I agree that the configuration you describe may not be typical. I have not seen it in the field either but it may be done somewhere. There may be a mistake in the drawing so your RFI to the engineer is the proper course of action. At a minimum it will show your concerns, recommendations and it may help you in the future no matter what the engineer decides to do.
From an engineering point of view, what argument do you propose that an ANSI/ASME B16.5, BS 1560 or API Spec 6A slip on flange to reducer (either end) to be not acceptable?
Thermal expansion, allowable stress factors, joint effeciency are not compromised by this type of joint.
This is commonly used when space limitations are considered but can be used without any consideration for space.
As far as B31.3 is concerned, it presents typical details for slip on flanges and does not attempt to address all details to be encountered in construction P&IDs.
The "Code" or any other ASME code does not attempt to "support" and (excerpt from Foreword) "is not a handbook, and cannot substitute for education, experience and sound engineering judgment."
I do admire your consideration on this issue and concurr that an RFI to the engineer is generated and logged in your book.
My past experience has taught me that RFIs and Request for Deviations to the PE brought needed attention to the issue at hand.
Keep us informed and good luck to ya,
QCRobert
Because the key word is typical. It also say's not every configuration is addressed. I gues I am a little confused about why you think welding slip on flanges on a reducer is a problem? Its a piece of pipe. My second question and it's something I and you should be concerned about, and that is your engineering group deferring to QC about a design issue. Sounds to me like you don't really have an engineering group.
Jim