API 650 TANK UNDERGOING CHANGE OF SERVICE

[inammanj123]

Hello,

I am working on an API 650 external floating roof, naphta tank, which will be undergoing change of service from Naphta to Crude oil. In this perspective what things I need to do from an engineer contractor point of view. It is in FEL-2(feed) stage. Below is what I think I need to do:

1- Prepare SOW for tank inspection and integrity company as per API 653. They will do full calculation, i.e. thickness evaluation for new S.G and other requirement. I can do preliminary calculation but final calculation will be done by some certified API 653 inspection company. Kindly advice what normally is the line of action in change of service of tanks, I mean do we have to involve inspection company or just do thickness evaluation myself and tell client its safe to change service. Note that I asked client to provide me with latest UT report so now I also have update thickness report of tank


Regards,
IK

 

[MJCronin]

I believe that you will also need to evaluate filling and discharge nozzle sizes as well as venting requirements.

You may be restricting operations with filling and discharge nozzles that are too small.

You have to consider the tank internal configuration and internal coatings when changing from NAPTHA to CRUDE ....

Most crude oil storage tanks have a bottom "cone-up" configuration, whereas NAPTHA tanks (as I understand) do not ....

Most modern CRUDE OIL tanks also have a larger CORROSION ALLOWANCE on the shell and bottom than a NAPTHA tank would

Most modern CRUDE OIL tanks have a thick water-resistant internal coating up the bottom six feet of the tank

Most modern CRUDE OIL tanks have provisions and nozzles for periodic bottom water drainage.

Please post many more details of your NAPTHA tank and we can tell you more information

Please post design drawing excerpts of the NAPTHA tank if possible ..

Regards

MJCronin
Sr. Process Engineer