B Factor in chart

[leedrong]

When external pressure calculation of tubes ,matrial
SA213Gr.T1 and design temperature is 1004 F .
To read B Factor from the chart , the exteranl pressure chart limit value is up to 900 F .
How can we take value of factor B ?

And how about yield strenth value limit ?
there listed only under 1000F in code.

 

[Christine74]

You cannot extrapolate the values shown in those charts for higher temperatures.

See UG-20(c).

 

[GenB]

If not in the tables, you may need to calculate the whole thing or you may not be allowed to use the material for external design pressure at those temp and pressure,
the vessel/pipe will just collapse on external pressure,
a lot of materials barely make it on internal pressure at hi-temp.
ER

 

[jte]

leedrong-

You weren't too specific in your application and the previous responses assume a Section VIII application in which case I mostly agree with their responses. If your design temperature is 1004°F and you are concerned about using allowable tensile stresses limited to 1000°F then you need a quick study in significant figures and engineering judgement: I'll just bet that the 1004°F (4 sig. figs) value is actually derived from a nice round 540°C (2 sig. figs). In other words, consider the design temperature 5.4*10^2 °C or 1.0*10^3 °F and you're fine.

However... you are talking about tubes at high temperatures, and that makes me think that you are looking at fired heater tubing such as the coils in a coker furnace. In this case, the design is not Section VIII, but API 530. I didn't find SA213-T1 in IID (I'm sure it's there; just didn't look enough) but if its a C-½Mo material then API 530 will allow you to use it up to 1100°F and 1325°F for limited durations.

External pressure on tubes is usually a joke. Run the numbers on a 5" tube 0.1" thick (L/Do>10, Do/t = 50 so A ~ 0.0005). Use Young's modulus (~20e6)instead of temperature to enter the curves in Fig. CS-2 and you'll find that the allowable external pressure (at 1000°F)is around 100 psi. You can check this result using VIII-1 UG-28(c) Step 7.

jt

 

[leedrong]

Many thanks everyone for your input.
We are talking with client to use MDMT for design and also
Asking to ASME whether they give us B Factor from the committee.