When is a tank not "new"

[IFRs]

During the construction of a new tank, a nozzle is placed incorrectly. A shell insert plate must be used with a repad nozzle to correctly position the nozzle. Does the insert comply with API 650 weld spacing or may it use API 653? For a 3/4" shell 650 has 10" spacing between repad welds and shell butt welds while 653 has 6" spacing.

 

[JStephen]

If you look at the "scope" section of API-653, it says that it applies to tanks "that have been placed in service".

Realistically, such repair work that is not covered under API-650 would normally be done under API-653 for lack of a better standard. I don't know that you say this applies to reduced weld spacing.

 

[IFRs]

Same tank, another issue. During hydro, the bottom settled and the foundation settled. API 650 seems silent on the acceptable critera for settlement prior to being put in service. Do we use 653 even though this is still a new tank?

 

[FrCivEng]

If your new tank is to API 650 11th, foundation settlement mesured at full hydrotest shall comply with API 650 11th Art 7.3.6.6.

If your new tank is to API 650 10th, there is no foundation settlement criteria for a new tank at full hydrotest ; in that case, it is usual to consider Pr De Beer criteria, still referred by Ph. Myers (AST book, 1997) which is :

?Si <= L/450.

With :

- ?Si : edge foundation differential deflection calculated at each point of tank circumference, from settlement measurements and analysis,
- L : distance between 2 points considered on tank circumference ;
- ?Si = Si – (S i-1 + S i+1) / 2
- Si : variable settlement calculated from total settlement measured (levelling measurements on site) reduced of uniform settlement (definition as per API 653 - App B)

API 653 is applicable to in service tanks only