API 650 11th Hydrotest settlement criteria (new tank) 1

[FrCivEng]

Lets consider an API650 tank 83 m diam x 20 m ht

New API 6550 11th § 7.3.6.6 provides with allowable settlement criteria at hydrotest for new tanks :
- Differential settlement <= 13 mm per 10 m of circumference,
- Uniform settlement <= 50 mm

These criteria seem to be very stringent compared to the ones applied in the past as :
- Differential settlement : Pr De Beer criteria (1969)
?si/L ? 1/450 ; With ?si : Relative deflection between 2 points distant from L ; so :
For L = ? D / 28 = 9,313 m, ?si = 9.313 / 450 = 20 mm,
For L = 10 m , about 22 mm (instead of 13 with API 650 11th)
- Uniform settlement : to avoid piping connection deformations : 300 mm (no standard)

Does somebody have any feed back about API650-11th settlement criteria applicability on recently built tanks, particularly the differential settlement?

 

[786392]

I understand this is 1/200of vertical height for new tanks.

Best Regards
Qalander(Chem)

 

[FrCivEng]

Thank you ; what chapter of API 650 11th ?

 

[Bonswa]

Check out section 7.3.6

in particular, 7.3.6.6

"If settlement measurements are specified by the Purchaser, any differential settlement greater than 13 mm per 10 m (1/2 in. per 32 ft) of circumference or a uniform settlement over 50 mm (2 in.) shall be reported to the Purchaser for evaluation. Filling of the tank shall be stopped until cleared by the Purchaser."

 

[Bonswa]

sorry, i didnt see your previous citations

 

[Bonswa]

I believe that 786392 is talking about dimensional tolerances. In particular, out-of-plumbness.

7.5.2 Plumbness
a. The maximum out-of-plumbness of the top of the shell relative to the bottom of the shell shall not exceed 1/200 of the total tank height. The out-of-plumbness in one shell course shall not exceed the permissible variations for flatness and waviness as specified in ASTM A 6M/A 6, ASTM A 20M/A 20, or ASTM A 480M/A 480, whichever is applicable.
b. The maximum out-of-plumbness of roof columns, guide poles, or other vertical internal components shall not exceed 1/200 of the total height. The 1/200 criteria shall also apply to fixed roof columns. For tanks with internal floating roofs, apply the criteria of this section or Appendix H, whichever is more stringent.

 

[786392]

Thanks Bonswa indeed!
You've done great helping support,as I was out& away.

Best Regards
Qalander(Chem)

 

[IFRs]

The settlement numbers you read are not the allowable criteria for the foundation. They are thresholds above wich the purchaser must be notified if (and only if) the purchaser has requested settlement measurements. API 653 has additional information on allowable settlement.

 

[FrCivEng]

The 1/200 condition is a shell tolerance condition, not a foundation settlement criteria. Same fot the plumbness.

AI 653 covers in service tanks only, not new built ones during hydrotest.

Does somebody have any recently built tank feed back about new 2007 API650-11th (§ 7.3.3.6)settlement criteria at hydrotest applicability, particularly the differential settlement?

I ask this question because this seems to be a very stringent criteria compared to other Codes (EN, FR, ect) , may be unrealistic.
As API 650 is THE reference, there is probably a good reason to such criteria.