Flange Rating per ASME B16.5 - NONMANDATORY APPENDIX A Doesn't seem to Match Flange P-T Tables

[WYSIWYG67]

I am working on evaluating pressure limits for an air system to be run at various temperatures in the creep range. This question concerns evaluating flange pressure limits according to ASME B16.5 (2009). I took a look at the pressure rating table for a 316ss flange at 1300°F (B16.5-Table II-2-2.2) and it doesn't jive with the pressure and temperature with which the facility was commissioned and has been running for decades.

316 is a Group 2 material and, per B16.5-NM Appendix A-2.3 the procedure states that for materials in the creep range (>950°F) that the allowable strength of BPVC Section II-D (2010) should be used. It also has notes about using 70% of yield strength at temperature, but yield strength isn't listed in the code beyond 1000°F.

So applying formula B16.5-2.1(eqn3)

Pt = C1*S1/8750*Pr ≤ Pc
C1=1
S1=4100 psi (@ 1300°F)
Pr=flange class=1500
Pc=ceiling pressure per B16.5-Table A-2= 685 psi

Pt=702.9 psi which is not less than 685 psi, so the flange should be rated to 685 psi. However, Table II-2-2.2 (2009) shows that at 1300°F the flange has a listed pressure rating of 585 psi. Our facility has been around since the 1960's an the guys who designed it were pretty smart fellas, so I know they would not have made such a basic mistake.

My main question is why doesn't B16.5-2.1(eqn3) come up with the same rating as B16.5-Table II-2-2.2? In B16.5 it states that "Pressure–temperature ratings for this Standard have been determined by the procedures described in this Nonmandatory Appendix."

This is puzzling me and our operations engineers. Thanks for any input.

 

[GD2]

What is the construction code for your facility?

GDD
Canada

 

[WYSIWYG67]

If you mean what code was used for the piping it was the ASME BPVC. I'm sure it was the latest rev back then - looks like it was 1977 by the dates on some of the piping assembly drawings. The specific flange I was looking at was a 14" Class 1500 pound ANSI flange. My question is more to why the calculation from the NM Appendix doesn't match the flange rating chart?

 

[FacEngrPE]

ASME B31.1 (Power Piping) or B31.3 (Process Piping) could also be involved - as far as your piping is concerned, History of ASME B31.3
The design basis in ASME B31.1 and 31.3 differ. see this for a summary

http://www.psig.sg/a1.pdf,

also attached. Also there have been some changes over time to the design basis of all 3 codes. If you need to dig into this you will need copies of the code of construction, which can still be obtained from ASME, and some resellers.

 

[LittleInch]

Where did you get the S-1 number from? Becasue you say "but yield strength isn't listed in the code beyond 1000°F"

So where did 4100 psi @ 1300F come from?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bcd]

The rating is still 585 psi in the 2020 edition of B16.5. Most likely, one of the other materials in the group is establishing this rating for the group of materials. You need to check the Section II Part D allowable stresses for all the materials in the group to determine which one is determining the rating.

 

[WYSIWYG67]

FacEngrPE - I believe the piping was according to B31.3, but the drawing I'm looking at only references the BPVC (1977) and B16.5, so I can't say that for sure. My group now uses both depending upon application, and its essentially the same group but things have changed a lot in 44 years. Those guys were good back in the day.

LittleInch - The S1 number of 4100 psi came from BPVC Section II-D-Table 1A (2010) for S31600 (line 15 for forgings) at 1300°F.

bcd - Thanks I hadn't thought of that. I assume the rating that I calculated from B16.5-2.1(eqn3), which ended up being the ceiling pressure anyway would be valid for this individual material then (316ss) and if so that takes the mystery away I think.

Does B16.5-2.1(eqn3) take precedence over the flange rating chart?

 

[bcd]

No, only the rating for the entire group in the Table is applicable. The Appendix with the calculation method is just for information. The committee responsible for B16 standards have grouped similar materials together in the Tables. Likely that a mixture of these may all be used for various valves, fittings, and flanges in a piping system. Based on this, the minimum rating for the group of materials at each temperature dictates the rating for the entire group.

 

[WYSIWYG67]

B16.5-NM Appendix A-2.3 does say the following...

[pre]A-1.5 Material Groups
Materials are grouped in Table 1A based on identical
or closely matched allowable stress and yield strength
values. When these values are not identical for each
material listed, the lowest value has been used. Note
that material groups in this Standard are not numbered
consecutively. The unlisted numbers, numbers that are
not part of this Standard, may be found in the materials
tables of ASME B16.34.[/pre]

So you are right about that, bcd. I took a quick look at B16.34 as well and there isn't anything particularly revealing there. I think I'll have to take a trip down the history path to see if ratings an/or strengths were different back in the day. I find it hard to believe the guys would have designed a facility not rated for the right conditions.

Something still seems odd here. For B16.5 lists the following for materials in Group 2.2 which is where 316ss is in the table:
Forgings - A182: Grades F316, F316H, F317
Castings - A351: Grades CF3M, CF8M, CG8M
Plate - A240: Grades 316, 316H, 317

Forgings and plate the allowable stress for all the materials at 1300°F is 4.1 ksi per the tables in Section II-D. For castings only A351-CF8M is allowed at 1300°F. Its allowable strength is 3.4 ksi.

So if I update my calculation...
Pt = C1*S1/8750*Pr ≤ Pc
C1=1
S1=3400 psi (@ 1300°F)
Pr=flange class=1500
Pc=ceiling pressure per B16.5-Table A-2= 685 psi

Pt=582.9 psi which is below ceiling and close to the table value of 585 psi, but some the other materials aren't even allowed up to 1300°F per Section II-D. CF3M is good up to 850°F and CG8M up to 1000°F for BPVC Section VIII-1. Not sure what to make of that.

 

[WYSIWYG67]

Interestingly this person created a presentation showing the history of valve pressure ratings which includes some excerpts from ASME B16.5-1957 on slides 7-10. The 1957 spec shows that a 316ss 1500# class flange was rated for... you guessed it 685 psi at 1300°F.

From this document it looks like some updates to flange ratings occurred. It could be that the design team was using an earlier version of the specification and flange rating tables (see slide 7 of the linked doc).

Anyone have access to B16.5-1977 or a PT chart for 316ss flanges from that version?