1. What is a metal rectangular right-angle expansion joint? How is it different from ordinary rectangular expansion joint?
Anyone who has worked in plumbing knows that ordinaryMetal rectangular expansion jointTypically mounted on straight pipe sections, it absorbs axial and transverse displacement. However, where the space turns-for example, the flue and air duct need to turn 90 degrees-the traditional practice is to install two expansion joints and an elbow, which not only takes up space, but it is easy to fight under stress.
Metal rectangular right-angle expansion jointTo put it bluntly, it is to crumple this set of combination punches into a whole. It makes the bellows structure into a right-angle elbow shape, with one end in and one end out, which can not only absorb the axial displacement caused by thermal expansion and contraction of the pipeline, but also handle the lateral deformation in two directions, and even torsion can digest part of it. Compared with ordinary rectangular expansion joints, the biggest difference is that the ordinary one is a "straight bobbin", which is "L-shaped" and usually equipped withguide tubeTo guide the flow direction of the medium and avoid direct flushing of the bellows.
Can't you just use two ordinary expansion joints? Of course, but at the cost of two more flange joints, a bunch of more welds, and doubling the leakage point. The right-angle expansion joint is formed in one piece, and the sealing surface is less than half. For scenes such as high-temperature flue gas and corrosive media, less leakage points are less fathers.
Second, what is the use of right-angle structure in engineering? — — Take a case of flue in a power plant as an example
Helped a 300MW unit deal with flue problems last year. There is a 90-degree turn between the outlet of their boiler and the desulfurization tower. It turns out that there are two boilers installedCorrugated expansion joint for power station industryAdd an ordinary elbow, and within half a year of running, the weld on the outside of the elbow will crack, and it will be stopped twice, resulting in millions of losses.
On-site measurement, the problem lies in the fact that the thermal displacement direction is too complicated: the axial extension of the pipeline is 30mm, the transverse deviation is 8mm, and the elbow itself generates torsional stress. Ordinary expansion joints can only absorb one direction, and the force is all held in the elbow.
Later replaced withMetal rectangular right-angle expansion jointWhen selecting the model, the displacement (±25mm in axial direction and ±10mm in transverse direction) was checked, and the tie rod structure was equipped to limit the excessive blind plate force. It's been three years since I installed it, and I haven't had another leak. The owner's maintenance supervisor said while drinking with me: If I knew this thing, the two sets the year before lastFlue gas baffle doorNor will it be pulled and deformed. Tsk, design institutes sometimes try to save trouble, draw a straight line for the pipeline, and don't care how you install it on the spot.
Third, have you avoided the pits that are easiest to fall into when selecting?
The first pit: ignore the pressure thrust.Because of the structural asymmetry of the right-angle expansion joint, the medium pressure will generate a large blind plate force, which is directed toward the outside of the elbow. If you don't addtie rodOrhingeRestraint, the pipe rack is pushed askew every minute. Many novices calculate according to the parameters of ordinary rectangular expansion joints, but accidents happen as soon as they are suppressed.
Second pit: Install the guide tube in reverse direction.This sounds simple, but 20% of the faults on the site are on this. The guide tube must be facing the direction of media flow, otherwise the airflow will directly rush into the bellows trough, and dust accumulation, wear and vibration will come together. In our stationSpecific Function of Expansion Joint Guide TubeIt was clear in that question and answer that once the trough was worn out, the whole equipment would be wasted.
The third pit: the amount of pre-stretch smacks the head to set.Right-angle expansion joint absorbs displacement in both directions at the same time, and pre-stretching cannot only be counted as axial direction. The correct way is to decompose the resultant displacement into two directions, and then pre-stretch or pre-compress the corresponding corrugated segments respectively. If you only pull one side, the other side may be loaded beyond the allowable value. The problem is inDo you need to remove the screw of the expansion joint、How to adjust the tie rod nut of expansion jointThere are specific operating steps in these questions and answers, so it is recommended to read them before starting.
4. Installation and debugging: tie rod nut, guide tube, pre-stretching, none of them should be careless
Check before installationtie rod nutIs it in factory pre-installed condition. Usually, the manufacturer will leave a few millimeters of adjustment margin, and the site will adjust it according to the actual displacement. Note: The tie rod is not a permanent support. After the pipeline is pressed and the hot operation is stable, the tie rod nut should be loosened to the design gap, otherwise the expansion joint will be locked, which will be useless.
The arrow of the deflector must be consistent with the flow direction of the medium-don't laugh, I have seen some masters look at the sign backwards, and after installing and turning on, they waste one directly. In addition,Pre-stretchingIt is the soul of the right-angle expansion joint. For example: if the operating temperature of the pipe rises from 20℃ to 300℃, the axial expansion is 30mm, and the transverse displacement is 10mm, then the axial bellows should be compressed by 15mm (i.e., pre-stretched by 15mm) and the transverse bellows should be offset by 5mm before installation. The specific value should be calculated according to the stiffness curve provided by the manufacturer, don't rely on feeling.
When welding, be sure to plug the gap between the guide tube and the bellows with asbestos cloth to prevent the welding slag from splashing in and jamming the corrugations. Remove it after welding and clean it up. If you save this step, you will be annoyed to death later.
5. Maintenance and lifespan: Do you think it will be ignored if you install it? That would be wrong
Service life of expansion jointDepends on three things: material, working condition, maintenance. Stainless steel 304 is used in 300℃ flue gas, and the design life is 8~10 years. But if the flue gas contains sulfur and no preservation is done, the trough will become a sieve in three years. It is best to check the bellows surface every six months, and check the trough wall thickness with an ultrasonic thickness gauge. If it is lower than 70% of the design value, it should be ready to be replaced.
The anti-loosening of the tie rod nut is also easy to overlook. The pipeline vibration will shake the nut loose, causing the expansion joint to lose its constraint and exceed the displacement standard. It is recommended to tighten all the nuts once after one month of first operation, and then twist them quarterly.
Wear inspection of deflectors is equally critical – especially dusty smoke. When the wear is serious, the guide tube is perforated, and the dust directly washes the bellows, which will be scrapped in a few months. If a perforation is found, either change the guide tube or add a wear-resistant liner on the outside. Also, don't think that it will be installed once and for all. Regularly check the corrosion of flange sealing surface and bolts. These messes will be dragged out for a long time, and the maintenance cost will double.
One thousand words, one thousand,Metal rectangular right-angle expansion jointIt's a good thing. When used properly, it can save ten years of trouble in the plumbing system. But the premise is to choose the right parameters, install the right direction and maintain it in place. Dealing with equipment, spend an extra minute in the early stage, and you can save ten hours of emergency repair later. Can you settle this account?