Don't rush to replace the metal expansion joint when it is broken: a set of standard repair procedures, saving tens of thousands
Problems with metal expansion joints in factories are nothing more than those situations: bellows cracking, flange leakage, tie rod deformation and guide tube falling off. I met a customer two days ago, a high-temperature steam pipelineAxial expansion jointAfter three years of use, water seeped at the weld, and the on-site maintenance worker directly repaired it with electric welding. As a result, the more it repaired, the more it leaked-this is not repair, but demolition. To fix it, you have to figure out how it broke. Fatigue fracture is the most common, especially in pipelines that start and stop frequently, and every wave peak of bellows is the stress concentration point. Second, the expansion joint behind the desulfurization flue gas baffle door, the medium contains sulfur, the right material is not selected, and the inner wall is quickly perforated. There are also many installation problems: pre-stretching is not done well, the tie rod nut is not adjusted, and the guide support is missing, which can make the expansion joint scrapped in advance.
You have to make a diagnosis before you start repairing it
Without any precision instruments on the spot, three steps are enough:A look at the appearance-Is there any bulging, scratching or discoloration in the bellows? Are there any rust marks at the flange connection? Is the deflector off?2. Listen to the sound-The expansion joint should not have a hissing or metal crash sound during normal operation.Three-measure displacement— — Take a ruler to measure the actual expansion and contraction of the expansion joint, and compare it with the design value. For example,Straight pipe pressure balanced expansion jointIf the displacement on both sides is asymmetric, 80% of it is a problem with the pipe support. After the diagnosis is clear, decide whether to repair it partially or replace it overall.
Formal repair process is divided into four steps
Step 1 Safe Isolation: Stop the media, relieve the pressure, replace, and list the lock. Don't try to save trouble. Some factories rush the schedule, dismantle the medium before it is cleaned, and spray high-temperature steam. That's no joke.
Step 2 Disassembly: First remove the pull rod or limit device, and pay attention to mark the original position. ForLarge diameter thick wall expansion jointYou have to use hoisting equipment, don't pry it hard. Two days ago, a master took a crowbar to pin it hard. As a result, the sealing surface of the flange was scratched, and it leaked even more when put back.
Step 3 Check: The removed bellows should be detected by coloring flaw detection or magnetic particle detection to see cracks, and the wall thickness reduction should be measured. If only the deflector is worn out, it can be replaced separately; If the bellows has already penetrated, it will have to be replaced.
Step 4 Installation: The model, material and wave number of the new expansion joint must be consistent with the original design. During installation, the amount of pre-stretching or pre-compression should be adjusted according to the value given by the manufacturer. Refer to our previous technical article for the adjustment method of the tie rod nut. Remember to lock it after adjustment. Many masters ignore the locking step. After several months of operation, the tie rod is loose, and the expansion joint is directly disengaged.
Different repairs in different working conditions, different pits
High-temperature axial expansion joints, such as those used in power station industry, should pay attention to the sudden change of temperature after the insulation layer is damaged when disassembling and assembling, which is prone to thermal stress. Of the cement industryMetal corrugated expansion joint, the interior may accumulate serious dust, purge with compressed air before disassembly. Thin-walled parts such as special vacuum hoses will leak even if a hole with a large needle hole, so it is of little significance to repair them, so they can be replaced directly. One more point that is easy to overlook:rubber compensatorAndRubber PTFE compensatorYou can't use the same set of repair techniques as metal expansion joints. After the rubber parts age, they can only be replaced as a whole, and they can't be repaired.
Alas, when it comes to vacuum special hoses, a customer asked two days ago, saying that if a small hole was found, could it be welded? I refused directly-the thin-walled parts burned through as soon as they were welded, and even if they were repaired, the stress of the weld was concentrated, and it didn't take long to crack again. In this case, it is more cost-effective to replace it with a new one than to repair it.
After repairs, everything will not be fine, we have to take precautions
For steam pipingUniversal corrugated expansion jointStillExternal pressure single axial expansion joint？ For desulfurization systemsDouble-sealed flapper doorWith non-metal expansion joints? When installing, is the position of the guide bracket and the fixed bracket correct? Does the screw of the expansion joint tie rod need to be removed? These questions have been addressed in the previous FAQ. In the daily inspection, the bellows surface is checked once a month, and the displacement is checked once a year, which is recorded. The data speaks for itself. Which kind of expansion joint is prone to problems in which position. Statistics are put out, and the next maintenance will give priority to it. The cost of repairing it once is not low, but it is much better than stopping the production of exploded pipes.
Think about it, if the expansion joint of a high-temperature steam line bursts, how much will it be lost if it is shut down for emergency repair in one day? Less say tens of thousands. Spending hundreds of dollars for inspection regularly can save tens of thousands of replacement costs, and anyone will settle this account. Is that the truth?