SA209-moly carbon steels exhibit higher creep than plain carbon steel, and are widely used in the manufacture of high temperature boilers. These steels nominally contain 0.5% molybdenum. In case of exposure to temperatures above 400 ° C -500 ° C for long periods of time, carbon-moly steels are also prone to graphitization. Again, the phenomenon is the section of dependent dimensions, and using the pipe of this degree above 520 ° C is not recommended. The carbide phase is not stable, and graphitization will occur. See ASME Standard and allowable pressure, "Section I", lists allowable stresses for carbon-molybdenum steel up to 520 ° C.
Carbon steel alloyed with Chrome
SA213-T2 This steel alloy has a lower graphitization strength and higher creep resistance than carbon-molybdenum steels. Corrosion resistance is comparable to carbon molybdenum.
Chromium in all alloys stabilizes carbon in the form of chromium carbides, making them immune to graphitization.
SA213-T12 This is a 1-chromium, 1/2-molybdenum alloy, limited to a maximum temperature of 550 ° C,
SA213-T11 This grade has the same creep properties as T12. It is more resistant to corrosion than chromium-carbon steels, and is quite resistant to oxidation at high temperatures, due to its superior silicon and chromium content.
Resistance to oxidation is important, because metals exposed to high temperatures for long periods of time, will accumulate a protective layer and at a certain minimum temperature, this layer will no longer have adhesion and will gradually turn into flakes, causing particle erosion. turbine solids.
Permissible temperature up to 550 ° C
SA213-T22 This chromium 2-1 / 4, a molybdenum alloy has extremely important creep properties, but is limited by applications at 530 ° C, because at a higher temperature it can exfoliate. It is listed in ASME at temperatures of 650 ° C.
SA213-T9 A 9-chromium-molybdenum 1, T9 offers very good corrosion resistance, with good high temperature resistance. It also has good oxidation resistance and can be used for up to 650 ° C. Sometimes T9 is a suitable substitute for grades of stainless steel that are more expensive. lT9 is limited to 650 ° C.
Class Pipes for boilers
Stainless steels - austenitic stainless steel
Austenitic stainless steels are presented in ASME and pressure vessel Code boilers with two sets of allowable stresses. The reason for this is their relatively low yield strength. Higher allowable stress values were determined at temperatures where short-term traction properties would be limited.
Higher voltages exceed 62-1 / 2%, but do not exceed 90% of the flow limit. At these stresses, small amounts of plastic deformation can be expected. These higher stress values are usually used for superheating
The boiler code lists the maximum allowable stresses for different temperatures, depending on the degree of requirement of austenitic stainless steel.
SA213-T304 Variations of this 18 chrome stainless steel, class 8 nickel include 304L, 304LN, 304H and 304N. Each of them offers excellent corrosion resistance and oxidation resistance, along with high strengths the high strengths are maintained at low carbon levels by controlling the nitrogen content.
T304 has superior carbon and a low annealing temperature solution that ensures good long-term resistance to high temperature.
Stainless steel of class T304 are limited to 900 ° C, under oxidizing conditions. Section I of the ASME Boiler Code lists permissible voltages up to 800 ° C.
T316 is similar to T304, but offers better corrosion resistance and creep resistance. T316 stainless steel molybdenum increases hardness, elasticity and corrosion resistance.
Variations of this quality include 316L, 316LN, 316H and 316N.
T347 and T321 and 347 are variations compared to T304 and have comparable minimum traction properties. These two classes are stabilized with titanium additives, together with a suitable heat treatment.
To ensure good power for a long time at high temperatures, the T321H and 347H — such as the 304H — were developed with higher carbon content and the minimum solution specified at the annealing temperature.
Of all stainless steels, T309 (25 chrome, 13 nickel) and T310 (25 chrome, 20 nickel) offer maximum resistance to oxidation and corrosion. They offer