Regarding shell to curb angle welding category and NDT requirement

[GOSP75]

In our API 650 tank project we have curb angle to shell welding - Butt welding with full penetration.
My query is now the curb angle is considered as permanent attachment and NDT requirement have to be followed accordingly or permanent attachment weld requirement not applicable to shell to curb angle butt weld.

 

[r6155]

NDT is required.

 

[HTURKAK]

I have copy and pasted of the relevant clause at API 650.
8.1.1 Application
Radiographic examination is required for shell butt-welds (see 8.1.2.2, 8.1.2.3, and 8.1.2.4), annular-plate butt-welds
(see 8.1.2.9), and flush-type connections with butt-welds (see 5.7.8.11). Radiographic examination is not required for
the following: roof-plate welds, bottom-plate welds, welds joining the top angle to either the roof or shell, welds joining
the shell plate to the bottom plate, ...

My interpretation for the Shell to curb angle butt weld is, RT is not required by standard , but could be required by client. My vote is VT ( visual testing) is sufficient.

 

[JStephen]

I don't think it's the intention of API-650 to include either the roof plate, compression rings, or top angles in the "permanent attachments" in Section 5.8. IE, they are considered part of the shell or roof, not attachments to the shell or roof.

 

[r6155]

The top angle butt-welded to the shell is part of the shell: RT is required.
VT always.

 

[JStephen]

r6155, see HTURKAK's quote above, which specifically excludes that weld from radiography.

 

[r6155]

Please see:

5.9.5.5 The section modulus of the stiffening ring shall be based on the properties of the applied members and may include a portion of the tank shell for a distance of16t below and, if applicable, above the shell-ring attachment where tis the as-built shell thickness, unless otherwise specified. When top angles are attached to the top edge of the shell ring bybutt-welding, this distance shall be reduced by the width of the vertical leg of the angle (see Figure 5.24 and Table 5.19a and Table5.19b)

Shell Height*: Specify the distance from the top surface of the bottom plate or annular ring to the upper edge of the cylindrical shell including top angle, if any.

It is clear that the top angle with butt welded to the shell is part of the shell.

Regards

 

[Dhurjati Sen]

Much easier would be to modify the drawing appropriately (after taking necessary approvals) by replacing full penetration with fillet welds.
What benefit would we have a full penetration weld in this case?
Design engineers may not be aware of code ambiguities and field difficulties, hence proper liaison with construction engineers is necessary.

 

[r6155]

Sometimes a design may seem expensive but is convenient for the manufacturer.
Each manufacturer has its own manufacturing process, which can be very different from other manufacturers. It generally depends on the machines available and the experience of the operators.