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Difference between B 31.1 & b31.3

Difference between B 31.1 & b31.3

Difference between B 31.1 & b31.3

Any one can help me . what are the main salient features when between codes B31.1 & b31.3. in design and fabrication? How these codes are differentiated between power piping and petrroleum?


RE: Difference between B 31.1 & b31.3

Allowable stresses.  B31.1 allowables are lower than B31.3.  I'd be curious to hear what our code experts have to offer on why B31.1 applies a higher safety factor than B31.3  So far, I've only had the misfortune a few times to do stress work on B31.1 piping, so I'm not as familiar with the basis on that code.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

RE: Difference between B 31.1 & b31.3


Ed you knew this would draw me out of the woodwork.

This question has been aske several times before on this board and the "things" board under ASME Code.  It might be worth having a look, mah99.

One major difference is that the B31.1 Code allowable stress is based upon a factor of safety of 4 and the B31.3 Code allowable stress is based upon a factor of safety of 3.  B31.1 tries to stay parallel with Section I of the ASME B&PV Code on most issues.

Also, the B31.1 Code has a MUCH narrower scope - Power Plants and District Heating Plants.  It focuses on the steam - water loop.  B31.3 has the greatest width of scope of any B31 Pressure Piping Code.  That is why B31.3 created several "fluid services", each with specific rules.

Dr. Chuck Becht has published a new book on B31.3 that you might want to look into.  Go to:


Best regards, John.

RE: Difference between B 31.1 & b31.3

In Ontario, most general plant piping (steam, compressed air, oxygen, nitrogen, high pressure water, etc) falls under B31.1. B31.3 is applied to petro-chem, pulp & paper mills, etc. It's always a good idea to talk to the inspection authorities for whatever jurisdiction you're working in. There are LOTS of local spins on this stuff.

RE: Difference between B 31.1 & b31.3

why does b31.1 uses a 3 to FS where B31.3 has a 4 to 1 ratio aside for b31.1 aligning their reqt with PV&B code.

i refer you to the seminar conducted by glyn woods.
according to him the b31.3 plants generally have a plant life of of about 20 to 30 years. B31.1 on the other is about 40 years. Aside from the life, the fs also reflect the differences in plant cost.

The other point he raised was reliability. with a lower fs, a lower reliability can be tolerated. Power Code got to have a higher reliability since when it goess down, a hundred thousand people and industries will be affected.

when i took my couse in Coade, and the same question was raised, Coade says.
In b31.3 the SIF are computed separately. You dont do that in B31.1
B31.1 does not recognize extruded welding tee nor weldolet. I f u do then one has to condsider the validity of using the SIF drom b31.3
b31.1 explicitly defines the equation for the sustained stress. The b31.3 does not.
b31.3 instruct the user to remove the CA from the Z before making sustained and occasional stress calcs. Other simply warned of the deleterious effect of the corrosion when joined in cyclic loadings.

RE: Difference between B 31.1 & b31.3

Hi Ralphsare and all,

Be careful, you got it backwards in your last post.  B31.1 has a factor of safety (on allowable stress) of 4 and B31.3 has a factor of safety (on allowable stress) of 3.  B31.1 is MORE conservative than B31.3.

In the B31.1 Code, the SIF used is the LARGER of the two (inplane as compared to out-of-plane)and this larger SIF is applied to both of the bending moments occuring about mutually perpendiculat axes.  The B31.3 Code applies the inplane SIF to the Inplane moment and the out-of-plane SIF to the out-of-plane moment (all SIF's calculated per Appendices "D" of both Codes).

There are many detail differences between the B31.1 Code and the B31.3 Code and these simply reflect the difference in design philosophy of the two Code Committees.  

Both Codes spell out thier intended scopes and both Codes and their rules are "valid" for the intended scope.  Always remember that the B31 Pressure Piping Codes are "voluntary consensus Codes".  When a local building Code (which IS the law) requires the use of one of the B31 Codes, ONLY then does it have "the force of law".  As has been pointed out many times in these discussion boards, always check with your local juridiction to see what piping Code is REQUIRED by the law.

Regards, John.

RE: Difference between B 31.1 & b31.3

its a typo on my part and i stand corrected. Talking more about the SIF (on this i guess i did not erred on my last post), ive come across wrc 330.
Finding point out that b31.1 (power piping) erred and so does B31.3 on this subject.

There are difference bu there are also lots of similarities. Notable among them is that both uses the same exact expression for pressure stress, both does not address the issue of the bourdon pressure effects.

RE: Difference between B 31.1 & b31.3

Back again.  Hello all.

The B31 Codes tell us that the SIF's and FF's that are offered in Appendix "A" are to be used if the designer does not have better information to use.  The basic SIF's have been in the Codes since the 1955 edition - based on the work of A.R.C. Markl et. al. at Tube Turns Inc. There have been several "band-aids" applied to the basic information through the years but it is still basically "olde" information.  If you read the notes in Appendices "A", you will see factors for addressing pressure stiffening and for addressing loss of flexibility in elbows (bends) with flanges attached have been added.  The SIF's and FF's in the Code are the best data that was available at the time and it was published to assist the designer (I think it is a little harsh to say B31 "erred", it was the best data they had at the time).  Better "stuff" is comming but in the interim, the designer should be aware of the limitations of the Code data (READ ALL the notes in Appendices "A").

It should be recognized that all the experiments done at Tube Turns Inc. in the late '40s and early '50s (on which the Appendix "A" SIF's are based) involved exclusively, NPS 4, schedule 40, ASTM A-53, carbon steel pipe and pipe fittings.  these data were "extrpolated" to cover pipe sized from NPS 1/2 (not too much of a stretch) up to NPS 72 (wow).  This "one size fits all" approach got the data quickly into the hands of the designers but it was predictable that with time the data would get have to get better.  BUT, as approximate as these data are, the use of these Codes have greatly reduced piping system failures.

The Code Committee has been working towards including changes to make theses data more accurate.  Everett Rodabaugh and Glynn Woods are actively experimenting and the Welding Research Council are underwriting more research.  The results of these efforts will eventually get into the B31 Codes. These two gentlemen are real experts on this subject - in fact, Everett Rodabaugh was one of the original Tube Turns Inc. engineers who gave the Committee the SIF data for the 1955 edition (these were the first rules to address fatigue in piping).  As Ralphsare has pointed out, the WRC has already published some of the new data.  

We seem to have gotten a little "off" the original question but I hope some of this will be of interest.

Best regards, John.

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