Why is it necessary to install metal expansion joints on "three measures and two cases"? Don't wait for it to blow up
Two days ago, a friend from a power station project called and said that their steam pipelineHigh temperature axial expansion jointOnly three months into operation, the bellows cracked. After inspection, it was not pre-stretched during installation, and the direction of the guide tube was reversed. You say it's irritating or not? In fact, this kind of accident can be completely avoided through a reliable "three measures and two cases"-organizational measures, technical measures, safety measures plus construction plans and emergency plans. Don't wait until the pipeline blows up and people are injured before remembering to fill up documents. The metal expansion joint looked like an iron lump, but the wall thickness of the bellows was only a few tenths of a millimeter to a few millimeters, and the internal pressure was dozens of kilograms and the temperature was hundreds of degrees. Leaks, instability, and even bursts are not unusual if you are not careful. So, today I'll take this experience apart and crumble it for you to see.
Organizational measures: Who is in charge and what is in charge-the division of responsibilities from project manager to welder
Many projects write "three measures and two cases" into templates, and just copy them once. However, in the installation of metal expansion joints, organizational measures must be implemented to the head. Take a real case: a cement plant installedMetal Corrugated Expansion Joints in Cement IndustryThe project manager only signed it, and no one at the site cared about the pre-stretching data. As a result, the welder pulled by feel, pulled over, and the bellows wrinkled directly.
My suggestion: The project manager is responsible for reviewing and approving materials and coordinating resources; The technical leader (or engineer) is responsible for preparing the technical briefing and checking whether the expansion joint model is consistent with the design drawings-e.g. Compound hinge transverse expansion joint andStraight pipe pressure balanced expansion jointThe installation direction of is completely different; Quality inspectors are responsible for the acceptance of each process, especially flange parallelism and bolt torque; Welders must hold a certificate to work, and the welding process parameters must be signed and confirmed. To put it bluntly, whoever is blamed will take the blame. If something goes wrong, it will be directly traced back to people.
Technical measures: Expansion joint selection and hard fingers of pre-stretching, guide tube and tie rod under different working conditions
Technical measures are the core and the most error-prone link. Speak first:Three measures and two cases of metal expansion jointHow to write technical measures in? Don't stack articles, write data.
Selection:High temperature steam pipeline, such as temperature ≥400℃, pressure ≥2.5MPa, preferredHigh temperature axial expansion jointOrExternal pressure single axial expansion joint。 Flue gas pipelines, such as desulfurization systems, have large temperature fluctuations and are highly corrosive.Non-metallic expansion joint (fabric fiber expansion joint)Orrubber compensatorMore cost-effective. Do not putUniversal corrugated expansion jointWhen used in high-pressure and large-caliber situations, the wall thickness of that thing is not enough.
Pre-stretching:Axial type expansion joints are generally carried with transport rods when they leave the factory. Before installation, the tensile amount should be calculated according to the pipeline design compensation amount-the data should be written in the measures, such as the compensation amount of 50mm and the tensile amount of 40mm. After the stretching is completed, check whether the wave pitch of the bellows is uniform. If it is not uniform, it is deviated.
Guide tube:The function of the guide tube is to reduce the scouring of the bellows by the medium, and at the same time reduce the flow resistance. The installation direction must coincide with the flow direction of the media, and the direction of the arrow is the flow direction. If installed backwards, the deflector will hold the medium, creating vortices and accelerating wear. This has been mentioned in the FAQ, so I won't repeat it.
Tie rod:LikeLarge tie rod expansion jointOrCompound hinge transverse expansion jointThe tie rod is mainly used to restrain the blind plate force. After installation, the nut should be adjusted in place: first loosen the transport nut, and then tighten the working nut according to the design angle or displacement. Don't screw to death, leave an adjustment margin.
Safety Measures: High Temperature, High Pressure, Large Pipeline-Six High Risk Links in the Construction of Metal Expansion Joints
Safety measures are not copying safety operating procedures, but should be aimed at the characteristics of metal expansion joint construction. I summarized six high-risk links:
1. Hoisting operations:Large diameter expansion joints, such asLarge diameter thick wall expansion joint, weighing a few hundred kilograms to a few tons. The lifting point must be selected on the ear plate or the connecting pipe. It is strictly forbidden to directly lift the bellows, otherwise the bellows will be deformed and scrapped.
