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API 650 Roundness

API 650 Roundness

API 650 Roundness

Hi there, I have a question about roundness measurements required in a 40.000 m3 storage tank. I have been assigned to follow QC on this job when the 6 courses and top reinforcement angle were already installed. Performing a walkdown on the jobsite, I have noticed lots of local deviations on all the 6 courses and VT of the inside of the Shell from the top, confirmed them. Doing research on the paperwork available, I have found a roundness report up till the third course, where the most relevant radious was +65 mm (25 mm by code).While I was up there doing a VT I have noticed the 2nd course is out of level with respect to the third one in quite few spots. Due to this matter, I have asked the contractor to perform roundness checks on all the 3 last courses,and check for plumbness as well. Contractor says, there is no where in the API 650 code where it states that those measurements have to be taken in all 6 courses, which is true, but since my concern about the quality of their work, my question is if API 650 back me up in any paragraph (havent found any) to have them do that if the main concern is to know how round and vertical the tank is at this point?
Any info will be appreciatted.
Best regards

RE: API 650 Roundness

The contractor is not required to measure radii except at the bottom. The roundness of the upper plates is given in 7.5.2 and 7.5.3. To assure roundness, API talks about plumbness and local deviations.

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 A6M/A6, ASTM A20M/A20, or ASTM A480M/A480, 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 Annex H, whichever is more stringent.

7.5.4 Local Deviations
Local deviations from the theoretical shape (for example, weld discontinuities and flat spots) shall be limited as follows.
a) Deviations (peaking) at vertical weld joints shall not exceed 13 mm (1/2 in.). Peaking at vertical weld joints shall be determined using a horizontal sweep board 900 mm (36 in.) long. The sweep board shall be made to the nominal radius of the tank.
b) Deviations (banding) at horizontal weld joints shall not exceed 13 mm (1/2 in.). Banding at horizontal weld joints shall be determined using a straight edge vertical sweep board 900 mm (36 in.) long.
c) Flat spots measured in the vertical plane shall not exceed the appropriate plate flatness and waviness requirements given in 7.5.2.

RE: API 650 Roundness

Section 7.5 is all you have unless you have a separate tank specification document which adds requirements to API 65.

If all you asked for is an "API 650" tank then that's what you'll get...

However quote section at him... ( I do like the "first class" bit...) All work of fabricating API e.g. 650 tanks shall be done in accordance with this standard and with the
permissible alternatives specified in the Purchaser’s inquiry or order. The workmanship and finish shall be first class
in every respect
and subject to the closest inspection by the Manufacturer’s inspector even if the Purchaser has
waived any part of the inspection.

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