API 650 Tanks - Minimum Spacing Requirements of Shell Openings

[Alirashid]

According to API 650 5.7.1.1 Minimum Dimension Between Weld Toes or Weld Center-lines should be 75 MM. what is the corrective action if this space(75mm from weld center line to other i.e nozzle welds toe)is not maintainable.

 

[JStephen]

If the spacing is between welds around repads, then use a single larger repad around both fittings.
If it's the spacing around nozzle necks, move one of the nozzles.
In addition to code issues, watch for weld distortion in those cases- when you weld one nozzle, it can move the adjacent nozzle.

 

[IFRs]

This weld spacing is now in 5.7.3, not sure how old your edition is. Using the methods suggested by JStephen it is almost always possible to design it per the standard. Since you are talking about "corrective action" may we assume this is an existing tank? For a better answer, post an image ( with dimensions ) of the issue and include the shell plate material and thickness in your post.

 

[Alirashid]

Yes Mr.FIRs you are right its 5.7.3 in 12th edition of API650 but the subject we are discussing starts from 5.7.1.
yes this is an existing tank under construction, the space or dimension measured is coming 50 to 60 mm as shown in figure 5.6 dimension B for an individual nozzle without repad (S-N). So what have to do, what is the corrective action.

 

[IFRs]

The only options I see for nozzles without repads is to move the nozzles or use an insert plate that crosses through the horizontal joint and contains the nozzles.

Figure 5.9 detail C is not intended to be for S-N nozzles but I'm not sure I see why it could not be used if you added a repad and did the NDE. What is your shell thickness and grade?

What size are these nozzles? Are the flanges hitting or are these couplings without flanges?

 

[Alirashid]

Shell Thickness 9 mm & 6mm. Material SA516-Gr.60N.
NOZZLES SIZE 2". PIPE + FLANGE.

 

[IFRs]

I think your best option may be to install a rectangular shell insert patch plate crossing the horizontal joint sized to maintain all weld spacing.