Difference between inches and mm in B31.3
Difference between inches and mm in B31.3
(OP)
Dear Contributors,
I am confused when I see the Table 331.1.1 of B31.3. Thickness range for carbon steel where PWHT gets compulsory is greater than 20mm but in inches its 3/4in which equals 19mm. What to follow? Or it is one and the same thing? Please guide
I am confused when I see the Table 331.1.1 of B31.3. Thickness range for carbon steel where PWHT gets compulsory is greater than 20mm but in inches its 3/4in which equals 19mm. What to follow? Or it is one and the same thing? Please guide





RE: Difference between inches and mm in B31.3
Do you in fact have a pipe with a >= 20mm wall thickness? What is the exact wt you are considering?
RE: Difference between inches and mm in B31.3
RE: Difference between inches and mm in B31.3
ASME B31.3-2012 was approved by the American National National Standards Institute on May 9, 2012.
Hope that helps,
Cheers,
DD
RE: Difference between inches and mm in B31.3
RE: Difference between inches and mm in B31.3
RE: Difference between inches and mm in B31.3
I thought I had given you a reference - copy and paste straight from 2012 edition ????
RE: Difference between inches and mm in B31.3
RE: Difference between inches and mm in B31.3
3/4"is actually 19.05 mm so if you were going to round something off you would presume it would be to the nearest whole number.
I wonder if it was done to clarify PWHT requirements (there are various pipe sizes with 19.05 wall thickness) and in the old B31.3 PWHT was required for greater than/equal to 19 mm ???
Cheers,
DD
RE: Difference between inches and mm in B31.3
RE: Difference between inches and mm in B31.3
First, I'll stay out of the 19mm vs 20mm for PWHT issue... Not my expertise. As I mentioned earlier, I'm more of a vessel guy - so for B31 things may be similar but different.
For vessel design, either SI or US Customary can be used. But only one can be the system of record. In other words, once you choose a system of units to use, you must complete the design using that system. For example, if we had the same PWHT cutoffs at 0.75" and 20mm, I could not choose to use USC as the system of record and calculate a wall thickness of 0.77" and then claim to be exempt from PWHT on the basis of being les than 20mm
I've already mentioned that I like the info in VIII Div. 2; an alternative is VIII Div. 1 Appendix GG which goes through philosophy of conversions with a focus on implied precision of significant digits (e.g. 14.7 psi converts to 101 kPa while 15 psi converts to 100 kPa).
As for what's required in B31.3, perhaps the final paragraph in the Foreword would provide some help:
As for "hard" vs. "soft", see part 1 at http://metricationmatters.com/mm-newsletter-2011-0...