Find out first: Do you need to install expansion joints in your flue?
The flue, to put it bluntly, is an exhaust passage. However, as soon as the temperature rises, the pipeline expands and contracts, and it is easy to break the weld joint or crook the bracket without a buffer device. Think back, have you ever seen smoke, air leakage, or heard a cracking noise at the flue interface? That means thermal displacement is holding its strength.
To determine whether to install it or not, look at three points: ① Does the operating temperature of the flue exceed 100℃? ② The length of the straight section of the flue exceeds 20 meters? ③ Does the flue pass through rigid connection points such as elbows and valves? As long as you win one, it is recommended that you seriously consider adding it. There is no need to wait until the flue bulge is deformed before regretting it, and the maintenance cost at that time is not the money of an expansion joint.
Picking the Right Product: Which Flue Expansion Joint Should I Choose?
The working conditions of the flue are special, with high temperature, much dust and some corrosive smoke. Before choosing, find out several parameters of your flue: medium temperature, pressure, diameter size, displacement (axial or transverse).
When the temperature is lower than 400℃ and the dust is not large, it can be consideredUniversal corrugated expansion jointOrMetal rectangular expansion joint； If the flue gas contains sulfur and is corrosive, thenPTFE-lined hoseOrPTFE compensatorMore resistant to manufacturing; If the section of the flue is square, don't push it round,Metal rectangular expansion jointAndRectangular non-metallic expansion jointThat's the right answer. In addition, if the flue is used in the desulfurization system, directly selectDesulfurization flue gas baffle doorcomplementaryNon-metallic expansion joint (fabric fiber expansion joint)Corrosion resistance and convenient maintenance.
Don't buy cheap ones with mismatched sizes. When the expansion joint is installed, the amount of pre-stretching or pre-compression is wrong, and it is also scrap iron when installed. Two days ago, I met a customer, and I bought a general-purpose model to save trouble. As a result, the displacement was miscalculated, and it collapsed in two months-do you think it's a loss?
Hands-on Installation: 7 Key Steps to Install Expansion Joints in Flues
Installation is not directly welding the expansion joint, and it is done. If the order is wrong, there will still be problems.
- Step 1: Cut off the flue first and make temporary support.After the flue is cut into sections, the two ends are easy to sink, so it is supported by a jack or bracket in advance.
- Step 2: Clean the notch burrs and weld slag.Don't underestimate this step, residual welding slag will scratch the bellows during operation. And guess what? Some people thought the trouble was not clear, but as a result, the bellows drew a groove and leaked in half a year.
- Step 3: Confirm the expansion joint model and flow direction arrow.Generally, there are arrows pointing to the direction of medium flow on the expansion joint, which will aggravate the erosion wear if installed backwards. The arrow direction of the expansion joint is specifically talked about in the FAQ of this site. It is recommended to turn it out and have a look.
- Step 4: Install the expansion joint and fix it by spot welding first.Do not weld to death at once, leaving room for adjustment.
- Step 5: Adjust the tie rod nut.For expansion joints with tie rods (e.g.Compound hinge transverse expansion jointOrLarge tie rod expansion joint), remove the transport fixtures after installation, and adjust the amount of pre-tension/pre-compression according to the design requirements. How exactly to adjust? Refer to the question and answer of this site "How to adjust the tie rod nut of expansion joint".
- Step 6: Formal welding.Pay attention to protecting the bellows when welding, which can be covered with a damp cloth or fire blanket. High-temperature flue (such as flue of power station boiler) is recommendedCorrugated expansion joint for power station industryOrHigh temperature axial expansion jointAllow sufficient insulation spacing when installing.
- Step 7: Remove the temporary support and check that all the bolts are tight.
Pit Avoidance Guide: 3 Most Common Mistakes to Make in the Installation Process
Mistake 1: Thinking that expansion energy saves absorbing displacement in all directions.Virtually every expansion joint has a design compensation direction, such asAxial typeCan only absorb axial expansion and contraction,Transverse type(e.g.Compound hinge transverse expansion joint) to absorb lateral displacement. If you choose the wrong direction, loading it is equal to not loading it.
Mistake 2: Ignore the role of the deflector.expansion joint guide tubeInstead of decoration, it can guide the high-temperature flue gas to the center of the pipe to avoid the bellows from being directly washed. Many customers perforate the bellows within a few months of installation, and nine times out of ten, the guide tube is not installed or installed backwards. There is a question and answer on this site dedicated to "the specific function of the expansion joint guide tube". You can go and have a look.
Mistake 3: The installation position is near the elbow or the valve is too close.The fluid disturbance at the elbow is large, and there is additional stress at the valve. It is recommended that the expansion joint be installed in the straight pipe section, at least 1.5 times the flue diameter from the elbow or valve. In addition, don't bury the expansion joint in the flue insulation layer, in case of leakage, it can't be found at all. If you need regular inspection, leave an observation port.
How to check and accept after installation? What to pay attention to in routine maintenance?
In the first step, low-temperature flue gas is introduced to test the pressure, and the weld seam and the expansion joint body are checked for air leakage. You can brush the bubbling method with soapy water. In the second step, raise to the rated temperature and observe whether the expansion joint expands and contracts smoothly and whether there is any sticking. Step 3, check the bolts and brackets again after 24 hours for any looseness.
Check the bellows surface for corrosion pits, cracks or wear thinning every six months. If it isNon-metallic expansion jointFocus on whether the fabric layer has aged, become brittle or layered. If you find an abnormality, replace it in time. Don't wait for it to be broken before replacing it. At that time, the dust in the flue can make people faint.
By the way, if your flue is from the cement industry, it is recommended to clean up the dust regularly, becauseMetal Corrugated Expansion Joints in Cement IndustryThe most afraid of acid scale corrosion. In industrial matters, prevention always saves money than maintenance, isn't that the truth?