Weld Overlay on ASME B 16.5 Flanges

........ and with a little more time, I guess I should elaborate.

There is not a problem with removing the raised face as per B16.5 - 6.4.1, but it is a concern when you start removing more material.

In the off-chance that your flanges are thicker than required (t_f) due to the allowable tolerance on thickness (paragraph 7.4):

• NPS ≤ 18 : +3.0 mm, -0.0 mm
• NPS ≥ 20 : +5.0 mm, -0.0 mm

Then, as long as you remain above the required minimum thickness (t_f), you will be alright.

However, if you machine the base metal to lower than the required thickness, you will have a non-standard flange and will need to design as per Appendix 2 of ASME VIII-1.

However, be mindful of the cases where even standard B16.5 flanges do not meet the criteria of Appendix 2.

With the analysis of App 2, it may be fair to invoke the clauses of UCL-23 (ASME VIII-1) pertaining to allowable stresses of clad materials.

Lastly, use proper welding procedures and testing as per section UCL.

I do this allot on pressure vessels that require a corrosive resistant metal overlay. I have not ever had a problem with my AI accepting this. We usually put all the metal and more back on the flange and then machine it down for the gasket sealing surface. I did calculations to show the base metal of the flange is still thick enough for the heat and pressure that the flanges will see during operation. I also qualified the correct welding procedure, specification and welders for the ER-312-16 welding electrodes that we use per the ASME section II and IV. One thing about corrosive resistant overlay is that I do not count the thickness of the overlay in calculations for pressure rating of the vessel. I have 15 fairly large 14 ft. OD vessels that I do this on from the lower flange to 30ft high that run somewhere around 500 degrees F. and 130 to 150 PSI.