I hate to repeat myself, but why are you expecting ASME marking on an AISI material?
If this photo is of an ASME registered vessel / piping / etc. and that's the only marking on the plate then you've got a big problem.
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I've been designing large...
Here's some info I found by Googling. If what I say below is wrong that's my poor Googling! Maybe you could try Google?
The AISI manual listed chemistry only. They may have included "typical" physical properties, but testing was not required.
AISI no longer publishes this manual, however...
Figure 2-4(11) refers to Figure UW-13.2 sketches [m] and [n] for full-penetration. You PDF is exactly sketch [n]. Assuming you match the dimensions in sketch [n], and do a back-chipped full-pen weld, then it is an integral flange.
Edited to change (n) into [n] as intended.
I believe ASME Section VIII Division 1 clause UG-21 makes it clear that the specified design pressure must be greater than any possible operating condition.
I would not be using individual reinforcing plates on each nozzle. I would use a thickened insert (try 2 times tshell) or perhaps a full thickened ring though I'm not sure where the large nozzle on the far side is.
I have never used PV Elite so I don't know how to specify an insert like this...
For a loose-type flange g0 is the"thickness of hub at small end" as defined in clause 2-3, so neither of the dimensions in your sketch. See Figure 2-4 Detail (1) or (2).
The neck thickness is only considered for optional or integral flanges.
Not sure I understand the "ridged cylinder". Sketch?
If there's just an upper fillet isn't that a pinned rather than moment connection?
Is the pressure high enough to fall within ASME Section VIII Division 1 and thus you should follow the details and rules in UG-34?
If you are a student why aren't you posting your question in the student forum? : https://www.eng-tips.com/forums/student-engineer-general-discussion.1630/
While API 650 says you should not do this, it also provides rules for where there is no other feasible option.
This forum is about storage tanks, like those covered by API 650 or AWWA D100.
You seem to have pressure vessel question which would be better asked in either https://www.eng-tips.com/forums/boiler-and-pressure-vessel-engineering.794/ or...
There are times when I wish the Code Committee would explain their response, not just yes or no.
I have re-read the Code and I can't see where the Committee is finding this requirement. It seems to me that they've added a requirement that isn't actually in the Code.
Nonetheless, UG-34 is...
UG-39(a) addresses opening in flat heads. This does reference the rules in UG-36(c)(3) for opening size and spacing limits.
If you meet these size and spacing limits then the blind flange does not need to be reinforced for these openings.
ASME Section VIII clause UG-42 addresses closely spaced openings.
We always join the two circles with tangential lines rather than the "bar bell" shape you've shown.