Dear members,

Please let me know if anybody clearly knows about the second notes of definition of “Stress Ratio” in ASME B31.3-2004, Fig.323.2.2.B Reduction in Minimum Design Metal Temperature Without Impact Test.
Note (2) of (a) “for piping pressure components with pressure ratings, the pressure for the condition under consideration divided by the pressure rating at the design minimum temperature”


My question is ;
What’s the definition of “the pressure rating” in Note (2) of (a) ?
-Does it mean flange rating(150, 300,..) or max. working pressure in the B16.5/B16.47 standards ? If operating pressure is 150 psi at -45 oC and flange rating is Class 150 of B16.5, is stress ratio 1.0 ?
-Does it mean rating of fittings(3000#,6000#,…) in B16.11 ?
-how about for cast valves ?

I would like Mr. John Breen or John C. Luf to give a comment.

Q1 What’s the definition of “the pressure rating” in Note (2) of (a) ?

R1 As stated for piping components with listed ratings... listed components such as listed flanges and wrought fittings designed and manufactured in accordance with one of the listed standards in B31.3. In other words whatever the applicable standard rates a component.


Q2 Does it mean rating of fittings(3000#,6000#,…) in B16.11 ?
R2 yes


Q3 -how about for cast valves
R3 for valves that are listed components whatever the standard rates them at see Q1 R1 above.

I hope this helps, if you need more help consider submitting a formal inquiry but this seems straight forward to me unless I am missing something!

John,

Thanks for your answer. I would like to make sure some more because I am still not sure about this “pressure rating” in Fig.323.2.2.B.

Here is an example;
Service : Fuel Gas
Insulation : bare pipe outside building
Min. outside ambient temp. : -45 deg. C
Max. possible pressure at -45 deg.C : 175 psig
Pipe : ASTM A106-B (1/2” ~ 10”)
Flange rating : Class 150, ASME B16.5

Need to calculate the stress ratio to find the temperature reduction from Fig.323.2.2B in ASME B31.3. What are the stress ratios of (1) and (2) shown above ratings calculated based on the general notes (a)-(2) in Fig. 323.2.2B ?

Forged fitting rating : A105, Class 3000 (size ½”~1-1/2”) ---- stress ratio = 175/3000
Flange rating : A105, Class 150, WNRF -------------------------- stress ratio = 175/150
Forged valve : A105, Class 800, API (size ½”~1-1/2”) ------------------ stress ratio = 175/800
Cast valve : A216-WCB, Class 150 (size 2”~10”) --------------------- stress ratio = 175/150

Based on above calculation, it seems that the max. stress ratio is 1.17(=175/150) and it does mean the temperature reduction is not allowed. Am I correct ?

In these days, lots of plants are using LTCS for fuel gas, instrument air and other Category Fluid D services where plants are exposed to -45 deg.C ambient temperature at winter season. If these lines are insulated or heat traced, normal carbon steel can be used. However, one of client has a question if we can use normal carbon steel without impact test in lieu of LTCS because many plants designed 20 years ago had used normal carbon steel without either impact tested or insulation and they have been operated successfully.

Any comment would be appreciated.

Best regards,

The pressure rating for the Class 150 flanges is 285 psi, not 150 psi.

The pressure rating for 3000# fittings is not 3000 psi, it is the pressure rating of matching pipe and the relevant standard states which pipe schedule is considered to be matching pipe. E.g for B16.11 fittings, Sch 160 for threaded and Sch 80 for socket weld.

It is the pressure rating for the component, not the class. This includes pressure ratings of unlisted components.

Thanks for standing in Chuck! Details, details I always cringe when somebody says 150 pound flange or 3000 pound SW fitting.

It usually means as in this case the listed standard has never been read. Because if it had been read the reader would clearly see the word "Class" used in the listed standard!

In this particular case with so much riding on the outcome read the listed standards! And if you don't have a copy buy one!

Class 150 flange doesn’t relate to 150 psi; a 12” pipe tells not of its diameter; don’t think about sleeping on a Sleeper either.

Indeed, misnomers pervade over the piping-mechanical industry. After all, ASME B31.3 - 2004 Code wasn’t really issued in A.D. 2004, and regretfully, nor is a Universal Joint open to all for happy hours.

I heard tell folks are getting arrested in Bars in Texas for drinking alcohol! No Universal Joints there!