on the non-metallic one. Like oursrubber compensatorAndRubber PTFE compensatorWhich is particularly useful in low-temperature corrosion areas.
Third, see if the guide tube has fallen off.Sometimes the guide tube itself is not welded firmly or worn and broken, and it falls off and blocks the expansion joint, which leaks into a big hole. In this case, it is necessary to regularly check the state of the guide tube, especially when the furnace is shut down for maintenance. It takes less than ten minutes to open the expansion joint and take a look.
Fourth, see if the installation has dead bends.If the flue pipe is hard pulled into place, the expansion joint is precompressed or prestretched to fail. After normal installation, the transport screw should be removed to allow the expansion joint to move freely. Do you ask if the screw of the expansion joint needs to be removed? The Q&A of our station makes it clear: the transportation fixtures must be removed, and the tie rod depends on the design requirements.
Refinery flue expansion joint is actually a "system job". Don't expect one product alone to solve all the problems. Read more product information on this site, communicate with technology more, and ask with the working condition parameters if you are really unsure. After all, our goal is the same-to keep the device running safely for ten or eight years, and no one wants to be called for emergency repair in the middle of the night.