When is a tank not "new"
When is a tank not "new"
(OP)
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.





RE: When is a tank not "new"
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.
RE: When is a tank not "new"
RE: When is a tank not "new"
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 :
ΔSi <= L/450.
With :
- ΔSi : 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 ;
- ΔSi = 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