Comparison of B31.1 vs. B31.3 1

[BTD]

Do any of you know where I can find a published comparison of B31.1 vs B31.3.

I have copies of both but don't have time to do a rigorous review.

This request is the result of a casual observation that basic plant piping systems such as instrument air, potable water, lube oil, and fuel gas (500 psig max) end up physically the same regardless of the code used.

The only detailed investigation I've done regards min. wall thickness vs. allowable stress. The result was that, for the systems investigated, even though the allowable stresses were different, the actual pipe selection was the same.

Thanks for the help.

 

[Rich2001]

The biggest difference that I remember between the two codes is with B31.1 is the requirements for an ASME PP or S stamp for welding or heat treating the piping around boilers. Certification of welders and Material certifications. If I remember right allowable stress are greater in the B31.3 code.

Rich

 

[lalaith]

B31.1 Does pertain to Boiler External and Non-Boiler External Piping. However one of the major differences is the Jurisdictional and Administrative Responsibilities for B31.1 piping. B31.1 piping will refer you back to ASME Section I Boiler Code whereas B31.1 usually provides all of the guidelines in that Section.

There is not actually a code stamp required on B31.1 piping unless it is is Boiler External Piping and the Code stamp requirements for Boiler External Piping are actually in ASME Section I. This in turn does affect the inspection and NDE requirements.

 

[BREEN]

Hello BTD,

Actually, the biggest difference is that B31.1 allowable stresses are based upon a factor of safety of 4 while B31.3 allowable stresses are based upon a factor of safety of 3 (if we assume we are below creep ranges for both).

B31.1 focuses upon a very narrow application - power generation plants and district steam plants. The B31.1 Code has an appendix (Appendix V) which addresses maintenance, modification, replacement and repair. This appendix is rich in guidance for maintaining ANY piping system.

B31.3 is perhaps the most broadly scoped of all the B31 Pressure Piping Codes. B31.3 is so broad that the concept of "Fluid Services" was incorporated within the Code (category "D", regular service, and category "M&quotto allow the appropriate gegree of rigor to be applied to various "severities of service" for design within the Code. Also, B31.3 has a high pressure Section. Also, B31.3 introduces the concept of "safeguarding". Check out Glynn Wood's book "Guide to B31.3 Process Piping" from CASTI Publishing.

Each of theses 2 "books" has a description of its intended scope. It is important to pay attention to it. Many plants use B31.3 for all process piping and if they have a boiler house they use B31.1 just for the steam - water circuit of the steam plant.

Best regards, John.

 

[br549]

It perty simple B31.1 is power piping (read this as steam)

B31.3,is chemical piping or any thing that's not steam

The big differnce is the safety factor use in the calcuation
b31.1 is more strigent ie higher safety factor/more inspection.

 

[DavidCR]

I´d like a confirmation of what I´ve been told on this:

"B31.1 has higher safety factors but B31.3 is more strict on inspection."

 

[KernOily]

Unfortunatley there are no shortcuts to the info - you gotta read the Codes. I have been through this a zillion times with clients.

Wait 'til you try to draw the distinction between 31.3 and 31.4... that one will make you bang your head against the wall...

Your basic observation is correct - utilities and low-pressure steam distribution systems (non-nuke) will usually have the same design parameters. Your insurance company will usually make the call there.

Your boiler external piping could be designed to 31.3 or 31.1 as far as I know. In the oilfields, the on-skid steam generator piping is designed to 31.1. The last flange on the generator skid is the break to 31.3. All offsite distribution piping is designed to 31.3 (1200 psig). Note that we have seen a difference in the layout of systems, e.g. the spacing of expansion loops is closer in 31.1 due to the lower hot allowable stresses relative to 31.3. The system owners in this area have decided though that they can defend their decision to use 31.3 for offsite steam distribution piping.

For a given fluid service, the differences in wall thickness will start showing up when you are using different metallurgies (i.e. different allowable stresses).

Pete Chandler
Bakersfield, California

 

[ralphsare]

ive seen this thread played over a couple of times in different piping forums. a lot has missed the point regarding the impact of the difference in safety factor. a lot has also missed to point out that there are also an overlapping covereage between the power and non-power codes and it has also similarities.

Safety Factor. Pointed out that its 4:1 for power codes and 3:1 for process piping. What does it mean? well it means thicker wall for the lower and moderate range temp. It also means plant build to b31.1 will cost more. But the good news is it will have better reliability owing to a thicker wall and of course it will last longer (important if your doing an lcc evaluation part of feed).

Is that it? No, that's not it as far as differences is concern. there is also the difference in how the sif are treated. B31.3 separates the in-plane and out-plane SIF while the power code has one sif and it intensify the the torsion (not so in B31.3). There's also the corrosion allowance. The treatment is different between the power and process piping. It has been said many times about the sustained load in this forum and a lot has failed to mentioned that B31.3 does NOT provide explicit equation for sustained stress calc. Not so with the power codes.

for the similarities and overlaps - well lets cover it in another thread.

 

[sturg]

what are the guidelines to repair non boiler external piping in the state of michiagan?

 

[sturg]

can you refer me to someone that has a section 23 excemption in the state of michigan

 

[sturg]

can you refer me to someone that has a section 23 excemption in the state of michigan

 

[KernOily]

31.3 came from 31.1. The sustained loading for a system governed by 31.3 is calculated using the 31.1 equation. Sometimes you can use 31.1 to interpret 31.3, e.g., sustained load analysis. That was a good point.

I'm not sure I'd agree with a generalized statement that, in general, increased wall thickness leads to increased reliability. There are too many other factors involved. It just depends on the process.
Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com