Are you sure the tubesheet is Admiralty brass? Normally, the tubesheets are Muntz metal with Admiralty brass condenser tubes. Muntz metal can be welded to carbon steel shells.
We're repairing an existing unit. The tubes are C44300, and we quoted SB-171 tubesheets. I'm not familiar with Muntz metal, but can offer that instead if it's a more logical material, and is still Code-compliant.
weldgal;
First off, for any weld repairs to an existing pressure retaining item you need or should follow an in-service repair code (in this case I recommend the National Board Inspection Code). Second, you need to confirm the materials of construction, and that includes the original tubesheet material. Do not guess and do not make recommendations unless you know the specific design conditions for this heat exchanger. Your weld repair should follow the requirements of the code of construction, which in this case is ASME, Section VIII, Div 1 requirements. Also, does your organization have a Certificate from the National Board to weld repair these types of pressure retaining items? If not, I would not perform this repair.
Maybe I have been unclear. The repair will be performed per NBIC as our "R" stamp mandates. We are not guessing at the materials. The existing unit is a standard product that is no longer manufactured by the original fabricator. We have verified the performance of the C44300 materials, and they meet the performance criteria of the unit. I am questioning whether or not we should offer an alternate to the C44300 tubesheet if joining it to the SA516-70 shell could pose a problem.
weldgal;
Ok, now you are clear. If you offer an alternative material this could be construed as an alteration, see Part RC of the NBIC. An alteration opens a whole set of new issues that if you have an R-Stamp you should be well aware.
Are you sure the tubesheet is welded to the shell? Do you have any access to design documents or drawings for this heater that would help you to develop a repair plan?
Customer can't even confirm that the existing unit is a U-stamped vessel. If we upgrade the material we'll still do it as a repair (per Appendix 6-2000 r). And the drawing is so illegible, we won't know about welding between tubesheet and shell unless we get the order (at bid stage).
Ok. Check with ASME Section II for allowable stress values and go with the Ni-Al-Bronze alloy for the tubesheet, ASME SB-171 UNS 63000. This alloy has good weldability and can be welded to carbon steel using an SFA 5.7 ERCu-Al A2 aluminum bronze filler metal. You most likely will need to qualify a WPS for this repair.
