1. Three measures and two cases are not formal-why is this process necessary for the construction of metal expansion joints?
Two days ago, I met a customer. On the project, the metal expansion joint was installed and the pressure was not tested, and the bellows bulged. Party A's supervision turned over the construction plan and found that there was no shadow of "three measures and two cases"-OK, stop work for rectification, and the construction period was directly delayed for two months. Do you say this is wrongful or not?
Many people think that "three measures and two cases" is the paper skill to cope with the inspection. However, old birds who have done pipeline installation know that the metal expansion joint itself absorbs the displacement by the flexible deformation of the bellows-you screw one less tie rod nut when installing, or burn through the guide tube when welding, and later leakage, jamming and stress concentration will all come to your door. Organizational measures, technical measures, safety measures, construction plans and emergency plans, one of these five lacks, that is, gambling on the life of the equipment.
Why do you have to have this process? Because the metal expansion joint is not like ordinary steel pipe, it is pre-deformed when it leaves the factory. For example, the general-purpose corrugated expansion joint is usually pre-stretched or pre-compressed by the manufacturer according to the compensation amount. If you don't check the design drawings during construction, you can directly push it hard, and the actual fatigue life of the bellows may be directly halved. The core of the three measures and two cases is to lock up "who will do it, what to use, how to do it, and what to do if something goes wrong" in advance-this is not a formality, but a life-saving talisman.
2. Organizational measures and technical measures: who will do it, what products to use, and how to get stuck in key processes
Let's start with organizational measures. For metal expansion joint installation, the project manager should appoint a special person to be responsible for technical disclosure and process supervision. Welders must hold a certificate, stainless steel bellows welding should use argon arc welding, and the welding wire grade can't be wrong. These have to be written on paper, on the sign-in form-check back if something goes wrong, and the responsibility is clear.
Do you choose high-temperature axial expansion joint or external pressure single axial type for steam pipeline in power station? Cement material air duct for cement industry metal corrugated expansion joint, wear-resistant coating has been done? The desulfurization flue gas pipeline must be fitted with the desulfurization flue gas baffle door and the non-metal expansion joint, so the metal can't bear the corrosion. You turn through the product list of this site-the general corrugated expansion joint is suitable for low pressure and normal temperature, the double hinge transverse expansion joint is dedicated to absorbing transverse displacement, and the straight pipe pressure balance expansion joint is used in the occasion where the blind plate force needs to be eliminated. Wrong choice, three measures and two cases, no matter how beautiful they are written, will be useless.
How to get stuck in key processes? First, check the product identification plate before installation to confirm that the design compensation direction is consistent with the pipeline displacement direction. Second, pay attention to protecting the bellows when welding, and splashing and scalding are common problems. Third, the adjustment of the tie rod nut-the question and answer of this site specifically said "how to adjust the tie rod nut of the expansion joint". After installation, it should be loosened or tightened according to the pre-deformation amount, not screwed to the end. Fourth, the pressure stabilization time and pressure value must be recorded during pressure test. These process cards are clearly listed one by one in the technical measures, and the construction team leader signs for confirmation.
3. Focus on safety measures: from hoisting to pressure test, the easiest pit to step on when installing metal expansion joints
It is easiest to smash people when hoisting. The weight of metal expansion joints with a diameter exceeding DN500 is not small, especially the large-diameter thick-walled expansion joints, which can easily weigh several hundred kilograms. The hoisting belt should be hit on the hoisting lug or pipe, and it is strictly forbidden to hold the bellows directly-it will deform once it is strangled. And guess what? Some construction maps save trouble with hard bundling of steel wire ropes, and corrugated pipes are directly scrapped.
Safety issues during welding-high temperature slag falls and the surrounding combustible must be cleaned up. The pressure test is even more fatal: the risk of air pressure test is extremely high, in case the bellows bursts and debris splashes. Therefore, the safety measures must stipulate that the pressure test area should pull a warning line, personnel should evacuate to a safe distance, and the pressure gauge should be checked and within the validity period. There is also a small pit: many expansion joints come with "expansion joint guide tube" when they leave the factory, and there should be a gap between the guide tube and the bellows. If the welding nodule blocks the gap, the guide tube may deform and squeeze the bellows during pressure test. This one is easy to ignore.
