Stainless Steel Pipe Fittings

High Temperature Properties Stainless Steel By yaang.com

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High Temperature Properties Stainless Steel By yaang.com

Stainless steel have good strength and good resistance to corrosion and oxidation at elevated temperatures. Stainless steel are used at temperatures up to 1700° F for stainless steel 304 and stainless steel 316 and up to 2000 F for the high temperature stainless steel grade 309(S) and up to 2100° F for 310(S). Stainless steel is used extensively in heat exchanger, super-heaters, boiler, feed water heaters, valves and main steam lines as well as aircraft and aerospace applications.

Figure 1 gives a broad concept of the hot strength advantages of stainless steel in comparison to low carbon unalloyed steel. Table 1 shows the short term tensile strength and yield strength vs temperature. Table 2 shows the generally accepted temperatures for both intermittent and continuous service.

With time and temperature, changes in metallurgical structure can be expected with any metal. In stainless steel, the changes can be softening, carbide precipitation, or embrittlement. Softening or loss of strength occurs in the 300 series (304, 316, etc.) stainless steel at about 1000° F and at about 900° F for the hardenable 400 (410<, 420, 440) series and 800° F for the non-hardenable 400 (409, 430) series (refer to Table 1).

Carbide precipitation can occur in the 300 series in the temperature range 800 – 1600° F. It can be deterred by choosing a grade designed to prevent carbide precipitation i.e., 347 (Cb added) or 321 (Titanium added). If carbide precipitation does occur, it can be removed by heating above 1900° and cooling quickly.

Hardenable 400 series with greater than 12% chromium as well as the non-hardenable 400 series and the duplex stainless steel are subject to embrittlement when exposed to temperature of 700 – 950° F over an extended period of time. This is sometimes call 885F embrittlement because this is the temperature at which the embrittlement is the most rapid. 885F embrittlement results in low ductility and increased hardness and tensile strength at room temperature, but retains its desirable mechanical properties at operating temperatures.

High-Temperature-Property-Stainless-Steel

Table 1 Short Term Tensile Strength vs Temperature (in the annealed condition except for 410)

Temperature 304 Stainless Steel & TSksi 316 Stainless Steel YSksi 309 Stainless Steel & TSksi 309S Stainless Steel YSksi 310 Stainless Steel & TSksi

310S Stainless Steel YSksi

410* Stainless Steel TSksi
YS
ksi
430 Stainless Steel TSksi
YS
ksi
Room Temp. 84 42 90 45 90 45 110 85 75 50
400°F 82 36 80 38 84 34 108 85 65 38
600°F 77 32 75 36 82 31 102 82 62 36
800°F 74 28 71 34 78 28 92 80 55 35
1000°F 70 26 64 30 70 26 74 70 38 28
1200°F 58 23 53 27 59 25 44 40 22 16
1400°F 34 20 35 20 41 24 10 8
1600°F 24 18 25 20 26 22 5 4

heat treated by oil quenching from 1800° F and tempering at 1200° F

Table 2 Generally Accepted Service Temperatures

Material Intermittent 
Service Temperature
Continuous 
Service Temperature
Austenitic    
304 1600°F (870°C) 1700°F (925°C)
316 1600°F (870°C) 1700°F (925°C)
309 1800°F (980°C) 2000°F (1095°C)
310 1900°F (1035°C) 2100°F (1150°C)
Martensitic    
410 1500°F (815°C) 1300°F (705°C)
420 1350°F (735°C) 1150°F (620°C)
Ferritic    
430 1600°F (870°C) 1500°F (815°C)

It may seem to be illogical that the “continuous” service temperature would be higher than the “intermittent” service temperature for the 300 series grades. The answer is that intermittent service involves “thermal cycling”, which can cause the high temperature scale formed to crack and spall. This occurs because of the difference in the coefficient of expansion between the stainless steel and the scale. As a result of this scaling and cracking, there is a greater deterioration of thesurface than will occur if the temperature is continuous. Therefore the suggested intermittent service temperatures are lower. This is not the case for the 400 series (both ferritic and martensitic grades). The reason for this is not known.

Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)

Article Categories:
Stainless Steel

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