The upper surface of a plate is bolted with ASTM B21 naval brass bolts. The bottom surface of the plate is fully insulated. The upper plate surface is exposed to convection at an air temperature of 50°C and a convection heat transfer coefficient of 5 W/m2•K. Also, thermal radiation exchange occurs between the upper plate surface and the surrounding surface temperature of 300°C. The emissivity of the plate surface and the bolts is 0.3. The ASME Code for Process Piping (ASME B31.3-2014) limits the maximum use temperature of B21 bolts to 149°C. Determine whether the ASTM B21 bolts on the plate comply with the ASME code.

Question

Answer 1

A series of ASTM B21 naval brass bolts are bolted on the upper surface of a plate. The upper surface is exposed to convection with air and radiation with the surrounding surface. Determine whether the use of the bolts complies with the ASME Code for Process Piping, where 149°C is the maximum use temperature for ASTM B21 bolts.

Assumptions1 Heat transfer is steady. 2 Kirchhoff’s law is applicable. 3 Surrounding surface is treated as blackbody. 4 Uniform surface temperature at the upper plate surface. 5 The temperature of the bolts is equal to the upper plate surface temperature.

Properties The emissivity of the plate and bolts is given as 0.3.



Analysis Since the bottom surface is well-insulated, heat transfer occurs at the upper surface only. From surface energy balance, we have



Assuming the temperature of the bolts is equal to the upper surface temperature of the plate,



Solving for Ts yields



Discussion The temperature of the bolts exceeds the maximum use temperature by 149°C. The use of the ASTM B21 bolts under these conditions does not comply with the ASME Code for Process Piping (ASME B31.3-2014). Another type of bolts should be considered for use under these conditions. For example, the ASTM A193 B8M steel bolts have a maximum use temperature of 538°C.