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B16.9 - Fitting Pressure & Temperature Ratings

B16.9 - Fitting Pressure & Temperature Ratings

B16.9 - Fitting Pressure & Temperature Ratings

I am making up a larger fitting (which has to be registered) out of several standard fitting components (ie WN Flanges, piping tees, piping etc).  By ASME B31.3 I am permitted to use the established ratings for listed components (ie B16.5 lists P & T ratings for various material groups and flange rating classes).  Meaning I do not need to submit calcs for these items as long as my MAWP and Max T fall into this range.

When it comes to standard welding Tees (or elbows etc for that matter), does B16.9 have a similar set of ratings? (I dont have a copy nearby) or do I have to calculate the max pressure (or min thick) for a given temperature based on piping calculations?

I guess I have always assumed that items such as tees, elbows etc just follow the piping calcs in terms of rating.

In short are there standard ratings for these types of fittings?    

RE: B16.9 - Fitting Pressure & Temperature Ratings

Whew.....where to start...??

By "larger fitting" i assume that you are making up a piping "spool piece"....use this term....not "larger fitting"

I am guessing that this is your first time dealing with piping systems ? Is this correct ?

Your question:

"When it comes to standard welding Tees (or elbows etc for that matter), does B16.9 have a similar set of ratings? .. or do I have to calculate the max pressure (or min thick) for a given temperature based on piping calculations?"

shows that you do not understand the basic piping engineering and design process.

Components for piping systems are developed into "piping line specifications" and these are used for certain liquids/gasses at certain pressures/temperature ranges. Tees and elbows are defined here

When the line specification were developed, B31.3 calculations were done to ensure that the wall thicknesses of the piping system/rees etc...were acceptable.

Piping components are the arranged into systems with prequallified components. As long as the system operates within the maxima defined  in the line specification, everything is OK.


Your client or your engineering organization probably has discarded all of these important references and hired a group of MBAs...

My opinion only



RE: B16.9 - Fitting Pressure & Temperature Ratings


Actually your wrong on all accounts and perhaps I didnt give you enough info or the question was too general...my bad

1)Yes the larger fitting could technically be called "spool piece" although in this case it is considered a Class H fitting (Canada) because of its stand alone end use (ie similar to valve). It has to be registered separately as it not being designed for any specific piping system at this time. As such  the evaluation need only concern itself with loads resulting from internal pressure such that a MAWP and Design Temp can be applied for registration purposes.

Once it is incorporated into a specific piping system the pipeline designer will determine whether other external loadings (i.e thermal, seismic etc) limit the fitting use when they do a stress analysis on the system.

The "spool piece" itself is made up of standard piping components (WN Flanges, welded piping tees & Weldolets etc) in the 12"Dia to 16"Dia range.

2) Since I am not designing part of any specific existing piping system, the overall MAWP and desing Temp I register the "As fabricated class H fitting" with depends upon the weakest link in the assembly.  In this case the desired design temperature is getting up into the 950F - 1000F range, it is made from  F9 and P9 materials (9% Cr), as a result the "pucker" factor goes up a bit.  

As you well know in terms of the WN flanges I dont need to calculate the max pressure for them I can go to B16.5 and out of table F2-1.14 for a 300# flange my max pressure for the fitting at 1000F is 255 psig, providing I deem there are no other exceptionals loadings resulting from the configuration, B31.3 permits me to use 255 psig as the MAWP for the flange fitting should I desire it (Listed fitting). Obviously a similar pressure rating evaluation has to be done for each of the individual components making up the larger assembly.

3) So my question simply was this: Is there are standard set of pressure-temperature ratings available for standard piping fittings such as Tees & Elbows (butt welding end...not flanged) based on the common piping schedules they are available in?...to my knowledge these components are not assigned class ratings (150#, 300# etc) unless they are provided with a rated fitting.

I have seen Pressure-Temperature rating charts for the various piping materials and pipng schedules (which are generally based on B31.3/B31.1 calcs)...so they do exist for piping, thought someone might have done something up for some of the standard fittings or perhaps its irrelevant as described below.

So  my next question is given pressure and temperature are the only variables at this stage is it acceptable to equate  the pressure-temperature ratings of standard sized & scheduled straight piping to the equivalent standard "piping fittings" such as tees or elbows....or should I be doing a more formal stress analysis (ie such as a branch connection calculation for a tee) to determine the rating, which they would likely pass when based only on temp & pressure...(to my knowledge B16.9 does not specify what the corner radius is to be in the branch region other than it is assumed to be within the tolerances for piping for the given piping schedule)

Obviously the lowest common denominator determines the final rating of the assembly...the limiting components may very well be the flanges.

Note that I fully understand that once you incorporate the  assembly into a piping system it is necessary to evaluate it with regard to the other piping loads that may exist, however that is not the case in this situation I am simply trying to rate the fitting for registration.     

RE: B16.9 - Fitting Pressure & Temperature Ratings

Fittings complying with B16.9 have pressure ratings of straight seamless pipe of equivalent material.  

RE: B16.9 - Fitting Pressure & Temperature Ratings

Thanks John, thats what I thought .... I didnt have a copy of B16.9 handy to verify that....although B31.3 infers as much.


RE: B16.9 - Fitting Pressure & Temperature Ratings


Yes, and, in *my* opinion, no.

See, for example, ASME's choice of words in B31.3-2006 for the definition of R1 in Paragraph 304.2.1 (3e), immediately below their mathematical treatment of Lorenz factors.

While it is "understood" that fittings made to an accepted and listed standard can be treated as straight pipe for pressure design (and I do "understand" that now), it nonethelss is not readily apparent to someone without a lot of experience and code savvy, and it confused a lot of my experienced colleagues whom I consider to be otherwise smart people.



RE: B16.9 - Fitting Pressure & Temperature Ratings


Your point is well taken...

If your like me and spend most of your time designing for 150 psig to 300 psig saturated steam conditions you dont really give the fitting rating and piping thickness a whole lot of "direct" thought after awhile, at least as far as temp and pressure are concerned. There are generally more pressing design issues to deal with which might affect final piping thickness etc. Not that it is not a concern from time to time.

However if you are designing piping to operate in the more extreme pressure and temperature ranges it certainly becomes more of an issue and behoves you to spend more time looking at this issue more thoroughly for sure.



RE: B16.9 - Fitting Pressure & Temperature Ratings

The allowable P/T ratings of any pipe or fitting (off the shelf of course) is dependent on the material (C.S.,SS,Alloy,etc.) wt. class or schedule no.. There are tables where this has already been worked out (try the Navco Piping Datalog this is just one source). Remember one thing, fitting wt.class or schedule must match the wt.class or schedule of the pipe.

With this in mind, all you need do is find the least max, allowable pressure at a given temp. for all the components and this becomes the max. allowable press. for the fixture. Which is what I've gathered is required for registration.   

RE: B16.9 - Fitting Pressure & Temperature Ratings

To All,
       Just a general query on this Post. Since all of the Standards quoted are recognised ASME standards (B31.3, B16.9, B16.5) I just wondered why this question has been posted in the ANSI Forum instead of the more applicable ASME forum?

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