Flip the drawings before installation: flange standards, sealing surfaces and bolt specifications must not be missing
Many people are anxious to install the expansion joint when they get it, and they don't even look at the drawings. And the result? The flanges don't match, the sealing surfaces don't match, and the bolts are screwed halfway to find the wrong specifications-the rework is light, and maybe the whole pipe has to be reworked. What's the difference between this and driving with your eyes closed?
The first step in installing the metal expansion joint flange is not to screw the bolts, but to turn over the drawings. You have to first figure out which standard the flange performs: HG/T 20592, GB/T 9119 or ASME B16.5? Don't think that the same diameter can be universal. Once we met a customer who put the power stationUniversal corrugated expansion jointIt was installed on the chemical pipeline. As a result, the sealing surface of the flange was a protruding surface (RF), while the pipeline flange was a concave and convex surface (MFM), which leaked within two days after hard installation.
Then there is the type of sealing surface. Common protruding surface, full plane, concave and convex surface, tongue and groove surface, which is the expansion joint flange in your hand? If it is tongue and groove surface, the gasket must be equipped with a special octagonal pad or oval pad, and the ordinary winding pad will be wasted when stuffed in. And the bolt specs-you can check themModel and size of expansion jointThread diameter, pitch, and number of bolts are clearly listed above. Don't estimate by experience, take a caliper to measure it, and it can't be tightened by half the pitch.
If the pipeline is filled with corrosive media, such as sulfuric acid and hydrochloric acid, the flange material must match the media. You may considerPTFE-lined hoseOrPTFE compensatorTheir flange surfaces are usually lined, so they should be protected and not scratched during installation.
Flange Alignment and Clearance Control: One or two millimeters away, the seal may be scrapped
The flange alignment seemed unremarkable, but if it wasn't done well, it would be a disaster. Two days ago, a friend who made steam pipes asked me, "My bolts are broken, why are they still leaking?" I asked him to take a photo. At a glance, the two flanges were misaligned by nearly 3mm, and half of the sealing gasket was flattened and half suspended. Do you think this can not leak?
When metal expansion joint flange is installed, the alignment error of two flanges should be controlled within 1mm in theory. How is it right? The simple and rude method is to use a rectangular ruler and a gauge, first check whether the outer circle of the flange is concentric, and then check whether the end faces are parallel. If there is a deviation, adjust it with a jack or temporary support. Remember: the expansion joint itself is a flexible compensating element, and its flange cannot be used to forcibly correct pipe deviations. Forcibly pulling, from bellows deformation to weld tearing-by then, no matter how good it isLarge diameter thick wall expansion jointIt won't save you.
What about the mounting clearance? Generally, leave a gap of 2 to 4 mm. See the design drawings for specific values. The clearance is too large and the gasket is not compressed firmly; Too small, not enough bolt preload. Here is a practical trick: first bring all the bolts in, but don't tighten them, and insert a gauge along the circumference to see if the gap is even. If the clearance on one side is obviously too large, it means that the flange is crooked and has to be readjusted.
Sequence and torque of bolt tightening: not tightening the tighter the better, in three steps
Many people think that the tighter the bolts are tightened, the better, and they can't wait to take the afterburner to screw the bolts until they are deformed before they can rest assured. Wrong. If the bolt preloading force is too large, the flange surface will warp and deform, the gasket will lose its elasticity, and the seal will fail instead; If the preload force is too small, the gasket will be blown off as soon as the medium is pressurized. Therefore, it must be tightened according to the prescribed moment.
How do you check the torque? One is the drawings, and the other isMetal expansion joint weight tableOrStiffness and Calculation Formula of BellowsSuggested values are generally given in. If not, you can follow the standard of ASME PCC-1: for carbon steel flanges, the bolt stress after lubrication is controlled at 200~250 MPa; Stainless steel flange is appropriately low, 180~200 MPa. Don't tell me "I just feel". No matter how accurate the hand is, it can't compare to a torque wrench.
Screw three times according to the cross-over method. Pre-tighten with 50% torque for the first pass, 80% for the second pass, and 100% in place for the third pass. Why in three steps? Because the flange will be bent and deformed during the tightening process, step-by-step screwing can gradually release the stress and make the flange surface fit evenly. If you try to save trouble and screw it in place, the middle bolts will suffer the greatest force, and the two sides will be loose.
Some expansion joints come with tie rods, such asLarge tie rod expansion jointOrCompound hinge transverse expansion joint。 The bolts of these tie rods also need to be tightened according to the specifications, and the locking nut of the tie rod cannot be screwed to death, so the displacement margin of the expansion joint should be left-how to adjust it for details, you can refer to our stationHow to adjust the tie rod nut of expansion joint。
Differences in installation under different working conditions: How to deal with high temperature, high pressure and corrosive media
The working conditions have changed, and the method of installing the metal expansion joint flange has to change accordingly.
