Build-up weld all around critical zone of a tank

[Hansac]

Dear all.

Does API 653 allow for build-up weld for shell-to-bottom plate all around the tank (internally or externally)?

Reading API 653 Section 9.10, there is no limitation on weld length but my colleague says 653 prohibit the build-up weld for all around the critical zone due to

"9.10.1.6 ... The weld repair of bottom plate corrosion is permitted if all of the following conditions are satisfied.
a) The sum of the pit dimensions along an arc parallel to the shell-to-bottom joint does not exceed 2 in. in an 8-in.
length.
b) There must be sufficient remaining bottom plate thickness for completion of a sound weld and to avoid burnthrough.
The minimum acceptable bottom plate thickness for weld repairs is 0.10 in. A lesser thickness is permitted
for weld repairs only if reviewed and approved by an engineer experienced in storage tank design and repair."

In my opinion, this paragraph permits unlimited weld length on the critical zone:

"9.10.1.2.1 No welding or weld overlays are permitted within the critical zone except for the welding of: widely
scattered pits (see 4.3.2.2), pinholes, cracks in the bottom plates, the shell-to-bottom weld, welded-on patch plates, or
where the bottom plate welded to the shell is being replaced."

All opinions appreciated.

Thanks.

 

[Ripz]

You are right. No restriction for weld buildup of Shell-to-bottom weld as per 9.10.1.2.1

9.10.1.6 refers to weld buildup of corroded areas on the bottom plate in the critical zone.

"9.10.1.6 The repair of corroded plates in the critical zone is
limited to pit welding or overlay welding as noted in this section."
...

I'm curious though, did your weld lose metal thickness? And why did it lose thickness but not your plates?
Or was its original size not according to the construction code?

 

[racookpe1978]

Do you seriously intend to interpret a clause permitting "widely scattered repair" (of isolated pits in a pressure vessel) into some sort of permission to apply continuous weld buildup across the entire vessel metal, applying that weld so thick that the vessel is somehow now thicker and can withstand more internal pressure? Safely?