Dual Dimensions on a Section VIII Div 1 Vessel

[ShwaZmoto]

I'm sub-vending some metric vessels for a project in Canada and can't quite remember the rules regarding dimensions and units. If I remember correctly, the use of dual dimensions on shop drawings and/or in calculations is prohibited by ASME Section VIII Division 1, correct?

Also, since these are metric vessels, the pipe should be specified by the nomial DN sized and not NPS, correct? For example, the nozzle schedule would show DN 100 mm Schedule 40 instead of NPS 4" Schedule 40.

Thanks in advance for your responses.

 

[vesselfab]

NO the ASME does not prohibit this.

It says "may" be in customary units of fabricator.

we call out material as it is on mtr. 4" s/120 is 4" s/120

we put alternate units in brackets and and design data is shown in our customary units with metrics in brackets.

of course this could easily be reversed with metrics show as primary and customary US units in brackets.

Let Autocad (assumption of software) do all the conversions for you. draw it in metrics the set factor for alternate units.

 

[trottiey]

The rules are in U-4 and Appendix GG. "It is acceptable to show alternate units parenthetically."

I don't think there's any explicit rule about using DN on metric drawings. But depending on your inspector, that might fall within the general rule: "In general, it is expected that a single system of units shall be used for all aspects of design except where unfeasible or impractical."

Both DN and NPS are non-dimensional, so they should be written as DN 100 and NPS 4.

 

[ShwaZmoto]

Thanks for the advice. I've never designed vessels for Canada, only the US, and I don't have a copy of Section VIII Div 1 in front of me (I'm not the fabricator). I just remembered that section of the code that states, "it is expected that a single system of units shall be used for all aspects of design except where unfeasible or impractical," and wanted to make sure it's okay for me to ask my vendor to use dual parenthetic units on the shop drawings.