Welding overlay of Monel (Alloy N04400) on SA-516 Gr-60

[Mohammad Saad]

A crude distillation column has base metal SA-516 Gr-60. The top dome and 2 adjacent shell covers are hot-cladded with Monel (Alloy NO4400 as per ASME Section II, SB-127). The cladding is damaged due to corrosion, and it is decided to perform weld overlay of Monel SB-127 over corroded area (10m[sup]2[/sup]), using ERNiCu-7 and GTAW. The manufacturing thickness of clad was 4.37~4.54 mm, while the remaining thickness of clad is 1.27~4.21 mm. The base CS metal is 21mm thick. I have been assigned a task to conduct research on the possible effects (distortion, etc.) of base metal (CS) due to the welding. Moreover, I need to study the best method and procedure of welding, and to ensure that the remaining cladding won't be affected by it. (There is no PWHT requirement for base metal as per drawings). If any of you could give your input and guide me to the best relevant resources to study, I would be obliged. Thanks in advance.

 

[weldstan]

If parts of the cladding will be removed to base metal, the first pass should be nickel (ERNi-1)to prevent potential cracking. If not, after proper preparation and cleaning, the filler as chosen is fine. That's a lot of area to be welded with GTAW. I would recommend pulsed GMAW to both limit distortion and reduce repair time. I don't expect distortion to be a major issue with either process.

 

[EdStainless]

I'll second Stan's comments and add a couple.
1. Clean, Clean, Clean.
2. This was roll clad? No signs of any disbonding?
3. A bit of pre-heat and careful attention to the weld pattern will keep you out of distortion risk.
And yes pulsed GMAW would be the logical way to since you have a rather large area.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Mohammad Saad]

weldstan

Thank you for your reply. I will definitely look up the benefits of GMAW for this task. Also, can you please suggest how to study the potential of distortion in the base metal? The conditions, as you also mentioned, do not lead to the distortion but I have to do the technical analysis of it. It would be of great help if you guide me to the relevant resources. Thanks

 

[Mohammad Saad]

EdStainless

It was indeed roll clad and there were no signs of distortion as per the last inspection report. There was mostly pitting due to corrosion. Also, you mentioned pre-heating, can you please let me know the relevant API/Standard that could help me out in this regard i.e. to know how much pre-heating would be enough, and other details? Also, I missed this before, but we have a window of 18-20 days as the plant is going to be shut down for maintenance purpose.

Thank you for your help.