Fig 323.2.2B ASME B31.3 "Reduction in MDMT Curve"

[RSB1968]

Question:

Has anybody used this curve to get impact exemption below the MDMT of various grades of pipe? Note 3 on page 49 of B31.3 (99 edition)states "Impact testing is not required if the design MDMT is below -20° but above -155°F and the stress ratio defined in fig 323.2.2B does not exceed 0.3 time S"

Looking at using A106 Gr. B on a flare system instead of A333 to save $ and the note above does not make sense when you look at the referenced fig 323.2.2B. Has there been addenda to this section I have the 00 addenda with this figure (page 50.1)

Appreciate your help.

 

[reichertc]

Well, i have not had a chance to sit down and muddle my way through these stress ratios yet, but I did a quick check on the B31.3b-2001 and there were no changes.

That note is very confusing! The way I am reading it, The Stress ratio will always be a small number. (Less than one.) 0.3 times S will always be large. This would mean that when note 3 is applied, impact testing would never have to be done between -155°F and -20°F, regardless of the stress ratios. I do not think this is the intent. If you take out the words "times S" this would make a lot more sense to me.

I have been meaning to familiarize myself with this new addition to the code for quite a while now. I know of one person in my company who has used this section for some new designs. I think I'll do some more research into this and figure out what is going on here...

 

According to the note (3) of ASME B31.3 Table 323.2.2, for example, when the MDMT = -101C (-150F), A335 series pipes, minimum calculated thickness=3mm, nominal used thickness=11mm (corrosion allowance neglected), stress ratio<0.3 are applied, it is not required the Impact Test.

Even if the note (3) of ASME B31.3 Table 323.2.2 [when stress ratio<0.3] and ASME Section VIII Div.1, UCS66(b)(3) [when stress ratio<0.35] permits the exemption from Impact Test for above case, I privately expect the exemption note (3) of B31.3, Table 323.2.2 and ASME Section VIII Div.1, UCS66(b)(3) may be revised to selectively apply as per the materials, yield strength, heat treatment, temperature, chemical composition, geometry, etc. in the future.


Thomas Eun
Natco Canada
thomase@natco.ab.ca
thomaseun@hanmail.net

 

Gentlemen,

This discussion presents is a very good example of why the B31 Codes invite &quot;inquiries&quot;. If you go to Appendix &quot;Z&quot; of B31.3, &quot;Preparation of Technical Inquiries&quot;, you will find the procedure for submitting an &quot;inquiry&quot;. I can assure you the B31.3 Committee will provide an &quot;interpretation&quot; to answer your question. You must frame the question as unambiguously as you can and you may ask more than one question - just be very specific. The committee will likely restate your question(s) so that they can answer with a &quot;yes&quot; or &quot;no&quot; so keep that in mind.

Regards, John.

 

[meca]

I agree with reichertc, I think the note was intended to read &quot;...the stress ratio as defined in Fig. 323.2.2B does not exceed 0.3&quot;. Drop the &quot;times S&quot;, it does not make sense.

Regards,

Chris

 

The &quot;times S&quot; is an error. I will bring it up for revision at the next ASME B31.3 Code Committee meeting, to delete &quot;times S&quot; from note (3) to Table 323.2.2. The intent is to not require impact testing if the ratio is less than 0.3 (which is less than or equal to 1/10 the tensile strength).