Imperial vs Metric Pipe etc

[JSPCGY]

Dear Experts,
Is there any difference between imperial vs metric pipe,
Are they 100% exactly the same and fully interchangeable ?
Does Metric pipe actually exist ?
e.g. for A106-B
if I order DN 150 x 10.97mm WT Pipe, will I get NPS 6 x Sch 80 pipe ?

Our normal practice is to use SI units for everything else except for pipe size and stud bolts. I am just wondering why can't we switch the pipe to metric also ?

Thanks for your anticipated reply.

 

[rneill]

Sort answer is yes. DN 150 is the same as NPS 6, which is the same as 168.3 mm OD pipe.

In my specs I reference NPS sizing throughout but provide an equivalency table for NPS to DN to Outside Diameter. No reason you couldn't switch the pipe to DN sizing throughout.

With regards to stud bolts, there I think you have to be careful as I think that Metric sizing is actually different than traditional imperial sizing.

 

[jte]

A-106 and SA-106 pipe is fabricated to ASME B36.10 so yes, they are interchangable. See ASME B36.10M-2004 Table 1: A 6" Sch 80 shares the line with DN150 x 10.97.

jt

 

[kalmari]

"Does Metric pipe actually exist? e.g. for A106-B"

For several specifications is both imperial and metric specifications e.g. A335/A335M. But it is strange that just your example A106 which is adopted to ASME IIA is referring only to imperial unit specification not to metric unit specification. And ordering information of A106/SA106 states using NPS and schedule or O.D. and W.T. but not with DN-size. So at least our AI has advised to state always in the purchase order of SA-106 also the imperial units in addition to SI-units.

 

[jte]

kalmari

The material spec does not get into pipe dimensions. ASME B36.10 does, and yes, DN is included.

jt

 

[11echo]

FYI There IS a dimensional difference in pipe fittings!

 

[rneill]

11echo,

Can you give us an example ? I have not come across that situation before and am wondering if this might be an issue with threaded fittings being made to different standards rather than ASME or API components being ordered metric vs. imperial.

 

[11echo]

rneill ...Your just interested in "threaded" fittings? ...For use with A106-B pipe!??

 

[rneill]

Nope, I have just never seen an issue with butt weld or socket welded fittings having different actual sizes when specified to an ASME or API standard based on being ordered as metric vs. imperial.

If you look at ASME B16.9 "Buttweld Fittings" the metric dimensions shown in the base document are exactly the same as the imperial dimensions shown in Appendix I. Likewise, in ASME B16.11 "Forged Fittings, Socket Welding and Threaded" the metric dimensions in the base document are exactly the same as the imperial dimensions shown in Appendix I. The same holds true for ASME B16.5 (for flanges) and ASME B36.10 (for pipe).

Consequently, there should be no difference for ASME components whether ordered in Metric or Imperial.

My thought was that there tend to be a lot of different standards published by many different organizations for threaded components and perhaps you encountered a situation where you had a "metric" threaded fitting made to one standard that was different from an "imperial" threaded fitting made to another standard from another standards organization.

In another example, instrument tubing and fittings are available both in "true" metric sizing and the old imperial sizing and a 3/8" tube fitting is not the same as a 10 mm tube fitting.

Don't know but in 20 years, I've never encountered an issue with typical ASME and API components.