Standard Flange rating (ASME B16.5) selection 1

[vinothsvk]

Hi all,

I have one clarification on selection of Flange rating.
Normally for Standard Flange (ASME B16.5), we select the Rating based on design conditions(design pressure and Design temperature) only.
But, My vendor select the flange rating based on total required bolt area calculation as per ASME Sec VIII Div I Mandatory Appendix 2-1.

Here I would like to elaborate what happened.
Now, i am looking plate and Frame Heat exchanger. As per design condition of this Equipment (Design Pressure 14.6 & Design temperature 155 degree Celsius, Flange Material is Carbon steel), the Equipment nozzle falls under 150# rating. But, my vendor changed the nozzle rating into 300# based on total required bolt area calculation as per ASME Sec VIII Div I Mandatory Appendix 2-1.

Please confirm, ASME Sec VIII Div I Mandatory Appendix 2-1 is applicable for standard flanges (ASME B16.5)?

 

[Krausen]

Yes this is acceptable. You can design any flange with standardized B16.5 dimensions under VIII-1 MA2, so long as you use the allowable stresses under VIII-1.

 

[david339933]

No, App. 2 is not meant for B16.5 flanges.

 

[Krausen]

MA2 is not meant for standard B16.5 flanges typically under VIII, but it can be done if the designer chooses to. The code does not prohibit it.

You will often find you’ll end up with a lower pressure-temperature rating under MA2 compared to the standard 16.5 ratings though.

However, if working under the B31.3 piping code & designing a standard 16.5 flange using MA2 (which is allowed under B31.3, so long as you use B31.3 allowable stresses), you’ll find you can increase the pressure-temperature rating of some B16.5 flanges

 

[JStephen]

If you use the appendix on larger flanges, it may reduce the flange pressure rating, but may also reduce the required weld sizes considerably, so that's another reason to consider that approach.

 

[LittleInch]

Well it's pretty marginal for group 1.1 materials -P-T rating is 15.8 @ 150 C, so going to class 300 isn't too much of a stretch.

But Yes I thin the vendor could have used the B16.5 ratings as they are a code nominated in ASME VIII. Use of MA2 almost always results in the next class up or "failure" of the flange. However the ratings in B 16.5 have been proven for a long time and are therefore generally acceptable.

But does it matter? Just connect with a class 300 flange and be done with it. You get a bit more strength and capability and it just means you have a class 300 flange on lower pressure pipe, but that's not uncommon.

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

 

[r6155]

Depends of gasket. See 5.4.3 in B16.5

Regards

 

[davefitz]

It is my understanding that B16.5 flanges were originally designed "by eye" around 1931, and their rating was based on a hydrotest failure test, the rated pressure being perhaps 1/2 of the failure burst or leakage test results. No calculations were used at that time. They are used today based on tradition and that 90 yrs service proves their adequacy, even if they do not meet present day calculations as in MA2.

The B16.5 flanges are not optimal in terms of mass, thermal stress during fast startups, or long term leakage. Flanges designed as per calcualtions of section 8 div 1 or 2 generally have much less mass and lower thermal stress during fast transients, and are sometimes called "compact flanges".

B16.5 flanges seem to be part of our heritage, as are the parts of section I dealing with steam locomotives.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[XL83NL]

Have a look at BJI's 12 LPS post.

https://www.eng-tips.com/viewthread.cfm?qid=454965

Huub
- You never get what you expect, you only get what you inspect.

 

[SnTMan]

Wow, 12 LPS for one post. That must be a record

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[LittleInch]

I recall that one and it answered a huge range of questions about how and where for the flange ratings.

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

 

[XL83NL]

Wow, 12 LPS for one post. That must be a record

Well, this one takes it a little step further;

https://www.eng-tips.com/viewthread.cfm?qid=189629.

24 (and still counting).
JohnBreen's replies quite often had a lot of LPSs, he will probably hold the record.

Huub
- You never get what you expect, you only get what you inspect.

 

[SnTMan]

Well then, I stand corrected

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[XL83NL]

25 LPS and counting. As time goes by, that post still gets attention.

Huub
- You never get what you expect, you only get what you inspect.