High temperature operating condition, such as power station pipelines or flue gas pipelines, with temperatures exceeding 400℃. At this time, the flange bolt will slack under high temperature, and the preload force will drop. It is recommended to use a slightly higher preload during installation, or a disc spring washer to compensate for thermal relaxation. In addition, the gasket has to be replaced at high temperature, and the graphite winding pad or metal ring pad is more reliable than the ordinary non-asbestos pad. We have a client who usesHigh temperature axial expansion jointThe flange surface is tapered, and the neutrality requirement is higher during installation. A difference of 0.5 mm may lead to high temperature leakage.
High pressure operating condition, such as chemical industry and air separation industry. When pressures exceed 10 MPa, the flanges are generally high neck flanges (WN) with larger bolt specifications. At this time, pay attention to bolt lubrication, and use molybdenum disulfide or high-temperature anti-jam agent to avoid the thread bite to death. Leaks in high-pressure systems are often catastrophic, so pressure tests must be done after installation-this is specifically said later.
Corrosive mediaFor example, wet chlorine and dilute sulfuric acid. At this time, the materials of flanges and bolts should be corrosion-resistant, such as Monel or Hastelloy. In addition, it is best to use concave and convex surfaces or tongue and groove surfaces for flange sealing surfaces, with ptfe gaskets. If you are usingPTFE-lined hoseOrTetrafluorine compensatorDon't break the liner when installing, it will leak if it is broken.
Treatment of pull rod and guide tube: Disassemble what should be disassembled, adjust what should be adjusted, don't go in the opposite direction
The draw rod and guide tube on the expansion joint are not decorations, so don't treat them as decorations.
The role of the tie rod is to limit the excessive deformation of the bellows during transportation and installation, and to prevent the bellows from being accidentally stretched or compressed. Once in place, the locking nut on the tie rod should be loosened-note that it is loosened, not removed. The purpose of loosening is to allow the bellows to deform freely and absorb the thermal displacement of the pipe. If you screw the nut to death, the expansion joint is equal to a rigid pipe, and it loses its compensation effect. Conversely, if itDirect buried (fully buried) type expansion jointIts tie rod may need to retain a certain preload force after installation, because directly buried pipelines can't be as convenient to overhaul as overhead pipelines. How to deal with it specifically? Read the product manual and don't take it for granted.
What about the deflector, many novices will install it backwards. There is usually an arrow direction on the expansion joint pointing to the direction of the flow of the medium. The role of the guide tube is to guide the medium to flow smoothly through the bellows, reducing scour and vortex. If it is installed backwards, the guide tube not only fails to protect, but also directly impacts the medium on the bellows, accelerating fatigue failure. By the way,The direction of the arrow of the expansion joint refers toMake sure to verify the flow direction of the medium before installation.
Some people think that the deflector should be removed because it is "in the way". Never tear it apart! The guide tube is a structural part, which supports the inside of the bellows. If the bellows is disassembled, it will become unstable. There is only one situation that can be disassembled-when the pipeline is purged and cleaned, in order to prevent the guide tube from being blocked by debris, it is temporarily disassembled, and then put it back after blowing.
Pressure test and inspection after installation: Discover problems before passing the media
After installation, don't rush to turn it on. Do the stress test first, this is the last insurance.
Generally, the hydraulic pressure test is performed, and the test pressure is 1.5 times the design pressure, but it does not exceed the maximum test pressure allowed by the bellows. Note: Open the exhaust valve to exhaust the air during the hydraulic test, otherwise the reading of the pressure gauge will be inaccurate. The pressure boost should be slow and the pressure is maintained in stages. For example, if the design pressure is 1.0 MPa, the test pressure will be hit to 1.5 MPa, which is divided into three steps: first hit 0.5 MPa to stabilize the pressure for 5 minutes to check the leakage, then hit 1.0 MPa to stabilize the pressure for 5 minutes, and finally hit 1.5 MPa to stabilize the pressure for 10 minutes. During the pressure holding period, apply soapy water to all flange joints, welds and tie rod nuts to observe for air bubbles. No bubbles qualify.
If the air pressure test is done (such as a medium where water residue is not allowed), the test pressure is 1.15 times the design pressure, but safety measures must be taken-the air pressure test is far more dangerous than the water pressure, and once the expansion joint ruptures, the energy is huge. Therefore, the personnel should be evacuated during the air pressure test.
In addition to the pressure test, check whether the displacement of the expansion joint is within the allowable range. Such asUniversal corrugated expansion jointWhat is the axial compensation amount of?External pressure single axial expansion jointIs the lateral displacement of exceeding the limit? These data are all available in the product sample. Take a ruler and measure it, don't rely on guessing.
After the pressure test is qualified, tighten the flange bolts again. Because the pressure fluctuation during the pressure test will cause the bolts to loosen slightly, re-tightening can eliminate hidden dangers.
The installation of metal expansion joint flange looks simple, but in fact, there are quite a lot of doorways. Look at the drawings when selecting the type, divide the central control clearance and fastening into three steps, don't ignore the working conditions, don't move the draw rod guide tube, and put the pressure test in place. With these six points in place, the pipeline system can basically run steadily for several years. Otherwise? When the media leaks and then repairs it, the loss is more than just the maintenance cost.