Find out these three things before you start: selection, end face and direction
Many people get the expansion joint and go directly to the pipeline. As a result, they find air leakage, displacement, and even pull the bellows after installation. Don't worry, let's take five minutes to figure out three things out.
First, the choice should be correct.Are you going to connect a steam pipe, a flue gas pipe, or a pipe with a corrosive medium? Is the pressure high or not? What's the temperature? For example, in high temperature and high pressure situations, choose honestlyHigh temperature axial expansion jointOrExternal pressure single axial expansion jointDon't make do with a general-purpose corrugated expansion joint for cheap. Media corrosive? That's upPTFE-lined hoseOrPTFE compensator。 If you want to lay it in the ground, just lookDirect buried (fully buried) type expansion joint— — It comes with its own protective cover, so there is no need to do extra anti-corrosion.
Second, check the end face.The end faces of pipe joints must be flat, burr-free and rust-free. The flange connection also depends on whether the flange surface has bumps and whether the sealing groove is clean. And guess what? Two days ago, there was a customer who didn't find a small pit on the flange surface. After installation, it began to seep water when it was halfway pressed. Later, it was disassembled and repolished. Working all morning for nothing.
Third, look in the direction.There are generally arrows or marks on the expansion joints to tell you the direction of the medium flow. Some models likeCorrugated expansion joint for power station industryWith a guide tube inside, if the direction is reversed, the guide tube will become a resistance piece, and the bellows will be washed, and the life will be directly folded in half. Don't know how to argue? Refer to the article "The direction of the arrow of the expansion joint refers to" in our station, which is very thorough.
Flange connection: 90% of the occasions use it, follow these 5 steps to be sure
Flange connection is the most mainstream connection method. Universal corrugated expansion joint, rubber compensator and non-metallic expansion joint are all standard flanges. If you follow the following 5 steps, you will basically not roll over.
Step 1: Flange alignment.Lift the expansion joint to the installation position and align the flange hole with the bolt hole of the pipe flange. Caution – don't deadlift with brute force! If the deviation exceeds 1mm, you have to adjust the pipe support or level it with a gasket. Twisting the bolts hard will twist the bellows and hurt it internally before it can be used.
Step 2: Install the gasket.Select the gasket to see the medium and temperature. Rubber pads for cold water pipes, metal winding pads for steam pipes, and PTFE pads on corrosive media. The gasket should be placed in the center, not blocking the media flow channel. Tip: Apply a thin layer of sealant on both sides of the gasket to prevent micro-infiltration.
Step 3: Thread the bolts and pre-tighten diagonally.The bolt goes through the inside of the flange and the nut is on the outside. First screw it by hand until it sticks tightly, then use a wrench in diagonal order-for example, a four-hole flange, the order is 1-3-2-4; Eight-hole flange, press cross. The preload force is controlled at about 60% of the design torque, so don't die once.
Step 4: Tighten to the specified torque in portions.Split into two or three wheels with 20% more torque per wheel. Notice,rubber compensatorAndRectangular non-metallic expansion jointThe torque of this kind of flexible flange should not be too large, otherwise it will deform the edge of the flange. See the product manual for the specific torque value, don't feel it by your hands.
Step 5: Check the gap.After all the bolts are tightened, check the clearance around the flange with a gauge, and the maximum error shall not exceed 0.5mm. If one side is loose and the other is tight, it means that the flange surface is uneven or the expansion joint itself is crooked, so you have to do it again.
Welding Joints: Hardcore Operations for High Temperature and High Pressure Scenarios
Welding is mainly used in large diameter, high temperature and high pressure occasions, such as the main steam pipeline of power plants and the kiln tail pipeline of cement plants. Common welding models areLarge diameter thick wall expansion joint、Double hinge expansion joint for air-cooled island vacuum pipeline、Compound hinge transverse expansion jointEtc.
Before welding, the grooves at both ends of the expansion joint and the pipe grooves must be polished clean to expose the metallic luster. The groove angle is generally 30°-35°, leaving a 2mm blunt edge. The welding electrode is made of the same material as the base metal, and the stainless steel corrugated pipe must be made of stainless steel welding electrode; Just use J427 for carbon steel pipes.
The welding sequence is particular:Sectional jump welding, each section is welded about 100mm, cooled to room temperature before welding the next section. Never weld to the end in a continuous circle, so the heat will be concentrated, the bellows will be thermally deformed, and the sealing will be directly scrapped.
Immediately after welding, heat insulation and slow cooling, especially stainless steel, otherwise the weld seam is prone to intergranular corrosion. After cooling, do non-destructive testing-radiation or ultrasound to ensure that there are no pores and slag inclusions. By the way, if there are no testing conditions at the site, at least a hydraulic test should be done (which will be talked about later).
