12.5% under tolerance

[svi]

Ref:

http://www.eng-tips.com/viewthread.cfm?qid=157136

ASME B31.3 Appendix S shows an example of evaluating the thickness required for pipes.

T = t + c

A wall thick is selected from the pipe table and multiplied 0.875 the resuting thk is compared with the above T.

How can this method be different to another conventional method of finding the value corresponding to (t + c)/0.875 and then selecting the next higher thk schedule from the pipe thickness table.

Is there anything implied by code in this example shown in appendix S that it should be method to be adopted in a standard pipe wall thickness calculation?

Unconnected to the above point but related to Appendix S, it also says under para 'design conditions in the appendix S,

"For example, ASME B16.5 requires a minimum
of Class 300 for ASTM A 105 flanges"

Is there such a reference in B16.5? What does this mean?

 

[DSB123]

svi,
The first method is correct. In the second method you could have the situation were the (pressure thickness plus corrosion) is greater than the nominal pipe thickness less mill tolerance BUT because you are dividing (t + c) by 0.875 and then comparing to the nominal thickness all will look OK, however if you did the calc the first way and multiplied the nominal thickness by 0.875 the the result could be under t+c. Try it out for yourself!!!

 

[svi]

If I am picking a schedule with a thickness that is higher than (t + c)/0.875, then Tnom * 0.875 cannot be less than t + c. I think it does not have any implied meaning for the Appendix S method?