The "Three Highs" Problem of Dry Coke Quenching Condition: Why is the Metal Compensator Easy to "Roll Over"?
What goes on in the dry quenching pipeline? High-temperature coke, high-concentration dust, and violently fluctuating pressure-to put it bluntly, they are the three mountains of "high temperature, high pressure and high wear". Think about it, a metal corrugated expansion joint is inserted, and the bellows wall is only a few millimeters thick. The coke powder particles rush over like bullets, and it will wear through the trough in a few months. Not to mention that metal fatigue cracking is common when the temperature rises.
Two days ago, I met a customer who said that the average life of the metal compensator in their factory was less than half a year, and it was changed three times. The removed pipe wall looked like a sieve. Tsk, there are a lot of people stepping on this pit. Metal expansion joints work well on conventional steam pipelines, but in dry quenching conditions, high-temperature oxidation and particle erosion make metal unable to bear it at all. You say replace it with non-metallic? By the way, that's the right answer.
Structural disassembly of non-metallic high temperature compensator: fabric fiber layer, thermal insulation layer and sealing layer perform their respective functions
Dry-quenching non-metallic high-temperature compensator, to put it bluntly, is a multilayer composite structure. The outermost layer is a fabric fiber layer, generally with high-temperature resistant silicone cloth or fluororubber cloth, which is responsible for anti-wear and sealing; The middle is an insulation layer, with ceramic fiber blanket or glass wool, with a thickness of tens of millimeters, to keep the heat out of the pipe; The innermost layer is a guide tube (mostly made of stainless steel), which guides the airflow to reduce vortex wear.
What is the temperature resistance limit? Let's put it this way, the conventional non-metallic expansion joint (fabric fiber expansion joint) can carry above 1000℃, but the actual pipe wall temperature under dry quenching is only 500 to 600 degrees, and the margin is sufficient. Unlike metal expansion joints, expensive alloy materials have to be used as soon as the temperature exceeds 500℃. Not to mention that the cost doubles, it is still easy to have problems. But remember-the temperature resistance rating is only the basis, and the following selection parameters are the key.
Key parameters of model selection: temperature gradient, pressure fluctuation, installation space
Don't just look at the maximum temperature resistance figure. The temperature gradient of the dry quenching pipeline is the invisible killer. For example, when the temperature rises rapidly from normal temperature to 800℃, the metal compensator will bulge due to uneven thermal stress. Although the non-metal compensator has good flexibility, if the insulation layer is not properly designed, the surface temperature can still burn people to death. What about that? When selecting the type, be sure to provide the actual operating temperature curve of the pipeline, don't only give a peak value.
Pressure fluctuations also need to be figured out. Dry quenching systems often have positive and negative pressures alternating, and the rigid frame of the non-metallic compensator must be able to resist negative pressure instability. In order to save costs, some manufacturers use thin plates for the frame, and as a result, the negative pressure is directly deflated. There is also installation space-dry quenching pipes tend to have a narrow space, and non-metallic compensators can be made into rectangular cross-sections (rectangular non-metallic expansion joints), which save more space than circular ones. However, the stress at the corner of rectangular structure is concentrated, so reinforcing ribs must be added.
What's the worst thing? Many people regard non-metallic expansion joints as a jack-of-all-world, and they choose the same model no matter what working conditions. And the result? Either the material of the guide tube is wrong (for example, ordinary 304 stainless steel can't withstand high-temperature vulcanization corrosion), or the thickness of the thermal insulation layer is not enough, which leads to overheating and deformation of the external metal frame. Anyone who has stepped on these pits knows.
Installation and Maintenance Records: Summary of Common Errors
Do you want to adjust the tie rod nut? Many masters think that the tie rod is load-bearing. In fact, the tie rod of non-metallic compensator is only temporarily fixed for transportation. Once installed in place, the nut must be loosened to allow the compensator to expand and contract freely. If you don't release it, it's no different from a rigid connection.
Should the screw be disassembled? The transport screw is to prevent deformation during transportation, and the installation must be removed! Someone forgot to dismantle it. After driving, the pipe heat expanded, and the screw directly pulled the compensator apart.
And what happens if the guide tube is installed backwards? The function of the guide tube is to guide the air flow and protect the non-metallic layer. In the reverse direction, the airflow directly impacts the fabric layer and wears out in a few days. Remember: the arrow of the guide tube points in the direction of the airflow, which is clearly stated in the question and answer on the specific role of the expansion joint guide tube. The direction of the arrow of the expansion joint points to the direction of the medium flow, so don't install it backwards.
In addition, the adjustment method of the tie rod of the expansion joint is also very critical-the tie rod of the non-metallic compensator usually has no adjustment function, so it is loosened first, and then it is decided whether to keep the limit nut according to the actual displacement. For details, you can see the question and answer of "How to adjust the tie rod nut of the expansion joint" in our station.
Dry Quenching vs Other High Temperature Pipes: Why is the Non-Metal Scheme More Worry-Free Than the Metal Corrugated Expansion Joint?
Calculate an economic account. A DN800 metal corrugated expansion joint is made of high-temperature resistant alloy (such as Incoloy 800), with a starting price of 20,000 yuan and a life of half a year. What about non-metallic high temperature compensators (non-metallic expansion joints)? Early over 10,000, with a lifespan of more than two years. Moreover, the replacement cycle of non-metals is longer and the downtime loss is less. More importantly, metal corrugated expansion joints are prone to stress corrosion cracking under dry coke quenching conditions, but non-metal joints have no such problem at all.
Of course, non-metallic compensators also have shortcomings: their pressure capacity is not as good as that of metals. However, the pressure of dry quenching pipeline generally does not exceed 0.1MPa, and non-metals are completely sufficient. Compared with the metal corrugated expansion joint, the non-metal scheme is dominant in wear resistance, high temperature resistance and corrosion resistance. If you calculate the total cost for three years, you can save more than one third by choosing non-metals.
Therefore, select a compensator for dry quenching pipeline, and stop staring at the metal. Dry quenching non-metallic high temperature compensator is the optimal solution for this working condition. But remember: don't just look at the temperature resistance grade, temperature gradient, pressure fluctuation, guide tube direction, tie rod nut treatment-every detail is related to how long it can last. We have rectangular non-metallic expansion joints and round non-metallic expansion joints in various specifications on our station. Choose according to the actual parameters, don't pat your head.