Operating temperature of composite panels
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Looking at the questions and answers regarding pressure vessels, Secretary Shou replied as follows: “The maximum operating temperature for composite plates is 400 degrees, while the maximum operating temperature for surfacing structures should depend on the operating temperature range of the base material of that equipment.” He also said that “since the base layer and the overlay layer of composite plates are bonded together physically, they are far inferior to surfacing structures in terms of safety and service life.” I have a question: The maximum operating temperature for surfacing structures depends on the operating temperature range of the base material； So how was the 400-degree value for that composite panel determined?
The new standard has eliminated the reference to 400 degrees.
Thank you for the reply from above. What I was thinking is: could it be that when the temperature is high, the linear expansion coefficients of the stainless steel composite layer and the base layer differ, which makes it easy for the joint to separate?； The bond at the surfacing layer is formed through atomic bonding, so it’s not as easy for that layer to come loose. However, according to the standards, the minimum required shear strength for the bond between the composite plate and the surfacing layer is the same. I’m confused – can any expert provide an answer? Thank you!
1. It is necessary to consider the maximum operating temperatures for base metals and clad materials; for example, carbon steel and carbon-manganese steel tend to graphitize at certain temperatures, while austenitic stainless steels become sensitive within a specific temperature range, which leads to a decrease in their strength and resistance to internal corrosion. 2. The bonding condition and properties of the interface between the base layer and the overlay layer deteriorate at high temperatures. 3. Thermal stress caused by temperature differences can also lead to a deterioration in the bonding state and properties.
Thank you for the reply from above. Is it true that the latter two situations do not occur in case of surfacing? So, as long as the base layer can withstand the temperature, there is no problem with surfacing； And composite boards don’t work?
Another perspective: at high temperatures, the difference in thermal expansion coefficients between the base layer and the overlay layer leads to excessive shear stress at the interface. For example, in composite plates made of austenitic stainless steel and low-alloy steel such as Q345R, the theoretical shear stress resulting from this expansion difference at 350 degrees Celsius is 231.7 Mpa, which exceeds the allowable value of 210 Mpa; hence, there is a safety risk.
I have another question: after explosive compounding, is it necessary to carry out performance-restoring heat treatment? What exactly is the metal layer on that composite interface? Based on the metallographic photographs, grain growth is indeed observed at 100 um in some interfaces. But does grain growth here mean that this portion of metal is in a cast state and requires heat treatment to restore its properties? For composite panels made of certain materials, it is not that easy to restore their performance once again.
At 400°C, the graphitization tendency of the carbide phases in steel needs to be considered when carbon steel and carbon-manganese steel are used for extended periods at temperatures above 425°C. Since the base material of your composite plate is carbon-manganese steel, the temperature cannot exceed 400°C. If your medium requires corrosion resistance, the operating temperature must not fall within the sensitization range of austenitic stainless steels; the sensitization temperature range for austenitic stainless steels is 400–850°C. I hope this can help you.