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Roundness and plumbness

Roundness and plumbness

Roundness and plumbness

Dear experts,

We are building the tank with Jacking method. The top shell course will be erected first on the temporary supports.

The third party inspector keep asking me to check the roundness and plumpness of this top course after fit up and after welding and use the tolerance as specified in API 650.

I am arguing with the inspector since API 650 clearly stated that roundness is check the radius of the tank measured from the center of the tank to the shell 300 mm above the corner weld. Plumbness is checked from the top shell course to the bottom shell course.

If we want to check the plumbness of individual shell course we need to refer to ASTM A6 or ASTM A20 as stated in API 650 about the same.

We did check the circumference of the tank and its about 18 mm above the theoretical circumferential.

Any comments ?

RE: Roundness and plumbness

The third party inspector is not getting confused with peaking and banding is he ?

RE: Roundness and plumbness

I'm thinking those tolerances apply to the finished tank, not at every intermediate stage of erection. As a matter of controlling the geometry, you'd want to keep an eye on things as you build, but tolerances wouldn't normally be applied then. For example, putting the wind girder on a tank or putting structure in a tank can both act to round it up (or the opposite!).

RE: Roundness and plumbness


No the TPI is fully understand about peaking on vertical joint and banding on horizontal joint.

I am agree with JS, those tolerance shall applied after the whole tank shells are completely erected and welded before hydrotesting.

This point also been addressed to the TPI. His concern is how to ensure the final stage will be meet tolerance if we are not checking every shell course during erection.

API does not addressed the radius tolerance on each shell course. API does address how to measure plumpness on every shell course by referring to ASTM A6 or A20 whichever applicable.

RE: Roundness and plumbness

It's not the TPI's problem or his business how to achieve the tolerances - that's the erector's job. If the erector can put up a square tank and make it round at the end that's OK ! While it is interesting to watch, the TPI should butt out until the end at which time he can say "great work" or "not good enough".

RE: Roundness and plumbness

At that point 'not good enough' would result in the TPI getting a beat down.

Ask him to provide you WHAT information would satisfy him THEN ask him to reference some or any tolerances for a tank built via this method. It's not black and white. At the end like previously stated the final result is what counts.. unless some moron put a hold on the ITP for each course being put up. Then I'm sorry.

RE: Roundness and plumbness

congratulations to you Bro, the TPI inspector is experienced in the field. his points is right,how can you control the final tolerance of plumbness from the top to the bottom of the tank shell,even no check requirement during erection by the API650,but as an constructor,you must control the plumbness of each shell course to achieve the final requirement.

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