Consider a Pipe 6" NPS, MOC A106 Gr.B SMLS appearing against various services on a line list. If we compare the pressures and temperatures then invariably the highest design temperature for any given service will not have the highest design pressure. On the other hand the highest design pressure for some other service may not have the the highest design temperature. If we need to calculate a single pipe thk that should satisfy all the conditions then how do we identify the worst condition?

A detail engineering project is under way to double the facility and we are re validating the design parameters.

A look at the attachment would put up my question even better. On the spread sheet, all 6" Pipes & A106 Gr.B Material Of Construction(MOC) are filtered out as an example. Fluid compatibility with A106 is verified. We have few process services, rest are steam and other utilities. The point is we just need to design based on the pressure temperature data.

Also, the data is that of an existing plant where common pipe thickness of Sch80 for size 1/2 to 1.1/2" and Std Wt for 2" and above sizes of pipes, for various specs of 150# and 300# are in use.

Now if we were to calculate a single pipe thk that should satisfy all the conditions then how do we identify the worst condition out of this lot?

Considering the highest temp and highest pressure from different services would not be wise as it would push the system unnecessarily into a higher rating, so it would be over designed (I suppose).

Is there a thumb rule for the same? Or any specific method as per ASME B 31.3?

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