The "hard flaw" of compressor pipe: thermal expansion, contraction and vibration, why can't it be carried hard?
As soon as the compressor was turned on, the pipe was winding up-the high-temperature gas rushed over, the temperature of the pipe jumped up, and when it cooled down, it retracted. The range of thermal expansion and contraction, a pipe hundreds of millimeters long, can be casually different by more than ten millimeters. Coupled with the vibration and airflow pulsation of the compressor itself, the pipeline is "shaking its legs" every day. Why don't you try it hard? I've seen no fewer than ten accidents of flange bolts, cracked welds, and even overall displacement of pipes. Two days ago, a buddy from a chemical factory told me that they didn't install expansion joints. As a result, the compressor outlet pipeline cracked twice in three months, and the loss from production shutdown was enough to buy dozens of expansion joints. Therefore, don't compete with the laws of physics, you have to pretend when you need to.
The "hard core" ability of stainless steel expansion joint: how to calculate the material, corrugated structure, pressure and temperature resistance?
The reason why the compressor metal stainless steel expansion joint is standard is the corrosion resistance and high temperature resistance of stainless steel. Brands like 304 and 316L will not rust out quickly in the environment of compressor oil mist and water vapor. Corrugated structure is key-one corrugation is equivalent to a spring, and multiple corrugations stacked together can absorb large axial displacement. How to calculate pressure and temperature resistance? Simply put, the design pressure should be multiplied by the safety factor of 1.5 times. If the temperature exceeds 400℃, you have to consider using superalloy. For example, the "high-temperature axial expansion joint" of this station is specially designed to deal with the high-temperature and high-pressure working conditions at the compressor outlet. When selecting the specific type, you should also look at the parameters of the number of corrugated layers, wall thickness and wave height, not just the nominal diameter.
Guide to selection and pit avoidance: general type, high-temperature axial type, pressure balance type, who should I choose?
There are many models of expansion joints on the market, but for compressor pipelines, there are three main categories:
Universal corrugated expansion joint: Suitable for low temperature, low pressure and small displacement. For example, the air inlet pipe of the compressor, the temperature difference is within 50℃, and the general type is enough.
High temperature axial expansion joint: The compressor outlet temperature is always above 200℃, and the general-purpose type can't bear it, so you have to use this. The design temperature of the "high-temperature axial expansion joint" of this station can reach 600℃, and the pressure resistance grade is also high.
Pressure balanced expansion joint: When the pressure in the pipeline is high and there is blind plate force, such as a valve or diameter reduction at the outlet of the compressor, the ordinary expansion joint will be pushed open by pressure, so it is necessary to use "straight pipe pressure balance expansion joint" or "curved pipe pressure balance expansion joint", which balance the blind plate force with a tie rod or ring plate to prevent the pipeline from displacing.
Don't ask "which is the best", it depends on the working conditions. If you take the general-purpose type to top the high temperature and high pressure, it will bulge in three months, and it will be more expensive to replace it.
Installation and maintenance: Screw disassembly or not? Does the deflector fit or not? How to adjust the tie rod nut?
Is the transport screw disassembled or not? Remember that the adjustment screw (that is, the transport fixing bolt) must be loosened or removed before installation, otherwise the expansion joint will not be able to expand and contract freely, which is equivalent to a free installation. Second question: Will the deflector be installed? If the flow rate of the medium in the tube is high or there are particles (such as compressed air with water droplets), a guide tube must be installed-as specifically mentioned in the Q&A of this site, "the specific function of the guide tube of the expansion joint" is to protect the bellows from being washed and worn by high-speed medium. Third question: How to adjust the tie rod nut? The role of the tie rod is to prevent the expansion joint from over-stretching or compressing. During installation, according to the design displacement, adjust the nut to the corresponding position, and do not lock it. Specific method: First, let the expansion joint be at a free length, then make the pipe cold tight or pre-stretch, and then tighten the outer nut to leave a thermal expansion margin. I've seen workers weld the tie rod to death directly, which is just like not installing the expansion joint. Sooner or later, something will happen.
Comparison in the same field: metal stainless steel expansion joint vs non-metal compensator vs sleeve compensator, who is more suitable for compressor?
Let's have a "tournament".
Metal stainless steel expansion joint: High pressure resistance, high temperature resistance, good seal, suitable for such high-demand occasions as compressor. The disadvantage is that it requires high installation accuracy and cannot bear excessive torque.
Non-Metallic Compensator (Fabric Fiber Expansion Joint): It is cheap, light in weight, and can absorb multi-dimensional displacement, but it has poor pressure resistance. It is generally only used for low-pressure smoke ducts. The pressure of compressor pipes is often above 1.6MPa, and non-metals can't bear it at all.
Sleeve type pipe expansion joint: Also called sleeve compensator, it is sealed by packing and can absorb axial displacement, but it has a high risk of leakage and can't withstand radial vibration. The compressor pipe vibrates heavily, and the sleeve will leak soon after it is used.
Conclusion: Metal stainless steel expansion joint is preferred for compressor pipe! The specific model is selected from "general corrugated expansion joint", "high temperature axial expansion joint" and "straight pipe pressure balance expansion joint" according to the temperature, pressure and displacement type. Don't choose non-metal or sleeve cheaply, which saves the purchase cost and loses the maintenance cost, which is not cost-effective.