For a typical line stop in one uninsulated hot piping, what could be the allowable shear stress for the following parameters:

applicable code - B 31.3
structural steel for line stop - A 36M
pipe flexibility temperature - 300 C

As the structural steel for line stop is placed below shoe, can we take temperature as ambient for this while considering the allowable stress in shear (0.8 times that in tension as per B 31.3) ?

Is this approach right or can we take AISC stress allowable at ambient temperature (say 0.4 * Yield stress) ?

regards,

sam

Q1:"As the structural steel for line stop is placed below shoe, can we take temperature as ambient for this.... ?"

A1: No because you know that the steel will be hotter than ambient use the rule of thumb of -100Deg F / Inch of exposed metal to calculate what the heat would be at the weld then adjust your calcs if req'd for that temperature (it may be low enough so that the S value is moot)

Q2:" considering the allowable stress in shear (0.8 times that in tension as per B 31.3) ?"

A2: Yes

Q3:"Is this approach right or can we take AISC stress allowable at ambient temperature (say 0.4 * Yield stress) ?"

A3: Maybe see number 1 above....

These are one mans opinion and I'm sure others may have some added insights also Sam I suggest attaching a sketch of what your talking about it would be helpful

Since you are designing according to B31.3, I would suggest using the allowable as specified in that code.

As to the temperature, B31.3 seems to suggest the use of 95% of the design temperature for uninsulated components attached to the pipe. However given your circumstances I think you would be better off doing a heat transfer calc.

Sirs,

It is a typical large bore piping shoe with two structural members attached to shoe to act as linestop at two sides of the beam on which pipe is supported.

A heat transfer calculation can be used to justify a support design temperature considered lower than 95% of design temperature with some convenient ambient temperature & forced convection with a reasonable wind speed figure. Although it may not be ambient, but as Luf-Sir pointed out, it may be low enough to have a reasonable allowable stress for shear.

regards,

sam

Sam,

Are you referring to the design of the particular line stop or the local stress on the pipe due to the attachment?

For the adequacy of the design of the line stop, I would prefer to check the adequacy of the weld size also, based on the procedures outlined in O.W.Blodgett.

Regards

Not regarding the local stress on the pipe, I referred to the line stop design. You are correct that weld size & weld length participating in shear need to checked.

regards,

sam