4. How does the construction plan land? Talking about practical operation in combination with general-purpose type/high-temperature axial type/double-type hinge type
The construction scheme is not copying the template. For example, you get a general-purpose corrugated expansion joint, which usually comes with its own limit rod. Keep the tie rod during installation, and loosen the tie rod nut after all the pipeline systems are in place and the fixed bracket is welded to death-this is called "cold tightening". The high-temperature axial expansion joint is used in the main steam pipeline of the power station. The medium temperature is 500 to 600 degrees. The temperature difference between the ambient temperature and the working temperature during installation is large, and the pre-stretching amount must be accurate to millimeters according to the calculated value of the manufacturer. How to stretch? Use the screw rod and the jack to cooperate, pull in place, lock the nut and then weld the pipes on both sides.
The double hinge transverse expansion joint is more particular. It has two bellows and hinged construction that absorbs only lateral displacement. Install so that the hinge rotation plane is parallel to the pipe displacement direction. Crooked, the hinge stuck, and the bellows broke hard. There are also double hinge expansion joints of air-cooled island vacuum pipelines for air-cooled islands, with an installation height of tens of meters. The aerial work scheme and windproof measures have to be written into the construction scheme. When writing the plan, the installation steps, tool list and inspection standards of each product are written separately-the construction team follows the work, and the supervisor follows the inspection, so there is no mistake.
5. Emergency plan is not copying template: how to respond quickly to common faults (bellows leakage, tie rod stuck)
The most taboo emergency plan is to write "stop work immediately and report to the chief engineer". The emergency response of the metal expansion joint should be specific to the action. For example, bellows leakage: if it is a slight pinhole, the low-pressure pipeline at normal temperature can be temporarily repaired with stainless steel welding electrode, but it must be stopped to reduce pressure; If it is torn in the circumferential direction, if there is no spare part, you can only install a bypass pipe to isolate the leakage section, and then notify the manufacturer for emergency supply. How to deal with a stuck tie rod? First, judge whether the reason for the stuck is thread corrosion or inadequate pre-deformation. Thread corrosion can be dripped with loosening agent and repeatedly twisted with pipe forceps; If the pre-deformation is incorrect, it is necessary to recalculate the compensation amount, loosen the connecting bolts to reset the pipeline and then adjust it. If the tie rod itself is bent and deformed, never knock hard-just replace it with a spare one.
The expansion joint guide tube fell off. High-speed airflow scour, deflector weld crack, debris damage bellows. In the emergency plan, it should be written: abnormal noise or abnormal pressure drop is found, emergency shutdown and pressure stop, disassemble and check the guide tube. For these actions, the more detailed the emergency plan is written, the more efficient the rescue. Don't be fooled by the generic template on the Internet, and it will be wasted when something goes wrong.
6. Closed loop of acceptance and documents: After the implementation of three measures and two cases, how can you prove that you are right?
The last step, acceptance. Three measures and two cases are not finished, but have to have signatures, photos and data. Sign-in forms for organizational measures, key process inspection records (welding parameters, tie rod adjustment values, pressure test curves) in technical measures, on-site oaths and monitoring records for safety measures-all filed. After the metal expansion joint is installed, the supervisor should check item by item: Is the product model consistent with the design? Does the compensation direction arrow coincide with the pipe displacement direction? In the FAQ of this site, I asked "What is the direction of the arrow of the expansion joint?" The arrow points to the flow direction or displacement direction of the medium, which must be checked. Is the amount of pre-stretch recorded? Fastener moment value All this data goes into the completion data.
In addition, the closed loop of documents also includes product certificate and material certificate. Using these to prove that "three measures and two cases" is not a formality-what has been done, what evidence has been left, and there is a starting point for future maintenance, investigation and accountability. In the final analysis, the installation of metal expansion joints depends on the product and seven on the installation. Three measures and two cases are written in place and implemented well, and the pipeline system will not be bad for ten years; If you fool things, something will go wrong in half a year.