I met a customer two days ago. I just installed a batch last yearflue expansion jointIt leaked before it was used for a full maintenance cycle. When I removed it, I saw that the guide tube was washed up by the smoke like a knife-it was installed backwards. No one looked at the direction of the arrow. You say it was wrong or not? There is no problem with the equipment itself. As soon as there is a mistake in the installation link, it will be completed later. Today, break these five steps into pieces and explain them clearly. Follow them, and at least step on half the pit.
First, recognize the model number and arrow direction before installation
Don't rush up when you get the expansion joint. One glance at the nameplate, one glance at the arrow. That arrow is not an ornament, it represents where the medium flows. Once the orientation of the guide tube is reversed, the high-temperature dusty flue gas directly washes the root of the bellows, and it will wear out in less than a few months. Common ones areMetal rectangular expansion jointAndNon-metallic expansion joints (fabric fiber expansion joints)— — The former carries high temperatures, such as the flue of power station boilers; The latter is corrosion resistant, and the wet flue gas working conditions in the desulfurization system all depend on it. If you select the model correctly, you must confirm that the arrow is consistent with the actual pipe flow direction before installation.
In addition, the nuts on the tie rods are in a pre-tensioned state when they leave the factory. In order to protect the bellows from being stretched or compressed during transportation, the manufacturer will adjust a fixed position. Don't loosen it in advance, and adjust it according to the drawings when the hoisting is in place.
Second, bracket arrangement is the real technical activity
Many people think that the expansion joint is a flexible joint, and it is finished by welding it. And the result? Once the pipe heats up, the bellows are either jacked to death or pulled apart. The problem is with the bracket arrangement. Both sides of the flue expansion joint must be setFixed bracketAnd in the middleguide bracketEnsure that the displacement only goes in the design direction.
Used by a cement plantMetal Corrugated Expansion Joints in Cement IndustryNo guide brackets were installed at both ends, and the thermal expansion twisted the bellows into a twist, which was scrapped in two months. The strength of the fixed bracket should be able to withstand the pressure thrust of the pipeline. The expansion joint itself does not bear this force, it is only responsible for absorbing displacement. Don't let the expansion joint carry it on its own, it can't carry it.
3. Hoisting alignment and welding sequence
Never use wire rope to directly strangle the corrugated part when hoisting. When the wire rope is strangled, the corrugation is deformed, the local stress is concentrated, and the life is directly discounted. The correct way is to hold the end tube with a sling and lift it smoothly. The gap between counterparts should be uniform, generally controlled at 2~4mm, too big or too small.
Weld one end first and naturally cool to room temperature before welding the other end. Both sides are welded simultaneously or continuously, and the thermal stress will deform the bellows. If it is a flange connection, tighten it symmetrically with a torque wrench, and the sealing gasket should be temperature-resistant and corrosion-resistant-non-metallic expansion joints are usually equipped with fluorine rubber pads, so don't use ordinary asbestos pads for cheap. Don't rush to remove the tie rod after welding, wait until the pipeline system is completely fixed.
4. Cold tightening amount and tie rod adjustment
The operating temperature of the flue is always several hundred degrees Celsius, and the thermal expansion of the pipe is very large. Therefore, when leaving the factory, the expansion joint often hasPre-stretchingOrPre-compressionThis value is called cold tightness. The tie rod nuts must be adjusted according to the values specified in the design drawings during installation. Tighten the locking nut after adjustment to prevent loosening.
After the system heats up to the design temperature, the transport rod needs to be removed. How to dismantle it specifically? This site has a special question and answer "Does the screw of the expansion joint need to be disassembled", which is very clear. Anyway, remember: without removing the tie rod, the bellows can't expand and contract freely, and the pressure is all held on the corrugation, which will bulge soon.
V. Post-installation acceptance and common pits
An airtightness test must be done before smoking. Focus on checking the weld and flange surface, and use soapy water or leak detector. During trial operation, observe whether the displacement is smooth, and stick your ear to the pipe to listen to any abnormal noise. If it is found that one side of the expansion joint is bulging and the other side is overstretched, 80% of it is that the guide bracket is stuck or the tie rod is not adjusted in place.
Expansion joints near desulfurization flue gas baffle doors are particularly prone to corrosion. Wet flue gas contains sulfuric acid and sulfurous acid, and the corrosion rate is several times faster than dry flue gas. SoDesulfurization flue gas baffle doorThe matching expansion joint must be checked to see if the anti-corrosion coating is intact. Even if a small piece of the coating falls off, it can be pierced in half a year.
Install this work, the details make or break. The drawings do not match the actual object? Then stop and ask, don't push it. Find a reliable manufacturer (such as us), and do a thorough technical briefing, which will be much less worried later.