Hello,

Anybody familiar with CSA Z662 code gives me your opinion about conservatism between CSA Z662 and B31.3

Most of my coworkers believe that following B31.3 is more conservative than CSA Z662 just because the allowable stress in B31.3 is lower than the others. For special case, B31.3 and ASME materials are adapted although regulation specifies CSA Z662.

But allowable stress for expansion case in CSAZ662 is 0.72*T*S which might be much less than f*(1.25 Sc+0.25Sh) in B31.3. In the case that common carbon steel pipe Sc = 2/3 S (SMYS) and Sh=Sc up to 100 deg C and f=1, the thermal expansion allowable stress range in B31.3 is 1.083*S greater than 0.72*S (T=1). Actually, B31.3 is using higher allowable stress values for thermal expansion load case.

If I am wrong, please share your opinion!

Thanks,

I don't think it matters that much as usally regulatory requirements require you to meet one code or the other and one is for pipeline and one is plant piping.

As to your question it appears it is possible for B31.3 in some cases to have a larger expansion stress range especialy if you use the 'liberal' stress equation.

But Z662 allowable is based on 2/3rds yield rather then the lower of 1/3 tensile or 2/3rds yeild so your Sc for A106 is 1/3(60ksi) rather than 2/3(35ki)

These are two different codes with different philosophies and Safety factors so it is difficult to say which is more conservative.

Thanks Greg. It is a kind of incorrect Myth.

Let’s take carbon steel for an example. Sy=240 MPa (35kips), Su=415 MPa (60 kips)
B31.3 takes Sc=Sh=138 (1/3 Su) MPa and allowable Sa=206 MPa. CSA Z662 allows Sa = 0.72*Sy = 173 MPa for expansion load case and Sa=Sy=240 MPa for operation load case. B31.3 allowable value of 206 MPa is way bigger than CSA 173 MPa. If liberal stress is allowed, Sa (206MPa) in B31.3 goes high as 340 MPa (just a simple L shape with anchors) which is way high: two times CSA EXP and 1.5 times CSA OPE.

Most people says B31.3 is way conservative than CSA, but I believe it is not.

Thanks,

I missed a factor of 1.5 times when I was replying and I was doing it quickly without referenceing code so after looking back at the code for expansion stress I suppose Z662 is more conservative. Hoop Stress though is a different story. The wall thickness calculation, which sets material cost, is more conservative under B31.3. CSA's calc P=2St/S *FLJT. With Location temperature and joint factors set to 1 and F at .8 your Hoop stress can be a maximum of .8S which is less conservative then B31.3