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dtn6770 (Mechanical)
23 Dec 09 9:43
ASME Section II, Part D, page 82...the materials listed in lines 38 and 39 are both identified as SA-240 304L plate with the same P-No., Group No., min. tensile and yield strengths,  and external pressure chart no.  Their applicability and max. temp. limits (page 83) are the same except for the line 39 material isn't permitted in Section III applications.  For the most part they have different notes.

Now, getting to their maximum allowable stresses...their values diverge after 100F.  That is, one material (line 38) maintains a 16.7 ksi max. allowable stress up to 300F whereas the line 39 material is only good for 12.8.

I believe these materials are different and feel that this position is supported by the fact that our PV Code calculation software's material database contains "SA-240 Gr. 304L, High" and "SA-240 Gr. 304L."

I discussed this with our formed head supplier who takes the position that SA-240 304L is the only material spec and that there is only one product by that designation.  After getting them to open Sec. II their claim became that the different lines (38 vs 39) just identified the allowable stress range that SA-240 304L has to meet.  That is, for the 300F example the material can have an allowable stress between 16.7 and 12.8 ksi.  (That kind of makes it had to design with.)

I don't agree with their assessment and think that I'm within my rights to specify either material and for lack of anything better would do so by using the clarifiers "high strength" or "low strength."

How far off in left field am I?
 
Helpful Member!  stanweld (Materials)
23 Dec 09 10:30
There is only one grade 304L minimum mechanical properties defined under SA-240. The design allowable stresses permitted in ASME II D (high or low) are employed at the Vessel Manufacturers'/Engineers' discretion.    

Helpful Member!  metengr (Materials)
23 Dec 09 10:35
Please read the Notes in Section II, Part D, Table 1A applicable to stress lines 38 and 39 for SA 240 304L. Most people simply read stress lines for the same material and grade and never bother to read applicable Notes.

I will provide a hint instead of telling you exactly because this forces one to look up information. Review carefully Note G5 followed by Notes T4 and T6.
 
dtn6770 (Mechanical)
23 Dec 09 10:52
Gotcha metengr.  I'd previously read each of the notes but obviously didn't take G5 to heart.  Having gone through it again (more slowly) I get the subtlety now.  It's that 'they' chose to do it that way.

Thanks.
unclesyd (Materials)
23 Dec 09 11:48
The approach to using either or was if you can allow a little distortion use the "high" and if you want no distortion use the "low". This means that you would use the "low" for flanges and the "high" for most everything else.
This generalization needs to be reevaluated on each design.  
vesselfab (Mechanical)
23 Dec 09 11:58
My opinion has always been simple for an old simple mind

the lower values are for where distortion is not allowed, like a plate flange or bolted head.

the higher stress values are for where distortion can be tolerated, like a vessel head or shell.

We have never been questioned by a client or AI about this, so I am assuming we have been correct.   LOL
dtn6770 (Mechanical)
23 Dec 09 12:06
Fortunately for my applications, formed heads, using the lower allowable stress values don't force me to go with a thicker material.

We don't play with stainless much so I'm sure our QC department would freak out if they had Code calculation reports listing the head material as "SA-240 Gr. 304L, High" (as APV does when that is what's selected) and the MTRs list just "SA-240 Gr. 304L."
 
MrBTU (Mechanical)
28 Dec 09 16:13
I just got a comment from a reviewer overseas (this was a PED job) that insisted I use the LOW values for shell and tube heat exchanger tubes.  I, like VesselFab above, only used the low value for flanges, so this was new for me.  I sent it back to the reviewing company (who happens to be our AI as well) and asked for an interpretation - whether the PED reviewer's comment is legit, and whether this interpretation applies only to PED jobs or to ASME as well.  I'll advise the outcome.   
SnTMan (Mechanical)
4 Jan 10 13:32
dtn6770, the practices related above are very common, i.e., low allowables for bolted joints, high allowables for just about everything else. However I have worked to customer specs that do not permit the use of higher allowables at all.

If you browse Sec II, Part D for the stainless and some other materials you will find the same situation exists for product forms other than plate and also find forgings and bolting sorted by thickeness. It is important to CHECK that you (or your software) has selected the correct allowable stress.

And if your QC department freaks due to their own unfamiliarity with the Code, well, you'll just have to educate 'em.

Regards,

Mike
bernoullies123 (Mechanical)
4 Jan 10 17:36
For flange ratings the use of either the lower or higher value can be used depending on if the notes indicate that the stress is greater than 2/3 yield for which the lower must be used.  Refer to ASME B16.5-2009 A-2.2 (e).

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