API 650 Storage Tank Fabrication Sequence 2

[sollapalooza]

Hello

I would like to ask about storage tank fabrication sequence, I do not find anything regarding to this in API 650. A fabricator plans to do blasting + primer on all plates prior to rolling, then transport them plates to site and finish all the welding + final coat. Is this a good practice?

Personally I foresee a lot of touch up needs to be done at site since the primer may be damaged by the rolling machine. On top of that, the surface profile generated from blasting may be ruined by the rolling machine as well.

Should we proceed with the sequence (blast+prime -> roll -> final coat), is there any code that specifies acceptance criteria of the surface profile and primer? I think not all damaged profile has to be repaired.

 

[IFRs]

Here's what I've seen: blast both sides (keeps distortion from blasting to a minimum), apply weldable primer to the outside, apply intermediate coat to the outside but not within 3" of the edges, bevel and roll the plates, stack and deliver them. Plan to weld, then blast and intermediate coat the seams, water clean it all, put the final coat on the whole tank shell. In many jurisdictions, the tank must be white to be put in service and a white intermediate coat even if scratched is sufficient. Assuming the intermediate coat has a decent re-coat time (I've seen 12 months) then the water clean and the final coat is not a time critical task to put the tank in service.

 

[Dhurjati Sen]

Dear sollapalooza,

Your contractor is adhering to a widely practiced sequence.


Once you carry out primer, you do not require surface profile.

Yes, touch up needs to be carried out, but Inorganice Zinc Silicate primer is quite tough.

Regards.


DHURJATI SEN
Kolkata, India