Special connections: Installation points of sleeve type, direct burial type and non-metallic expansion joints
These three kinds of expansion joints are relatively unpopular, but you have to know them when you encounter them.
Sleeve type pipe expansion joint
The sliding surface of the sleeve should be coated with grease, generally using lithium molybdenum disulfide-based grease. After the outer sleeve and the pipe are welded, the inner sleeve should leave half of the designed displacement, and cannot be pushed to the head. In addition, the sleeve type is generally equipped with a guide bracket, which must be set at 4 times the pipe diameter on both sides of the expansion joint, otherwise it will be stuck.
Direct buried (fully buried) type expansion joint
The buried expansion joint directly contacts the soil, and anti-corrosion is the vital gate. Before installation, check whether the outer protective layer is damaged and whether the bellows part is tightly wrapped. When backfilling, fine sand should be used, layered and compacted, and there should be no stones. If you encounter groundwater, you have to make a drainage ditch or set up a sump. The one in our stationDirect buried (fully buried) type expansion jointIt comes with anti-corrosion coating and waterproof end cap, but the joint still needs to be heat-shrink sleeve or cold-wrapped tape on site.
Non-metallic expansion joint (fabric fiber expansion joint)
Non-metallic expansion joints are resistant to high temperatures and corrosion, but have low strength. The flange bolts should not be tightened too tightly during installation, otherwise the flange will be crushed. Its flange surface is soft, and the gasket can be rubber cushion or no gasket (see the manufacturer's requirements). Note: The non-metallic expansion joint cannot withstand axial thrust, so fixed brackets must be set at both ends of the pipe to digest the thrust away, otherwise it will be pulled and cracked.
Don't go in a hurry after installation: Tie rod adjustment and pressure test check
Installing the expansion joint is only the first step, and there are two key actions behind it.
Tie rod adjustment.Many expansion joints come from the factory with tie rods and nuts, such asLarge tie rod expansion joint、Straight pipe pressure balanced expansion joint。 These tie rods are locked when transported and installed to protect the bellows. After installation and pipeline butting, it is necessary to loosen the tie rod nut until the bellows can expand and contract freely. How much looser exactly? Generally, leave a gap of 5-10mm between the tie rod nut and the ear plate. If you don't understand, look through "How to Adjust the Expansion Joint Tie Rod Nut" in our station, with pictures and texts.
Pressure test check.Clean the air in the pipe before pressurising. The test pressure is usually 1.5 times of the design pressure, and the pressure is held for 30 minutes. The pressure drop does not exceed 5%. During pressure test, people should not face the expansion joint to prevent bursting and injuring people. Focus on checking flange surfaces, welds, bellows troughs – these are the places most prone to leaks. If water seepage is found, re-tighten the bolts or repair welds after pressure relief.
Pits stepped on by old drivers: 6 common mistakes in expansion joint connections
Tell me a few blood and tear lessons, and you can avoid detours after seeing them.
- Error 1: Use the expansion joint directly as the pipeline compensator, and forget to set the fixed bracket.The expansion joint can only absorb displacement and cannot withstand pipe thrust. Without fixing brackets, the whole line will twist like a snake. EspeciallySingle-axis double-flapper doorFixing brackets must be in place before and after such equipment.
- Mistake 2: The flange bolt was tightened too tightly and crushed the bellows.Some people feel that the tighter the better, and as a result, the flange deforms, the bellows wave pitch is elongated, and the fatigue life plummets.
- Mistake 3: There was no protection during welding, and the splash burned through the bellows.Cover the bellows part with asbestos cloth before welding, and clean the welding slag after welding.
- Mistake 4: Use large stones when backfilling with directly buried expansion joints.The earth and stone directly hit the protective layer and cracked, and after two years, it will corrode and perforate.
- Error 5: The non-metallic expansion joint is installed in the horizontal section of high temperature pipe, neglecting drainage.The internal water is bubbled for a long time, and the fabric layer is rot. Drainage outlets must be provided or the installation direction must be sloped.
- Mistake 6: Forgot to remove the transport tie rod.This is the silly one, but someone has done it. The tie rod is not loose, and the expansion joint is equivalent to a rigid connection. The thermal expansion and contraction of the pipeline directly pulls the pipeline bracket, and finally the bracket is bent.
Okay, how to connect the expansion joint to the pipe? These four methods are enough for you. If you are still unsure, flip through the installation instructions of each product in our station, or ask the technician directly. It's better to take a second look before you start, rather than rework it after installation. Do you think that's the case?