ASME B 31.3 and ASME B31.8

[Khalid Hameed]

P= PD/2(SEW+PY) , pipe thickness calculation a/c to ASME B 31.3 , S = allowable stress value for the pipe material
(and)
P=PD/2000SFET , pipe thickness calculation a/c to ASME B 31.8 , S = Specified minimum yield strength of the gas pipeline

what is the difference between S values , used in different formulas?

I am a novice and trying to learn the difference from the masters.

Regards,
Khalid Hameed -Mech

 

[Si-bo]

Not to be rude but it's not a code issue: you are missing the basic knowledge of mechanical engeneering.
Please check the difference between tensile, yield and allowable material stresses.

 

[LittleInch]

Well I don't know where you got those equations, but the first one you are calculating t, thickness of the pipe, not P, Pressure...

Similarly the B 31.8 its t, not P. Be careful in the second one that you use the correct units - P is in kPa

In B 31.3 you obtain the value S from the tables at the back in table A-1, which gives you the value S for each material at different temperatures. This value S is predetermined and is approximately the lower of 0.33 x UTS or 0.66 x SMYS. but it's not precise and you just need to use the figures in the table.

B31.8 just uses the stated SMYS of the material and then modifies that by multiplying various factors, the main one being the design factor which varies from 0.4 to 0.8

 

[Khalid Hameed]

I understand my mistake , thanks for your reply.

 

[Khalid Hameed]

Not to be rude but it's not a code issue: you are missing the basic knowledge of mechanical engeneering.
Please check the difference between tensile, yield and allowable material stresses.

Alright @Si-bo . Thanks for highlighting my mistake.