2. Welding Jobs:When welding the bellows and the connecting pipe, water cooling or filled with protective gas should be adopted to prevent high temperature from burning through the thin wall. Clean the root and preheat it before welding (especially important for stainless steel materials).
3. Flange fastening:The bolts should be tightened diagonally in 3-4 times, and the torque should be according to the design value. For example, the recommended value of M20 bolt torque is 400-450N·m. After tightening, measure the flange clearance, and the deviation shall not exceed 0.5mm.
4. Pressure test:After the installation is completed, a water pressure or air pressure test must be done, and the test pressure should be 1.5 times the design pressure. During the test, keep away from the connection of blind plate and flange to prevent accidental collapse.
5. Operations in high temperature areas:For example, near the boiler of the power station, the ambient temperature is high, so it is necessary to prevent heatstroke and avoid electric shock caused by the damage of the welding machine cable.
6. Crossover jobs:Pipeline installation often crosses with other specialties (steel structure, electrical), so it is necessary to pull a warning line and be supervised by a special person.
Construction plan: From bellows assembly to welding and flange fastening, each step of process control is stuck
The construction plan should be written like a "recipe", and every step can be operated. I'll give you an example, install aCompound straight pipe bypass pressure balanced expansion joint：
The first step, Check the appearance:There are no scratches or pits in the bellows, the guide tube is in the correct position and the tie rod is intact. Measure the total length of the expansion joint, and the error is not allowed to exceed ±5mm.
In the second step, Group pair:Hoist the expansion joint to the reserved position of the pipeline, fix one end by spot welding first, and adjust the coaxiality of the other end. The deviation is controlled within 1mm/m.
The third step, Welding:Adopt argon arc welding base and manual arc welding cover. Welding parameters: current 100-130A, voltage 20-25V, interlayer temperature ≤150℃. The weld should be colored inspection or radiographic sampling.
Step 4, Pre-stretching:Stretch into place according to the data of the technical measure and tighten the nut.
Step 5, Flange fastening:Using a torque wrench, tighten in diagonal order in fractional intervals. Check the sealing face clearance when finished.
Step 6, Removing transport tie rod:Attention! Many workers forget to dismantle it, resulting in the expansion joint being unable to expand and contract freely, and the consequence is that the bellows is cracked. I've stressed this a hundred times.
Emergency Plans: Leaks, Instability, Breaking Bolts-Quick Disposal Logic for Common Failures
Emergency plans are not written for people to see, they can be used in case of an accident. There are three common faults of metal expansion joints:
Leakage:It could be cracked bellows or damaged flange sealing surface. If it is a trace leak, and the medium is non-toxic and non-flammable, the leak can be temporarily plugged with fixtures and sealants, and the shutdown for maintenance can be arranged at the same time. If the leakage is large, immediately cut off the upstream and downstream valves, vent the pipe, and replace the expansion joint. Don't force pressure to plug leaks, the risk is too high.
Instability:Bellows appear bulging or plane instability, mostly due to excessive pressure or deviation of installation. Disposal: Stop the machine and check the pressure gauge to confirm if there is overpressure. If it is a design selection problem, such as usingUniversal corrugated expansion jointHowever, the actual pressure exceeds, and a product with a higher resistance pressure class must be replaced, such asDirect buried (fully buried) type expansion jointOrCurved tube pressure balance expansion joint。
Bolt fracture:Flange bolts are usually broken because of excessive torque or material fatigue. Once discovered, install temporary bolts adjacent to the broken bolts immediately, and then stop the machine to remove and replace them. When replacing, replace all bolts together and re-check the torque.
Another point: the emergency plan should include a list of emergency materials-spare expansion joints, bolts, gaskets, torque wrenches, safety ropes, protective masks, etc. The storage location and the phone number of the person in charge must be clearly written. Don't look for wrenches all over the factory when the day lilies are cold.
Having written so much, to conclude:Three measures and two cases of metal expansion jointIt is not waste paper to cope with inspections, but real skills to save lives and equipment. If you write according to this logic, there will be no mistakes at the scene, the owner will not trouble you, and you can sleep yourself. If you are unsure of anything else, flip through the product page on our site-fromCorrugated expansion joint for power station industryToDesulfurization flue gas baffle doorEach model has technical parameters, so it's always right to write against it.